Thieme: Imaging of the Temporal Bone

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Fourth Edition fm 1/7/09 12:23 PM Page ii fm 1/7/09 12:23 PM Page iii

Imaging of the Temporal Bone

Fourth Edition

Joel D. Swartz, MD President Germantown Imaging Associates Gladwyne, Pennsylvania

Laurie A. Loevner, MD Professor of Radiology and Otorhinolaryngology—Head and Neck Surgery Department of Radiology Neuroradiology Section University of Pennsylvania School of Medicine and Health System Philadelphia, Pennsylvania

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Library of Congress Cataloging-in-Publication Data

Imaging of the temporal bone / [edited by] Joel D. Swartz, Laurie A. Loevner.– 4th ed. p. ; cm. Rev. ed. of: Imaging of the temporal bone / Joel D. Swartz, H. Ric Harnsberger. 3rd ed. 1998. Includes bibliographical references and index. ISBN 978-1-58890-345-7 1. Temporal bone—Imaging. 2. Temporal bone—Diseases—Diagnosis. I. Swartz, Joel D. II. Loevner, Laurie A. [DNLM: 1. Temporal Bone—radiography. 2. Magnetic Resonance Imaging. 3. Temporal Bone—pathology. 4. Tomography, X-Ray Computed. WE 705 I31 2008] RF235.S93 2008 617'.514–dc22 2008026874

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Printed in the United States

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ISBN 978-1-58890-345-7 fm 1/7/09 12:23 PM Page v

To Mrs. Charles Zale Swartz.

—Joel D. Swartz

To Joel Swartz—your passion, persistence, pride, and patience made this important project happen. To my family, immediate and extended—thanks for your love and support.

—Laurie A. Loevner fm 1/7/09 12:23 PM Page vi fm 1/7/09 12:23 PM Page vii

Contents

Preface ...... ix Contributors ...... xi 1. Temporal Bone Imaging Technique ...... 1 Paul A. Caruso, Jennifer L. Smullen, Robert Liu, Mary Beth Cunnane, and Hugh D. Curtin

2. The External Auditory Canal and Pinna ...... 25 Valerie L. Jewells, Mauricio Castillo, and Craig Buchman 3. The Middle Ear and Mastoid ...... 58 Joel D. Swartz 4. Temporal Bone Vascular Anatomy, Anomalies, and Disease, with an Emphasis on Pulsatile Tinnitus ...... 247 Gul Moonis, Ann Kim, Douglas Bigelow, and Laurie A. Loevner 5. The Inner Ear and Otodystrophies ...... 298 Joel D. Swartz and Suresh K. Mukherji 6. Temporal Bone Trauma ...... 412 Edwin Y. Wang, Deborah Shatzkes, and Joel D. Swartz 7. Anatomy and Development of the Facial Nerve ...... 444 C. Douglas Phillips, George Hashisaki, and Francis Veillon 8. The Vestibulocochlear Nerve, with an Emphasis on the Normal and Diseased Internal Auditory Canal and Cerebellopontine Angle ...... 480 Christine M. Glastonbury Index ...... 559 fm 1/7/09 12:23 PM Page viii fm 1/7/09 12:23 PM Page ix

Preface

Well, it wasn't easy! But then again, very few things that Chapter 1 has accomplished that objective. Paul Caruso are worthwhile come easily. Losing a renaissance man was the lead author and he and his colleagues Jennifer such as Ric Harnsberger as an editor/contributor would Smullen, Robert Liu, Mary Beth Cunane, and Hugh Curtin certainly be expected to make any task more difficult, but provided us with a highly detailed contribution useful to 10 years between editions was more than we could have radiologists, otolaryngologists, and technologists alike. possibly anticipated! Paul was also very helpful by providing us with many Production was complicated by a number of foresee- images utilized in this book, especially those pertaining to able and unforeseeable events and was not without high normal anatomy and congenital malformations. levels of drama and anxiety as well as an obligatory high- Our good friend, Doug Phillips, spearheaded an out- wire act. But after all is said and done, this story has a standing contribution on the facial nerve for Chapter 7 happy ending. We are very proud of this authoritative with a very tight deadline and we are deeply indebted to monograph. him and his coauthors George Hashisaki and Francis Imaging of the Temporal Bone continues to evolve as a Veillon. Doug was also very helpful to us in procuring a comprehensive reference book. The text has been number of images used in this book. The editors also wish rewritten and expanded throughout, the illustrations to to thank Lucianna Ramos Taboada, Maher Abu Eid, and a large extent have been replaced by more cutting edge Sophie Riehm for their outstanding contributions. high resolution CT and MR images, and the bibliography Mauricio Castillo is a productive neuroradiologist, has been extensively updated. The index has been author, editor, administrator, and friend who took time expanded as well and is now on par with other contem- from his increasingly busy schedule along with lead porary reference books. Our main focus is centered on author Valerie Jewells to produce Chapter 2 on the external the imaging specialist, but we continue to hope that our auditory canal. clinical colleagues find our contribution of interest and Tim Larson provided considerable help with the postop- importance as well. The chapter organization remains erative middle ear and mastoid in Chapter 3. His experience identical to previous editions. If it's not broken, why and support allowed us to successfully update and expand fix it? this important section. This edition has substantially more contributors than Gul Moonis, Ann Kim, and clinical colleague and friend the previous editions. This was necessitated by a number Douglas Bigelow did a wonderful job with the subject of of factors, not the least of which are the exploding ad- vascular anatomy and tinnitus in Chapter 4, and our vances in imaging technology, as well as the increasing friend Christine Glastonbury provided an outstanding subspecialization within neuro-otology which results in contribution on imaging the cerebellopontine angle and certain facilities seeing specific types of cases more than internal auditory canal in Chapter 8. We are also indebted others. to Deborah Shatzkes and Edwin Wang for their contribution Comments from dedicated readers were the driving to temporal bone trauma, Chapter 6. force behind many of the changes in this fourth edition. We would like to take this opportunity to thank our Foremost among these suggestions was the request for superb medical illustrator, Lori Goldstein Motis, for many the introductory chapter to expand the “cookbook” of the beautiful drawings found throughout this book. approach to evaluating and imaging the temporal bone. And an enormous thank you to the entire staff at Thieme fm 1/7/09 12:23 PM Page x

x Preface

for their support, patience, and hard work in completing this and images that follow interesting and educational. project. And last, but not least, we especially want to thank We are greatly interested in any of our readers' our families, spouses Nina and Steve, and children Matthew comments or suggestions. Please feel free to e-mail us at and Laura, Daniel, Chuck, Benjamin, and Alexander. Where [email protected] or [email protected]. would we be without you? To the readership, we especially thank you for your Joel D. Swartz continued support. We hope that you find the information Laurie A. Loevner fm 1/7/09 12:23 PM Page xi

Contributors

Douglas Bigelow, MD Hugh D. Curtin, MD Associate Professor of Otorhinolaryngology—Head and Professor of Radiology Neck Surgery Department of Radiology Department of Otorhinolaryngology—Head and Neck Harvard Medical School Surgery Massachusetts Eye and Ear Infirmary University of Pennsylvania School of Medicine Boston, Massachusetts Philadelphia, Pennsylvania Christine M. Glastonbury, MBBS Associate Professor of Clinical Radiology Craig Buchman, MD Department of Radiology Associate Professor of Otolaryngology University of California, San Francisco Chief of Otology San Francisco, California Department of Otolaryngology University of North Carolina George Hashisaki, MD Chapel Hill, North Carolina Associate Professor Otolaryngology—Head and Neck Surgery Department of Otolaryngology—Head and Neck Surgery Paul A. Caruso, MD University of Virginia Health Systems Instructor of Radiology Charlottesville, Virginia Department of Radiology Harvard Medical School Valerie L. Jewells, DO Massachusetts Eye and Ear Infirmary Assistant Professor of Neuroradiology Boston, Massachusetts Department of Radiology University of North Carolina Chapel Hill, North Carolina Mauricio Castillo, MD Professor of Neuroradiology, Section Chief Ann Kim, MD Department of Radiology Assistant Professor of Radiology University of North Carolina Department of Radiology Chapel Hill, North Carolina University of Pennsylvania School of Medicine Philadelphia, Pennsylvania

Mary Beth Cunnane, MD Robert Liu, PhD Instructor of Radiology Instructor of Radiologic Physics Department of Radiology Department of Radiologic Physics Harvard Medical School Harvard Medical School Massachusetts Eye and Ear Infirmary Massachusetts General Hospital Boston, Massachusetts Boston, Massachusetts fm 1/7/09 12:23 PM Page xii

xii Contributors

Laurie A. Loevner, MD Deborah Shatzkes, MD Professor of Radiology and Otorhinolaryngology–Head Associate Professor of Radiology and Neck Surgery Department of Radiology Department of Radiology Columbia University College of Physicians and Surgeons Neuroradiology Section Director of Head and Neck Imaging University of Pennsylvania School of Medicine and St. Lukes–Roosevelt Hospital Center Health System New York, New York Philadelphia, Pennsylvania Jennifer L. Smullen, MD Gul Moonis, MD Instructor of Otology Assistant Professor of Radiology Department of Otology Department of Radiology Harvard Medical School Harvard Medical School Massachusetts Eye and Ear Infirmary Beth Israel Deaconess Medical Center Boston, Massachusetts Boston, Massachusetts Joel D. Swartz, MD Suresh K. Mukherji, MD President Professor and Chief of Neuroradiology and Head and Germantown Imaging Associates Neck Radiology Gladwyne, Pennsylvania Professor of Radiology, Otolaryngology–Head Neck Surgery, and Radiation Oncology University of Michigan Health System Francis Veillon, MD Ann Arbor, Michigan Professor of Medical Imaging Head of Ear, Nose, Throat, Visceral Imaging C. Douglas Phillips, MD Service de Radiologie I Professor of Radiology, Neurosurgery, and Hôpital de Hautepierre Otolaryngology–Head and Neck Surgery Strasbourg Cedex, France Departments of Radiology, Neurosurgery, and Otolaryngology–Head and Neck Surgery Edwin Y. Wang, MD University of Virginia Health Systems Diagnostic Imaging of Salem Charlottesville, Virginia Salem, Oregon ch01 9/19/08 10:52 AM Page 1

Temporal Bone Imaging Technique 1 Paul A. Caruso, Jennifer L. Smullen, Robert Liu, Mary Beth Cunnane, and Hugh D. Curtin

This chapter on the technique for imaging the temporal The anatomy and pathology of the temporal bone bone is a practical “how to” written in two parts. In the involve small structures; resolution is thus highly impor- first part, we explain how to image the temporal bone: tant. Collimation is of optimal importance to achieve high how to run the hardware and obtain the images. We present resolution. the imaging modalities and technical parameters routinely We routinely use a collimator of 0.6 mm and most used for imaging of the temporal bone. In addition, we commercially available units can be collimated to at least provide guidelines for the technologist or radiologist as 1 mm. Collimation wider than 1 mm is not usually used, to how to determine which parameters to enter into the as the resolution is often insufficient. computed tomography (CT) or magnetic resonance imaging For 40 to 64 detector scanners, the effective mAs (MRI) scanner. In the second part, we explain how to read (defined as the mA the gantry cycle time/helical pitch) and report the results of temporal bone imaging studies. is adjusted according to the age and head size. Usually, it is

Here we provide a plan of action for the radiologist who, 150 effective mAs (CTDIvol [volume CT dose index] 34 mil-

faced with a request for a temporal bone imaging study on ligray [mGy]) for neonates, 200 effective mAs (CTDIvol a particular patient, must protocol the case, interpret the 45 mGy) for children ages 1 to 10 years, 250 effective

images, and report the findings in a way that answers the mAs (CTDIvol 57 mGy) for adolescents, and 320 (CTDIvol referring clinician’s questions. The major indications for 72 mGy) for adults. The gantry cycle time is set at 1 cycle imaging of the temporal bone are thus reviewed, and or gantry rotation/second. The kilovolt peak (kVp) is protocols, interpretive strategies, and template reports are usually 120. provided for each of these indications. A helical mode is chosen. Although traditionally, some imagers maintain that nonhelical scans provide better resolution, it is our experience that the difference in reso- Imaging Modalities and Technical lution between nonhelical and helical acquisitions at thin collimation is not appreciable, and helical acquisitions Parameters allow for clearer coronal or oblique reformats and decrease susceptibility to motion artifact. CT and MRI are primarily used for imaging of the tempo- Intravenous (IV) contrast is usually of the low osmolar ral bone. We first present the standard technique and type; it is administered by power injector at standard protocols most often used, then review the special doses of 1 mL/lb to a maximum of 80 to 100 mL for adults. considerations for both modalities. A brief overview of IV contrast is used for the evaluation of vascular pathology the roles of plain radiographs, ultrasound (US), positron (e.g., dissection, tumors) and may be considered for some emission tomography (PET), and PET/CT is given at the types of infections such as coalescent mastoiditis or for end of this section. the evaluation of abscesses. However, it is not routinely used to evaluate for otomastoiditis or hearing loss. The raw data from each ear are separated and recon- Computed Tomography structed into 0.6 mm (slice thickness) axial images in bone algorithm at a dual field of view (DFOV) of 100 mm Routine Technique that effectively magnifies the images. Then the 0.6 mm The patient is placed supine in the gantry and positioned to images for each ear are brought up on the CT scanner place the lens of the eye as far as possible out of the path- console, where the raw data are displayed in three way of the x-ray beam to minimize exposure to the lens. orthogonal planes. The technologist scrolls through the Gantry tilt may need to be avoided to facilitate image sagittal data to find an image where the anterior and pos- reconstruction and reformats. A lateral topogram is then terior limbs of the lateral semicircular canal are displayed performed. The scan excursion is plotted from the arcuate in cross section (Fig. 1.1). An axial dataset is then made in eminence (the summit of the temporal bone) through the a plane parallel to the lateral semicircular canal (LSCC). mastoid tip. The technologist “connects the two dots” of the LSCC and

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2 Imaging of the Temporal Bone

A B

C D Fig. 1.1 Making the standard axial and coronal computed tomogra- 0.1 mm overlap parallel to this plane. (C) If the axial reconstructions phy (CT) dataset. (A) Once the source data are brought up in the have been done correctly, the axial dataset should produce an image three-dimensional (3D) viewer on the scanner console, the sagittal where the entire lateral semicircular canal is displayed and, as in images are scrolled through until a sagittal image through the ante- (D,E), where the cochlear fossette, modiolus, and stapes footplate rior and posterior limbs (short white arrows) of the lateral semicircular are clearly delineated. canal (LSCC) are found. (B) A set of axial images is then generated with ch01 9/19/08 10:52 AM Page 3

Chapter 1 Temporal Bone Imaging Technique 3

E F

G H Fig. 1.1 (Continued) (F) The coronal reconstructions are made in a simi- plane. (G) This technique should yield a set of coronal images where lar fashion. Starting with the sagittal image in (A), a plane perpendicular to Prussak’s space (short white arrow) and (H) the facial nerve canal (short the LSCC is established, and the coronal reformats are made along this white arrow) are clearly delineated. ch01 9/19/08 10:52 AM Page 4

4 Imaging of the Temporal Bone

makes a 0.6 mm (image thickness) 0.5 (distance between are brought up on the console viewer in three orthogonal images) axial dataset in this plane parallel to the LSCC; planes: axial, coronal, and sagittal. As above, the technol- 0.6 0.5 mm coronal images are made in a plane perpen- ogist scrolls through the sagittal plane until a view of the dicular to the axial images. The raw data are also recon- LSCC is obtained represented by the two “dots” of the structed into 2 mm axial images in soft tissue algorithm anterior and posterior limbs (Fig. 1.3). The axial plane is to include both ears and the brain at 180–210 mm DFOV. then established by connecting the two dots. The tech- This protocol generates seven sets of images, three for nologist then scrolls through the axial dataset until an each ear—the source 0.6 mm images (in a variable axial image of the summit of the SSC is viewed. The Pöschl plane), the 0.6 mm reformats in the axial plane parallel to reformats are then made by tracing a line parallel to the the LSCC, the 0.6 mm reformats in the coronal plane, and long axis of the summit of the SSC at 0.6 0.5 mm a set of 2 mm axial images in soft tissue algorithm of the intervals. The line must be made as parallel as possible to entire scan volume. the axis of the summit of the SSC. A slight obliquity may spuriously obscure a dehiscence by volume averaging with the temporal bone on either side of the summit of Multidetector Computed Tomography Reformats the SSC. Multidetector CT provides shorter acquisition times, a decrease in tube current load, and improved spatial resolution.1 Short acquisition is useful in temporal bone imag- Computed Tomography Arteriography ing to reduce motion artifact, particularly in children who and Computed Tomography Venography require sedation or are imaged postprandially without CT arteriography (CTA) or CT venography (CTV) of the pharmacologic sedation. Although the radiation dose temporal bone may be used to evaluate for tinnitus. At our with multidetector scanners in high-quality mode remains institution, the standard CT protocol for temporal bone an issue compared with single detector scanners, the imaging is employed, but the injection rate is increased to improved spatial resolution allows for high-quality refor- 3 to 4 cc per second for CTA. A power injector is employed mats that essentially obviate the need for rescanning the if a 22-gauge IV or larger is available. patient in a second coronal plane.1 Reformats may, moreover, be obtained in sagittal or oblique planes to improve the detection of pathology in specific clinical settings such as superior semicircular Radiation Dose Reduction Techniques canal dehiscence (SSCD) as discussed below in the section and Considerations for Pediatric Patients Vertigo and Dizziness. Compared with most radiography procedures, CT exams deliver higher radiation dosages to patients. The quantity Stenvers Reformat CTDIvol is used to describe the patient dose. CTDIvol repre- Similar to the method explained above, for making the sents the average dose in a given scan volume. When a standard axial and coronal images, the 0.6 mm raw data scan is prescribed, the system displays the CTDIvol in mGy are brought up on the console viewer in three orthogo- on the console. However, the dose displayed is not the nal planes: axial, coronal, and sagittal. As above, the true dose for the specific patient under examination. Instead, technologist scrolls through the sagittal plane until a it is the dose value when the patient is replaced with an view of the LSCC is obtained represented by the two acrylic phantom while the same imaging parameters are “dots” of the anterior and posterior limbs (Fig. 1.2). The used. The head phantom is a cylinder with a diameter of axial plane is then established by connecting the two 16 cm and a height of 15 cm. dots. The technologist scrolls through the axial dataset The effective dose E is used to assess the radiation until an image of the summit of the SSC is viewed. The detriment from partial-body as opposed to whole-body Stenvers reformats are then made by tracing a line per- irradiation (e.g., irradiation of only the head or only the pendicular to the long axis of the summit of the SSC at abdomen). The effective dose is a weighted sum of the 0.6 0.5 mm intervals. This plane is effectively perpen- doses to all exposed tissues. E (wt Ht), where Ht is dicular to the roof of the SSC and displays the roof of the the equivalent dose to a specific tissue and wt is the SSC in cross section. weight factor representing the relative radiosensitivity of that tissue. The unit of effective dose is sievert (Sv). The effective dose for a typical CT exam of the temporal Pöschl Reformat bone is 1 mSv (i.e., 1/1000 Sv). In comparison, the Similar to the method explained above, for making the average effective dose from cosmic rays, radioisotopes in standard axial and coronal images, the 0.6 mm raw data the soil, radon, and so on, is 3 mSv per year in the ch01 9/19/08 10:52 AM Page 5

Chapter 1 Temporal Bone Imaging Technique 5

A B

Fig. 1.2 How to make a Stenvers reformat. (A) Once the source data are brought up in the three-dimensional viewer on the scanner console, the axial images are scrolled through until an image through the summit of the superior semicircular canal (SSC; short white arrows) is found. (B) The Stenvers reformats are made in a plane perpendicular to the long axis of the SSC, and (C) should yield a cross-sectional view of the SSC (short C white arrow).

United States. The effective dose can be estimated from according to the linear nonthreshold dose–response 3 the dose-length product (DLP CTDIvol scan length), model. which is also displayed on the CT scanner console. The For CT of the temporal bone, the primary concern for effective dose for a head study in mSv is 0.0021 DLP deterministic effect is the dose to the lens. The minimum (mGy cm).2 dose required to produce a progressive cataract is 2 Gy in a single exposure.4 If the lens is in the direct x-ray beam, Radiation Risks The biological effect of radiation is either the dose to the lens from CT of the temporal bone is in the deterministic or stochastic. The deterministic effect will range of 0.03 to 0.06 Gy, but it could be as high as 0.13 Gy. not occur unless a threshold dose is exceeded. However, If the patient is positioned in such a way that the lens is the stochastic effects may occur at any dose level, and the outside the direct x-ray beam, the dose is in the order of probability of occurrence increases with dose linearly 0.003 Gy.5 Although the typical dose to the lens from a single ch01 9/19/08 10:52 AM Page 6

6 Imaging of the Temporal Bone

A B

Fig. 1.3 How to make a Poschl reformat. (A) Once the source data are brought up in the three-dimensional viewer on the scanner console, the axial images are scrolled through until an image through the summit of the superior semicircular canal (SSC) is found. (B) The Poschl reformats are made in a plane perpendicular to the long axis of the SSC, and (C) should yield a view of the entire excursion of the SSC (short white C arrows) from anterior to posterior.

CT scan is much lower than the threshold value for a Factors Influencing the Patient Dose The CT scanning cataract, multiple nonoptimized scans in a short time with protocols should be optimized such that the quality of the lens in the x-ray beam can result in a lens dose close to images is sufficient for diagnosis and the patient dose is the threshold. Every effort should be made to keep the lens kept as low as reasonably achievable (ALARA). To get the outside a direct x-ray beam if it is possible. best balance of the image quality and patient dose, it is Stochastic effects include carcinogenesis and the induc- important to understand the effects of imaging parameters tion of genetic mutations. Children are inherently more on the dose and imaging quality. sensitive to radiation because they have more dividing Patient dose depends on three factors: equipment- cells, and radiation acts on dividing cells. Also, children related factors, patient-related factors, and application- have more time to express a cancer than do adults.6 related factors. ch01 9/19/08 10:52 AM Page 7

Chapter 1 Temporal Bone Imaging Technique 7

The factors in the first group include x-ray beam filtra- and adjust these parameters to reduce dose, while main- tion, x-ray beam collimation, system geometry, and detec- taining image quality. tor efficiency. Although users do not have control of most Often these adjustments are done empirically, and the of these factors, it is important to understand that the technique described above (see Routine Technique sec- z-axis dose efficiency is reduced when the total x-ray beam tion) represents our experience with such adjustments. width becomes very small for multidetector CT due to the need to keep the beam penumbra out of any detector row. The dose is strongly dependent on patient size. If the Magnetic Resonance Imaging same technique is used to image the heads of an average Routine Technique adult and a newborn, the dose to the newborn is significantly higher. The standard MRI protocol for evaluation of the temporal Imaging parameters such as kVp, mAs (the product of bone in adults is detailed below for a 1.5T (Tesla) magnet. the tube current and the time in seconds per rotation), The patient is placed in the supine position in the head and pitch (the table travel per rotation divided by the total coil. x-ray beam width) are selected by the operator. Sagittal T1-weighted, axial T2-weighted, axial fluid If all other parameters are fixed, the patient dose is attenuated inversion recovery (FLAIR), and axial diffusion proportional to the effective mAs which is defined as the weighted images (DWIs) are obtained through the whole mAs (mA seconds per rotation) divided by the pitch. brain. The dependency of dose to kVp is more complicated. In Axial T1-weighted images are obtained through the general, the dose increases as a power function of kVp temporal bone from the arcuate eminence through the (D kVpp) if all other parameters are fixed. The value of p is mastoid tip using the following parameters: TR (time to in the order of 2 to 3 depending on the type of scanner. repetition) 300 milliseconds; TE (echo time) 12 milliseconds; flip angle 90 degrees; slice thickness 3 mm; Image Quality Image quality is characterized by spatial distance factor 0.10; matrix 192 256 (phase to fre- resolution, contrast resolution, image noise, and other quency encoding steps); FOV 180 mm; two acquisitions, quantities. It is difficult to use a single variable to characterize one saturation, time 3 minutes, 15 seconds. completely the quality of an image. However, in practice, Axial CISS (constructive interference in steady state; image noise has been widely used to judge the CT image Siemens AG, Berlin/Munich, Germany) or 3D (three- quality because the detectability of low-contrast objects is dimensional) FIESTA (fast imaging employing steady-state strongly dependent on the contrast-to-noise ratio. The acquisition; General Electric Healthcare, Waukesha, WI) standard deviation of a region of interest (ROI) in the image images are obtained through the internal auditory canals is usually used to represent the noise. In CT, for a given and pons using the following parameters: TR 12.25; reconstruction kernel, the noise is primarily due to the TE 5.9; flip angle 70 degrees; one slab, slab thickness fluctuation of the x-ray photons reaching the detector. 32 mm; effective thickness 0.7 mm; number of partitions The noise is approximately inversely proportional to the 46; matrix 230 512; FOV 200; swap left (L) to right square root of the patient dose. To reduce the noise by a factor (R), no saturation, time 4 minutes, 20 seconds. of 2, the dose must be increased by a factor of 4. In general, Gadolinium is then administered. image quality is better when the patient dose is increased. Axial T1-weighted images are obtained through the whole brain. Thin section axial T1-weighted images of the temporal Strategy for Dose Reduction To optimize the CT technique, bone are performed in two interleaved sets, using the fol- the image quality required for the specific indication is lowing parameters: TR 450 milliseconds; TE 15 milli- assessed based on the radiologist’s experience. The imaging seconds; flip angle 90 degrees; slice thickness 2 mm; parameters are then selected based on the patient size and distance factor 0.10; matrix 192 256 (phase to fre- organ type under exam such that the required image quency encoding steps); FOV 170 mm; two acquisitions, quality is achieved, while the patient dose is kept as low as swap L to R, one saturation, time 4 minutes, 20 seconds possible. Weight- or age-based pediatric protocols should be for each set; total time 8 minutes, 40 seconds. established and special attention should be paid to children Coronal T1-weighted images are obtained through the under age 2 because their heads are small and under rapid internal auditory canals using the following parameters: development. TR 450 milliseconds, TE 15 milliseconds, flip angle In general, the technologist and radiologist should keep 90 degrees, slice thickness 3 mm, no gap, matrix 192 256 in mind that (phase to frequency encoding steps), FOV 170 mm, three Dose mA, time in seconds per rotation of the gantry, acquisitions, swap L to R, one saturation, time 4 minutes kVp2.5, and 1/pitch 22 seconds. ch01 9/19/08 10:52 AM Page 8

8 Imaging of the Temporal Bone

Additional Considerations Safety Considerations Coronal high-resolution T1-weighted images may be use- Standard MRI safety considerations obtain in the tem- ful for more detailed imaging of the temporal bone; the poral bone, and the reader is referred to publications indications for the use of this sequence are reviewed in that list the safety of various prostheses.7 For those the Indications section. The technical parameters are as institutions with a busy otology service, the issue of follows: TR 528 milliseconds; TE 12 milliseconds; flip MRI compatibility of stapes prostheses, total ossicular angle 90 degrees; slice thickness 3 mm; distance replacement prostheses (TORPs), and partial ossicular factor 0.20; matrix 338 512 (phase to frequency replacement prostheses (PORPs) may arise. These pros- encoding steps); FOV 200 mm; two acquisitions, swap L theses are listed as well in the standard MRI safety to R, no saturation, time 5 minutes, 7 seconds. references. Most stapes prostheses do not deflect significantly in a 1.5 T unit.

Magnetic Resonance Angiography Plain Film Radiography The imaging parameters for MRA (provided here for a 3T magnet) are TR 25 milliseconds; TE 3.5 milliseconds; Plain film radiographs have limited application to imaging flip angle 20 degrees; slice volume 140; R to L of the temporal bone. A plain radiograph in the Stenvers fold-over direction, superior venous saturation band, dis- projection, however, may be used for intraoperative or tance factor 0.10; matrix 496 284; FOV 200 mm; postoperative confirmation of position of a cochlear one acquisition, time 6 minutes. implant lead. The patient’s head is placed in a 45-degree The most common indication for MRA is in the evalua- obliquity contralateral to the implanted ear that places the tion for tinnitus. For this indication, MRA is used to axis of the implanted temporal bone parallel to the film evaluate for dural arteriovenous fistulas, aneurysms, and then in a 15-degree Townes projection. For example, vasculopathies such as fibromuscular dysplasia, or arteri- if the left ear has been implanted, the radiographer would ovenous malformations (AVMs). turn the head 45 degrees to the right, with the film behind There are two important considerations for MRA the head of the patient, and shoot a single radiograph in the evaluation of tinnitus: data acquisition and with the beam tilted 15 degrees inferiorly toward the postprocessing. patient (Fig. 1.4). Familiarity with this projection and with Suppression of normal venous flow-related signal is the proper position of a cochlear implant is one of the key to increase the specificity of the scan for abnormal few instances in current imaging where plain film radiog- arterialized flow in the major dural venous sinuses that run raphy is critical, as the intraoperative assessment is often along the temporal bone; thus, care should be taken to made while the patient is still anesthetized on the operat- place the venous saturation band so that normal venous ing room table. inflow is suppressed. The radiologist should be familiar with the normal artifacts that his or her MRI scanner produces in the dural sinuses on MRA so as to adjust the level Ultrasound of specificity accordingly when interpreting MRAs in patients with pulsatile tinnitus. On some current 3T units, Ultrasound may be used for evaluation of periauricular for example, there is essentially no flow-related signal in cystic lesions such as first pharyngeal arch anomalies or the dural sinuses when the venous saturation bands are ultrasound-guided biopsies of periauricular lesions. placed appropriately. For postprocessing, the technologist must provide the entire source dataset to the radiologist for review. Many Positron Emission Tomography (PET) technologists are trained to MIP (to perform maximum or PET/CT intensity projections of) only the circle of Willis—the PET or PET/CT may be used for the assessment of temporal internal carotid artery, middle cerebral artery (MCA), bone masses or nodal metastases. anterior cerebral artery (ACA), posterior cerebral artery (PCA), and basilar artery and to “cut out” the peripheral data. In the evaluation of tinnitus, however, the data on the edge of the scan are the principal data of interest. Referrals and Imaging Strategies Dural arteriovenous formations (AVFs) may occur on the edge of the dataset near the dural sinuses. The source In this part of the chapter, we address the major clinical data must be reviewed, and if MIPs are performed, they indications for which a patient may be referred for temporal should include the entire dataset. bone imaging. The indications are listed in alphabetical ch01 9/19/08 10:52 AM Page 9

Chapter 1 Temporal Bone Imaging Technique 9

suppurative labyrinthitis, facial nerve inflammation, and meningitis, but CT is overall the preferred initial study.

Interpretation Clinical Background Commonly, patients with AOM present with a bulging ear drum and otalgia and appear sick with fever, malaise, and lethargy. Depending on the level of clinical concern for severity and sequelae of the AOM, the clinician will refer the patient for imaging to evaluate for intratemporal and extratemporal complications of AOM. Long-term antibiotic therapy may be indicated, for instance in the setting of coalescent mastoiditis.8

Clinical Questions • Are there intratemporal (local auricular) complications of AOM, such as coalescent mastoiditis, osseous erosion, facial nerve involvement, or suppurative labyrinthitis? • Are there extratemporal complications of AOM, such as sigmoid sinus thrombosis, epidural abscess, or meningitis? Fig. 1.4 A Stenvers radiograph for cochlear implantation. If the Sten- vers radiograph is performed correctly, the cochlear implant lead (short white arrow) should lay coiled in the cochlea, anterior and inferior to Approach the vestibule and lateral and superior semicircular canals (SSCs; summit Evaluate for evidence of intratemporal complications of of SSC marked by long white arrow). AOM.

• Inspect the osseous margins of the mastoid for evi- order, and for each clinical indication, the following points dence of demineralization (bone algorithm images) are addressed. and for subperiosteal abscess (soft tissue algorithm images) that may reflect a coalescent mastoiditis. It is 1. How to protocol the case. You have the requisition in our experience that asymmetry of the central trabecu- hand. What type of scan do you ask the technologist to lation of the mastoids is not specific for the diagnosis do? of coalescent mastoiditis and that demineralization 2. How to interpret the study. An interpretive strategy is along the external or cisternal walls of the sinus is a provided that first considers the clinical background, more reliable sign. then highlights the clinical questions most commonly • Inspect the osseous margins of the facial nerve canal asked by clinicians. Accordingly, a checklist approach for demineralization that would suggest inflammatory to the images is presented. dehiscence. This evaluation is problematic on CT, as the 3. How to report the findings. A report template is provided wall of the tympanic segment is naturally papyraceous. to help with the dictation. An MRI would be a more sensitive modality for detection of neuritis. • Evaluate for erosion of the walls of the membranous Acute Otitis Media labyrinth that would suggest a suppurative labyrinthitis. Again, an MRI would be a more sensitive modality Protocol for evaluation for enhancement of the labyrinth. A routine CT scan of the temporal bone is the standard • Evaluate for a middle ear cavity cholesteatoma. protocol. If there is clinical concern for sinus thrombosis or coales- Evaluate for extratemporal sequelae of AOM. cent mastoiditis, the study is performed with IV contrast. MRI is a more sensitive modality for evaluation of some • Inspect the margins of the middle ear cavity (MEC) and of the complications of acute otitis media (AOM), such as mastoid for evidence of epidural or Bezold abscess. ch01 9/19/08 10:52 AM Page 10

10 Imaging of the Temporal Bone

• Evaluate the transverse and sigmoid sinus for evidence • Is the mastoid healthy or diseased, and what is the size of thrombosis. of the mastoid? • Evaluate the meninges for evidence of meningitis. Here • What is the state of the ossicular chain? again, an MRI would be a more sensitive modality. • Is the external auditory canal (EAC) eroded? • How well aerated is the MEC?

Report Active Chronic Otitis Media with Cholesteatoma It is On the right/left, the external auditory canal is severely important to keep in mind that the radiologist may not opacified. The middle ear cavity is completely opacified, and sometimes need to make the diagnosis of COM (or severe periauricular inflammation is noted. There are no sometimes cholesteatoma) if such has been made by the findings specific for a coalescent mastoiditis. No erosion otologist already. is seen along the course of the facial nerve canal or walls For a patient wth COM and a cholesteatoma, the clini- of the inner ear. No lobular opacity is seen specific for a cian in his or her consideration of surgical management cholesteatoma. No extratemporal sequela of acute otitis confers with the radiologist to help answer the following media is seen: no Bezold or epidural abscess, sinus thrombosis, three questions. or meningitis is seen. • Is the cholesteaoma limited to the attic? • Is the mastoid well pneumatized and aerated (healthy) and what is the size of the mastoid? Chronic Otitis Media, Chronic • Is the EAC eroded? Otomastoiditis Protocol The answers to these questions may lead to three distinct surgical procedures. A noncontrast CT of the temporal bone is the preferred If the cholesteatoma is confined to Prussak’s space, and modality. the lateral attic and the mastoid are healthy (well pneumatized and aerated), then an anterior atticotomy may be performed, where the surgeon removes the scutum and Interpretation lateral attic and leaves the mastoid intact. Clinical Background If the cholesteatoma extends beyond the attic, and the mastoid is healthy, then a canal wall up (CWU) technique Otologists divide patients with chronic otitis media is preferred with a planned second-look procedure. (COM) into three groups: If the cholesteatoma is beyond the attic, and the mastoid is unhealthy, or if there is erosion of the EAC, then a 1. Active COM with or without cholesteatoma canal wall down (CWD) technique is preferred. 2. Inactive COM with retraction pocket, perforation, Other clinical considerations may lead to a CWD tech- ossicular resorption, or fixation nique such as surgical preference, single hearing dis- 3. Inactive COM with frequent reactivation eased ear (each surgery carries a 1% risk of sensorineural hearing loss), poor patient compliance, or poor patient The goal of imaging, therefore, is to guide the clinical health, such that a CWU with second-look would be management (including surgery) in each of these three problematic. groups and to evaluate for complications. Active Chronic Otitis Media without Cholesteatoma If the patient has active COM without cholesteatoma, then the Clinical Questions surgical management depends on the health and size of There are six questions to answer in evaluating a patient the mastoid. Hence, the most important question to be with COM. If the radiologist addresses these issues, what- addressed: ever the group of COM, the major clinical questions will have been answered. • Is the mastoid well pneumatized and aerated, and what is the size of the mastoid? • Is there a cholesteatoma, is it confined to the external attic, or has it spread beyond the attic? The larger the mastoid, the more problematic a CWD • Are there any complications of COM, such as perilym- procedure becomes, as it may be difficult to manage a phatic or horizontal canal fistulas, tegmen dehiscence, large mastoid cavity, status post CWD, postoperatively, or fallopian canal dehiscence? while waiting for the mastoid bowl to reepithelialize. ch01 9/19/08 10:52 AM Page 11

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On the other hand, the more severe the mastoid granu- words, air cells that are inflamed or filled with serous lation tissue and inflammation (reflected by opacity on effusion versus those air cells that never developed. If CT), the more a CWD procedure is indicated. there is active COM with cholesteatoma, then the sur- Thus, the decision between CWU and CWD is a balance gery depends on the health of the mastoid, as above. If between the severity of mastoid granulation tissue and there is active COM without cholesteatoma, then a the size of the mastoid. A patient with a severely opaci- CWU technique is preferred if the mastoid is healthy, fied small sclerotic mastoid would be a good candidate for and a CWD is preferred if the mastoid is severely diseased. CWD. A patient with a large, well-aerated mastoid would • Report any surgical landmines. There are three surgi- be a good candidate for CWU. cal landmarks that must be assessed not only for COM surgery, but whenever a CWD or CWU technique is Inactive Chronic Otitis Media There are two reasons to contemplated: image in the setting of inactive COM: presurgical planning • The position of the jugular bulb. As the surgeon ap- and to evaluate for complications of COM. In other words, proaches the mastoid and MEC from lateral to medial, inactive COM is not in itself an indication for surgery, but a jugular bulb that ascends above the floor of the MEC the sequela of prior COM such as ossicular erosion leading can prove to be a surgical hazard and thus should be to conductive hearing loss (CHL) may be an indication. reported. Describing the intactness of the ossicular chain in this • The position of the sigmoid sinus with respect to the setting, for example, will help to guide the tympanoplasty posterior wall of the EAC. This distance helps to deter- (MEC and/or ossicular reconstruction). mine the operative window (in the sagittal plane) that Therefore, for inactive COM, there are two questions to may be safely opened in the mastoid. be answered. • The position of the mastoid tegmen with respect to the roof of the MEC and a low-lying tympanic tegmen. • What is the state of the ossicular chain? A low-lying mastoid tegmen can prove to be a surgical • How well aerated is the MEC? hazard and should be reported.

The state of the ossicular chain will guide the choice of In addition to these considerations, other surgical haz- ossicular reconstruction. The aeration of the MEC is impor- ards such as a dehiscent CN VII or horizontal canal fistula tant for determining the prognosis for hearing outcome should be reported. after ossicular chain reconstruction.

Inactive Chronic Otitis Media with Frequent Reactivation Report Inactive COM with frequent reactivation can be managed On the right/left, the EAC is well aerated, and no erosion is with CWU or CWD mastoidectomy. seen. The tympanic membrane (TM) appears thick, which may reflect myringosclerosis. There are no findings specific Approach for cholesteatoma. The middle ear cavity is moderately A lateral-to-medial approach may be used. opacified, which likely reflects granulation tissue in the setting of the reported chronic otitis media. The ossicles are intact. • Evaluate the EAC for erosion. If the EAC is eroded in the The mastoid appears small, sclerotic, and completely opaci- setting of active COM with or without cholesteatoma, a fied. The jugular bulb is not high-riding. The sigmoid notch CWD procedure will be preferred to remove the diseased is 15 mm posterior to the posterior wall of the external cells along the EAC. auditory canal. The mastoid tegmen is in normal position. • Address the issue of cholesteatoma. Are there findings CN VII describes a normal course. No inner ear dysplasia is that suggest or raise concern for a cholesteatoma? If so, seen. The internal auditory canal appears normal. describe its extent especially with regard to the attic. In this case, the imaging findings are most consistent • Describe the aeration or opacification of the MEC. with chronic otitis media without cholesteatoma, and the • Evaluate the ossicular chain. If there is CHL in the set- patient would most likely undergo a canal wall down mas- ting of inactive COM, then the reconstructive procedure toidectomy in light of the severely diseased mastoid. (e.g., tympanoplasty, TORP, or PORP) will depend on the intactness of the ossicular chain. • Evaluate the mastoid for size and pneumatization and Cochlear Implantation for those imaging findings such as sclerosis and opaci- Protocol fication that may suggest mastoid inflammation. Here, it is important to recognize the difference between a A standard CT of the temporal bone is prescribed without sclerotic mastoid and an opacified mastoid in other IV contrast. ch01 9/19/08 10:52 AM Page 12

12 Imaging of the Temporal Bone

If there is clinical concern or CT findings that raise con- • Inspect the facial recess, where the electrode is usually cern for hypoplasia of CN VIII (e.g., stenosis of the cochlear threaded from the mastoid into the tympanic cavity, fossette or internal auditory canal [IAC]), a noncontrast and evaluate the pneumatization of the recess and MRI of the temporal bone that may be limited to 3D FIESTA, describe the position of the facial nerve with respect to CISS, or DRIVE (driven equilibrium) sequence should be the recess. An aberrant or dehiscent nerve or a laterally considered for evaluation of CN VIII. positioned posterior genu may lead to injury and require an alternate approach to the MEC. • Inspect the MEC and round window niche, at the site Interpretation of cochleostomy, for aeration. Clinical Background • Evaluate the inner ear for evidence of malformation that may reduce the efficacy of the implant or make Candidates for cochlear implantation have severe bilat- insertion more challenging. Cochlear malformation may 9 eral sensorineural hearing loss (SNHL). The otologic require modification of electrode insertion techniques. work-up and audiogram have already identified a defect Inner ear malformations may raise the risk of meningitis. that involves the hair cells in the organ of Corti within Labyrinthitis ossificans (LO) that may be a sequela of the cochlea, and a decision has been made to consider the prior meningitis may limit the ability of the surgeon to patient for an implant. The focus is thus less on diagnosis advance the electrode.10,11 If there is evidence of LO, an of the cause of the SNHL and more on the preoperative MRI should be performed to determine better the caliber planning. In general, successful implantation depends on of the membranous labyrinth. a patent cochlea, an intact CN VIII, and adequate mastoid • Evaluate the cochlear fossette (bony canal for CN VIII aeration for access to the facial recess. at the base of the cochlea) for evidence of stenosis that may herald a hypoplastic nerve or dysplasia that Clinical Questions may increase the risk for a cerebrospinal fluid (CSF) leak. • Are there any potential hazards based on the patient’s • Check the otic capsule for evidence of otospongiosis or, anatomy that the surgeon may encounter while placing for example, Paget disease that may increase the risk of the implant? facial nerve stimulation from the electrode.12 • Describe the IAC. If the canal appears stenotic, an MRI should be considered to evaluate the intactness Approach of CN VIII, as IAC stenosis may be associated with The approach is thus to inspect the temporal bone moving CN VIII hypoplasia or aplasia, a contraindication to from superficial to deep, as if you were the surgeon plac- implantation. ing the cochlear implant electrode and threading it into • Evaluate the temporal bone for evidence of COM. Active position, keeping in mind the potential surgical pitfalls. COM is a contraindication to implantation. • Report any surgical landmines. There are three surgical • Inspect the thickness of the skull 4 to 5 cm posterior and landmarks that must be assessed: superior to the spine of Henle (posterosuperior margin • The position of the jugular bulb. As the surgeon of the EAC at the osteocartilaginous junction). The implant approaches the mastoid and MEC from lateral to device consists of a receiver stimulator package and a medial, a jugular bulb that ascends above the floor multichannel electrode. The receiver–stimulator pack- of the MEC can prove to be a surgical hazard and age is placed in a depression drilled on the external table thus should be reported. of the skull in this region.9 If the bone is thin, this finding • The position of the sigmoid sinus with respect to the should be reported; the implant receiver–stimulator posterior wall of the EAC. This distance helps to deter- may need to be placed against dura, and the dura may mine the operative window (in the sagittal plane) that need to be exposed intraoperatively. may be safely opened in the mastoid. • Report the pneumatization of the mastoid. If the mas- • The position of the mastoid tegmen with respect to toid is underdeveloped, the drilling will require more the roof of the MEC and a low-lying tympanic tegmen. effort, and if one ear is better pneumatized than the A low-lying mastoid tegmen can prove to be a surgical other, the more pneumatized side may be preferred. hazard and should be reported. • Evaluate the cisternal face of the petrous temporal bone for arachnoid granulations and for a lateral position of Report the sigmoid notch that may prove to be surgical obsta- cles. The position of the sigmoid notch may be reported The report summarizes this interpretive superficial-to-deep with respect to the posterior wall of the EAC. approach. ch01 9/19/08 10:52 AM Page 13

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On the right/left, the mastoids are well pneumatized and stapes are normal, surgery may be considered with aerated. The sigmoid notch is in normal position 15 mm parental consent. Otherwise, surgery for unilateral con- posterior to the posterior wall of the external auditory ductive hearing loss is usually delayed until the patient canal. The retrotympanum and facial recess are well aer- can consent.13 In cases of unilateral hearing loss, surgery ated. The CN VII describes a normal course; there is no carries a risk of SNHL. As long as the opposite ear pro- evidence of dehiscence along the facial recess. The middle vides the child with sufficient hearing for educational ear cavity is well aerated, including at the standard site of needs, surgery may be left until the patient is of the age cochleostomy. There are no findings specific for labyrinthitis of consent. ossificans. No otospongiosis is seen. No inner ear dysplasia Although most cases of congenital aural dysplasia is seen. The internal auditory canal appears normal. The (CAD) are isolated, there are also syndromic cases that external auditory canal, tympanic membrane, and ossicular may be associated with other craniofacial malforma- chain appear normal. tions that may require imaging. At least 30 distinctive Impression: Temporal bone anatomy, as detailed above. hereditary syndromes with hearing loss and abnormali- The EAC, TM, and ossicular chain are mentioned at the ties of the external ear have been described.14 Such syn- end of the report as they are not the primary considera- dromes may involve (1) the mandible, such as the tions for implantation. mandibulofacial dysostoses, oculo–auriculo–vertebral spectrum, or del22q (DiGeorge syndrome); (2) facial clefts, such as the HMC syndrome (hypertelorism– Congenital Aural Atresia, External Auditory microtia–clefting); (3) cervical cysts or fistulas, such as Canal Stenosis the branchio–oto–renal syndrome; (4) craniosynostoses, Protocol such as Apert or Crouzon syndrome; (5) the airway, such as the CHARGE association (a nonrandom pattern The routine CT temporal bone will answer most questions of congenital anomalies comprising colobomata, heart with regard to preoperative planning for atresiaplasty, which defect, choanal atresia, retarded growth and is the most common indication in this group of patients. development, genital hypoplasia, and ear abnormalities There are two protocol decisions, however, that you and/or deafness), or (6) less commonly, anomalies need to make when you have the requisition in hand, of the lacrimal drainage system, such as the lacrimo– before you check off the routine noncontrast CT temporal auriculo–dento–digital (LADD) syndrome. If time per- bone box. mits, inspection of the patient or focused interview of First, is the patient the correct age for imaging? Radio- the patient or parent may suggest a syndrome, and if so, logic evaluation is usually deferred until at least 5 years of coordination of the imaging with the oromaxillofacial age because microtia surgery, which is done to coincide surgeon, pediatric ear–nose–throat (ENT) physician, or with the atresia surgery, usually involves harvesting oculoplastic surgeon may save time and spare the patient of the costal cartilage that takes until 5 years of age to radiation and further anesthesia. mature sufficiently for surgical use.13 Second, if it is elected to study the craniofacial bones as well as the temporal bone (see Clinical Background section Clinical Questions directly below), the protocol may be modified to include the The surgical questions you will need to answer when abnormal bones in question; for a child with mandibulofa- patients with CAD are sent for imaging are as follows. cial dysostosis, for example, the scan should be carried from The atresiaplasty surgeon would like to know if the the frontal sinuses (or calvaria) through the hyoid bone to patient’s anatomy is such that the external auditory canal include the mandible using a 1 mm (instead of the standard and middle ear can be reconstructed and how difficult the 0.6 mm) collimator. The resolution of the temporal bone atresiaplasty may prove to be.13 images will be less than that of the standard 0.6 mm collimation technique, but allows for adequate evaluation of the • How pneumatized and large are the mastoid and mid- temporal bone anatomy, reduces the radiation dose, and dle ear cavity (i.e., will it be hard to drill the mastoid)? allows for 3D modeling of the craniofacial structures. • Is the facial nerve at risk for injury? • Are the oval window and stapes normal? Interpretation • Are the inner ear structures normal (i.e., what is the risk of acoustic injury to the inner ear during surgery)? Clinical Background • What is the status of the ossicular chain? In patients with bilateral atresia, multistage surgery commences around 6 years of age. In unilateral atresia, There is also a genetics question associated with imaging if the atresia plate is thin and the oval window and a CAD patient. ch01 9/19/08 10:52 AM Page 14

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• Is there an associated syndrome or evidence of other • Evaluate the orbits for ocular malformations, such as extraauricular malformation that may affect the patient’s coloboma, that may be seen in CHARGE association or prognosis? lacrimal drainage system abnormalities that may be seen, for example, in BOR, OAV, or LADD syndromes. The clinical goal is to use the CT to identify radiographic • Evaluate the maxillae and palate for evidence of clefting evidence of any associated finding that may aid in syn- disorder. dromic diagnosis. Although often a geneticist will have • Check the choanae for choanal stenosis that may be seen the patient, and the syndromic diagnosis will have seen, for example, in the CHARGE association. been made, a brief organized review of the images may unveil unexpected findings that may make or confirm the diagnosis. Report The report should answer the surgical questions for Approach which the patient was most likely referred in anatomical order from lateral to medial and then address the ques- To answer the surgical questions, the images are reviewed tion of associated syndrome, if there is any evidence from lateral to medial. thereof. An example of an isolated case of CAD follows. On the right/left, the mastoid air cells and middle ear • Describe the pneumatization of the mastoid and middle cavity are well pneumatized and aerated. The facial nerve ear cavity. describes an anomalous course: the labyrinthine and proxi- • Describe the course of CN VII, paying particular mal tympanic segments of CN VII appear normal, but the attention to segments that may be aberrant. Also, report nerve appears dehiscent along a 5 mm segment as it courses the anteroposterior (AP) distance from the posterior above the oval window and turns laterally into the meso- margin of the glenoid fossa to the descending portion of tympanum. The anteroposterior distance between the mas- the facial nerve because this space is where the surgi- toid segment of the facial nerve and the posterior margin of cally created external auditory canal will pass. the glenoid measures 7 mm. The mastoid segment is well • Describe the oval window and stapes. covered but exits into the posterior aspect of the deficient • Describe the appearance of the inner ear and the IAC. If glenoid fossa. The oval window appears normal. The the cochlear fossette or the IAC is stenotic, an MRI malleus appears fused to the atresia plate along the lateral should be considered with a 3D FIESTA, CISS, or DRIVE wall of the middle ear cavity. The incus is hypoplastic. The sequence for better delineation of the nerve. stapes appears normal. The middle ear cavity is mildly • Describe any other findings associated with CAD, such hypoplastic but well aerated. No inner ear dysplasia is seen. as ossicular dysplasias. The malleus and incus are com- The internal auditory canal appears normal. The external monly fused, and in nonsyndromic CAD, the stapes is auditory canal is atretic. The tympanic portion of the usually normal. temporal bone is deficient. The osseous component of the • Describe the thickness of the skull. The option to atre- atresia plate measures 6 mm at the level of the oval window siaplasty is a bone-anchored hearing aid (BAHA), which niche. is placed typically 5 cm behind the atretic canal. No other malformation is seen. Impression: Congential aural dysplasia, detailed above, Next, the genetic question is addressed, by doing a review with well-pneumatized mastoid and middle ear cavity, of the extraauricular components of the scan performed aberrant facial nerve, and normal-appearing inner ear from lateral to medial.

• Study the visualized cranial sutures to evaluate for Otitis Externa craniosynostosis (e.g., Apert or Crouzon syndrome). Protocol • Evaluate the periauricular soft tissues to search for fistulas or cysts that may be seen in BOR syndrome. A routine noncontrast CT scan is the modality of choice • Inspect the visualized zygomas; zygomatic deficiency for evaluation for otitis externa (OE) in both immunocom- is a common finding in first pharyngeal arch syn- petent and immunocompromised patients. Most of the dromes, such as the mandibulofacial dysostoses and relevant clinical questions (see the Interpretation section the OAV (oculo–auriculo–vertebral) spectrum. below) can be answered without IV contrast. Because • Inspect the visualized mandible to pick up those syn- evaluation of cartilaginous involvement is important in dromic cases that may be associated with mandibular OE, 2 mm coronal reformats in soft tissue algorithm are dysplasia, such as the OAV spectrum or mandibulofa- added to the protocol. Contrast-enhanced MRI may be cial dysostosis. performed in cases recalcitrant to initial therapy or with ch01 9/19/08 10:52 AM Page 15

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neurologic symptoms where intracranial infection becomes Report a consideration.15 The report should answer the pertinent clinical questions with regard to severity and extent of infection and any Interpretation identifiable cause. On the right/left, the external auditory canal is nearly Clinical Background completely opacified, consistent with the reported otitis Inflammation of the external auditory canal is usually externa. The cartilaginous margin of the external auditory apparent clinically before the patient is sent to imaging. canal appears blurred. There is no evidence of erosion of the A key clinical datum for the clinician and radiologist is a external auditory canal or mastoid. The middle ear cavity history of immunocompromise because necrotizing exter- and mastoid are only mildly opacified. No auricular inflam- nal otitis (NEO), otherwise known as malignant otitis mation is defined. There is mild reticulation of the periauric- externa (MOE), occurs classically in this group of patients ular soft tissues, consistent with cellulitis. No osseous erosion is (e.g., elderly diabetic patients or patients with HIV).16 seen. The ossicles appear normal. CN VII describes a normal course. The inner ear and internal auditory canal appear Clinical Questions normal. No abnormal-appearing lymph nodes are seen. • Is there evidence of NEO/MOE or otitis externa? For Impression: Findings consistent with right otitis externa example, is there bony involvement or inflammation with severe opacification of the external auditory canal and that extends into the soft tissues inferior to the EAC mild cellulitis that would suggest NEO? • What is the extent and severity of infection? • Are there any sequelae of infection? • Is there an identifiable nidus or cause of infection? Facial Nerve Disorders Protocol One sound interpretive strategy is to begin with the EAC and to move from lateral to medial, to assess the ear For atypical Bell’s palsy, multiple cranial neuropathies, for spread of inflammation. or facial nerve paresis of uncertain etiology, MRI of the facial nerve is the preferred modality. Atypical Bell’s palsy is a facial nerve palsy that has either slow onset Approach (progresses over weeks or months rather than days), • Inspect the auricle and periauricular soft tissues for incomplete recovery (failure to recover in 6 months), chondritis or cellulitis. Inflammation extending inferior or recurs. A high-resolution coronal postgadolinium to the EAC may indicate NEO. T1-weighted sequence through the course of the facial • Assess the severity of opacification of the EAC. The nerve and pregadolinium axial T1- and T2-weighted coronal soft tissue images are key in evaluating for car- sequences through the parotid gland should be added to tilage involvement that is the site of origin of NEO. In the standard temporal bone MRI protocol. MRI provides external otitis, the canal may stenose, and evaluation of superior imaging of the facial nerve nucleus and cister- the aerated lumen, following treatment of the acute nal segments of the nerve that are not well imaged by infection, may be a preoperative question for canalplasty. CT (Fig. 1.5). The canal is inspected as well for a foreign body that In the setting of trauma, a noncontrast standard CT may occasionally be at the origin of the inflammation.17 scan of the temporal bone is the preferred modality. • Describe the degree of opacification of the middle ear cavity (MEC) and mastoid, as these may be inflamed as well. It is important to keep in mind that it is not Interpretation unusual to have opacification of some middle ear air Clinical Background cells in the setting of EO and that otomastoid opacification alone does not indicate NEO. Most patients sent for imaging of the facial nerve fall into • Scrutinize the bone for erosion, especially the tympanic two categories: atypical “Bell’s palsy” or posttraumatic and mastoid components of the temporal bone. Bony facial nerve paresis. erosion suggests NEO and may indicate the need for Bell’s palsy accounts for 80% of peripheral facial nerve long-term parenteral antibiotics. If there is evidence of paresis. Certain clinical features of CN VII paresis, however, skull base erosion and osteomyelitis, an MRI should be may prompt the clinician to question a diagnosis of Bell’s considered to evaluate for intracranial involvement, for palsy, such as recurrent episodes of paresis, slow progres- example, an abscess or sinus thrombosis.15 sive course, symptoms referable to other cranial nerves, ch01 9/19/08 10:52 AM Page 16

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A B

Fig. 1.5 The normal appearance of CN VII on DRIVE (driven equilibrium) sequence versus hypoplasia of CN VII. (A) An axial CISS (constructive interference in steady state) image shows the normal-appearing CN VII in the right internal auditory canal (IAC; short arrow), but CSF signal within the superoanterior quadrant of the left IAC. (B) A sagittal oblique reformat obtained in a plane perpendicular to the right IAC that shows the facial nerve (short white arrow), vestibular, and cochlear nerves in cross section. (C) A sagittal oblique reformat along the left IAC where the C facial nerve is not defined, consistent with aplasia or severe hypoplasia.

twitching or spasm that may suggest vascular compres- clinician may turn to CT for diagnosis and localization of sion, or failure of return of function within 6 months.18 the suspected facial nerve injury. In the posttraumatic setting, the differential diagnosis includes facial nerve interruption and posttraumatic facial Clinical Questions nerve swelling with compression. The onset of paresis can help differentiate between these two, and interruption The primary clinical question in the case of atypical Bell’s should lead to immediate paresis, whereas facial nerve palsy is straightforward. swelling is more subacute. Coexisting injuries may prevent a timely examination in the trauma patient, and the • Is there a lesion along the course of CN VII? ch01 9/19/08 10:52 AM Page 17

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In the setting of trauma, the principal clinical question is there is no evidence of lesion along the course of CN VII. No brainstem nuclear lesion is seen. • Is there a fracture along the course of CN VII? Impression: No evidence of right facial nerve lesion However, the report may describe findings that are most suggestive of Bell’s palsy but that require further follow up. Approach On the right/left, the labyrinthine and lateral canalicular Atypical Bell’s palsy segments of CN VII enhance slightly prominently, but no expansion of the nerve is seen, and no nodule or mass is defined. • Inspect the axial FLAIR, T2-weighted, and postgadolin- Impression: Findings most suggestive of inflammation of ium T1-weighted images and DWI images for evidence of CN VII that may occur in the setting of Bell’s palsy. A follow- a nuclear lesion, such as a brainstem tumor or demyeli- up scan should be considered in 3 to 6 months for further nating plaque. evaluation. • Use the CISS, 3D FIESTA, or DRIVE sequence to review the cisternal segment of the nerve for tumor or for hypoplasia. If there is a history of hemifacial spasm, these Hearing Loss sequences may be useful for evaluating any significant Protocol vascular impingement on CN VII; however, abutment of a vessel against the cisternal and canalicular segments of For conductive hearing loss, in both children and adults, a CNs VII and VIII is often a nonspecific finding. noncontrast CT scan of the temporal bone is performed. • Review the thin section pre- and postgadolinium For sensorineural hearing loss in adult patients, a T1-weighted and coronal high-resolution T1-weighted contrast-enhanced MRI is performed. images to study the canalicular, labyrinthine, genicu- For sensorineural hearing loss in children, either a CT late, tympanic, and mastoid segments of the nerve and scan (with dose reduction protocol) or an MRI may be the stylomastoid foramen for evidence of abnormal considered, depending on the history of the patient. In enhancement, such as may be seen in the lateral aspect the authors’ experience, CT is more sensitive and less of the cisternal segment of CN VII in a Bell’s palsy, or prone to motion and susceptibility artifacts for identify- abnormal expansion or nodularity along the course of ing subtle cochlear dysplasias, such as dilatational anom- the nerve that may reflect a schwannoma. alies of the cochlea or stenosis of the cochlear fossette, • Review the axial images through the parotid gland to whereas MRI offers superior delineation of the cochlear evaluate the parotid course of the nerve and to search nerve and of white matter or metabolic disorders that for lesions in this location, for example, a parotid tumor may be associated with SNHL. such as an adenoid cystic carcinoma that may be associated with perineural tumor spread. Interpretation Posttraumatic facial nerve injury Clinical Background • Inspect the facial nerve along the labyrinthine segment, Before arriving at the imaging suite, patients referred by geniculate ganglion, tympanic, and mastoid segments, an ENT have likely undergone physical exam and audio- checking closely for fracture or disruption of the osseous gram that have characterized the hearing loss as either margin of the fallopian canal. The most likely site of sensorineural or conductive. compression is along the labyrinthine segment because In the case of CHL, the history and otoscopic evaluation the fallopian canal is narrowest there. Close attention may have revealed evidence of middle ear inflammation should be paid to the osseous margins of each segment or malformation that may focus the review of the images. and for any free fragments or soft tissue swelling along In the case of SNHL, imaging is performed to evaluate for these segments. CPA masses or inflammatory disease and is usually indicated when there is a sudden onset of SNHL or an asymmetric hearing loss. Asymmetric hearing loss is defined as a Report difference between the two ears in hearing thresholds For atypical Bell’s palsy or posttraumatic facial nerve (more than 10 dB in three consecutive frequencies or 15 dB assessment, the report may either describe a lesion, if in two consecutive frequencies) or a difference in word present, or simply summarize the negative results of the recognition scores (more than 15 points difference). interpretive search strategy, as follows. SNHL can be cochlear or retrocochlear. Cochlear causes of On the right/left, the entire course of the facial nerve was rapid or asymmetric hearing loss include sudden SNHL visualized from the brainstem through the parotid gland; (SSNHL), autoimmune inner ear disease (AIED), and Meniere ch01 9/19/08 10:52 AM Page 18

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disease, conditions that are not usually diagnosed on imag- that may be seen in labyrinthitis, or loss of signal in ing. Retrocochlear causes of rapid or asymmetric hearing the membranous labyrinth that may reflect labyrinthitis loss include CPA or IAC lesions and central nervous system (ossificans). (CNS) causes, such as disorders of myelination, metabolic • Trace the cochlear nerve from the cochlear fossette to disorders, or vascular pathology such as infarcts. the brainstem, to identify an abnormal nodule that may represent a schwannoma, abnormal enhancement that may suggest a leptomeningeal process investing CN Clinical Questions VIII, and for intactness of the nerve. Conductive Hearing Loss • Evaluate the IAC and CPA cistern for a mass. • Is there a lesion of the EAC, TM, MEC, or ossicles? • Evaluate the cochlear nuclei and brainstem for evidence • Is there evidence of an osseous lesion, such as otospon- of an infarct, mass, or disorder of myelination. giosis (or more rarely, other bone disorders, such as • Trace the postnuclear auditory fibers from the cochlear Paget disease)? nuclei as they ascend in both the medial and lateral • Is there evidence of an inner ear disorder associated lemnisci to the medial geniculate nucleus and from with CHL? there to Heschl’s gyri. • Check the whole-brain images for any evidence of dis- Sensorineural Hearing Loss order of myelination, malformation such as a Chiari I, • Is there a cochlear or retrocochlear lesion? meningitis, or CNS hypotension or hypertension.22–27

The term retrocochlear refers to any lesion deep to the Report cochlea, including CN VIII, the brainstem, or auditory cortex. Conductive Hearing Loss On the right/left, the external auditory canal appears normal and well aerated. The Approach tympanic membrane is well defined and in normal position. Conductive Hearing Loss The middle ear cavity and mastoids are well aerated. The A lateral-to-medial approach may be used. ossicular chain appears normal. No otospongiosis is seen. No inner ear dysplasia is seen. CN VII describes a normal • Inspect the EAC for blockage or stenosis. course. The internal auditory canal appears normal. • Inspect the TM for evidence of perforation, retraction, Impression: No evidence of external auditory canal or or thickening that may reflect myringosclerosis. middle ear cavity lesion • Evaluate the MEC for opacification that may reflect sequelae of (chronic) otitis media, such as granulation Sensorineural Hearing Loss On the right/left, no cochlear tissue, tympanosclerosis, or cholesteatoma, or middle lesion is seen. No retrocochlear lesion is seen. No mass is seen. ear masses. There are no findings specific for a disorder of myelination. • Inspect the ossicular chain for evidence of erosion or The cerebrospinal fluid spaces appear normal. dysplasia or ossicular attachment (e.g., ossicular fusion Impression: No evidence of cochlear or retrocochlear lesion or bar). • Check the oval window niche (fissula antefenestram) and Masses otic capsule for evidence of otosclerosis (otospongiosis) Protocol or other osseous lesion, such as Paget disease. • Evaluate the inner ear for evidence of inner ear abnor- Referrals for imaging of temporal bone masses usually malities that may produce CHL, such as SSCD, enlarged concern either a retrotympanic mass noticed on otoscopic vestibular aqueduct, or LSCC dysplasia.19–21 If the stan- evaluation or an auricular mass that is obvious on external dard coronal and axial reformats do not clearly demon- inspection. strate intactness of the roof of the SSC, Stenvers and For retrotympanic lesions seen on otoscopy, CT and MRI Poschl reformats are used (as described in the first part are complementary. Noncontrast CT is often performed first of this chapter) for evaluation for dehiscence of the SSC. because the effect of the lesion on bone such as ossicular or scutal erosion that may help to identify the lesion as a Sensorineural Hearing Loss cholesteatoma are better depicted on CT. Contrast-enhanced A lateral-to-medial approach may be used. MRI may be performed if the CT findings raise concern for a neoplasm. • Inspect the cochlea and inner ear for evidence of dyspla- For auricular or periauricular masses such as squamous sia, abnormal elevated signal on the T1-weighted images or basal cell carcinomas, a contrast-enhanced MRI of the that may suggest hemorrhage, abnormal enhancement temporal bone is the modality of choice, as it more clearly ch01 9/19/08 10:52 AM Page 19

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delineates tumor versus obstructive secretions in the EAC vascular lesion, such as an aberrant carotid artery, or and MEC. The protocol should include a high-resolution with a neoplasm? If so, what is the extent of the lesion? coronal postgadolinium T1-weighted sequence and sequences through the neck (e.g., T1- or T2-weighted) to Auricular Masses evaluate for nodal metastases. A noncontrast CT of the • What is the extent of the lesion? temporal bone may be performed as a preoperative base- • Are there any nodal metastases? line to assess for osseous erosion. Approach Interpretation Retrotympanic Mass Clinical Background • Measure the lesion in three dimensions and describe the lesion in terms of its density or signal characteris- A retrotympanic mass is usually encountered by the clini- tics. Any mineralized component (e.g., that may suggest cian during otoscopic evaluation for hearing loss, otalgia, a meningioma) may be described here. or tinnitus. In some cases, the lesion will appear otoscopi- • Describe the anatomical relations of the lesion. For cally as a “pearly white mass,” classic for a cholesteatoma; completeness, a reporting scheme that lists the spatial mention of a pearly white mass on the requisition should directions is recommended (see below): superiorly, clue the radiologist into the clinical diagnosis. In some inferiorly, medially, laterally, anteriorly, and posteri- cases, the lesion will appear otoscopically as a vascular or orly, the lesion is described as it relates to the impor- red mass, in which case the major clinical considerations tant adjacent anatomy. For a lesion centered in the are a high-riding jugular bulb, a neoplasm such as a para- MEC, some of the major clinical considerations are ganglioma (e.g., glomus tympanicum), and an aberrant listed below. internal carotid artery. • Superiorly, does the lesion erode the tegmen tympani Invasive auricular masses are usually apparent on clin- or invade the middle cranial fossa? ical inspection. The pathologic diagnosis of the biopsied • Inferiorly, how does the lesion relate to the jugular lesion may already be available by the time the patient foramen, and what is its relation to the jugular vein reaches the imaging suite. The goals of imaging are to guide and CNs IX, X, and XI? surgery and to help the surgeon to elect one of four stan- • Medially, does the lesion erode the lateral SC or the dard surgical procedures. fallopian canal (canal for the facial nerve), and is there evidence of a perilymphatic fistula? • Sleeve resection removes the epithelium of the EAC and is • Laterally, does the lesion involve the ossicles, scutum, used for very limited noninvasive skin cancers of the EAC. or TM? • Lateral temporal bone resection is used to treat lesions • Anteriorly, does the lesion involve the carotid artery of the EAC that do not penetrate through the TM and or tympanic eustachian tube orifice? removes the EAC soft tissue and bone, the TM, the • Posteriorly, does the lesion extend into the mastoid malleus, and the incus. cavity? • Subtotal temporal bone resection removes tumors that go into the MEC and mastoid and removes en bloc the Auricular Mass intracranial and extracranial temporal bone but leaves • Measure the lesion in three dimensions and describe it the petrous apex. in terms of its density or signal characteristics. Is there • Total temporal bone resection, as the name implies, any evidence of bony erosion? removes the entire temporal bone, including the petrous • Describe the anatomical relations of the lesion. For com- apex. pleteness, a reporting scheme that lists the spatial direc- • A general principle of temporal bone oncologic surgery tions is recommended (see below): superiorly, inferiorly, is to adopt a surgical approach one level beyond that medially, laterally, anteriorly, and posteriorly, the lesion of the radiologically defined extent of the lesion. For is described as it relates to the important adjacent example, if a lesion is limited to the EAC, one would anatomy. For a lesion centered on the external auditory perform a lateral temporal bone resection. meatus, some of the major clinical considerations are listed below. • Superiorly, does the lesion erode the temporal Clinical Questions squamosa or invade the middle cranial fossa? Retrotympanic Masses • Inferiorly, does the lesion invade the parotid gland? • Are the imaging findings more consistent with an • Medially, how far does the lesion extend into the EAC, inflammatory lesion, such as a cholesteatoma, with a and does it transgress the TM and involve the MEC? ch01 9/19/08 10:52 AM Page 20

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• Laterally, does the lesion involve the pinna? image through the course of CN V, axial T1- (preferably • Posteriorly, does the lesion extend into the mastoid pregadolinium) or T2-weighted images through the cavity? parotid gland through the parotid course of CN VII, and of the cervical spine through C4. It may be necessary to change from the head to the neck coil following the tem- Report poral bone study to complete the excursion through the Retrotympanic Mass parotid gland and upper cervical spine, in which case, A 5 AP 4 TV 6 SI mm nonmineralized, smoothly mar- axial T2-weighted images postgadolinium may be per- ginated, homogeneous attenuation lesion is centered in formed for imaging of the parotid and the neck. Prussak’s space. Interpretation Superiorly, the lesion erodes the scutum, ascends into the external attic and rises to, but does not breach, the tegmen Clinical Background tympani and completely spares the middle cranial fossa. Clinicians divide patients with otalgia into two groups: Inferiorly, the lesion descends along the TM to the umbo, primary otalgia that is caused by lesions of the ear (e.g., where it surrounds and demineralizes the neck of the cancer, auriculitis, otitis externa, otitis media, or mastoidi- malleus. tis) and referred otalgia that is caused by a lesion related to Medially, the lesion closely approaches but spares the facial the sensory afferent nerves that innervate the ear. The nerve canal and cochlear promontory. auriculotemporal branch of CN V, the Ramsey–Hunt branch Laterally, the lesion bulges but appears limited by the TM of CN VII, the Jacobsen branch of CN IX, the Arnold branch and does not involve the EAC. of CN X, and the greater auricular or mastoid branches of Anteriorly, the lesion erodes the head of the malleus and the cervical plexus that arise from the C1 to C3 nerve abuts the tensor tympani tendon. roots.28,29 Disease of the organs or regions supplied by these Posteriorly, the lesion completely spares the aditus ad nerves may be referred to the ear and present as otalgia. antrum and mastoid. Temporomandibular joint (TMJ) arthropathy, dental infection, sinusitis, gastroesophageal reflux disease, upper Impression: Middle ear cavity mass most consistent with aerodigestive malignancies, tonsillitis, and cervical root a choleasteama, as detailed above compression are clinical considerations for referred otalgia.

Auricular Mass A 25 SI 20 AP 10 TV (deep) mm enhancing lesion is Clinical Questions centered around the external auditory meatus. • Is there evidence of primary otalgia from a lesion of the ear or temporal bone? Superiorly, the lesion invades the pinna. • Is there evidence of referred otalgia from a lesion along Inferiorly, the lesion invades the parotid gland. the course of the sensory afferents to the auricle? Medially, the lesion extends 10 mm deep to the external auditory meatus along the EAC but spares the TM and MEC. Laterally, the lesion invades the pinna. Approach Anteriorly, the lesion abuts but does not erode the mandible. Posteriorly, the lesion abuts but does not invade the mastoid Check for causes of primary otalgia, proceeding from sinus. lateral to medial. Check the auricle, then the EAC, the MEC, and mastoid, for a mass lesion or inflammation. Impression: Invasive-appearing periauricular and auric- Evaluate for causes of referred otalgia using the cranial ular mass, consistent with the reported biopsy diagnosis of nerve anatomy as a checklist. squamous cell carcinoma, as detailed above • Evaluate the trigeminal nerve (CN V) and look for evidence of disease along its afferent supply, including Otalgia temporomandibular arthropathy (the auriculotemporal branch), sinusitis (V2), periapical or periodontal dis- Protocol ease (V3), or for tumor that may involve perineural A routine noncontrast CT of the temporal bone is the ini- tumor spread along V1 to V3. tial study of choice. • Evaluate the facial nerve (CN VII) and look for evidence An MRI of the temporal bone may be considered next of disease along its afferent supply, including Bell’s and should include a high-resolution coronal T1-weighted palsy, CPA tumors, and parotid neoplasms. ch01 9/19/08 10:52 AM Page 21

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• Evaluate the glossopharyngeal nerve (CN IX) and vagus finding warrants a search for a vascular cause, such as a nerve and look for evidence of disease along their affer- carotid bruit (atherosclerosis), heart murmur, AVM or dural ent supply, including tonsillitis, pharyngitis, laryngitis, arteriovenous fistula (dAVF), or benign intracranial hyperten- Eagle syndrome, and pharyngeal or laryngeal tumors.30 sion. Head turn to the side of a dehiscent jugular bulb may • Evaluate the nerve root origins and branches of the cer- extinguish the tinnitus on that side. vical plexus and look for evidence of cervical degenera- Most cases of tinnitus do not require imaging. Indica- tive disk disease, cervical spine trauma, or lesion along tions for imaging include asymmetry (unilateral tinnitus the trapezius or sternocleidomastoid muscle. or tinnitus greater in one ear), pulsatile tinnitus, and tinnitus in the setting of other symptoms, such as headache or vision change. Report On the right/left, there is no evidence of mass or inflammation Clinical Questions of the auricle, external auditory canal, middle ear cavity, or • Is there a gross pathologic lesion causing tinnitus? mastoid. The tympanic membrane, ossicular chain, and inner ear appear normal. A 10 mm radiolucency caps the root apex of the right maxillary distal molar and demineralizes the Approach adjacent buccal cortex, which raises concern for a periapical Because of the large differential considerations for tinni- abscess. There is otherwise no evidence of lesion along the tus and because in some cases it is not clear from the req- sensory afferents to the auricle. uisition if the tinnitus is pulsatile or nonpulsatile, an Impression: Findings that raise concern for a periapical anatomical approach is useful, starting from lateral and abscess of the right maxillary distal molar that lies ipsilateral working medially across the axial images. to the reported side of otalgia. • Inspect the external auditory canal and mastoid for evidence of inflammation that may be associated with Tinnitus tinnitus. Protocol • Check the TMJ for evidence of degenerative disease that has been reported as a cause of tinnitus.31 A routine contrast-enhanced MRI of the temporal bone is • Evaluate the middle ear for evidence of inflammation, the initial study of choice, with an MRA if there is a history such as serous otitis, or lesion, such as a paraganglioma, of pulsatile tinnitus. hemangioma, or meningioma. Otospongiosis that may If the MRI or MRA evaluations are inconclusive, a CT cause pulsatile tinnitus from increased blood flow to scan may be useful to evaluate for dehiscence of the jugu- the promontory may occasionally be seen (if it is florid) lar bulb, for otospongiosis, or for small tumors, such as a as abnormal enhancement or signal abnormality on small paraganglioma along the tympanic plexus. the CISS, 3D FIESTA, or DRIVE sequence, but it cannot be excluded by MRI. CT is the preferred modality for such evaluation. Interpretation • Search for a vascular cause that may require review of the noncontrast-enhanced CISS, DRIVE, or 3D FIESTA Clinical Background sequence, the contrast-enhanced MRI, and the MRA. The first step in the clinical evaluation is to characterize the This search may be divided into arterial causes, venous tinnitus by history as pulsatile or nonpulsatile. Following causes, impingement, and AVMs and dural AVFs, as the history, a directed examination is performed with described below. otoscopy, head and neck exam, and auscultation to attempt • Arterial causes of tinnitus, such as carotid artery to determine what the tinnnitus sounds like (e.g., pulsatile, stenosis, atherosclerosis, aneurysm, or aberrancy, roaring, popping). may be difficult to diagnose conclusively on MRI; Nonpulsatile tinnitus is characterized by tone, volume, MRA may be needed to complement the MRI. A per- and location. The clinician may ask the patient if he or sistent stapedial artery may be difficult to define by she hears sounds like music, a typewriter, or a high- MRI; an MRA or CT scan may be needed. pitched tone and if the sound is unilateral or bilateral, or • Venous causes such as dural sinus stenosis diverticula asymmetric. or compression in pseudotumor cerebri may be appar- Pulsatile tinnitus is characterized by its rate, quality of ent on the contrast-enhanced MRI, but magnetic reso- sound, and attenuating factors such as head position. If nance venography (MRV) or computed tomography the rate of the tinnitus corresponds to the heartbeat, such venography (CTV) may be needed for confirmation. ch01 9/19/08 10:52 AM Page 22

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A dehiscent jugular bulb may be difficult to exclude on Report MRI, and CT may be needed to confirm this diagnosis. On the (right/left), the EAC, MEC, and mastoid appear nor- • Vascular impingement, for example, by the anterior mal. No mass is seen. No vascular abnormality is seen. No inferior cerebellar artery (AICA) on CN VIII. Recall that inner ear, brainstem, or intracranial lesion is seen. There are abutment of a vessel on CN VIII is often an incidental no findings to suggest a disorder of myelination. finding that may be seen in asymptomatic patients. Impression: No evidence of mass or vascular abnormality • AVMs may be seen on MRI, but dural AVFs may be difficult to detect on MRI. 3D TOF (time of flight) MRA is a simple and effective technique for detection of dural AVFs. If the venous saturation bands are Vertigo and Dizziness placed correctly, there is usually no or scant flow Protocol within the major dural sinuses, and the presence of arterialized flow within a sinus should raise concern Based on the clinical evaluation, the optimal imaging for a fistula (Fig. 1.6). modality is selected. • Evaluate the inner ear for evidence of labyrinthitis or If there is a clinical suspicion for a central cause of the dysplasia. vertigo, such as a stroke or CPA tumor, an MRI of the tem- • Check the IAC and CPA cistern for evidence of tumor, poral bone is the initial study of choice. such as a vestibular schwannoma. If there is high clinical suspicion of otospongiosis, • Evaluate the brain images for evidence of pseudotumor perilymphatic fistula, or SSCD, a noncontrast CT of the cerebri, Chiari I malformation, or lesion of the fifth or temporal bone should be performed. seventh nerves that may be associated with middle ear In those cases where the cause is unclear, an MRI is myoclonus or for a lesion of the brainstem, such as a usually performed as the initial study. demyelinating plaque, that may be associated with palatal or middle ear myoclonus.32–35 Interpretation Clinical Background The differential diagnosis of dizziness and vertigo includes Meniere disease, labyrinthitis, benign paroxysmal positional vertigo (BPPV), vestibular neuritis (vN), perilymphatic fis- tual (PLF), SSCD, migraine, stroke, Chiari I malformation, and CPA tumors. Most patients referred to the otologist have true vertigo, which is defined as a false sense of motion. Many patients with true vertigo can be further categorized based on the temporal pattern of the vertigo (persistent or episodic) and the presence or absence of hearing loss, into Meniere disease (episodic vertigo with hearing loss), labyrinthitis (persistent vertigo with hearing loss), BPPV (episodic vertigo, no hearing loss), and vN (persistent vertigo, no hearing loss). As with tinnitus, most often imaging is not indicated in the work-up of vertigo. When imaging is requested, the primary goal is to determine if there is a central cause for the vertigo.

Fig. 1.6 The use of three-dimensional time of flight magnetic reso- Clinical Questions nance angiography (3D TOF MRA) to detect a dural arteriovenous fistula. A source image from a 3D TOF MRA shows abnormal arterialized • Can we rule out a central cause of the vertigo, such as flow in the right sigmoid notch (short arrow) and transverse sinus ipsi- stroke, tumor, or Chiari malformation, so that the cause lateral to the patient’s symptoms of pulsatile tinnitus and multiple transmastoid perforators likely arising from the occipital branch of the of the vertigo can be attributed more definitively to the right external carotid artery. On the contralateral side, no flow-related inner ear? signal is seen in the dural sinus. • Is there evidence of labyrinthitis? ch01 9/19/08 10:52 AM Page 23

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• Is there evidence of bony erosion to suggest a perilym- • Check CN VIII, the IAC, and the CPA cistern for evidence phatic fistula? of tumor. Abnormal enhancement of CN VIII may con- • Is there evidence of SSCD? firm nerve pathology, such as neuritis or leptomeningeal disease. • Evalute the membranous labyrinth for evidence of Approach labyrinthitis. Look for either loss of signal on the CISS, 3D Because the primary goal of imaging is usually to rule out FIESTA, or DRIVE sequence or abnormal enhancement. a central cause for the vertigo, a medial-to-lateral (or • Evaluate for SSCD or perilymphatic fistula if CT is deep-to-superficial) approach may be used. available.

• Check the cerebellum, brainstem, and supratentorium Report for evidence of infarct (especially the vestibular nuclei in the medulla), disorder of myelination, malformation On the right/left, no vestibular lesion is seen. CN VIII appears such as a Chiari I, or evidence of neurodegeneration such normal; there are no findings specific for inflammation. The as spinocerebellar ataxia. In children this component of cerebellum and brainstem appear normal. There are no find- the evaluation should include a search for evidence of ings to suggest a disorder of myelination. The vertebral and neurodegenerative disorders, such as Friedreich ataxia, basilar arteries appear normal. mitochondrial disorder, or inherited disorder of myeli- Impression: No evidence of vestibular lesion nation, such as Fabry disease.36 • Evaluate the vertebrobasilar system for evidence of Acknowledgment The authors would like to acknowledge stenosis and atherosclerosis that may suggest verte- the contribution of Dr. Barbara Hum in the section on brobasilar insufficiency. tinnitus.

References 1. McCollough CH, Zink F. Performance evaluation of a 12. Rotteveel LJ, Proops D, Ramsden R, Saeed S, van Olphen A, multi-slice CT system. Med Phys 1999;26:2223–2230 Myalanus E. Cochlear implantation in 53 patients with 2. Jessen Kea. Dosimetry for optimization of patient protec- otosclerosis: demographics, computed tomographic scan- tion in computed tomography. Appl Radiat Isot 1999; ning, surgery, and complications. Otol Neurotol 2004;25: 50:165–172 943–952 3. National Council on Radiation Protection and Measure- 13. Chandrasekhar SS, De la Cruz A, Garrido E. Surgery of ments. Evaluation of the Linear-Nonthreshold Dose- congenital aural atresia. Am J Otol 1995;16:713–717 Response Model for Ionizing Radiation. Bethesda, MD: 14. Allanson J. Genetic hearing loss associated with external ear National Council on Radiation Protection and Measure- abnormalities. In: Gorlin R, Toriello H, Cohen M, eds. Hered- ments; 2001 itary Hearing Loss and Its Syndromes. New York/Oxford: 4. Hall E. Radiobiology for the Radiologist. Philadelphia: JB Oxford University Press;1995:62–104 Lippincott; 1994 15. Yang TH, Kuo S, Young Y. Necrotizing external otitis in a 5. Torizuka T, Hayakawa K. High-resolution CT of the tem- patient caused by Klebsiella pneumoniae. Eur Arch Otorhi- poral bone: a modified baseline. Radiology 1992;184: nolaryngol 2006;263:344–346 109–111 16. Hern JD, Almeyda J, Thomas D, Main J, Patel K. Malignant 6. Brenner DJ. Estimating cancer risks from pediatric CT: going otitis externa in HIV and AIDS. J Laryngol Otol 1996;110: from the qualitative to the quantitative. Pediatr Radiol 770–775 2002;32:228–230 17. Dubois M, Francois M, Hamrioui R. Foreign bodies in the 7. Shellock FG. Reference Manual for Magnetic Resonance ear: report of 40 cases. Arch Pediatr 1998;5:970–973 Safety, Implants, and Devices. Los Angeles, CA: Biomedical 18. Peitersen E. Bell’s palsy: the spontaneous course of 2,500 Research Publishing Company; 2007 peripheral facial nerve palsies of different etiologies. Acta 8. Gliklich RE, Eavey R, Iannuzzi R, Camacho A. A contempo- Otolaryngol Suppl 2002;549:4–30 rary analysis of acute mastoiditis. Arch Otolaryngol Head 19. Merchant SN, Rosowski J, McKenna M. Superior semicir- Neck Surg 1996;122:135–139 cular canal dehiscence mimicking otosclerotic hearing 9. Loeb GE. The functional replacement of the ear. Sci Am loss. Adv Otorhinolaryngol 2007;65:137–145 1985;353:104–111 20. Johnson J, Lalwani A. Sensorineural and conductive hearing 10. Reefhuis J, Honein MA, Whitney CG, et al. Risk of bacterial loss associated with lateral semicircular canal malforma- meningitis in children with cochlear implants. N Engl J tion. Laryngoscope 2000;110:1673–1679 Med 2003;349:435–445 21. Antonelli PJ, Nall A, Lemmerling M, Mancuso A, Kubilis P. 11. Arriaga MA, Carrier D. MRI and clinical decisions in cochlear Hearing loss with cochlear modiolar defects and large implantation. Am J Otol 1996;17:547–553 vestibular aqueducts. Am J Otol 1998;19:306–312 ch01 9/19/08 10:52 AM Page 24

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22. Xu MS, Tan C, Umapathi T, Lim C. Susac syndrome: serial 29. Olsen KD. The many causes of otalgia: infection, trauma, diffusion-weighted MR imaging. Magn Reson Imaging cancer. Postgrad Med 1986;80:50–52 2004;22:1295–1298 30. Subramaniam S, Majid M. Eagle’s syndrome. Med J Malaysia 23. Nadkarni T, Menon R, Shah A, Goel A. Chudley McCul- 2003;58:139–141 lough syndrome. Childs Nerv Syst 2008 24(4):541–544 31. Levine RA. Somatic (craniocervical) tinnitus and the dor- 24. Freeman SR, Jones P. Old age presentation of the Dandy- sal cochlear nucleus hypothesis. Am J Otol 1999;20: Walker syndrome associated with unilateral sudden sen- 351–362 sorineural deafness and vertigo. J Laryngol Otol 2002; 32. Oliveria CA, Negreiros Junior J, Cavalcante I, Bahmad 116:127–131 Junior F, Venosa A. Palatal and middle-ear myoclonus: 25. Ochi S, Nanki T, Komano Y, et al. A case report of hyper- a cause for objective tinnitus. Int Tinnitus J 2003;9: trophic pachymeningitis associated with systemic lupus 37–41 erythematosus, showing a headache and hearing loss 33. Zipfel TE, Kaza S, Greene J. Middle-ear myoclonus. resembling intracranial hypotension. Nihon Rinsho J Laryngol Otol 2000;114:207–209 Meneki Gakkai Kaishi 2007;30:55–60 34. Sismanis A. Pulsatile tinnitus: a 15 year experience. Am J 26. Peng PW. Intracranial hypotension with severe neurologi- Otol 1998;19:472–477 cal symptoms resolved by epidural blood patch. Can J 35. Albers FW, Ingels K. Otoneurological manifestations Neurol Sci 2004;31:569–571 in Chiari-I malformation. J Laryngol Otol 1993;107: 27. Murphy TP. Otologic manifestations of pseudotumor 441–443 cerebri. J Otolaryngol 1991;20:258–261 36. Vibert D, Blaser B, Ozdoba C, Hausler R. Fabry’s disease: 28. Kuttila S, Kuttila M, Le Bell Y. Characteristics of subjects otoneurologic findings in twelve members of one family. with secondary otalgia. J Orofac Pain 2004;18:226–234 Ann Otol Rhinol Laryngol 2006;115:412–418 ch02.qxd 1/7/09 12:22 PM Page 25

The External Auditory Canal 2 and Pinna Valerie L. Jewells, Mauricio Castillo, and Craig Buchman

The external ear, comprised of the pinna or auricle and includes sagittal T1-weighted images (4 mm thick), axial the external auditory canal (EAC), has a different embry- T1-weighted images (2 mm thick), axial T2-weighted ological origin than that of the middle and inner ears. This images (2 mm thick), and axial FLAIR (fluid attenuated unique embryonic origin, in conjunction with the superfi- inversion recovery T2-weighted images, 4 mm thick), all cial location of the pinna and EAC, results in a distinct obtained before contrast is administered. After gadolin- pathology spectrum when compared with that involving ium contrast administration, we obtain T1-weighted the middle and inner ears. Despite the ease of visualization (3 mm thick) images in axial and coronal planes through of these external structures by the otolaryngologist, the the regions of interest with and without fat suppression radiologist can assist with important information for techniques. Additionally, 4 to 5 mm thick axial and coro- surgical planning and aid in determining the type and nal postcontrast T1-weighted images are obtained to extent of the pathology. Intracranial complications arising include the entire brain. Images using heavily T2-weighted from disorders of the pinna and EAC can also be evaluated techniques with high resolution (constructive interference by the radiologist. in steady state; CISS) may be performed if anatomical assessment of the structures in the inner ear or internal auditory canal is required. For patients with facial paralysis, it is imperative that the imaging studies include the Imaging Techniques entire course of the facial nerves.

At our institution, we perform temporal bone computed tomography (CT) studies more frequently than magnetic resonance imaging (MRI) studies for examination of the Anatomy EAC because of CT’s superiority for the evaluation of bone erosion. With the use of a multislice CT scanner, At birth, the tympanic membrane (TM), ossicles, and otic submillimeter (0.6 to 0.75 mm) axial images are rou- capsule are already of adult size, but the EAC grows pro- tinely obtained and processed with bone and soft tissue gressively until the age of 9 years, when it achieves its algorithms. Although direct coronal imaging may be per- typical S-shaped course and adult size. The EAC extends formed using a similar protocol, coronal and sagittal from the meatus of the pinna to the TM, its medial reconstructions can also be obtained at 0.75 mm inter- boundary, which divides the external from the middle ear. vals with limited radiation exposure, which is especially The purpose of the pinna and EAC is presumably to collect desirable in children. For congenital lesions, noncontrast and funnel sound to the TM as a resonating tube resulting studies with bone windows will suffice for most patients. in a 10 to 20 dB gain.1 Thus, atresia and stenosis of the For some inflammatory and neoplastic lesions, contrast EAC can result in a conductive hearing loss of up to 60 dB, material may be given and images processed with soft manifested as an air–bone gap on audiological testing. tissue window settings. The adult EAC is 25 mm in length and air-filled in its MRI is usually used to assess the spread of tumor or normal state. The EAC is lined by squamous epithelium inflammatory processes intracranially. Although lesions that is continuous with the skin from the pinna. The canal that spread through bone into the middle cranial fossa travels inferiorly and posteriorly to the TM in a slightly can be obvious on reconstructed coronal and sagittal S-shaped course. The resulting cross-sectional diameter images, MRI is generally better for the assessment of soft has a roughly oblique oval configuration.2 The canal is tissue, brain, and dural extension. Subtle dural enhance- widest in diameter at its lateral/superficial end adjacent ment may be a first indication of intracranial involvement. to the pinna, where it flares out in a trumpet bell-like MRI is also sensitive for detection of bone marrow edema, configuration. The EAC has two portions: the lateral por- and it can occasionally demonstrate bony involvement tion (one third) is fibrocartilaginous and demonstrates an not suspected by CT in carcinoma cases. Our MRI protocol incomplete elastic cartilage ring measuring 8 mm in 25 ch02.qxd 1/7/09 12:22 PM Page 26

26 Imaging of the Temporal Bone

length. Inferiorly in the fibrocartilaginous portion are two trigeminal nerve (CN V) fibers arise via the mandibular deficiencies called the fissures of Santorini, which in- division as the auriculotemporal nerve. Recent studies crease the flexibility of the superficial portion of the EAC, regarding the somatosensory contribution of CN VII to the but may also allow transmission of infection and malig- external auditory canal have demonstrated these branches nancy.1 The fibrocartilaginous portion has thick skin with arise in the descending or mastoid portion of the facial hair follicles and cerumen glands. The medial two thirds nerve prior to CN VII’s exit from the stylomastoid fora- of the EAC, adjacent to the TM, is the osseous portion, men. The CN IX contribution, which supplies the medial which is surrounded by membranous bone and devoid of aspect of the TM, arises inferiorly in the hypotympanum cerumen glands and hair follicles, and is lined by a thin from the tympanic canaliculus. Similarly, CN X contributes layer of skin. The lack of thick skin and subcutaneous innervation to the medial aspect of the EAC via Arnold’s tissue makes this portion of the canal exquisitely sensitive nerve, which enters the temporal bone through the mas- to touch on clinical examination. The EAC has two areas of toid canaliculus and exits through the tympanomastoid narrowing: one at the isthmus (between the fibrocarti- suture.1 laginous and bony portions) and one distally and adjacent to the TM. The medial bony portion can have an anteroinferior area of dehiscence called the foramen of Embryology Huschke. The bony portion of the EAC is encircled by the squamous and mastoid segments of the temporal bone As with all discussions of embryology, we will begin with superiorly and posteriorly while the anterior and inferior the normal sequence of events occurring in utero. The portions of the bony EAC are surrounded by the tympanic pharyngeal (or branchial) arches arise from migration portion of the temporal bone.1 of neural crest cells by the fifth week of gestation. The first The TM is situated obliquely at the distal end of the branchial or mandibular arch gives origin to the mandible, EAC, is conical in shape, and measures 9 to 10 mm in maxilla, zygomatic temporal bone, squamous temporal diameter. It has a peripheral fibrocartilaginous annulus bone, and muscles of mastication, as well as the anterior that attaches to the tympanic ring in a well-defined bony belly of the digastric muscle, tensor tympani, tensor veli sulcus. This fibrocartilaginous ring has an area of defi- palatini, and mylohyoid muscles. Also derived from the ciency superiorly, above the short (or lateral) process of first arch are the head and neck of the malleus and the the malleus, called the notch of Rivinus. From this notch short process and body of the incus. Derivatives from arise anterior and posterior malleal ligaments that create the second branchial arch include the long process of the folds in the TM, extending to the attachment of the lateral incus and stapes superstructure, lesser horn (cornu) and process of the malleus. The TM is composed of both the upper rim of the hyoid bone, styloid process, stylohyoid pars flaccida and pars tensa portions. The pars tensa is ligament, muscles of facial expression, posterior belly of comprised of three layers: an inner mucosal epithelial the digastric muscle, and stapedius and stylohyoid mus- layer, a central fibrous layer, and an outer squamous cles.4 The EAC arises from the ectoderm of the first and epithelial layer. The inner fibrous layer gives this portion second branchial arches and therefore is composed of tis- of the TM a more rigid structure than the pars flaccida. sues from both the mandibular (first) and hyoid (second) The pars flaccida is substantially smaller in area than the arches. The formation of the EAC occurs during the sixth pars tensa and is superiorly located above the short week of fetal life as a cleft invaginates. By this time, the process of the malleus, covering the bony notch of Rivinius. tympanic cavity has already formed from invagination The pars flaccida of the TM is thinner and therefore more of the first pharyngeal pouch (tubotympanic recess) dur- flexible, and is the point of origin of many primary, ing the fourth gestational week. The TM forms from the acquired cholesteatomas (CHs) of the middle ear.3 meeting of these two invaginations as the collection of Arterial supply to the EAC is via branches of the exter- epithelial cells between them is canalized during the 26th nal carotid artery, namely, the posterior auricular, superfi- week of life.5 cial temporal, and internal maxillary arteries. The venous The pinna arises from the six hillocks of the first and drainage from this region is via the postauricular and second brachial arches along the course of the first superficial temporal veins into the sigmoid sinus and brachial cleft. The first three hillocks form the helix and internal and external jugular veins.1 Lymphatic drainage tragus, and the third through sixth hillocks form the re- is anteriorly into the preauricular nodes, posteriorly into maining auricle. Therefore, abnormal hillock development the mastoid nodes, and inferiorly into the subparotid leads to microtia or anotia of the pinna, the severity of nodes. All of these nodal stations drain to the digastric which is related to EAC canalization.6 Abnormal accessory nodes. The innervation of the external ear is from multi- hillocks can be seen in some patients as preauricular tags ple somatosensory nerves, including cranial nerves (CN) V, and/or cysts (Fig. 2.1). Pinna or auricle malformations VII, IX, and X, as well as cervical nerves C2 and C3. The occur in 1 out of 12,500 births, and arise during the 3rd to ch02.qxd 1/7/09 12:22 PM Page 27

Chapter 2 The External Auditory Canal and Pinna 27

can manifest as EAC atresia or stenosis as well as duplication anomalies, including cysts, sinuses, and fistulas. These anomalies rarely occur together, but have been reported to coexist with one another occasionally.11 EAC atresia occurs in 1 out of 10,000 births and more commonly involves the lateral membranous or fibrocartilaginous portion of the EAC than its bony portion. EAC atresia may be associated with deletions in 18q, and 66% of individuals with these deletions have congenital aural atresia or EAC stenosis.12 These anomalies may also be seen in Goldenhar, Treacher Collins, Pfeiffer, and Rasmussen syndromes.13 On physical examination, the right ear is more frequently Fig. 2.1 Axial computed tomography scan shows incidentally found affected, and patients have a conductive hearing loss. large bilateral preauricular cysts. These cysts may become sympto- Many of the severe cases may have a mixed hearing loss matic due to infection; however, many small ones remain clinically due to associated inner ear malformations. Because the silent throughout the life of the patient. EAC continues to grow during the first 2 years of life, the severity of the atresia may change during that time. Patients with EAC stenosis or atresia usually present prior to discharge from the newborn nursery because of either 12th fetal week of life, with the auricle and membranous an obvious visible deformity of the pinna or failure on a EAC developing from the same anlage. Because the bony EAC newborn hearing screening examination (Fig. 2.2). There is developing synchronously but from a different anlage, is a three-stage grading system for severity for EAC atresia, maldevelopment of the bony canal can also occur.7 as follows:14

1. Mild EAC atresia: Normal auricle, minimal ossicular Pathology deformity, and a normal middle ear cavity 2. Moderate EAC atresia: Small rudimentary pinna, small Embryologic middle ear cavity, severely deformed ossicles, and an aberrant course of the seventh cranial nerve (Fig. 2.2) Microtia and External Auditory Canal Dysplasias 3. Severe EAC atresia: Absent auricle and only a small Microtia, meaning a small auricle, is more common in cleft for the middle ear cavity with absent ossicles. Navajo and Japanese populations as well as in fetuses This severe form can also have inner ear deformities. exposed to thalidomide and retinoic acid.8 Microtia has three degrees of severity, according to the Weerda classification:9

• First degree: Microtia, prominent ear, pocket ear, absence of the upper helix, absence of the tragus, clefts, lobular deformities, and cup ear deformities type 1 and 2 • Second degree: Dysplasia as a cup ear deformity type 3 and mini-ear • Third degree: Absence (i.e., anotia) of a normal auricular structure (unilateral or bilateral), or severely dysplastic ears displaced inferiorly due to incomplete ascension from the neck

In a study by Mayer et al, one third of patients had first- or second-degree microtia, and two thirds had third- degree microtia. Seventy-five percent of patients with mild microtia have associated bony or cartilaginous EAC stenosis, and 75% of those with major microtia exhibit 10 EAC atresia. Fig. 2.2 Lateral patient photograph shows microtia with deformed Maldevelopment of the first brachial arch affecting the residual pinna and atresia of the external auditory canal. (See Color EAC can occur syndromically or nonsyndromically and Plate Fig. 2.2.) ch02.qxd 1/7/09 12:22 PM Page 28

28 Imaging of the Temporal Bone

There is also a classification by location and extent of The facial nerve is aberrant (common form with severity for EAC atresia, as follows:15 mandibulofacial dysostosis).

• Type A (meatal): Fibrocartilaginous only with a small Nonsyndromic causes of EAC stenosis and atresia are TM due to failure of canalization. This failure can be com- • Type B (partial): Fibrocartilaginous and osseous. The plete, resulting in atresia, or incomplete, resulting in malleus may be fixed, or the manubrium may be short stenosis (Fig. 2.3). It is well known that severe microtia or curved is often seen with EAC atresia, whereas milder microtia is • Type C (total): The EAC is absent, and there is a bony typically seen with EAC stenosis (Fig. 2.4). Associated dys- atretic plate with a normal-size middle ear cavity. The plasia of the ossicles occurs in 98% of patients and in 72% malleus is usually fused to the lateral wall. of them may involve all of the ossicles, including the • Type D (hypopneumatic total): The middle ear cavity is stapes. Accompanying round window atresia is found in small, and there is little or no mastoid pneumatization. 6% of patients and labyrinthine malformations in 13%, but

A B

Fig. 2.3 (A,B) Computed tomography (CT) three-dimensional reformations in a patient with nonsyndromic bilateral external auditory canal (EAC) atresia. In nonsyndromic EAC atresia, the zygomatic arch and mandible are normally formed, whereas they may be hypoplastic or even absent in syndromic EAC atresia. (C) Coronal CT view shows a thin atresia plate, small middle ear cavity, absent C ossicles, and soft tissue filling the epitympanic space. ch02.qxd 1/7/09 12:22 PM Page 29

Chapter 2 The External Auditory Canal and Pinna 29

A B Fig. 2.4 (A) Coronal computed tomography (CT) scan shows severe of the middle ear cavity is normal. (B) On the left, CT shows similar right-sided soft tissue and distal bony external auditory canal stenosis. findings in this patient with bilateral microtias. The long process of the incus is mildly deformed but not fused. The size

not atresia of the oval window.10,16 Common ossicular ear cavity may be small (68%), and the facial nerve may abnormalities include a short or absent manubrium of the be displaced.17,18 Less commonly, accessory ossicles can be malleus, a more pronounced deformity of the head of the seen with a type 2 first branchial cleft anomaly.19 The malleus than that of the incus, and misshapen stapes association of incus and malleus abnormalities with EAC crura. Ossicular fusion is seen in 54% of EAC atresia stenosis/atresia occurs due to the common (i.e., branchial) patients and most commonly involves the malleoincudal embryologic origin of all of the ossicles except for the joint (76%), followed by fusion of the ossicles to the atresia stapes footplate. EAC atresia and mallear manubrium plate. development are related, a finding that has been substan- The atresia plate may be bony or membranous (soft tiated in a knockout mouse model.20 Also associated with tissue) and of variable thickness (Fig. 2.5). Also, the middle microtia and EAC atresia are poor pneumatization of the

A B Fig. 2.5 (A) Coronal computed tomography scan shows right-sided slightly small. (B) On the left side, similar findings are seen. The deformed membranous atresia (note absence of bony atresia plate). The malleus incus is laterally fused. and incus are deformed and fused laterally. The middle ear cavity is ch02.qxd 1/7/09 12:22 PM Page 30

30 Imaging of the Temporal Bone

A B Fig. 2.6 (A) Axial computed tomography (CT) scan shows bone stenosis shows bone stenosis of the lateral aspect of the EAC with a large soft of the medial external auditory canal (EAC) with a small soft tissue mass tissue mass medially, also proven to be a cholesteatoma. medial, proven to be a cholesteatoma. (B) Axial CT in a different patient

mastoid, mandibular condyle dysplasia, zygomatic arch present with bilateral microtia as well as bilateral abnor- defects (50%), eustachian tube dysplasia (20 to 40%), ten- malities of the EAC, TM, ossicles, and middle ear cavity. sor tympani muscle hypoplasia (20 to 40%), oval window These patients will also have midface hypoplasia and absence (33%), labyrinthine dysplasia (13%), and/or round micrognathia.24,25 window absence (6%). Associated hypoplasia or aplasia of Pierre Robin syndrome (also known as Pierre Robin the internal carotid artery is rare.10 There can be associ- sequence) demonstrates retrognathia, glossoptosis, and ated CH of the middle ear medial to the atresia plate. bilateral cleft palate, as well as ear abnormalities. The ear More commonly, CH can develop in the EAC medial to a abnormalities include an abnormal pinna and ossicles, as stenosis (Fig. 2.6). The presence of a CH correlates with well as abnormal stapes footplates in 50% of patients. smaller EAC size, so that the rate of CH is 50% if the EAC Aplasia of the lateral semicircular canals (LSCCs), large is 4 mm or less in diameter.21 vestibular aqueducts, and unusually large otoconia Of the syndromes resulting in microtia and EAC atresia, are also seen, but not EAC atresia or stenosis.26 Because Goldenhar syndrome or hemifacial microsomia is the the middle ear arises from the branchial arches, whereas most common and is also the second most common cra- the inner ear does not, labyrinthine abnormalities such as niofacial anomaly after cleft lip and palate. There are four aplasia and partitioning deficiencies are typically not major components to Goldenhar syndrome: deformity of associated with microtia and EAC atresia/stenosis. the auricle, EAC atresia, malformation of the tympanic When we interpret CT studies of the temporal bones cavity, and ossicular abnormalities causing conductive performed in patients with congenital abnormalities, our hearing loss. Occasionally, there is also sensorineural report addresses the following: hearing loss due to stria vascularis and semicircular canal or cochlear abnormalities as well as hypoplastic or atretic • Extent of EAC atresia and its nature (membranous, oval window.21,22 Pfeiffer syndrome is another cause of bony, or a combination of both) EAC stenosis/atresia that results in moderate to severe • Thickness of the atresia plate conductive or mixed hearing loss in patients with cranio- • Amount of mastoid pneumatization facial abnormalities. In addition to the stenosis and/or • Normal or abnormal middle cranial fossa level (especially atresia of the EAC, there is hypoplasia of the middle ear if too low) cavity and occasionally hypoplastic ossicles. Typically, the • Temporomandibular joint location inner ear anatomy is normal, but middle ear effusions are • Presence or absence of CH (Fig. 2.7) frequently seen. Therefore, when Pfeiffer syndrome • Ossicular fusion—incudomallear and incudostapedial patients receive CT for craniofacial anomalies, examina- joint maintenance, and if the ossicles are fused to the tion of the temporal bones should also be performed.23 atresia plate (Fig. 2.8). (Rotation of the long incus process Treacher Collins syndrome is an autosomal dominant resulting in an obtuse angle to the lenticular process and genetic disorder that is also associated with temporal the incudomallear and incudostapedial joints being bone abnormalities. Eighty-five percent of these patients visible on the same axial slice should also be mentioned.) ch02.qxd 1/7/09 12:22 PM Page 31

Chapter 2 The External Auditory Canal and Pinna 31

A B

Fig. 2.7 (A) Three-dimensional computed tomography (CT) surface rendering in a patient with hemifacial microsomia shows an absent external auditory canal, a hypoplastic zygomatic arch, and a thin, small vertical mandibular ramus. (B) In a different patient also with hemifacial microsoma, CT surface rendering of bone shows an absent EAC, a partially absent zygomatic arch, and a hypoplastic ipsilateral mandible. (C) In the same patient, CT surface rendering of skin shows hypoplasia of the right side C of the face and an absent pinna on that side. (See Color Plate Fig. 2.7.)

• Stapes present, dysplastic, or absent (may be useful abnormal may exclude surgical intervention. If the IAC information if a prosthesis placement is required) is small, there can be associated cochlear nerve defi- • Size of the oval window (normal size is 2 mm in vertical ciency, but deficiency of the cochlear nerve can also be diameter)27,28 present with a normal-size IAC, and MRI may be indi- • Size of the middle ear cavity in all three axes (if 3 mm cated to assess the status of the cochlear nerve).29,30 in width from the lateral margin to the cochlear • Course of the facial nerve with special attention to its promontory, surgery may be precluded)28 horizontal portion in the middle ear and its descend- • Inner ear structures and size of the internal auditory ing portion (location of the stylomastoid foramen) canal (IAC; rarely affected with EAC dysplasia, but if (Fig. 2.9) ch02.qxd 1/7/09 12:22 PM Page 32

32 Imaging of the Temporal Bone

Fig. 2.8 Coronal computed tomography scan shows severe bony stenosis and membranous atresia. The small external auditory canal is vertically oriented. The malleus and incus are fused and deformed, and this ossicular mass is fused laterally. The facial nerve is directly behind the deformed ossicles, and the middle ear cavity is small.

Fig. 2.9 Drawing showing microtia, bony atresia, and deformed ossicles. The facial nerve descends anteriorly under the lateral semicircular canal and in front to the stapes and thus is prone to injuries when drilling the atresia plate to gain access to the middle ear cavity. (Courtesy of Suresh Mukherji, MD, Ann Arbor, MI.) (See Color Plate Surgical reconstruction for auricular and EAC atresia Fig. 2.9.) are considered separately. Usually, microtia is a cosmetic procedure that is undertaken prior to entering grade school. A variety of approaches and materials have been used, but currently autogenous rib grafting using a mul- For atresiaplasty, the EAC is created by drilling poste- tistage operation produces excellent results when per- rior to the glenoid fossa and anterior to the mastoid air formed by a highly experienced surgeon. Others have cells, entering the epitympanum and superior aspect of used alloplastic materials with very good results as well. the middle ear space just below the level of the middle The creation of an EAC with an intact conductive hearing cranial fossa dura.28 The ossicular chain is mobilized from mechanism usually follows the auricular surgery so the atresia plate, and a TM is created using a temporalis there is no interference with the healing of the skin flaps fascia graft. Finally, the canal is lined with a split-thickness and the implanted framework. EAC reconstruction is skin graft, and a meatoplasty is created by attaching undertaken either to improve hearing or when CH is the skin graft to a newly created meatal opening.14 Good present. Thus, bilateral involvement represents a clear hearing results (air–bone gap 25 dB) can usually be indication for surgical intervention. Following early obtained in 75% of patients and are dependent on favorable identification, these children are fit with a bone conduc- anatomical factors. In cases where good hearing is not tion hearing aid to ensure normal auditory receptive realized from the procedure, a conventional hearing aid can abilities prior to surgical intervention. With this device, be used with excellent results. For children where anatomical speech and language acquisition usually proceeds nor- factors preclude EAC reconstruction or the risks seem mally. Atresiaplasty in unilateral cases is reserved for unacceptable to the family, an osseointegrated cochlear those patients where the anatomy is favorable, the fam- stimulator (BAHA device, Cochlear Corp., Englewood, CO) ily expectations are appropriate, and the child is very can be considered. cooperative. Favorable anatomy is generally present Postoperative complications from EAC atresia recon- when inner ear and facial nerve morphology is normal, struction include facial paralysis, sensorineural hearing temporal bone pneumatization is good, and the ossicular loss, conductive hearing loss, TM perforation, cerebrospinal chain is only mildly deformed. Jahrsdorfer et al24 has fluid (CSF) leak, and meatal stenosis secondary to bony created a classification system to help in decision mak- regrowth or soft tissue stenosis. This latter complication is ing in this regard. widely considered the most frequently occurring.31 The ch02.qxd 1/7/09 12:22 PM Page 33

Chapter 2 The External Auditory Canal and Pinna 33

most dreaded complication of EAC atresia surgery is facial nerve injury. Although rare, the facial nerve is at risk of injury in both its descending segment and in the extracranial portion. In the intratemporal portion, anterior displacement of the descending segment is the norm, making it most vulnerable while drilling the ear canal inferiorly. The extratemporal portion of the facial nerve is at risk of injury during meatoplasty, especially when the cartilaginous framework from the microtia repair lies anterior to the newly created ear canal, requiring mobilization for realignment. Other complications of atresiaplasty include persistent conductive hearing loss from ear canal stenosis, TM perforation or lateralization, and ossicular chain discontinuity or fixation. Sensorineural hearing loss can occur from inadvertent labyrinthine injury while drilling around the ossicular chain. We have recently started to use a laser Fig. 2.10 Axial computed tomography (CT) scan shows a cystic to lyse the final attachments of the ossicular chain to avoid rounded mass in the lateral external auditory canal (EAC). This is a 30 such drill-induced trauma. proven type 1 branchial cleft cyst, which extended into the EAC via a defect in its floor. Brachial Cleft Cyst A brachial cleft cyst (BCC) is a congenital lesion that can Fistulography can also be performed to better assess the occur in the area of the EAC, and is the cause of one third course, anatomy, and topography of a fistulous tract, which of pediatric nonmalignant lesions in the region of the helps improve the rates of complete resection of a fistula parotid gland requiring surgery.32 BCCs arise from lack of associated with a BCC.36 involution of structures from the first through fourth In this chapter, we will concentrate on first BCCs branchial arches and are classified by location. Pathologi- because these occur in the region of the EAC. First BCCs are cally, BCCs are composed of a thin fibrous pseudocapsule less common than second BCC cysts and account for less with central squamoid epithelium and occasionally lym- than 8% of all BCCs. A first BCC arises in a periauricular phocytic and germinal tissues. The majority of BCCs are location, often parallels the EAC in orientation, and can be simple cysts (two thirds) with thick mucous contents, no enveloped by the parotid gland. A congenital tract or cutaneous or airway opening, and 3 cm or less in size. sinus from the BCC may communicate with the EAC. Due Due to their histologic components, BCCs are similar in to this embryological development, a first BCC can be their imaging appearance, regardless of their location. associated with other first cleft anomalies, including het- Rarely, a BCC undergoes malignant transformation into erotopic salivary gland tissue, which has a predisposition squamous cell carcinoma.33 On physical examination, a for malignant transformation,37 or CH.38 Although there BCC is compressible due to its fluid components and usu- are two possible subtypes of a first BCC, there are no strict ally painless. These lesions have a tendency to enlarge or well-defined histological and anatomical features for with upper respiratory tract infections due to lymphoid each one. The probability of an associated sinus with a secretions from follicles in the wall of the cyst and may first BCC is 56%, and a fistulous tract to the EAC at the become painful even in the absence of infection. cartilaginous–bony junction occurs in 31%, with the remain- BCCs are readily evaluated with CT. Their appearance is ing first BCCs having a simply cystic appearance.39 A first that of a well-circumscribed mass with fluidlike compo- BBC usually presents while the patient is a child, one nents centrally (Fig. 2.10).34 On MRI, a BCC is of low T1- and third of patients presenting acutely due to infection and high T2-weighted signal and may exhibit rim enhancement two thirds presenting with asymptomatic swelling, but following contrast administration. Increased proteinaceous may also present in teenagers or young adults if the lesion contents may lead to higher T1-weighted signal and occa- is purely cystic and not infected.40 On rare occasions with sionally low T2-weighted signal intensity. In the absence of any BCC, there can also be communication with the skin infection, FLAIR imaging will demonstrate the central fluid surface, producing a fistula. to have low signal. If there is accompanying infection, sur- Commonly, a BCC is treated by complete resection to rounding soft tissue edema (stranding of fat) will be present prevent recurrence and reduce complications.41 Because on CT and MRI, and the rim has a tendency to be thicker, many BCCs present as an abscess, they can be improperly nodular, and to enhance. MRI may be useful for locating diagnosed and treated with simple incision and drainage a sinus/fistula. CT better assesses bony abnormalities.35 rather than complete excision.42 The surgeon must be ch02.qxd 1/7/09 12:22 PM Page 34

34 Imaging of the Temporal Bone

careful to not injure the adjacent extratemporal portion of Different lesion types cannot always be differentiated by the seventh cranial nerve.39,43 Due to variable relationships imaging, but a cystic hygroma is the most common type.52 of BCCs to the facial nerve, imaging is important for surgi- Contrast administration is needed to assess these lesions cal planning. Even with identification of the facial nerve at because the presence of venous components may change surgery, there is a 21% incidence of temporary and 1% inci- the surgical approach. On imaging, the most distinguish- dence of permanent facial palsy after resection of a first ing feature of a cystic hygroma or lymphangioma is a ten- BCC. Additionally, the probability of facial nerve injury dency to insinuate itself into multiple compartments in a increases with the number of previous infections and transspatial manner and to surround normal anatomical surgeries.44 More recently, methods other than surgical structures such as muscles and blood vessels. Hence, a excision have been described for treatment of a BCC. An lymphangioma is less well circumscribed than a BCC. endoscopic approach for excision of a BCC through a small Lymphangiomas are most commonly multilocular and transcervical incision has been described and is said to nonenhancing, although they may rarely enhance if there have minimal morbidity.45 However, data regarding the is superimposed infection. Additionally, when infection is safety and efficacy of this approach are lacking. Also present, it may extend outside the lesion.53 On CT, these described is the use of ethanol injections for sclerotherapy lesions may display fluid-fluid levels and occasionally of a BCC.46 show venous (enhancing) components or areas of en- The differential diagnosis for a BCC includes other hancing soft tissue. On MRI, the lesions may have a simple cystic lesions, such as lymphangiomas, which are usually cystic appearance, but if there has been prior hemorrhage multiloculated, nonenhancing, and transspatial lesions. or proteinaceous fluid, they will have high T1-weighted Cystic lesions in the region of the parotid tail include lym- signal and/or fluid-fluid levels. phoepithelial cysts with AIDS, cysts of the parotid in The differential diagnosis for a lymphangioma includes Sjögren’s syndrome, and less commonly, cysts in Reiter’s other slowly growing neck masses, including neurofibroma, syndrome. Also, an infected intraparotid or suppurative schwannoma, hemangioma, vascular malformation, and jugular lymph node, or rarely, an intranodal necrotic sublingual salivary mucocele (i.e., ranula or pseudocyst). metastasis from squamous cell or thyroid cancers must Acute swelling and a more rapid presentation is seen in be considered.47,48 Lymphoma, both Hodgkin and non- suppurative lymphadenopathy secondary to sinusitis, Hodgkin types, are also in the differential diagnosis, but odontogenic infection, or abscess. A BCC with superim- typically demonstrate multiple masses/enlarged nodes.49 posed infection is more common than a lymphangioma. If Another uncommon entity in the differential is a cystic there has been a rapid clinical change such as swelling schwannoma from the facial nerve.50 and/or cranial nerve deficits, a malignant process such as rhabdomyosarcoma, Langerhans cell histiocytosis, Ewing sarcoma, osteogenic sarcoma, or metastatic neuroblastoma Cystic Hygroma and Cystic Lymphangioma should be considered.54 Lymphangiomas occur less frequently than BCCs. Embry- Lymphangiomas can be assessed before surgery with ologically, lymphangiomas may have two possible origins: ultrasound (US), CT, and/or MRI. In our institution, the they may arise secondary to failure of embryonic fusion majority of patients are assessed with contrast-enhanced between the central venous system and lymph sacs or neck CT because the diagnosis is not always known at pres- from sequestration of lymph sacs. In either case, the con- entation, and CT can exclude most of the other lesions dition is associated with Turner’s and Noonan’s syn- mentioned above in the differential. Imaging prior to surgical dromes as well as with fetal alcohol syndrome. Clinically, intervention allows for staging of the lesion, determination most cystic hygromas and lymphangiomas present in the of unilaterality or bilaterality, infra- or suprahyoid extent, first 2 years of life and only rarely in adulthood.51 On and mediastinal involvement. These differences in staging physical examination, lymphangiomas are compressible predict surgical outcomes as well as complication and masses, usually involving the submandibular and poste- morbidity rates.55 MRI reveals associated pathology not rior triangle regions, which may result in airway obstruc- seen with US in 20% of patients.56 MRI is also useful for tion. Lymphangiomas may also extend to the mucosal assessment of the amount of tracheal/airway compromise.57 surfaces of the oropharynx, tongue, or airway. Pathologi- Standard treatment of lymphangiomas is surgical. cally, they are composed of endothelial-lined dilated Recently, new types of intervention are being employed, endolymphatic spaces with septations of variable thick- including US-guided cavity aspiration with injection of ness and at times vascular structures. Depending upon bleomycin, which has resulted in a good response in more the size of the lymphatic spaces within a lesion, there is than 50% of patients.58,59 Also, administration of a four-dose a pathologic continuum with cavernous hemangioma, injection regimen of OK-432 (Picibanil) at 6- to 8-week capillary lymphangiomas (least common form with the intervals has shown an 86% success rate for obliteration or smallest spaces), and vasculolymphatic malformations. substantial reduction ( 60%) of the cystic hygromas.60 In a ch02.qxd 1/7/09 12:22 PM Page 35

Chapter 2 The External Auditory Canal and Pinna 35

minority of patients, lymphangiomas may resolve/involute present with pain, erythema, swelling, and severe tragal on their own.61 Lymphangiomas are known to have a ten- and auricular motion tenderness. Occasionally, a conduc- dency to recur, particularly if nonencapsulated; therefore, tive hearing loss may be present when canal swelling has they need to be followed closely regardless of the course of obliterated the patency of the EAC.64,65 Most commonly, therapy utilized. the condition is caused by a bacterial infection from Pseudomonas aeruginosa or Staphylococcus aureus. Oto- mycosis or fungal OE usually results from infection from Foramen of Huschke either Candida or Aspergillus species. Presentation usually Approximately 4.6% of patients have an area of medial follows the administration of multiple oral or topical anti- bony dehiscence involving the anterior and inferior EAC bacterial medications and can be quite refractory to 66 called the foramen of Huschke. Normally, the foramen of conventional therapy. There is also an increased risk of Huschke obliterates during childhood or infancy as the otomycosis among diabetic and/or immunocompromised 67 U-shaped EAC cartilage undergoes fusion into a complete patients. When otomycosis complicates perforated otitis ring. On physical examination, a persistent foramen may media or otitis media with a tympanostomy tube, therapy present as a small polyp or punctum on the anterior wall can be very challenging because most medications that of the EAC. These congenital fistulas are rare. The foramen are active against fungal species have not been approved is readily detected with high-resolution CT, is located pos- by the U.S. Food and Drug Administration or are safe for terior and medial to the temporomandibular joint (TMJ), middle ear usage. Uncommonly, acute OE can result from and measures 3 to 4 mm in size. A patent foramen of viral infection. Ramsay Hunt syndrome or herpes zoster Huschke is more common in females and can cause tran- oticus is due to infection of the seventh and eighth cranial sient otorrhea from TMJ synovial fluid. Rarely, soft tissue nerves by reactivation of latent herpes zoster virus in the posterior to the TMJ meniscus can herniate into the EAC geniculate, spiral (i.e., cochlear), and/or Scarpa’s (i.e., during mouth closure. Rarely, this tract can act as a portal vestibular) ganglia. Classically, this disease presents with for the spread of infection or tumor between the EAC and acute facial palsy and a vesicular eruption in the distribu- TMJ. Its presence can be identified with high-resolution tion of the somatosensory fibers of the facial nerve within 68 (0.6 mm thick) CT imaging, is seen as bony EAC thinning the EAC and auricle. When the vestibulocochlear nerve ( 1.0 mm) anteriorly and inferiorly, and is usually bilateral. is involved, sensorineural hearing loss and vertigo may be Normally, the foramen of Huschke closes by the age of present to varying degrees. Treatment of this disorder 5 years, and its persistence is an anatomical variant.62 usually requires systemic corticosteroid therapy and an Salivary otorrhea from a patent foramen of Huschke antiviral medication with efficacy against the offending presents with serous discharge from the EAC that occurs agent (i.e., valacyclovir). more frequently with meals. This fluid demonstrates the Imaging has a limited role in the diagnosis of acute OE presence of amylase when counterstained with iodine on unless it is recurrent or there is suspicion of an underly- a starch agar plate. Sialography may show the presence of a ing benign or malignant lesion. Refractory OE may result fistula to the EAC or just chronic parotid sialadenitis with- from chronic EAC obstruction from a variety of lesions. out a definite fistula. MRI reveals bright T2-weighted Similarly, malignant tumors may result in canal obstruc- signal within the adjacent parotid secondary to the tion or invasion, thereby mimicking clinical OE. CT may be sialadenitis and/or fluid in the EAC. Usually, the defect is very useful for assessing the anatomical details medial to repaired surgically using temporalis fascia and tragal a completely obstructed EAC. The presence of osseous perichondrial grafts.63 erosion may be the only clue to an underlying neoplastic process. When facial paralysis complicates any EAC disease, a comprehensive evaluation of the temporal bone Inflammatory including the facial nerve may be indicated. In some cases, this may require both MR and CT imaging. Specifi- Otitis Externa cally, the osseous or intratemporal facial nerve is best There are six forms of otitis externa (OE; also known as evaluated with fine-cut images through the temporal external otitis); acute, chronic, eczematous (dermatitis, bone. When IAC or cisternal involvement is suspected, psoriasis, lupus, or infantile eczema related), fungal, and MRI is more useful. For instance, when herpes zoster is necrotizing/malignant. suspected, MRI is the study of choice and demonstrates thickened seventh and eighth cranial nerves on high- resolution CISS images as well as fusiform enhancement Acute Uncomplicated External Otitis of the nerves within the IAC. The entire intratemporal Acute uncomplicated external otitis or swimmer’s ear is facial nerve (labyrinthine, tympanic, and mastoid segments) the most common external ear infection. Patients with OE enhances along with the geniculate ganglion and the ch02.qxd 1/7/09 12:22 PM Page 36

36 Imaging of the Temporal Bone

membranous labyrinth (especially the cochlea). The Patients with sclerosing external otitis are treated facial nucleus within the brainstem may also enhance.69 surgically if recurrent infection and otorrhea are present, Enhancement that is limited to the geniculate ganglion conductive hearing loss from EAC obstruction occurs, or and to the labyrinthine segment of the facial nerve indi- when the clinician suspects other pathologies, such as cates a good prognosis whereas a widespread enhance- squamous cell carcinoma. Clinical suspicion in these cases ment correlates with a poor prognosis.70 There can also be must be high, and the threshold for imaging these patients visible enhancement of the external ear vesicles. is very low. Associated chronic, unremitting pain is a clue to more ominous pathology. CT shows a soft tissue mass within the medial EAC that is inseparable from the TM Chronic External Otitis and has a crescentic appearance laterally without mastoid Chronic external otitis leading to EAC fibrosis and exos- or middle ear involvement. There is no bone erosion, and toses (see below) are two conditions that are commonly contrast enhancement is minimal and usually appears seen in swimmers, surfers, and divers who expose them- along the thickened and edematous walls of the EAC. selves repeatedly to cold water. It is known that trauma, There can be intense associated bony reaction and thick- a low pH within the EAC, and cerumen insufficiency ening of the EAC. MRI displays similar findings, with the predispose to chronic external otitis.67 As discussed mass exhibiting intermediate-to-low T2-weighted signal previously, imaging studies serve to better assess the intensity. Lower T2-weighted signal intensity is expected anatomical details deep to the obstructing lesion(s) as if fibrous components are extensive. Postcontrast images well as help to define the existence and extent of bony demonstrate mild EAC wall enhancement. The differential erosion. diagnosis is extensive, the most common causes being cerumen and debris in the EAC. In these cases, there will usually be air located between the EAC wall and the soft Chronic Stenosing External Otitis tissue mass, as well as lack of enhancement of the mass. Another entity in the differential is chronic stenosing Alternatively, soft tissue in the EAC with otorrhea may be external otitis (also known as medial meatal fibrosis or due to CH, but these patients have bony erosion of the postinflammatory acquired atresia). Medial canal fibrosis EAC and usually unilateral disease as well. The most wor- is a rare disorder found more frequently in males. Sixty risome diagnosis that one must consider is carcinoma, percent are bilateral and present as a fibrous plug caus- which may present in the setting of long-standing chronic ing stenosis or obstruction of the EAC. There may be otitis.75 Other conditions occurring secondary to chronic associated TM thickening in late stages. This entity is sec- OE include auricular cellulitis, chondritis, parotitis, and ondary to chronic OE or to recurrent otitis media with a development into malignant external otitis (MEO).67 Enti- perforated TM. It can also be secondary to trauma (often ties such as tuberculosis, syphilis, lupus, carcinoma, iatrogenic), radiation therapy for head and neck cancer, and histiocytosis may have mastoid and/or middle ear or tumor and inflammation, and usually develops at an involvement.76 Surgical treatment includes excision of the average of 14 years after the insult.71 Chronic inflamma- fibrous tissue with a wide canaloplasty and a meato- tion results in a subepithelial infiltration of inflammatory plasty, followed by reconstruction with a fascial graft cells that causes fibrosis and medial EAC stenosis. The and/or split skin grafts.77 stratified epithelium of the TM and of the adjacent bony meatus is destroyed and replaced by fibrotic tissue, Malignant External Otitis which has some similarity to the tissue seen with keloid formation. The fibrotic tissue can cover an underlying CH MEO or necrotizing otitis externa (NOE) generally presents and may recur after surgery. This process occurs in with otorrhea and severe otalgia in diabetics and immuno- sequential steps that include destruction of the epithe- compromised patients. This condition can also be associ- lium, formation of granulation tissue, fibrosis, and, finally, ated with a history of trauma. In most diabetics, the causes lining of the EAC with new meatal skin.72 Patients with of infection are gram-negative rods such as Pseudomonas hearing aids are at risk for this disease because the pres- aeruginosa.78 However, there are other immunosuppressed ence of the hearing aid, or of any other foreign body, may patients who have an increased incidence of MEO, such as result in abnormal migration of epithelial cells. The gran- those with hematological neoplasms, postchemotherapy, ulation tissue that forms ultimately results in the forma- and AIDS. In the immunocompromised host, such as AIDS tion of a fibrous plug. CHs can also form in this space; patients, MEO is often due to microorganisms other than when this occurs, the rate of recurrence is high.73,74 A his- Pseudomonas, and, unlike diabetics, there is no granula- tory of dermatitis (eczema or psoriasis) or other chronic tion tissue formation. MEO in AIDS patients also has a skin condition may predispose to this disease. This is a more fulminant course, with a mortality rate of 42% rare condition in children. compared with 4% in diabetics. Sometimes, MEO occurs ch02.qxd 1/7/09 12:22 PM Page 37

Chapter 2 The External Auditory Canal and Pinna 37

after cerumen removal and irrigation with tap water osseous marrow changes, meningeal disease, and parotid because these organisms thrive in moist environments. extension.84,85 In cases where MEO cannot be differenti- On physical examination, there is granulation tissue in ated from uncomplicated OE, technetium 99m methylene the inferior EAC, along the bony-cartilaginous junction. diphosphonate (Tc 99M MDP) may be useful in helping Commonly, the infection spreads inferiorly into the soft make the diagnosis. Tc 99M MDP may show positive areas tissues and TMJ. MEO readily spreads via the fissures of where CT and MRI show little if any changes. Conversely, Santorini from the EAC into the mastoid and subsequently Tc 99M MDP scanning is positive with bone erosion or into the TMJ and middle cranial fossa, causing sigmoid new bone formation with healing, and thus it is not effec- sinus thrombosis and secondary venous infarction. Mid- tive for differentiation of continued disease or healing. dle cranial fossa involvement can also result in meningi- Labeled white blood cell scans can also be helpful. Gal- tis, subdural empyema, and brain abscess. Spread through lium scans are sensitive for monitoring therapy.82 Therefore, the TM is unlikely; instead, middle ear involvement is gallium-67 single-photon emission computed tomogra- usually secondary to mastoid extension. MEO can also phy (SPECT) is advocated for follow-up and evaluation of extend insidiously along the skull base, resulting in multi- treatment.86 ple cranial neuropathies, osteomyelitis, and death.79,80 The differential diagnosis of MEO includes OE, chronic Most commonly, involvement of the facial nerve occurs at otitis media (COM) with CH, EAC CH and keratosis obtu- the level of the stylomastoid foramen.81 If spread along rans (KO), chronic granulomatous diseases, Langerhans the skull base occurs posteriorly and inferiorly into the cell histiocytosis, and carcinoma of the EAC. Characteristic region of the jugular foramen, the infection can involve among most of these pathologies is granulation tissue CN IX to XII, resulting in jugular foramen syndrome. MEO within the EAC. Differentiation among these varied has been classified into the following stages:82,83 pathologies ultimately may require microscopic evaluation, culture, and biopsy of the offending tissue. This • Stage I: Confined to the EAC with or without facial should only be considered when imaging has assessed the nerve paralysis (Fig. 2.11) involvement of the underlying middle ear, inner ear, and • Stage II: Superior extension, skull base osteitis, and/or facial nerve. multiple cranial nerve involvement • Stage III: Extension beyond the temporal bone or Other Causes of Inflammatory External Auditory intracranially and contralateral involvement Canal Pathology Imaging of MEO can be performed with CT and/or MRI Tuberculosis (TB) in the head and neck region usually to evaluate the initial extent of disease. CT is superior for presents as cervical lymphadenopathy (95%). In 2% of evaluation of bone destruction, but MRI is superior for eval- patients with head and neck involvement, TB presents in uation of soft tissue extension, cranial nerve involvement, the larynx, and in 1% of cases, it will present in the cervical spine, oropharynx, ear, or as a retropharyngeal abscess. Only 9% of patients will have a history of previous or subsequent TB.87 Tuberculous OE has been described as a punched-out ulcerative lesion on the tragus, an edematous and inflamed EAC, or a purulent nonmucoid discharge with facial palsy.88 Tubercular mastoiditis, petrous apicitis, and otitis media also occur.89 Typically, patients with EAC involvement present with otorrhea, hearing loss, and dizziness, and may have facial palsy. TB at imaging, in particular with CT, appears as an aggressive osteo- destructive process (Fig. 2.12).90 Wegener granulomatosis is a nonneoplastic, aseptic, necrotizing vasculitis that typically affects the sinonasal cavities, the orbits, oral cavity, nasopharynx, larynx, temporal bone, and skull base. In 70% of patients, there is an elevated erythrocyte sedimentation rate, and antineutrophil cytoplasmic antibody (C-ANCA) is present.91 There is respiratory and renal tract involvement in most patients; Fig. 2.11 Coronal computed tomography scan shows soft tissue filling the external auditory canal (EAC) in this diabetic patient with stage 1 19 to 38% of patients have otologic involvement, which (confined to the EAC) malignant otitis externa. The tympanic membrane may mimic relapsing polychondritis. Patients typically is thickened. present with ear pain, otitis media with effusion (40 to 70%), ch02.qxd 1/7/09 12:22 PM Page 38

38 Imaging of the Temporal Bone

A B Fig. 2.12 (A) Axial computed tomography (CT) scan shows aggressive poromandibular joint anteriorly, and medially into the middle ear. The process (proven tuberculosis) with destruction of the walls of the exter- ossicles show irregular borders due to early involvement. (B) Coronal nal auditory canal and extension into the mastoid posteriorly, to the tem- CT shows the degree of extension, particularly into the mastoid bone.

sensory neural hearing loss (8%), and tinnitus. Patients are Langerhans cell histiocytosis (LCH), if limited to bones, usually men 40 to 60 years of age. There is an increased is commonly referred to as eosinophilic granuloma. It is risk of superimposed infection and mastoiditis. Because characterized by an accumulation of abnormal histio- this disease is indolent, it can be present for years prior cytes, together with lymphocytes and eosinophils. Histio- to diagnosis, but the prognosis is poor if left untreated. cytosis can involve the temporal bone region in as many C-ANCA titer elevations are 85 to 98% specific and are used as 25% of patients93 and may mimic acute or chronic in- to follow up the response to corticosteroids and immuno- fectious ear disease.93,94 Ear involvement occurs in 13.5% suppressive agents. If renal disease is present, serum crea- of childhood cases and is associated with a younger age at tinine levels are high.92 Imaging studies may show bone diagnosis, multisystem disease (93.8%), and a higher risk destruction generally accompanied by soft tissue thicken- of poor response.95 The disease is often located adjacent ing throughout the temporal bone (Fig. 2.13). Unfortunately, to or within the area of the endolymphatic sac.96 At the imaging features are nonspecific and may be identical imaging, there are destructive bone lesions involving the to those seen in EAC carcinoma or chronic otitis. mastoid bone (Fig. 2.14). The squamous portion of the temporal bone and the middle ear are less commonly affected.97 At CT, the lesions produce significant bone destruction and enhance homogeneously. CT is the preferred study of choice for diagnosis, determining the extent of temporal bone involvement, and for monitoring response to treatment. Bone scans are less sensitive than CT for detection of lesions.97 With MRI, the lesions are bright on T2- weighted sequences, isointense to marrow on T1-weighted sequences, and enhance intensely.98 MRI is useful for evaluation of intracranial extent and assessment of vascular involvement, and thus is complementary to CT.99 Treatment can be with surgery, radiotherapy, and/or chemotherapy; preservation of hearing is the goal. The posttreated temporal bone re-ossifies and remodels.

Cholesteatoma Both CH and KO arise from exfoliation of squamous ep- Fig. 2.13 Axial computed tomography scan in a patient with Wegener ithelium into the EAC, but these processes occur in dif- granulomatosis shows destructive process centered in the right mastoid. There is extension of the disease into the middle ear cavity and ferent age groups; generally CH is found in individuals the ossicles show marginal erosive changes. over age 40, and KO in those under age 40.10 0 With CH, ch02.qxd 1/7/09 12:22 PM Page 39

A B

C D

E F Fig. 2.14 (A) Axial computed tomography (CT) scan in a young child domyosarcoma may have a similar appearance. (B) Axial CT in a differ- shows “punch-out” aggressive soft tissue mass involving the lateral as- ent and older child shows too a punch-out lesion involving the posterior pect of the right temporal bone and extending into the middle ear cav- wall of the right external auditory canal (EAC). Soft tissue fills the EAC. ity. Biopsy show eosinophilic granuloma. In a child, a middle ear rhab- This was also eosinophilic granuloma. ch02.qxd 1/7/09 12:22 PM Page 40

40 Imaging of the Temporal Bone

there is unilateral, dull, chronic ear pain and pruritus, typ- bright on diffusion weighted images.103 The staging aris- ically accompanied by otorrhea. There is erosion of the ing in the EAC is as follows101: posteroinferior wall of the EAC and a normal-appearing TM. EAC CH usually presents with normal hearing, unless • Stage I: Hyperplasia of the canal epithelium large, when it produces conductive hearing loss. Histolog- • Stage II: Hyperplasia with periostitis ically, CH arises from hyperplastic epithelium containing • Stage III: Necrosis/erosion of the bony canal inflammatory cells. Subsequently, there is invasive growth • Stage IV: Erosion of structures beyond the EAC of the lesion into the mesenchymal tissues with accumulation of necrobiotic keratin debris and bone erosion with Treatment of EAC CH includes débridement with exci- bony sequestra formation.101 There are several different sion of the matrix. Removal of necrotic bone adjacent to causes of EAC CH with the congenital form occurring with the soft tissue mass may be needed to prevent osteitis patients with EAC stenosis/atresia and the acquired form and recurrence, as well as to allow for normal squamous probably related to periostitis (Fig. 2.6). After EAC sur- epithelial migration. Because of its characteristic posterior gery, there is approximately a 1% chance that CH may and inferior location within the EAC, the descending seg- arise from inclusion cysts along the incision.102 ment of the facial nerve is at risk during treatment of this EAC CH is best assessed with CT, which demonstrates disorder. Great care must be exercised when removing bone erosion. EAC erosion is smooth or irregular and CH matrix in this location. CT imaging is of paramount tends to be focal. CH shows a soft tissue mass and erosion importance in determining the extent of involvement, and within the bony portion of the EAC (Fig. 2.15). When this supplementary facial nerve monitoring is recommended process is associated with acute periostitis, it may be during surgery in this region. Although the middle ear difficult to differentiate from carcinoma (Fig. 2.16). On space is usually spared in this disease, occasionally canal MRI, recurrent CHs have restricted diffusion and are erosion can extend inferior to the tympanic annulus and

A B

Fig. 2.15 (A) Coronal computed tomography (CT) scan in a patient with a cholesteatoma of the right external auditory canal (EAC). There is erosion of the floor of the EAC, and the soft tissue mass is contiguous with the pars tensa of the tympanic membrane. (B) Coronal CT in a patient with a typical pars flaccida acquired cholesteatoma. The rounded mass protrudes mostly into the EAC rather than into Prussak’s space. The tip of the scutum is blunted. (C) Axial CT in the same patient shows the rounded cholesteatoma C in the anterior aspect of the EAC. ch02.qxd 1/7/09 12:22 PM Page 41

Chapter 2 The External Auditory Canal and Pinna 41

A B Fig. 2.16 (A) Coronal computed tomography (CT) scan shows a large shows the mass expanding the EAC and pushing the tympanic mem- external auditory canal (EAC) cholesteatoma filling the EAC and remod- brane into the middle ear cavity. eling its superior and inferior walls. (B) Axial CT in the same patient

into the hypotympanum. This may create the appearance plug. This appearance is different from that produced by of a swinging annulus on clinical examination. The most CH in which there is focal erosion. Treatment involves commonly confused differential diagnosis for EAC CH is removal of the keratin plug and associated granulation KO. KO usually presents acutely in a younger age group tissues. Repeated débridement may be needed until heal- with severe pain and little bone erosion. Occasionally, ing occurs. Following healing, periodic cleaning of the an aggressive CH cannot be differentiated from KO or desquamated keratin is usually required indefinitely. squamous cell carcinoma until biopsy has been undertaken. A congenital form exists and presents in childhood at the floor of the EAC. Congenital CH also occurs in other loca- Tumors tions, including the petrous apex, mastoid, middle ear, the squamous portion of the temporal bone, and cerebello- Benign Soft Tissue Tumors 104 pontine angle. There are several benign soft tissue tumors that involve the EAC. These include aural polyps, lipoma, hemangioma, arteriovenous malformation (AVM), lymphangioma, Keratosis Obturans smooth muscle tumors (leiomyomas), tumors of glandular KO of the EAC generally occurs in individuals around origin, neural origin tumors (schwannomas and neurofi- 40 years of age and presents acutely with severe pain bromas), and myxomas.105,106 Myxomas of the EAC are and conductive hearing loss but no otorrhea. KO may extremely rare and occur in association with autosomal present after prior trauma or surgery. It may also associ- dominant familial pigmentation, endocrine tumors, and ated with sinusitis and bronchitis. The development of schwannoma syndrome.107 Some of these EAC soft tissue KO in these individuals is probably due to sympathetic tumors, in particular, the hemangiomas, AVMs, and neurofi- stimulation of the cerumen glands, resulting in hyper- bromas, can bleed extensively at surgery, and a preoperative emia and epidermal plug formation. Alternatively, it embolization may be desirable. could result from abnormal TM epithelial migration. On physical examination, there is thickening of the TM with Aural Polyps redness and erythema in the EAC accompanied by granulation tissue.10 0 Aural polyps are a consequence of chronic inflammation KO is best evaluated with CT, which demonstrates bony within the EAC or middle ear. They are soft tissue wall remodeling resulting in diffuse widening of the EAC masses that elicit no bone erosion or reaction (Fig. 2.18). (Fig. 2.17). This smooth, diffuse widening is thought to Biopsy is usually necessary for diagnosis because they result from pressure erosion by the chronic epidermal can mimic squamous or basal cell carcinomas and other ch02.qxd 1/7/09 12:22 PM Page 42

42 Imaging of the Temporal Bone

A B

C D Fig. 2.17 (A) Coronal computed tomography (CT) scan shows a soft canal. (B) Axial CT in the same patient shows that the mass results in tissue mass (proven keratosis obturans) in the fundus of the external minimal, benign appearing scalloping of the anterior wall of the EAC. auditory canal (EAC) and resulting in some scalloping of the floor of the

malignancies. Aural polyps have a high rate (52%) of under- physical examination. Differential diagnosis includes an lying CH. Due to this high rate, imaging is useful to deter- angiomyolipoma, of which there are 13 reported cases mine the extent of disease and surgical planning.108 In without von Hippel-Lindau disease, angiofibrolipoma, children, COM (43%) and retained tympanostomy tubes liposarcoma, and dermoid.110 – 113 Dermoids are more com- (23%) are a predisposing factor, as are mycobacterial mon in the region of the middle ear and eustachian tube infection and Langerhans cell histiocytosis.109 Treatment than in the EAC, and liposarcomas may show bone erosion. of an aural polyp depends on the underlying cause. Often, the underlying process becomes evident only after topi- Arteriovenous Malformations cal antimicrobial/corticosteroid therapy. The external ear is the second most common location for AVMs of the extracranial head and neck. A study of 44 such Lipoma lesions demonstrated that enlargement of the lesion can The diagnosis of lipoma is easily made with imaging due occur during childhood, adolescence, pregnancy, or adult- to the presence of fat on CT and very low signal on fat- hood. MRI demonstrates enlarged feeding and draining suppressed MRI (Fig. 2.19). Clinically, a lipoma is covered blood vessels with flow voids if the lesions are Schobinger by epithelium, and the diagnosis may not be obvious on stages II or III. Stage I and II lesions often remain stable ch02.qxd 1/7/09 12:22 PM Page 43

Chapter 2 The External Auditory Canal and Pinna 43

Smooth Muscle Tumors and Leiomyoma Smooth muscle tumors are very rare EAC tumors and may arise after trauma and result in conductive hearing loss.116 There are two types: one arises de novo from ectopic muscle called arrectores pilorum, and the other arises from smooth muscle at blood vessel walls.105 On CT, these lesions demonstrate no bone erosion and are well circumscribed and confined to the EAC.

Tumors of Glandular Origin The two most common benign glandular tumors of the EAC are ceruminoma (arising from glandular elements and hyperplastic myoepithelial elements) and adenoma/ pleomorphic adenoma (arising from only glandular elements).117 The latter type is more common. These benign lesions cannot be differentiated from one another, or even from malignancy, by imaging. These tumors arise from the cerumen glands or from ectopic salivary tissues. Usu- Fig. 2.18 Axial computed tomography scan shows a small, rounded ally, they present from age 30 to 60 years and result in polyp in the opening of the right external auditory canal. otorrhea and hearing loss without pain. On physical examination, there is a soft tissue mass in the EAC with- without treatment. Patients who experience lesion out bone erosion. There have been 25 reported cases of expansion can be treated with embolization alone or as a pleomorphic adenoma in the EAC; most commonly, the last resort with auricular amputation and prosthesis tumor arises at the posterior and posterosuperior walls.118 placement. Proximal vascular ligation does not result in Adenoid cystic carcinomas and adenocarcinoma are lesion obliteration.114 discussed in the section on malignant tumors.

Hemangioma Neurofibroma and Schwannoma Typically, hemangiomas have a bluish appearance on Ten to 60% of neural origin tumors involving the EAC and physical examination and enhance intensely on CT and pinna are found in individuals who have neurofibromato- MRI. Cavernous hemangiomas of the EAC with or without sis type I (NF1),106 and have been reported to have an inci- TM involvement are rare and need to be treated surgi- dence of 6% in a study of pediatric NF1 patients.119 Usually cally.115 Preoperative digital subtraction angiography and other neurofibromas will be visible in other regions on embolization may be useful. the scan, helping the radiologist to make the diagnosis. The more virulent form of neurofibromas, the plexiform type, often presents with conductive hearing loss. Even more rarely, a neurofibroma can degenerate into a sarcoma. Origination of a schwannoma from the EAC is very rare.120,121 However, secondary involvement of the EAC by schwannomas arising from CN VII or IX may occur.

Benign Bony Tumors Meningiomas Most commonly, meningiomas arise intracranially and spread to the temporal bone and EAC rather than arising from the temporal bone itself. In general, 20% of meningiomas may have extracranial spread and may occur in the Fig. 2.19 Coronal computed tomography scan shows a mass involving region of the temporal bone. Meningiomas involving the the entire right external auditory canal. Even in this study with bone temporal bone have a more infiltrative pattern than other window setting, the low density of this lipoma can be appreciated. intracranial meningiomas.122 Treatment of meningiomas ch02.qxd 1/7/09 12:22 PM Page 44

44 Imaging of the Temporal Bone

involving the temporal bone region is complete surgical composed of dense lamellar bone superficially with an un- excision with yearly follow-up imaging with CT or MRI.123 derlying layer of vascularized loosely compact bone. Similar findings have been demonstrated experimentally secondary to cold water infusion into the EAC in guinea pigs.125 Exos- Exostoses toses are extremely rare in African Americans. Exostoses can Exostoses are the most common benign tumors of the EAC. be diagnosed on physical examination, and the lesions are Exostoses are broad-based, bony growths that occur along found in the medial bony EAC near the tympanic annulus at EAC suture lines, which result in circumferential narrowing the tympanomastoid and tympanosquamous suture lines. of the EAC bilaterally. The majority of exostoses is found in Patients are usually asymptomatic until critical narrowing individuals who swim in cold water (surfer’s ear), and al- results in recurrent OE and conductive hearing loss. CT is though usually bilateral, patients have unilateral complaints the study of choice and demonstrates a broad-based bony (80%).124 Their cause is reactive hyperplastic bone formation narrowing of the EAC with normal-appearing, overlying soft secondary to repeated cold water exposure. The lesion is tissue that does not enhance (Fig. 2.20). Imaging also allows

A B

Fig. 2.20 (A) Axial computed tomography (CT) scan shows tiny, incidentally found, bone exostosis in the deep and anterior aspect of the right external auditory canal (EAC). (B) In a different patient, axial CT shows a larger bone exostosis in the lateral aspect of the left EAC. (C) In a third patient, axial CT shows a circumferential bone exostosis in the deep aspect C of the right EAC. (Case courtesy of Dr. Farida Benoudiba, Paris, France) ch02.qxd 1/7/09 12:22 PM Page 45

Chapter 2 The External Auditory Canal and Pinna 45

for assessment of the course of the facial nerve and aids in have a significant exposure to cold water for prolonged avoiding its injury126 during surgical intervention. On MRI, periods.130 There is also a predisposition for osteomas in these lesions have low T1-weighted and T2-weighted signal individuals who have had previous EAC surgery, and following that of cortical bone. they may be associated with CH.131 As with exostoses, The probability of an exostoses recurring depends on surgical intervention is indicated when EAC obstruction age at presentation and is more common in older individu- results in significant symptoms. Because of the peduncu- als. Additionally, refusal to wear earplugs when swimming, lated nature of these lesions, surgical excision is rarely or swimming year-round, especially when accompanied by difficult. sailing, diving, and surfing increases the risk of recurrence.127 Sixty-six percent of patients who undergo surgical Osteopetrosis removal, EAC exostoses have relief of symptoms, but in 29% symptoms remain unchanged; in 4% of patients symptoms Malignant (autosomal recessive) osteopetrosis is a rare become worse and 6% of patients require reoperation.128 bone disease secondary to the formation of dense, brittle bone that generally presents in the first 7 years of life. More than one half of patients present in the first Osteoma year of life. The consequences of this bone formation Osteomas, unlike exostoses, are usually unilateral, focal, are poor pneumatization of mastoid air cells and and pedunculated, arising from one wall of the EAC the EAC, IAC, and eustachian tube stenoses. Patients (Fig. 2.21). At pathology, exostoses and osteomas of the show hearing loss (100% conductive and 26% mixed EAC cannot be reliably differentiated, but their clinical sensorineural/conductive), unilateral facial paralysis appearance and CT appearance are usually specific.129 CT (16%), and otitis media.132 Intermediate autosomal is the most appropriate imaging modality. CT with bone recessive and milder autosomal dominant forms of algorithm can be used to determine the exact location of osteopetrosis (Albers–Schönberg disease or marble bone the lesion for surgical planning. An osteoma appears as a disease) also exist and present later in life.133 solitary focal, pedunculated, bony outgrowth. Overlying soft tissues are normal in appearance. Osteomas are located within the membranous portion of the EAC just Benign Osteonecrosis of the External Auditory Canal lateral to the isthmus and attached to the tympanosqua- Benign necrosis of the EAC is a focal, well-circumscribed, mous or tympanomastoid suture lines. Osteomas are less necrotizing (“bare bone”) lesion that occurs with chronic common than exostoses. As with exostoses, these lesions OE and has symptoms of otorrhea, itching, and/or otal- are more common in surfers (20%) and individuals who gia. Various underlying infections may be present, and with curettage, bone spicules are removed. This process is believed to be secondary to an inflammatory reaction and can be self-limiting, respond to steroids, or require hyperbaric oxygen therapy. Imaging with bone scan demonstrates nonspecific uptake in the temporal bone in the abnormal area, but CT shows no definite bone erosion with soft tissue prominence.134

Other Bony Lesions Giant cell tumors of the mastoid are very rare, with only 13 reported in the literature.135,136 Their imaging findings are nonspecific and include a destructive bone lesion accompanied by soft tissue mass (Fig. 2.22). The diagnosis is based on biopsy. Paget disease and fibrous dysplasia (FD) are two benign entities that cause cranial nerve deficits and osseous impingement upon the EAC, middle and inner ear structures, and orbits.137 FD generally presents during the fourth decade of life and is 3 times more common in females than in males. Fig. 2.21 Axial computed tomography scan shows dense osteoma involving the lateral aspect of the right external auditory canal and The monostotic form of FD is 6 times more common than resulting in significant narrowing. the polyostotic form and in 10% of cases involves the ch02.qxd 1/7/09 12:22 PM Page 46

46 Imaging of the Temporal Bone

A B Fig. 2.22 (A) Axial computed tomography (CT) scan shows an aggres- and has eroded through the temporal bone superiorly. There is dural sive and destructive lesion centered in the right external auditory enhancement and thickening in the middle cranial fossa. This was a canal, but extending posteriorly into the mastoid bone and anteriorly giant cell tumor at biopsy. (Case courtesy of Dr. Farida Benoudiba, into the temporomandibular joint. (B) Coronal postcontrast magnetic Paris, France.) resonance T1-weighted image shows that the tumor (T) enhances

temporal bone. The polyostotic form involves the cranio- Paget disease occurs in the sixth to eighth decades of facial regions in 50 to 100% of patients, and 24% of them have life and is seen in 2 to 3% of the population over the age involvement of the temporal bone. The McCune–Albright of 60 years. Paget disease is due to increased bone syndrome is characterized by the polyostotic form of turnover. In the lytic stage, there is a preponderance of FD in association with endocrinopathy and cutaneous osteoclastic activity. The mixed stage demonstrates hyperpigmentation. FD is linked to mutations in chromo- osteoclastic and osteoblastic changes, whereas the some 20q 13.2. EAC occlusion occurs in 22 to 42% of sclerotic form is only osteoblastic. Patients with Paget patients, resulting in a conductive hearing loss. A compli- disease involving the temporal bone present with mixed cation of entrapment of squamous debris within the hearing loss. Conductive hearing loss is due to bone canal is the formation of CH.138 This can secondarily changes such as EAC narrowing and relaxation of the TM erode bone, resulting in further conductive hearing loss, from the bone growth. Fibrous fixation of the ossicles facial paralysis, and even sensorineural hearing loss from and oval window changes also contribute to the conductive labyrinthine fistula. The otic capsule is characteristically hearing loss. In contrast to FD, Paget disease can involve spared by the osseous FD process. Thus, sensorineural the otic capsule primarily resulting in sensorineural hearing loss usually occurs from CH, as above, or as a hearing loss.139 Paget disease causes bone expansion, result of FD involvement of the internal auditory canal and its appearance on CT varies from lytic to blastic. On with narrowing and neural compression. FD results in a MRI, Paget disease is of low signal on T1- and high signal ground glass appearance of the bone at CT and radio- on T2-weighted images, with heterogeneous enhance- graphic imaging. This appearance is secondary to the mixed ment reflecting its hypervascular nature. Occasionally, osseous and fibrous components seen with the disease, dural enhancement is seen. Paget disease is usually and the amount of density or cystic appearance on CT is polyostotic. Rarely, sarcomatous degeneration of Paget variable. On MRI, FD shows variable signal intensities on disease of the skull occurs, and MRI is the most accurate both T1- and T2-weighted images with significant con- method for diagnosis, determining precise localization trast enhancement. The appearance of FD on MRI may be of the tumor and intracranial extension.140 The differential bizarre and confusing. diagnosis for Paget disease includes otosclerosis (occurring ch02.qxd 1/7/09 12:22 PM Page 47

Chapter 2 The External Auditory Canal and Pinna 47

in younger patients), osteoradionecrosis, fibrous dyspla- T1: EAC only—with no bone erosion or soft tissue in- sia (also in younger patients), and syphilis (demon- volvement strates labyrinthine enhancement). Although both FD T2: EAC only—bone erosion (less than full thickness)/soft and Paget disease may have to be surgically treated, new tissue mass of 0.5 cm drug therapies may become the standard of care in the T3: Full thickness bone erosion/soft tissue 0.5 cm/ future.136 middle ear or mastoid involvement T4: Cochlea, petrous apex, middle ear wall, carotid canal, jugular foramen, dural, TMJ, or styloid involve- Carcinomas ment; facial paresis and/or soft tissue 0.5 cm thick Carcinoma of the temporal bone represents 0.2% of all (Fig. 2.23) head and neck carcinomas. The Pittsburgh Staging Criteria are used to stage squamous cell carcinoma of the tempo- All malignant tumors of the EAC and those of the ral bone.139 The modified criteria are as follows: pinna that secondarily involve the EAC, regardless of

A B

C D Fig. 2.23 (A) Axial computed tomography scan with soft tissue window magnetic resonance (MR) T1-weighted image shows the mass extends setting shows a nonspecific mass involving the right temporal bone. medially into the parapharyngeal space and surrounds the mandibular (B) Corresponding bone window settings show the aggressive nature of condyle. (D) Coronal postcontrast T1-weighted MR image shows that the the mass that erodes the mastoid bone and extends into the middle ear tumor has eroded the temporal bone and invaded the undersurface of the cavity (stage 4 squamous cell carcinoma). (C) Axial contrast-enhanced temporal lobe. (Case courtesy of Dr. Farida Benoudiba, Paris, France.) ch02.qxd 1/7/09 12:22 PM Page 48

48 Imaging of the Temporal Bone

A B Fig. 2.24 (A) Axial computed tomography scan showing a squamous magnetic resonance image shows that the tumor involves the basi- cell carcinoma arising in the right external auditory canal and destroying sphenoid portion of the occipital bone and right-sided longus colli mus- the mastoid and temporomandibular joint. There is a permeative pat- cle. The tumor involves the mastoid, extended into the sigmoid sinus tern to the bones in the base of the skull medial to the tumor, suggest- and there is thickened and enhancing dura in the lateral aspect of the ing invasion. (B) Axial postcontrast magnetic resonance T1-weighted right posterior fossa.

their histological type, need to be imaged with CT and/or Because the pinna and EAC both contain squamous MRI. Imaging is performed not only to assess the primary epithelial tissue, squamous cell carcinoma (SCC) can in- tumor site and extent but also the possibility of metas- volve one or both structures, or less commonly originate tases. The most common sites of lymphatic metastases in the middle ear and spread to the EAC.141 SCC is signifi- are the parotid and jugulodigastric nodes, as these areas cantly more common in the region of the auricle, and 60 represent the normal drainage for the pinna and EAC. to 90% of all auricular carcinomas are squamous in origin. Further drainage is to the internal jugular nodes. Therefore, Approximately 20% of auricular carcinomas are adenoma- imaging needs to include the temporal bone, adjacent tous/glandular carcinomas and less commonly basal cell parotid gland, and neck. CT depicts subtle bone erosion, carcinomas, melanoma, and metastases. The probability whereas MRI helps to demonstrate involvement of cra- of a carcinoma metastasizing to the auricle is extremely nial nerve VII or along the superficial temporal nerve low, but it may occur with breast cancer or less commonly (a branch of the second division of the trigeminal nerve), with renal, lung, or prostate cancers. If the carcinoma is involvement of the pterygopalatine fossa, dura, and/or diagnosed early, no bone erosion is evident by CT, but as brain (Fig. 2.24). Due to the differences in resistance in the disease progresses, irregular bone erosion and then the membranous (lateral) and bony (medial) portions of destruction of the walls of the EAC occur. The thickness of the EAC, tumors can spread into the soft tissues (more the skin in the EAC varies from 0.1 to 0.2 mm.142 EAC SCC common with lateral EAC origin) or medially into the is typically found in elderly individuals and originates in middle ear through the TM (more common in the bony the EAC and extends to the pinna. There is usually accom- EAC). Extension of tumor can also occur through the fis- panying bone erosion on CT, but without biopsy, the sures of Santorini into the parotid gland and TMJ, as well lesion may not be distinguishable from a benign process, as through the tympanomastoid suture line to the mas- such as MOE or even CH.143 Prognosis is related to tumor toid bone and via the infratemporal fossa to the face stage and presence or absence of clear surgical margins.14 4 (Fig. 2.25).140 If extension occurs through the tympa- Tumor staging of EAC carcinomas by the Pittsburgh nomastoid suture, tumor will quickly spread to the entire classification145 correlates with survival rates. Combination mastoid, and from there it can gain intracranial access surgery/radiation therapy is the accepted method for most into the middle or posterior fossas. Also, extension from EAC carcinomas, although some T1 tumors may be treated the mastoid into the middle ear can track down the with either radiation or surgery alone.146 Surgery for EAC eustachian tube to the fossa of Rosenmüller. cancer usually involves excision via a lateral temporal bone ch02.qxd 1/7/09 12:22 PM Page 49

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A B

Fig. 2.25 (A) Axial computed tomography (CT) image shows a large adenocarcinoma that presumably arose in the left external auditory canal to have significant erosion of the base of the skull in the region of the temporomandibular joint as well as erosion of the mastoid. (B) Axial CT at a slightly lower level shows that the middle ear cavity is invaded, and ossicles are partially eroded. C

resection. This operation involves en bloc removal of the 41% for T4 stage tumors. Tumors are generally deemed EAC with its medial margin being the middle ear space. unresectable if there is internal carotid artery, dural, or Greater degrees of temporal bone resection usually require cerebral infiltration.147 piecemeal removal of the otic capsule and petrous apex Basal cell carcinoma of the EAC is a rare disease that bone or ablation by way of the pneumatic drill. En bloc has a poor prognosis and a high recurrence rate, even with total temporal bone resection including the internal carotid clear surgical margins.14 8 SCC is more common than artery has shown no therapeutic benefit and has substan- basal cell carcinoma in the region of the pinna.14 9 There is tial morbidity and mortality. We have recently used intra- an increased incidence of basal call carcinoma with operative radiation therapy in cases of advanced carcinoma Gorlin-Goltz syndrome (nevoid basal cell carcinoma of the temporal bone. The utility of this therapy remains to syndrome).150 be determined. Surgery and radiation therapy result in a 100% 5-year Cerumen Gland Origin Tumors survival rate if the carcinoma is limited to the EAC. If there is invasion of the adjacent temporal bone, the sur- Adenoid cystic and mucoepidermoid carcinomas are thought vival rate is 63%, and with tumor infiltration beyond the to arise from the cerumen glands. These tumors behave temporal bone, the survival rate is 38%. The 5-year aggressively and have a propensity to spread perineurally; survival rate for all patients is 61%, whereas the survival therefore, MRI is the imaging method of choice. The risk of rate is 86% for T1 and T2 tumors, 50% for T3 tumors, and metastases is 30% with adenoid cystic carcinoma of the ch02.qxd 1/7/09 12:22 PM Page 50

50 Imaging of the Temporal Bone

EAC.143 Also, bone erosion is less common than with SCC. On Chondroblastoma in the EAC is a rare tumor that presents MRI, adenoid cystic carcinoma demonstrates decreased with otalgia, hearing loss, otorrhea, tinnitus, aural fullness, T1- and increased or decreased T2-weighted signal with vertigo, and significant bony destruction.159–161 Chondrob- significant contrast enhancement. Those tumors with high lastoma presents at a mean age of 33 years. This tumor is signal on T2 in the neck are more likely to be of the tubular twice as common in males. The chondroid nature of a or cribriform types and have a better prognosis.151 tumor may be suggested by the presence of faint calcifications (sometimes in a whorling pattern) on CT. Other rare tumors of the auricle, pinna, and EAC are fibrosarcoma, Malignant Melanoma Kaposi angiosarcoma, and osteosarcoma. Rhabdomyosar- coma tends to occur in children and is more common in the Typically, malignant melanoma arises from the pinna in region of the external auditory meatus. Other uncommon the regions of the helix and antihelix or at the meatus of tumors in this area are chondrosarcomas and malignant the EAC, with secondary extension into the EAC. Primary fibrous histocytoma.162 involvement of the EAC is very rare; unfortunately, it None of these tumors have specific has a significantly worse prognosis.152 Melanoma of the imaging findings, and bone destruction may present in all external ear accounts for 7 to 16% of all head and neck (Fig. 2.26). melanomas. Treatment of melanoma of the ear is done by complete excision, with at least a 1 cm margin of Trauma surrounding normal tissue. As the entire EAC is often encompassed in these margins, temporal bone excision is Fractures of the anterior wall of the EAC are not uncommon needed to accomplish this resection. The role of neck dis- and tend to occur as a consequence of chin–dashboard section and parotidectomy remains controversial in injuries.163 Herniation of the mandibular condyle into patients with head and neck melanoma. Occult regional the EAC can also occur.16 4 Classically, temporal bone frac- neck disease has been identified in 42 to 60% of patients. tures resulting from blunt trauma to the skull may occur However, the therapeutic efficacy of this intervention along lines parallel (longitudinal) or perpendicular remains unclear.153 Moreover, patients with known (transverse) to the length of the petrous pyramid. Trans- metastatic melanoma to the neck also have a very poor verse fractures occur as a result of a lateral impact to the prognosis despite therapeutic neck dissection. skull. The fracture lines extend along the EAC, through the tympanic membrane, through the roof of the middle ear/floor of the middle cranial fossa, near the perigeniculate Metastases Spread of tumor from the adjacent parotid gland, although uncommon, probably accounts for the majority of metastases to the pinna/EAC. Direct invasion through bone, as well as spread through the fissures of Santorini, and Huschke’s foramen can occur. Perineural invasion into the temporal bone may also occur along the facial nerve. Tumors such as mucoepidermoid and adenoid cystic carcinoma are well known for their propensity for this mode of spread. Evaluation of parotid tumors with secondary temporal bone involvement should include CT to demonstrate bone or skull base erosion. MRI is best for demonstration of soft tissue tumor margins, muscle infiltration, intracranial extension, and vascular encasement.154 Other tumors that metastasize to the EAC are breast, renal cell, and prostatic carcinomas.155 These frequently involve the bone marrow spaces of the temporal bone but may secondarily present in the EAC. Fig. 2.26 Axial CT scan demonstrates a markedly aggressive process centered in the region of the right EAC. There is destruction of the Lymphoma and Other Rare Tumors mastoid bone and temporomandibular joint and extension into the middle ear with ossicular erosion. This tumor was a malignant fibrous 156 Primary lymphoma of the ear is very rare. Lymphoma can histiocytoma, and its features are nonspecific and indistinguishable also occur via direct extension from the nasopharynx.157,158 from the more common carcinomas. ch02.qxd 1/7/09 12:22 PM Page 51

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region of the facial nerve, and along the internal carotid artery and eustachian tube. These fractures characteristically spare the otic capsule but may disrupt the ossicular chain. Thus, presenting symptoms include conductive hearing loss, bloody otorrhea that may include CSF, and possibly a facial paralysis that is usually partial in nature and resolves in time. Postauricular hematoma (i.e., Battle’s sign) may be seen in these cases. By contrast, transverse fractures occur as a result of high- velocity impact to the frontal or occipital regions. Frac- ture lines extend from the posterior cranial fossa along the internal auditory canal and through the otic capsule. By their nature, these fractures usually do not involve the EAC. Facial paralysis is usually complete, and sensorineural hearing loss and vertigo are the rule. Clear indications for temporal bone imaging in the setting of blunt trauma to the skull are persistent CSF leakage, complete facial paralysis, and profound sensorineural Fig. 2.27 Axial computed tomography scan shows a metallic portion hearing loss. CT imaging may be able to identify the seg- of an earring within the right external auditory canal. ment of facial nerve involvement if surgical intervention is being contemplated. Moreover, the site of persistent CSF leakage or the location of a traumatic encephalocele may be apparent. Trauma to the pinna itself can result in a fracture of Radiation may also induce injuries of the temporal the cartilage.165 Foreign bodies within the EAC are also bone. Osteoradionecrosis of the temporal bone if not very common in children.16 6 CT can identify metallic for- treated aggressively with mastoidectomy may result in 167,16 8 eign bodies, but plastic and other nonmetals may have a intracranial extension/CSF leak and meningitis. similar appearance (Fig. 2.27). Extruded pressure equalization tubes into the EAC are commonly seen on CT Amyloidosis of the temporal bones in children and have a typical appearance (Fig. 2.28). Cotton plugs, particularly if moist, Amyloidosis involving the meatus and pinna has been re- may look like soft tissue masses. Soft tissue windows ported. Generally, this rare presentation occurs in patients may cause wood fragments to appear like air, while the with systemic disease. Amyloidosis in the EAC may result internal structure of wood is well visualized with wide in skin thickening and occasionally may be masslike.169,170 bone windows. Its imaging features are nonspecific.

A B Fig. 2.28 (A) Axial and (B) coronal computed tomography studies show an extruded pressure equalization tube in the lateral portion of the right external auditory canal. ch02.qxd 1/7/09 12:22 PM Page 52

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A B

C D Fig. 2.29 (A,B) Axial computed tomography views show a soft tissue larger intracranial component and a smaller component in the EAC mass in the middle ear cavity extending into the right external auditory (black arrow). Note the mass (white arrow) extending through the canal (EAC). The posterior bone wall of the EAC is eroded. (C) Coronal tegmen tympani. Also seen is a “tail” of dural enhancement posterior to postcontrast T1-weighted magnetic resonance imaging (MRI) shows a the intracranial portion of the mass, suggesting meningeal involve- large extraaxial mass in the right middle cranial fossa eroding the ment. This lesion was a primitive neuroectodermal tumor arising from tegmen tympani and extending into the EAC (arrow). (D) Parasagittal the meninges. postcontrast T1-weighted MRI shows the mass to be bilobed with one

Other Pathology Occasionally, intracranial masses may erode the temporal Primary highly malignant cerebral masses such as primi- bone and extend in the middle ear and through it into the tive neuroectodermal tumors may also erode the tempo- EAC. This may occur with histologically benign masses, ral bone and rarely present as a mass protruding through such as meningioma, but may also occur with sarcomas. the EAC (Fig. 2.29).

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Pagetic sarcoma of Lymphoma in the ear. ORL J Otorhinolaryngol Relat Spec the calvarium: report of two cases. Acta Neurol Belg 2000;62:274–277 1998;98(4):352–355 157. Gordin A, Ben-Arieh Y, Goldenberg D, Netzer A, Golz A. 139. Moody SA, Hirsch BE, Myers EN. Squamous cell carci- Extension of nasopharyngeal lymphoma to the middle noma of the external auditory canal: an evaluation of a and external ear. Ann Otol Rhinol Laryngol 2003;112(7): staging system. Am J Otol 2000;21(4):582–588 644–646 140. Prasad M, Kraus DH. Acinic cell carcinoma of the parotid 158. Shuto J, Ueyama T, Suzuki M, Mogi G. Primary lym- gland presenting as an external auditory canal mass. phoma of bilateral external auditory canals. Am J Oto- Head Neck 2004;26(1):85–88 laryngol 2002;23(1):49–52 141. Barrs DM. Temporal bone carcinoma. Otolaryngol Clin 159. Pontius A, Reder P, Ducic Y. Temporal bone chondroblas- North Am 2001;34(6):1197–1218 tomas. Am J Otolaryngol 2003;24(6):370–373 ch02.qxd 1/7/09 12:22 PM Page 57

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160. Narita Y, Morimoto T, Nishikawa R, et al. Chondroblas- without skin laceration or hematoma. Plast Reconstr toma of the temporal bone–report of a case and a review Surg 2006;117(3):1052–1053 of the literature of 54 cases. No To Shinkei 1992;44(2): 166. DiMuzio J Jr, Deschler DG. Emergency department man- 143–148 (abstract only) agement of foreign bodies of the external ear canal in 161. Pontius A, Reder P, Ducic Y. Temporal bond chondro- children. Otol Neurotol 2002;23(4):473–475 blastomas. Otolaryngol Head Neck Surg 2003;24(6): 167. Leonetti JP, Origitano T, Anderson D, Melian E, Severtson 370–373 M. Intracranial complications of temporal bone osteora- 162. Morita M, Yoshihara T, Narita N, Ishii T, Aiba M. Malig- dionecrosis. Am J Otol 1997;18(2):223–229 nant fibrous histiocytoma of the auricle: an immunohis- 168. Sharma RR, Keogh AJ, Small M, New NE. Osteora- tochemical and electron microscopic study. Auris Nasus dionecrosis of the petrous bone and recurrent cere- Larynx 1992;19(4):209–214 (abstract only) brospinal fluid otorrhoea. Br J Neurosurg 1993;7(3): 163. Schulze W, Kleinsasser O. Laryngeal ruptures [author’s 303–306 transl]. HNO 1977;25(4):117–121 (abstract only) 169. El-Sayed I, Busaba NY, Faquin WC. Otologic manifesta- 164. Moriyama M, Kodama S, Suzuki M. Spontaneous tem- tions of amyloidosis. Otol Neurotol 2002;23(2): poromandibular joint herniation into the external audi- 158–159 tory canal: a case report and review of the literature. 170. Panarese A, Roland NJ, Green B. Primary amyloidosis of Laryngoscope 2005;115(12):2174–2177 the external auditory canal: case report. J Laryngol Otol 165. Payasli C, Babuccu O, Kargi E, Hosnuter M, Tekerekoglu B. 1994;108(1):49–50 Traumatic prominent ear secondary to cartilage fracture ch03.qxd 9/23/08 11:35 AM Page 58

The Middle Ear and Mastoid 3 Joel D. Swartz

Anatomy and Normal Variations and contains the inner ear structures (vestibule, semicircular canals, cochlea) and virtually all major neurovascular Temporal Bone compartments (internal auditory canal [IAC], carotid canal, jugular fossa). The apex of the pyramid rests on the clivus The temporal bone consists of five definable segments: at the petrooccipital fissure. The tympanic bone makes up squamous, petrous, tympanic, mastoid, and styloid the bulk of the external auditory canal (EAC) and middle (Fig. 3.1).1, 2 The bulk of the external surface of temporal ear space. It is separated anteriorly and internally from the bone is comprised of the squamous portion, which has hor- petrous bone by the petrotympanic (glaserian) fissure and izontal and vertical components separated by the zygoma. anteriorly and externally from the squamous portion The squamous portion articulates with the occipital, pari- by the tympanosquamous suture. The mastoid portion etal, and sphenoid bones and forms part of the lateral wall contains the mastoid air cell system, articulates laterally of the middle cranial fossa and the medial wall of the tem- with the parietal and occipital bones, and communicates poral fossa. The zygomatic process forms the roof of the with the nasopharynx via the eustachian tube. There is temporomandibular fossa (TMJ). The external surface contiguity of the mastoid air cells and those of the of the temporal squama contains a sulcus for the superfi- petrous pyramid (petrous apex). The mastoid process cial temporal branch of the external carotid artery. The forms a bony protuberance in the retroauricular region and internal surface contains a sulcus for the superior petrosal is not ossified at birth. There is also a rudimentary styloid sinus. The petrosquamous suture (a portion of which is portion of the temporal bone, which originates in cartilage made up of Koerner’s septum) separates the squamous (second branchial arch) and makes up the posterior tympa- from the petrous temporal bone. The petrous portion is a num and styloid process. The temporal bone forms quadrangular pyramid that forms the bulk of the internal a portion of the floor of the middle and posterior cranial surface of the temporal bone, extends to the petrous apex, fossae (Table 3.1 and Table 3.2).

Table 3.1 Appropriate Projections to View Ossicles Best CT Projection Either Structure Axial Coronal (Both) Stapes footplate X Stapes superstructure X Incus lenticular process X Incus long process X Incus body X Malleus head X Malleus manubrium X Malleus neck X Malleus lateral (short) process X Fig. 3.1 Temporal bone–external surface (yellow, squamous; or- Malleoincudal articulation X ange, mastoid; blue, tympanic; green, styloid). The petrous portion is predominantly deep to the illustration; a segment is in orange Incudostapedial articulation X anterior to the tympanic portion. (Adapted from Platzer W. Pernkopf Stapediovestibular region X Anatomy, 3rd ed. Munich: Urban & Schwarzenberg; 1989.) (See Color Plate Fig. 3.1.) Abbreviations: CT, computed tomography.

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Table 3.2 Appropriate Projections for Other Middle Ear Structures Best CT Projection Either Structure Axial Coronal (Both) Prussak’s space X Attic X Scutum X Antrum and central mastoid tract X Aditus X Tegmen tympani X

Tensor tympani muscle X Fig. 3.2 Tympanic membrane (solid arrow, pars flaccida; outlined arrow, Sigmoid sinus groove X pars tensa; long thin arrow, umbo [malleus handle]). (Adapted from Platzer W. Pernkopf Anatomy, 3rd ed. Munich: Urban & Schwarzenberg; Tensor tympani tendon X 1989.) (See Color Plate Fig. 3.2.) Fossa incudis X plicae) separate the TM into a smaller, lax, but thicker pars Round window X flaccida above and a larger, taut, more fibrous pars tensa Facial recess X below.8–10 The pars tensa and pars flaccida both contain Pyramidal eminence X three layers, an external epidermal (squamous) layer continuous with the skin lining the EAC (ectoderm), an inner Sinus tympani X layer (mucosal) continuous with the middle ear mucosa Lateral mallear ligament X (endoderm), and an intermediate fibrous layer (meso- Superior mallear ligament X derm).11,12 The central fibrous (mesodermal) layer of the Anterior mallear ligament X pars flaccida is less well developed but contains more elastic fibers. A healing perforation of the pars tensa Pattern of pneumatization X may fail to reform this fibrous layer and is more likely to Tympanic membrane X retract. The normal pars tensa can be seen on axial and Anterior epitympanic recess (air cell) X coronal CT using appropriate windows and levels, and its Ponticulus X location can be further inferred from the position of the manubrium of the malleus on coronal images (Fig. 3.3 Subiculum X and Fig. 3.4). A thickened or significantly retracted pars Abbreviations: CT, computed tomography. tensa is easily appreciated (see below).4 Simple perfora- Source: From Swartz JD. High resolution computed tomography of tions themselves are difficult to identify; however, this is the middle ear and mastoid. Part I: Normal anatomy including normal variations. Radiology 1983;148:449–454. Reprinted with permissison. an inconsequential point because they are so easily visualized otoscopically. The pars flaccida is consistently seen on coronal sections in the normal patient, extending from the lateral process of the malleus to the scutum. Simple Tympanic Membrane retractions of this segment are also possible to discern with CT although they are also much more easily evalu- The tympanic membrane (TM) is 1 mm thick and sepa- ated otoscopically.13 Innervation of the TM is via contribu- rates the EAC from the middle ear (mesotympanum) tions from the mandibular nerve (V3), Arnold’s nerve (Fig. 3.2). The sites of attachment (tympanic annuli) are (vagus), and Jacobson’s nerve (glossopharyngeal). This well seen on both axial and coronal computed tomogra- complex arrangement partially explains the clinical diffi- phy (CT) projections (see Chapter 2).3,4 The elliptical or culties in differentiating referred otalgia from primary cone shape corresponds to the contour of this portion of causes of ear pain.14,15 the canal. In adults, it is angulated 140 degrees with respect to the superior border of the EAC. Standard measurements are 1 cm vertically and 9 mm horizontally.5–7 Ossicles, Suspensory Ligaments, The handle (manubrium) and lateral (short) process of and Tendons the malleus are embedded in the TM, forming the umbo and malleal prominence, respectively. Folds extending The normal ossicular chain consists of the malleus, incus, from the malleal prominence to the anterior and poste- and stapes (Fig. 3.5). The stapes weighs only 2.5 g and rior tympanic spines (anterior and posterior malleal as such is only about one tenth the weight of either of the ch03.qxd 9/23/08 11:35 AM Page 60

60 Imaging of the Temporal Bone

A B Fig. 3.3 (A) Coronal CT anatomy (sml, superior malleal ligament; mh, external auditory canal]; the lml and the p.flac. subtend Prussak’s space). malleus head; mn, malleus neck; man malleus, manubrium; s, scutum; (B) Sagittal CT image; long white arrow, facial nerve canal (labyrinthine p.flac, pars flaccida of tympanic membrane; lml, lateral malleal ligament; segment); long black arrow, cochleariform process (tensor tympani muscle); tt, tensor tympani muscle and tendon; tac, tegmental air cells [above triple black arrows, inferior tympanic canaliculus (nerve of Jacobson).

other two ossicles.1 A review of paleontology reveals that the largest ossicle, is made up of the body; however, the precursors of the ossicular chain were part of the jaw short, long, and lenticular processes are also described and that primitive vertebrates such as the bullfrog have (Figs. 3.6, 3.7, 3.9, 3.10). The short process lies posteriorly only one middle ear bone.16 The development of the ossic- within the fossa incudus and acts as a fulcrum on which ular chain was presumably a survival mechanism, as it the rest of the incus rotates. The fossa incudus is located amplifies sound pressure on the TM by 30%. A primitive immediately below the aditus and can only be appreci- stapes (solid, no crura) persists in various marsupials. The ated with axial and sagittal CT sections.4,10 Surgeons development of crura improved hearing, as the resultant are aware of the close relationship between the short ossicle is much lighter. The tympano-ossicular system is process and the second genu of the facial nerve, generally responsible for transmission of sound from the EAC to the in the 3 mm range.20 The very fine long process and cochlea in the normally functioning ear. This is referred to lenticular process represent the most vulnerable seg- as ossicular coupling. Direct stimulation of the oval and ments of the ossicular chain and are commonly eroded in round windows in those with a nonfunctioning ossicular the context of inflammatory disease.7, 21, 2 2 They meet at a chain is referred to as acoustic coupling.17 variable angle, usually almost 90 degrees (Fig. 3.11 and The malleus is described in terms of the head, neck, Fig. 3.12). The long process is visualized to best advantage lateral (short) process, anterior process, and handle on these coronal CT sections. The cup-shaped lenticular (manubrium) (Fig. 3.6, Fig. 3.7, Fig. 3.8). The lateral process articulates directly with the ball-shaped capitu- process and manubrium are embedded within the TM and lum (head) of the stapes via a cartilaginous disk and is are best seen utilizing coronal CT images.4,18 There is a also a synovial, diarthrodial articulation (Fig. 3.13, Fig. 3.14, diarthrodial articulation between the malleus and incus Fig. 3.15, Fig. 3.16, and Fig. 3.17).11,23–25 The stapes super- in the attic, the malleoincudal articulation, easily and structure is a term that is used to describe the portion of consistently seen on axial and sagittal CT images (Fig. 3.9 the stapes that is derived from the second branchial arch. and Fig. 3.10).6,19 There are medial and lateral incudomal- This includes the capitulum (head), anterior crus, poste- lear ligaments that are difficult to resolve even with the rior crus, and the tympanic portion of the footplate. The highest resolution CT equipment.19 The bulk of the incus, vestibular portion of the footplate and contiguous annular ch03.qxd 9/23/08 11:35 AM Page 61

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Fig. 3.4 (A) Short black arrow, facial nerve (labyrinthine segment); dotted white arrow, facial nerve (tympanic segment); cross-hatched white arrow, tensor tympani muscle; thin white arrow, tensor tympani tendon; thick white arrowhead, malleus neck. (B) Artist’s rendering of Prussak’s space (arrowheads). This is the space subtended by the lateral mallear ligament, the malleus neck, and the pars flaccida of the tympanic membrane. Insert: Otoscopic view of normal tympanic membrane. (C) Drawing, coronal plane (lml, lateral mallear ligament; sml, superior mallear ligament; mall, head of malleus). White arrow, pars flaccida of tympanic membrane (pf); double white arrows (pars tensa of tympanic membrane).

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62 Imaging of the Temporal Bone

Fig. 3.6 Axial anatomy (isp, incus short process; ib, incus body; mh, malleus head; cog, cog; aer, anterior epitympanic recess [single cell]; f. Fig. 3.5 Ossicular chain (SPM, malleus-short process; MH, malleus han- tymp, facial nerve tympanic segment; mia, malleoincudal articulation). dle; MIA, malleoincudal articulation; IB, incus body; SPI, incus, short process; LONG, incus, long process; LEN, incus, lenticular process; ISJ, incudostapedial joint; SH, stapes head; ANT, stapes, anterior crus; POST, stapes, posterior crus; SF, stapes footplate [note tympanic and vestibular segments]). (See Color Plate Fig. 3.5.)

A B Fig. 3.7 (A) Axial anatomy (aml, anterior malleal ligament; mia, White arrow, malleus head; outlined white arrow, incus body; short, thick malleoincudal articulation; isp, incus, short process [in fossa incudus]; fi, white arrow, incus short process; thin white arrow, tympanic membrane fossa incudus). Level-trapped fluid in petrous apex cell. (B) Sagittal view. (pars flaccida). ch03.qxd 9/23/08 11:35 AM Page 63

Chapter 3 The Middle Ear and Mastoid 63

Fig. 3.7 (Continued) (C) Drawing, sagittal plane; tympanic cavity (AML, anterior malleal ligament; CTN, chorda tympani nerve; M.HE, malleus head; MH, malleus handle; MIA, malleoincudal articulation; IB, incus body; SPI, Incus, short process; PIL, posterior incudal ligament; LPI, Incus, long process; LEN, incus, lenticular process [stapes is removed]; PT, pars tensa, tympanic membrane). (See Color Plate Fig. 3.7C.)

ligament are derived from the otic capsule (neuroecto- in the annular ligament that supports the syndesmotic derm). The space between the crura is referred to as the (fibrous) stapediovestibular articulation (Fig. 3.13D and obturator foramen.7 The stapedial artery resides in this Fig. 3.16B). location during fetal life. Persistence of this vessel is rare Contrary to popular belief, the vast bulk of the ossicu- (see Chapter 4). The footplate of the stapes is embedded lar chain is best appreciated on evaluation of axial CT sections. The malleoincudal and incudostapedial articulations as well as the stapes superstructure are all appreciated to best advantage in this projection.4 The oval window (stapes footplate/annular ligament) is of uniform thickness and has an anteroposterior orientation. In our opinion this structure is also best seen in this projection (Fig. 3.15).26,27 Coronal CT images allow for better appreciation of structures oriented vertically, such as the malleus and incus long process. The right-angle junction of the incus long and lenticular processes is also well appreciated in this projection. Axial, coronal, and sagittal CT images are therefore highly complementary for ossicular evaluation (Fig. 3.11 and Fig. 3.12).28,29 Sagittal CT imaging is more readily available with current techniques utilizing volumetric acquisitions (see Chapter 1). In this projection, the malleoincudal articulation is well seen as the classic “molar tooth” configuration (Fig. 3.7C and Fig. 3.9B). This appearance was originally described with complex motion tomography when direct sagittal (lateral) imaging was routine. Other structures visualized Fig. 3.8 Coronal computed tomography image, well positioned. Both in this projection include the recess for the stapedius mus- ears are appreciated in a symmetric fashion due to superb patient cle, the posterior semicircular canal, and the anterior tym- positioning (mild tilt; teg, tegmen tympani [roof of middle ear/attic]; mall, malleus head; tac, tegmental air cells [variable in number]; sc, panic spine (Fig. 3.9B, Fig. 3.11B,C, and Fig. 3.17B–D). The scutum; ttt, tensor tympani tendon [5th nerve, 1st branchial arch deri- latter forms the undersurface of the glaserian (anterior vation]; fnc, facial nerve canal; coch, apical/middle cochlear turns). tympanic) fissure and is a common fracture site. ch03.qxd 9/23/08 11:35 AM Page 64

64 Imaging of the Temporal Bone

A B Fig. 3.9 (A) Axial anatomy (law, lateral attic wall; ma, mastoid antrum; malleus (note the classic “molar tooth” appearance); thick white arrow, ssp, sigmoid sinus plate). (B) Sagittal computed tomography image. anterior tympanic spine; black arrow, glaserian fissure (passage of Thin white arrow, long process of incus; outlined white arrow, handle of chorda tympani nerve and anterior tympanic artery).

The malleus is supported by superior, anterior, and lateral mallear ligaments. These structures are well seen on a careful study of the CT scan.4 The superior and lateral ligaments are seen best on coronal sections and the anterior ligament best on axial sections (Fig. 3.4, Fig. 3.7, Fig. 3.13). A posterior incudal ligament exists; however, it is thin and not visualized on CT (Fig. 3.7C). The incus is therefore quite poorly supported, particularly distally (see Chapter 6).11,30–32 Two muscles, the tensor tympani, which is a first (Meckel) branchial arch derivative innervated by the fifth cranial nerve (CN V), and the stapedius, which is a second (Reichert) branchial arch derivative innervated by the CN VII, also participate in ossicular support. The tensor tympani muscle lies within a narrow bony channel (semicanal) parallel and medial to the eustachian tube.6,7,33,34 The tendon of this muscle continues to course posterolaterally until it reaches a spoon-shaped depression adjacent to the cochlea referred to as the cochleariform process. The latter is an important surgical landmark indicating proximity to the facial nerve canal. Fig. 3.10 Axial anatomy (aer, anterior epitympanic recess [multiple cells]; cog, cog; mh, malleus head; ib, incus body; adit, aditus ad From here, the tendon courses laterally to reach the neck of antrum; ma, mastoid antrum; ssp, sigmoid sinus plate; f.tymp, facial the malleus. The tendon is easily visualized on both coronal nerve, tympanic segment). and axial CT sections due to its mediolateral orientation ch03.qxd 9/23/08 11:35 AM Page 65

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A Fig. 3.11 (A) Coronal anatomy (ks, Koerner septum; ilp, incus, lenticular process; ilop, incus long process; st, stapes; s, scutum; f.tymp, facial nerve canal, tympanic segment; ita, inferior tympanic annulus [attachment of tympanic membrane]). (B) Sagittal image, more lateral. Black arrow, mandibular condyle; outlined white arrow, scutum; white arrow, attic (lateral to ossicular mass); double white arrows, mastoid antrum. (C) Sagittal image, more medial. Triple black arrows, canaliculus chordae tympani; white arrow, incus body.

(Fig. 3.8, Fig. 3.13, and Fig. 3.16). The stapedius muscle travels in a bony sulcus just medial to the second genu of the facial canal. It emerges from the pyramidal eminence and courses anteriorly to attach to the stapes anywhere from the incudostapedial region to the junction of the posterior crus with the footplate. It can only be appreciated on axial CT sections (Fig. 3.16). The tensor tendon tightens the TM, and the stapedius tendon stretches the annular ligament. As such, these muscles both play a role in damping the response of the ossicular chain, thus protecting the cochlea from intense acoustic stimulation.24,35

Recesses and Ridges The tympanic cavity contains numerous recesses and ridges.36 Most notable among these recesses is the supe- Fig. 3.12 Coronal anatomy (epi, epitympanum; lsc, lateral semicircular canal; prom, promontory [basilar turn of cochlea]; ilop, incus, long rior recess of the TM, better known as Prussak’s space, process; ilp, incus, lenticular process; ib, incus body; f.tymp, facial which is bordered laterally by pars flaccida, inferiorly by nerve canal, tympanic segment). the lateral (short) process of the malleus, superiorly by the ch03.qxd 9/23/08 11:35 AM Page 66

66 Imaging of the Temporal Bone

A B

C–E

Fig. 3.13 (A) Axial anatomy, right ear (mn, malleus neck; t, tensor tympani tendon; ilp, incus, long process; isj, incudostapedial joint; ss, stapes superstructure). (B) Axial anatomy, stapes superstructure. (C) Line drawing. (D) Anatomy of ossicular chain. Coronal drawing (slightly oblique). (E) Axial drawing (isj, incudostapedial joint; ttt, tensor tympani tendon; st, stapedius tendon; lpi, long process of incus; len, lenticular process of incus). (F) Artist’s rendering of normal ossicular chain and tendinous attachments. Derivations are indicated. Cross-hatched; first branchial arch; stippled: second branchial arch; filled: otic capsule (lamina stapedialis). (From Swartz JD, Glazer AU, Faerber EN, et al. Congenital middle ear deafness: CT study. Radiology F 1986;159:187–190. Reprinted with permission.) ch03.qxd 9/23/08 11:35 AM Page 67

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Fig. 3.14 Axial anatomy (p, pyramidal eminence; f, facial recess; s, sinus tympani; ps, posterior semicircular canal; ss, stapes superstructure).

Fig. 3.15 Axial anatomy (mn, malleus neck; asc, anterior stapes crus; psc, posterior stapes crus; ilp, incus, lenticular process; isj, incudostapedial joint; ow, oval window [stapes footplate/annular ligament]).

A B Fig. 3.16 (A) Axial anatomy (ttm, tensor tympani muscle; ttt, tensor head; ASC, stapes, anterior crus; PSC, stapes, posterior crus; SF, stapes tympani tendon; mn, malleus neck; ow, oval window [small unlabeled footplate [note tympanic and vestibular segments]; ST, stapedius ten- arrows, anterior and posterior margins]; asc, anterior stapes crus; psc, don; FN, facial nerve, second genu in pyramidal eminence; CN, cochlear posterior stapes crus; isj, incudostapedial joint). (B) Tympanic cavity, nerve; IVN, inferior vestibular nerve). (See Color Plate Fig. 3.16B.) corresponding axial illustration (CTN, chorda tympani nerve; SH, stapes ch03.qxd 9/23/08 11:35 AM Page 68

Fig. 3.17 (A) Posterior tympanum. Outlined black arrow, facial recess; outlined white arrow, pyramidal eminence; black arrow, sinus tympani; white arrow, incudostapedial articulation; dotted white arrow, chordal eminence. (B) Sagittal computed tomography (CT) image, more lateral. Black arrow, lateral semicircular canal; outlined black arrow, facial nerve canal, second genu; thin white arrow, sinus tympani; double black arrows, facial nerve canal (mastoid segment); outlined white arrow, stylomastoid foramen. (C) Sagittal CT image, more medial. Black arrow, pyramidal eminence; double black arrowheads, stapedius muscle canal; white arrow, incus lenticular process; white arrowhead, malleus neck. (D) Sagittal CT image, most medial. Outlined white arrow, subiculum; outlined black arrow, sinus tympani; dotted black arrow, lateral semicircular canal; long white arrow, facial nerve (tympanic segment); short white arrow, stapedial head; double white arrows, anterior tympanic spine; short thick black arrow, glaserian fissure (exit of chorda tympani nerve). (E) Posterior tympanum, coronal CT image. Outlined white arrow, facial recess; thick black arrow, pyramidal eminence; thick white arrow, sinus tympani.

B D

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lateral mallear ligament, and medially by the neck of the malleus (Fig. 3.4, Fig. 3.8). 4,9,36,37 The lateral mallear ligament courses from the scutum (junction of the lateral attic wall and EAC) to the neck of the malleus. Prussak’s space opens posteriorly into the epitympanum and represents the most common site of origin for acquired attic cholesteatoma (CH). The anterior epitympanic recess (AER), also known as the supratubal recess (STR), is located superior to the bony eustachian tube and anterior to the attic and consists of a variably sized single air cell (61%) or multiple small cells. There is symmetry in 78% of patients.38 This region is visualized on axial section anteromedial to the head of the malleus. It is bounded posteriorly by a thin transverse bony septum (“cog”) and anteriorly by the anterior petrosal tegmen (Fig. 3.6, Fig. 3.10, and Fig. 3.18). The middle cranial fossa forms a portion of the superior and anterior boundary. The chorda tympani nerve and the Fig. 3.19 Axial anatomy (aml, anterior malleal ligament; ks, Koerner tympanic bone form the lateral boundary.39 The “cog” may septum; st, sinus tympani; f.tymp, facial nerve canal, tympanic segment). be bony or fibrous and extends from the cochleariform process to the tegmen.40 The shape of this recess is determined by the embryologic development of the saccus an- complete by the end of gestation. The proximal tympanic ticus and anterior saccule of the saccus medius41; however, segment of the facial nerve canal lies immediately adja- development of the AER/STR is independent of the middle cent to the recess on its medial side (Fig. 3.10 and Fig. 3.18). ear/mastoid air cells system, instead relating directly to The mucosal fold investing the tensor tympani is also in eustachian tube formation.42 Growth of the AER/STR may close apposition.4,43,44 When this fold is embryologically continue into early childhood in contradistinction to the absent, cholesteatomatous masses have direct access to remainder of the attic, which is generally believed to be this segment of the facial nerve.45 Koerner’s septum (see below) is the posterior continuation of the “cog” and therefore has similar embryologic significance (Fig. 3.19).46 A complex set of recesses and ridges lies posterior to the bony tympanic annulus along the posterior and medial borders of the tympanic cavity. This region is referred to in the literature as the posterior tympanum or retrotympanum (Fig. 3.14, Fig. 3.17, Fig. 3.20, Fig. 3.21, Fig. 3.22, Fig. 3.23, and Fig. 3.24).36,47 The pyramidal eminence (PE), from which the stapedius tendon emerges, represents the most prominent ridge in the posterior wall. Immediately medial to the PE lies the sinus tympani, a recess of variable depth that is bordered medially by the cortical bone overlying the posterior semicircular canal.12,36,47 The ponticulus (an extension of the oval window niche) is its superior border; the subiculum forms the inferior border (Fig. 3.20A). The subiculum separates the sinus tympani from the round window niche (Fig. 3.23).4,48 Directly lateral to the PE lies the facial recess, which is often much shallower than its more medial counterpart. Lateral to the facial recess is the chordal eminence, which forms the medial border of the canaliculus chordae tympani through which the chorda tympani branch of the facial nerve enters the middle ear cavity. A chordal ridge is described that links the pyramidal Fig. 3.18 Anterior epitympanic recess. Outlined white arrow, anterior eminence to the chordal eminence. The facial recess is epitympanic recess (supratubal recess); thin white arrow, cog; outlined limited further laterally by the bony tympanic annulus black arrow, facial nerve/canal (tympanic segment). (origin of the TM). ch03.qxd 9/23/08 11:35 AM Page 70

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A Fig. 3.20 (A) Axial anatomy (p, ponticulus; rw, round window niche). (B) Artist’s rendering of posterior tympanum [C.T.N., chorda tympani nerve (arrow); F.R., facial recess (arrow); S.T., sinus tympani; SU, subiculum; R.W.N., round window niche (arrowhead); PON, ponticulus; P.E., pyramidal eminence (open arrowhead); stapedius tendon (arrow); SS, stapes superstructure]. B

The medial wall of the posterior tympanum is described tympani.12 Beneath the subiculum is the round window as having two ridges and three depressions (Fig. 3.14, niche, and superior to the ponticulus is the oval window. Fig. 3.20, Fig. 3.23, and Fig. 3.24). The ridges are the more These ridges are variable in size. They are identified with inferior subiculum (posterior prolongation of the cepha- difficulty on coronal section; however, their importance lad border of the round window) and the more superior is limited to both the surgeon and the radiologist. Two ponticulus, which extends from the pyramidal eminence to the promontory. Between these ridges lies the sinus

Fig. 3.21 Axial anatomy (pt, pars tensa, tympanic membrane; s, subicu- Fig. 3.22 Axial anatomy (ttm, tensor tympani muscle; cc, carotid canal, lum; f.mast, facial nerve canal, mastoid segment; hypo, hypotympa- horizontal portion; f.mast, facial nerve canal, mastoid segment; jf, jugular num; fo, foramen ovale; fs, foramen spinosum; cc, carotid canal). foramen; eac, external auditory canal; gs, glossopharyngeal sulcus). ch03.qxd 9/23/08 11:35 AM Page 71

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additional eminences, the styloid and the chordal, and tympanic (Jacobson’s) canaliculus with a similarly named two other depressions, the posterior and lateral tympanic branch of CN IX. It anastomoses with the tiny carotico- sinuses, are also probably identifiable on CT; however, tympanic branch (internal carotid artery [ICA]) and their importance is limited as well. The styloid and chordal provides the major supply of the hypotympanum. The eminences are inferior and posterior to the pyramidal anterior tympanic artery most often arises from the inter- eminence, respectively. The posterior tympanum is derived nal maxillary artery and subsequently courses posteriorly virtually in its entirety from the second branchial arch.7,12 through the petrotympanic (glaserian) fissure with the These recesses may be hidden from view during surgery chorda tympani nerve into the middle ear.11 This vessel and are often the site of residual collections of granula- provides the primary blood supply of the malleus and tion tissue or CH. They are consistently well seen on axial incus and the superior and lateral walls of the attic. CT section.4,49,50 CT visualization of the sinus tympani is The vascular supply of the distal ossicular chain and especially important preoperatively, as extensive involve- facial nerve canal is derived from the stylomastoid, ment in this location may require a retrofacial (nerve) superior tympanic, and superficial petrosal arteries. The surgical approach (Fig. 3.14 and Fig. 3.24). A highly posi- stylomastoid artery arises either from the posterior tioned jugular bulb and a contracted space between the auricular or occipital branches of the external carotid facial nerve and the posterior semicircular canal preclude artery and enters the stylomastoid foramen. It contains this type of exploration.47,48 a posterior tympanic branch, which courses with the These structures form the posterior portion of the tym- chorda tympani nerve via the canaliculus chorda panic cavity proper. The lateral border is the TM, and the tympani into the middle ear.51 The superior tympanic medial border is the labyrinth, particularly the promon- and superficial petrosal arteries are the first two tory. The roof of the epitympanum, which is referred to as endocranial branches of the middle meningeal artery the tegmen tympani, separates the epitympanum from the just after its entrance into the cranial cavity via the middle cranial fossa. The inferior wall of the tympanic foramen spinosum. These two branches course with the cavity (hypotympanum) is separated by plates of bone greater and lesser superficial petrosal nerves, respec- anteriorly from the carotid canal and posteriorly from the tively, into the middle ear. jugular bulb (Fig. 3.22). The nerve supply of the middle ear mucosa is primarily via the tympanic plexus of CN IX.

Blood Vessels and Nerves Pneumatization Numerous arteries contribute to the vascular supply of the middle ear (Table 3.3 and Fig. 3.25).11, 51 The inferior The degree of pneumatization of the temporal bone tympanic artery is most often a branch of the ascending is variable and dependent on several factors, including pharyngeal artery. It enters the middle ear via the inferior nutrition, heredity, and environment.7,24,35 The hereditary

Table 3.3 Vascular Supply of the Middle Ear* Artery (Origin) Entrance Accompanying Nerve Supply Inferior tympanic Inferior tympanic (Jacobson’s) Nerve of Jacobson Mucosa of middle ear (ascending pharyngeal) canaliculus (ninth cranial nerve) Caroticotympanic Carotid canal (adjacent foramen) Anterior hypotympanum (internal carotid) Anterior tympanic Glaserian (petrotympanic) fissure Chorda tympani Malleus, incus, superior (internal maxillary) lateral attic Stylomastoid Stylomastoid foramen Facial nerve Facial nerve canal (posterior auricular) (to midtympanic segment) Superior tympanic Facial hiatus Greater superficial petrosal nerve Facial nerve canal (first genu) (middle meningeal) Superior medial attic Superficial petrosal Accessory facial hiatus Lesser superficial petrosal nerve Facial nerve (middle meningeal) Posterior tympanic Canaliculus Chordae tympani Posterior tympanum (stylomastoid) Chorda tympani (posterior) *See Fig. 3.25. ch03.qxd 9/23/08 11:36 AM Page 72

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Fig. 3.23 (A) Coronal anatomy (lsc, lateral semicircular canal; ow, oval window [posteriormost aspect]; v, vestibule; rw, round window; hypo, hypotympanum; sub, subiculum). (B) Coronal computed tomography image. Outlined black arrow, oval window (posterior portion); thin white arrow, ponticulus; outlined white arrow, round window (cephalad border); thin black arrow, facial nerve canal, second genu. (C) Vestibule (V). Black arrow, round window (leading to scala tympani of basilar cochlear turn); white arrow, round window niche; large white arrow, C hypotympanum.

Fig. 3.24 Coronal anatomy (st, sinus tympani; f.mast, facial nerve, mastoid segment; smf, stylomastoid foramen). ch03.qxd 9/23/08 11:36 AM Page 73

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Fig. 3.25 (A) Vascular supply of the middle ear, sagittal (oblique) drawing. (B,C) Insets (ec, external carotid; ic, internal carotid; pa, posterior auricular; ap, ascending pharyngeal; o, occipital; im, internal maxillary; da, deep auricular; at, anterior tympanic; s, stylomastoid; it, inferior tympanic; st, superior tympanic; ct, caroticotympanic; pt, posterior tympanic; p, petrosal; et, eustachian tube). (Adapted from Hesselink JR, David KR, Taveras JM. Selective arteriography of glomus tympanicum and jugulare tumors: techniques, normal and pathologic arterial anatomy. AJNR Am J Neuroradiol 1981; 2:289–297. Reprinted with permission.)

B C

theory suggests that mastoid size is independent of the Individuals with unilateral depressed pneumatization status of the mesotympanum. The environmental theory will often have a history of chronic otitis media (COM). suggests that the degree of childhood middle ear disease Interestingly, patients with cystic fibrosis typically have determines the size of the mastoid air cell system.52 excellent pneumatization and a low incidence of infection.53 There is no uniform agreement on the embryologic onset, Pneumatization is described as pneumatic when complete, which is typically a symmetric process unless compli- diploic when partial, and sclerotic when essentially absent.54 cated by inflammatory disease. The frequency of bacter- In the latter two categories aeration is limited to an antrum ial infection (eustachian tube function) therefore plays a and central mastoid tract of variable size. The nonpneuma- critical role. The eustachian tube is responsible for mid- tized portion consists primarily of bone marrow (diploic) dle ear ventilation, protects it from pathogenic organ- or dense bone (sclerotic).24 Five pneumatized regions are isms, equilibrates pressure across the TM, and allows described: the middle ear, mastoid, perilabyrinthine, petrous drainage of secretions. It is essential for maintenance of apex, and accessory regions.55 There is extensive intercom- normal ventilation.1 munication (Table 3.4). ch03.qxd 9/23/08 11:36 AM Page 74

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Table 3.4 Pneumatization The middle ear is divided into three compartments Types in the coronal plane (epitympanum, mesotympanum, hypotympanum) and in the axial plane (protympanum, Pneumatic mesotympanum, posterior tympanum) (Fig. 3.26). The Diploic mesotympanum is located immediately opposite the Sclerotic pars tensa and may be separated from the more superi- Regions orly placed epitympanum and more inferiorly placed hypotympanum by tangential lines drawn through the Middle ear superior and inferior margins of the EAC, respectively. Epitympanum (attic) Similarly, the mesotympanum may also be separated Mesotympanum from the more anteriorly located protympanum and Hypotympanum more posteriorly located posterior tympanum by tangential lines drawn through the anterior and posterior Posterior tympanum aspects of the EAC, respectively (Fig. 3.26). Thus, there Protympanum are five definable areas of pneumatization within the Mastoid middle ear.7 Antrum The epitympanum (attic) contains the malleus head and incus body and lies within the notch of Rivinus, a fan- Central mastoid tract shaped recess in the tympanic bone. The tympanosqua- Peripheral mous suture line forms the anterior boundary and the Perilabyrinthine tympanomastoid suture, its posterior boundary. Supralabyrinthine Two communications have been extensively described between the mesotympanum and epitympanum. These Infralabyrinthine are referred to as the anterior and posterior tympanic Petrous Apex isthmus.7,44,49,56,57 These isthmi are vertical in orientation Petrosal and pierce the tympanic diaphragm, a series of mucosal Apical folds and ligaments that separate the mesotympanum from the epitympanum. The anterior isthmus lies between Accessory the tensor tympani tendon and the incudostapedial region, Zygomatic and the posterior tympanic isthmus between the short Squamous process of the incus and the stapedius tendon. They may 4,5,49 Occipital be appreciated in cross section on axial CT. They are Source: From Schuknecht HF. Pathology of the ear. 2nd ed. Philadelphia: Lea & Febiger; 1993. Reprinted with permission.

A B Fig. 3.26 Artist’s rendering of compartments of middle ear. (A) Coronal arteriography of glomus tympanicum and jugulare tumors: techniques, (Epi, epitympanum; Meso, mesotympanum; Hypo, hypotympanum). normal and pathologic arterial anatomy. AJNR Am J Neuroradiol (B) Axial (Pro, protympanum; Meso, mesotympanum; Post, posterior 1981;2:289–297. Reprinted with permission.) tympanum). (Adapted from Hesselink JR, David KR, Taveras JM. Selective ch03.qxd 9/23/08 11:36 AM Page 75

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prone to occlusion in the poorly pneumatized middle ear. of peritubal cells (adjacent to the eustachian tube, antero- Recently, other authors have disputed the anatomic pres- lateral to the carotid canal) and apical cells (anteromedial to ence of these isthmi and doubted that occlusive change the carotid canal).55,64 Pneumatization is far more common in predisposes to CH development.58,59 the peritubal region (65%). These peritubal cells often com- The mastoid region is subdivided into the mastoid municate directly with the eustachian tube instead of the antrum, which communicates with the epitympanum tympanic cavity. This anatomic fact may explain persistent (attic) via the aditus, the central mastoid tract (direct CSF leaks in individuals who have undergone middle ear inferior extension of the antrum), and the peripheral mas- obliterative surgery.65 Eradication of CSF otorhinorrhea toid area (additional cells that arise from the antrum).37 in this circumstance requires obliteration of several mil- This latter region is further subdivided into tegmental limeters of the osseous eustachian tube orifice. This may be cells (above the EAC), posterosuperior sinodural cells, difficult due to the anatomic proximity of the carotid canal. posteroinferior sinal cells (closely related to the sigmoid Accessory pneumatization may extend beyond the sinus), facial cells (related to mastoid segment of facial confines of the aforementioned regions into the zygomatic, nerve canal), and mastoid tip cells, which are divided into squamous temporal bone, occipital bone, and styloid medial and lateral portions by the digastric groove.7, 24 The process.24,37 mastoid antrum is present at birth. Peripheral pneumati- Developmental tracts of pneumatization may serve as zation continues through early childhood. pathways for disease within the temporal bone. These The tegmen is bone of variable thickness that forms include the posterosuperior cell tract, the posteromedial the roof of the epitympanum/middle ear (tegmen tym- cell tract (superior retrolabyrinthine), the subarcuate cell pani) and the roof of the mastoid (tegmen mastoideum) tract (translabyrinthine), the perilabyrinthine tract, and (Fig. 3.8). It is lined on the superior surface by dura and the peritubal tract. These tracts all intercommunicate and on the undersurface by mucosa.60 As such, the tegmen are named according to location. Of interest is that the provides a crucial barrier preventing the spread of infec- petrous apex may be pneumatized by all of these tracts. tion and leakage of cerebrospinal fluid. In autopsy series, The petrous apex is a truncated pyramid medial to the 1 to 5 focal defects are described in the tegmen in 15 to inner ear, the carotid artery, and the eustachian tube, and 34% of cases, most often in the well-pneumatized mas- is pneumatized in 30 to 35% of temporal bones.66–70 This toid. Rarely, multiple defects are described and may be pneumatization occasionally consists only of a single the source of some morbidity including spontaneous CSF giant air cell.71 Although these giant air cells were per- leaks and pneumocephalus. haps a differential diagnostic problem with conventional The anterolateral portion of the mastoid is derived radiographs and multidirectional tomography, their char- from the squamous portion of the temporal bone; the acteristic air density on CT presents little diagnostic diffi- posteromedial portion including the mastoid tip arises culty. Interestingly, it is the nonpneumatized petrous from the petrous portion.61 The Koerner’s (petrosqua- apex that can cause difficulty on magnetic resonance mous) septum (KS) is a structure of interest to both the imaging (MRI) (Fig. 3.27).67 Bright signal from marrow fat radiologist and otologic surgeon due to the surgical impli- can cause confusion because pathologic processes associ- cations when it is particularly thick, as it may be confused ated with hemorrhage, specifically cholesterol granuloma, with the medial wall of the antrum (see Normal Varia- may be imitated by the rapid T1 relaxation times. Com- tions subsection below) (Fig. 3.19). This structure begins puted tomography will typically be diagnostic in identifying at the glenoid fossa and extends inferiorly lateral to the asymptomatic petrous apex penumatization. T2-weighted facial nerve canal toward the mastoid tip. The KS is vari- sequences should reveal less signal intensity and as such ably sized and predisposes the patient with chronic otitis will easily document the presence of bone marrow (fat). to so-called attic block.46 This septum may be divided into The os suprapetrosum of Meckel is a small bony structure three portions: ventral (temporomandibular), middle located adjacent to the petrous apex that occurs as a normal (tympanic), and dorsal (mastoid). The ventral extremity variation.72 can be used as a surgical landmark for the mastoid seg- A mastoid pneumocele is a thin-walled generalized ment of the facial nerve canal.62 The septum appears air cell enlargement presumably due to a one-way ball essentially absent in the well-pneumatized temporal valve. This is differentiated from a pneumatocele, which bone; however, recent studies indicate that its size bears is a collection of loculated air under tension within the no relationship to the extent of pneumatization itself.62,63 soft tissues outside the abnormal cell. Compromise of The perilabyrinthine cells are located posterior to a the external auditory canal associated with conductive vertical plane passing through the modiolus of the hearing loss has been reported in this context.73 Defects cochlea and are described as being either supra- within the tympanosquamous and tympanomastoid labyrinthine or infralabyrinthine.7 The cochlea and the sutures are likely causative. Pneumocephalus has also petrous apex region are anterior to this plane and consist been described. ch03.qxd 9/23/08 11:36 AM Page 76

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A B

Fig. 3.27 Asymmetric petrous apex pneumatization (normal variant). (A) Axial computed tomography (CT) image reveals absence of pneumatization on the left (arrow). (B) Axial T1-weighted magnetic resonance image (T1WI) reveals hypersignal on the left secondary to the presence of fatty marrow (arrow). This could be confused with cholesterol granuloma if CT was unavailable. (C) Axial postcontrast T1WI reveals no pathologic enhancement (arrow). This would be a confusing image if C there was no precontrast study.

Normal Variations of the nerve should always be addressed when surgery for otosclerosis is being contemplated as it represents a A congenital gap in the bony facial nerve canal is referred potential hazard. In individuals with extensive middle ear to as a dehiscence.74,75 Such dehiscences are a well-known debris filling the middle ear cavity, the diagnosis may not surgical hazard and occur most commonly in the midtym- be possible because the density of CH and granulation panic segment above the oval window niche.76 A dehis- tissue is identical to that of the nerve. It is worthwhile to cence is difficult to appreciate with CT, as the bone is quite search for a “notch” on the inferior surface of the lateral thin, but recently observers have had some success in this semicircular canal in these patients. In my experience, a regard.74 The facial nerve is seen in cross section beneath clinically significant dehiscense/protrusion is usually not the lateral semicircular canal on coronal images at the present when this notch is visualized. An especially pro- level of the vestibule. The surgeon should be cautioned if nounced protrusion of the nerve into the oval window there is an especially noticeable inferior facial nerve con- niche could conceivably masquerade as a schwannoma or vexity in this plane, particularly when the oval window a congenital CH. niche appears compromised, because this may represent Preoperative knowledge of several other anatomic protrusion of the nerve through the dehiscence (Fig. 3.28). variations may be very helpful to the otologic surgeon.4,77 Such a protrusion will directly result in conductive hearing The dehiscent or high-riding jugular bulb is discussed in deficit (CHD) on rare occasions. The status of this segment Chapter 4.27 On occasion, we will identify a sigmoid sinus ch03.qxd 9/23/08 11:36 AM Page 77

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Specifically, a postauricular approach could be quite haz- ardous in the presence of this type of sigmoid sinus anomaly. The distance between the sinus and the EAC varies directly with the degree of pneumatization of the mastoid.79 On occasion, we will encounter an extremely deep sinus tympani (Fig. 3.30).4 Surgical exoneration of associated debris within this recess might then be difficult, and the surgeon should be cautioned. The difficulties that may be encountered by the surgeon in the tiny middle ear cavity are self-explanatory.47 A thick Koerner’s septum has been described in the past to be a source of surgical concern. In this situation the surgeon may believe that the entire antrum has been explored, when indeed the more medial aspect has not.60,61,77 The low-lying middle cranial fossa dura represents an obvious surgical hazard (Fig. 3.31). This occurs due to an absence of tegmental Fig. 3.28 Dehiscent (protruding) facial nerve. Coronal computed tomography image, right ear. There is a prominent inferior convexity pneumatization (above the EAC) in those with congeni- to the tympanic segment of the facial nerve (arrow). Such a finding tally thin superior EAC margins. This phenomenon is further should always be called to the surgeon’s attention. discussed in Chapter 2. Other variations and anomalies will be considered under their appropriate sections and subsections.

that is much more anteriorly and laterally located than normal (Fig. 3.29). This is much more common on the Embryology right presumably because the superior sagittal sinus often 78 drains preferentially into the right transverse sinus. The In this section, I provide a brief overview of the embry- size of the mastoid antrum may be compromised, and ological development of the middle ear. For more detail, this variation could make surgery more complicated, the reader is referred to Anson and Donaldson.33 depending on the approach preferred by the surgeon. The eustachian tube and tympanic cavity are formed from the first pharyngeal pouch (endoderm of tubotympanic recess), which is a foregut outpocketing.30,80,81 The dorsal end of the pouch develops initially into the eustachian tube and subsequently forms tympanic cavity.12 The extensions of the tympanic cavity, the attic (epitympanum), antrum, and mastoid air cells form after the tympanic cavity is developed. As these structures develop, the mesenchyme is replaced by endodermal epithelium. The tympanic cavity reaches adult size by 37 weeks of gestation. Four endothelial primary sacs develop from the first pharyngeal pouch between the 10th and 30th weeks of gestation and form the tympanic cavity. These include the saccus anticus, saccus posticus, saccus superior (squamous), and saccus medius.12 Mucosal folds form where these sacs contact each other. The saccus medius is particularly important because it is responsible for the development of most of the epitympanum, antrum, and mastoid air cell system. The saccus medius consists of three smaller saccules, the most medial of which forms Prussak’s space. The anterior epitympanum may be formed by the saccus anti- Fig. 3.29 Normal variant. Anteriorly and laterally placed sigmoid sinus cus in some circumstances. When this occurs, the anterior (SIG). and posterior epitympanum do not communicate.45 The ch03.qxd 9/23/08 11:36 AM Page 78

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A B

Fig. 3.30 Usually deep sinus tympani (arrow). This represents a site where cholesteatomatous debris may be out of the direct vision of the operating surgeon. (A) Right ear. (B) Left ear. (C) Different patient, sinus C tympani of extraordinary size. (C, Courtesy of Curtis Wushensky, MD.)

saccus superior lies between the malleus handle and and the rest of the mastoid air cell system continues for a incus long process and is responsible for pneumatization variable time into childhood.7 of the squamous temporal bone. Areas pneumatized by The first and second branchial arches (mesoderm) dif- the saccus medius and saccus superior subsequently ferentiate into the ossicular chain and its supporting liga- become separated by a variable petrosquamous lamina ments, muscles, and tendons (Fig. 3.13F). The first (Koerner’s septum). The saccus posticus forms the recesses branchial arch (Meckel’s cartilage) develops into the head and ridges of the posterior mesotympanum. of the malleus, the tensor tympani muscle and tendon, Pneumatization of the tympanic cavity and epitympa- and the body and short process of the incus.82 The second num is complete by week 34 of gestation in most cases; branchial arch (Reichert’s cartilage) develops into most of however, further pneumatization of the temporal bone the rest of the ossicular chain and also into the stapedius ch03.qxd 9/23/08 11:36 AM Page 79

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groove. The inner mucosal layer is derived from the endoderm of the first pharyngeal pouch.30 The tympanic ring (tympanic bone) is formed in membranous bone from four ossification centers. It is virtually completely developed by the 15th week of gestation. There is a defect in the ring superiorly, which is known as the notch of Rivinus. The TM inserts in this location. The tympanic ring provides the scaffolding for the TM. The TM is relatively horizontal at birth and does not assume the adult vertical orientation until 3 years of age.81 The tympanic ring also contributes to the development of the styloid process. It is this tympanic bone that forms the sides and floor of the bony EAC as it elongates.

Pathology and Treatment Inflammatory Disease Despite the obvious interrelationship, acute otomastoidi- Fig. 3.31 Low middle cranial fossa dura. Coronal computed tomogra- tis (AOM) and chronic otomastoiditis (COM) are consid- phy image. The tegmental air cells above the external auditory canal are ered as two different disease processes for the purposes of absent, and the temporal lobe is in direct apposition to the superior mar- this communication. Acute otomastoiditis is usually caused gin of the external auditory canal (L, arrow). Note that this patient does by bacterial infection often superimposed on eustachian have a tiny cholesteatoma (*) within the attic. The tegmen tympani tube obstruction, and chronic otomastoiditis by long- (t, arrow) is intact. The surgeon should be aware of this configuration prior to surgery. standing eustachian tube dysfunction. Similarly, each disease has its own specific set of complications. With respect to AOM, complications include middle ear effusion, coalescence, subperiosteal abscess, muscle and tendon. Other structures arising in whole, or labyrinthitis, and petrous apicitis, as well as intracranial in part, from the second arch include the mandibular involvement such as meningitis, abscess formation, and condyle, styloid process, and facial nerve canal.83 Ossicular dural sinus occlusive disease (see Table 3.5). COM may development occurs simultaneously with the formation result in middle ear effusion, TM retractions, acquired CH, and differentiation of the middle ear cavity and its out- granulation tissue, cholesterol granuloma, ossicular fixa- pouchings. The second half of this interval is primarily tion, and ossicular erosion. Certainly, complications of concerned with ossification, the ossicles having achieved AOM may be superimposed on COM. Facial nerve dys- adult size by the 15th week.84 Formation of the stapes is function may occur as a result of acute or chronic disease. not complete until week 38.85 Early in gestation the Despite this common misconception, there is no evidence stapes primordium is pierced by the stapedial artery and that acute or chronic otitis media are more prevalent in is separated from the developing facial nerve and pyramidal eminence (laterohyale) by the interohyale, which becomes the stapedius tendon.86 The stapes foot- Table 3.5 Complications of Acute Otomastoiditis plate has two layers: the tympanic portion, which is Coalescence derived from the second brachial arch, and the vestibular Subperiosteal abscess – external cortex defect portion (with its annular ligament), which develops from the otic capsule.81,84,85 The ossicles change little Bezold abscess – rare, petrous tip defect during life and, similar to the otic capsule, demonstrate a Meningitis limited capacity for repair. Parenchymal/extracerebral abscess, empyema The TM and the supportive tympanic ring are formed Dural sinus occlusive disease by the 18th week of gestation. Portions of the TM are derived from all three germ layers. The outer epithelial Otitic intracranial hypertension (otitic hydrocephalus) layer is derived from the ectoderm of the first branchial Facial nerve involvement groove (external auditory meatus). The middle fibrous Labyrinthitis layer is derived from the mesoderm, which insinuates Petrous apicitis itself between the tympanic cavity and the first branchial ch03.qxd 9/23/08 11:36 AM Page 80

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human immunodeficiency virus (HIV) patients.87 Aggres- due to drug-resistant organisms (penicillinase-producing sive fungal or pseudomonas mastoiditis may be seen, how- Streptococcus pneumoniae and beta-lactamase-producing ever, in severe HIV cases.88,89 strains of Moraxella and Haemophilus) and a change in As indicated in the previous paragraphs, middle ear microbial flora.95 effusions occur with both AOM and COM. Children are Mycotic disease is unusual. These infections may be predisposed to AOM and effusion for several reasons. The invasive when they occur in the immunocompromised eustachian tube in children is inherently dysfunctional host.96 Type I infections are limited to the EAC (otitis due to its relatively horizontal orientation and shorter externa). Type II infections involve extension into the length. Obstruction of the eustachian tube by prominent mastoid cavity (mastoiditis). Type III is invasive mastoidi- adenoidal tissue, release of inflammatory mediators from tis with facial palsy, and type IV infection is a fulminant adenoidal mast cells and adenoidal tissue acting as a skull base osteomyelitis.97–99 reservoir for bacteria are all mechanisms for the develop- Tuberculous otomastoiditis (TOM) is increasing in ment of middle ear effusion.90 prevalence due to the rising incidence of immunocom- The reader is cautioned that identification of debris promised hosts. There are many possible methods of suggestive of inflammatory disease within the mastoid is inoculation, but most commonly it is either hematogenous common, especially in children.91 Perhaps 10 to 15% of or extends directly from the nasopharynx. Classically, children and a substantial percentage of adults examined these patients present with chronic painless otorrhea and with MRI for other reasons will have heterogeneous an intact TM; however, wide variations in presentation T2-weighted hypersignal within the peripheral mastoid have been recently described.10 0,101 Pain, purulence, and and middle ear proper despite the absence of a history of EAC/TM involvement are all now considered to be common otitis media. The reason for this is unclear, but the observer presentations. Ossicular erosion, aggressive tumor-like should not misconstrue this common finding to be necessar- middle ear/mastoid destruction, and lymphadenopathy ily indicative of clinically significant inflammatory disease. are all associated with this disease (Fig. 3.32). The lym- A common error is to refer to abnormal signal in this phadenopathy commonly involves the postauricular region as mastoiditis, a clinical diagnosis. I refer to this region but may involve the parotid gland or other upper type of finding as “nonspecific mastoid debris” and rec- cervical lymph nodes.10 0 TOM should be considered in any ommend CT, if clinically indicated. patient regardless of immune state who fails to respond to antibacterial therapy.102,103 Peridural disease and facial nerve involvement are especially common in these Acute Otomastoiditis and Complications patients. In fact, the classic clinical triad of TOM is multiple Most cases of acute otomastoiditis occur in children and TM perforations, “pale” granulation tissue, and facial manifest clinically as otalgia, fever, and erythema/edema paralysis.104 Atypical mycobacteria are most frequently of the TM. The middle ear and mastoid are generally associated with chronic intractable granulation tissue. considered an extension of the upper respiratory tract Often, these patients are also immunosuppressed.105 and subject to bacterial invasion via the eustachian tube. Complications of acute otomastoiditis include coales- Mucoperiosteal inflammation results initially in serous cent mastoiditis, subperiosteal abscess, Bezold abscess, effusion, which may become mucoid or purulent.92 Fluid meningitis, parenchymal/extracerebral abscess, empyema, levels are commonly demonstrated at CT provided that dural sinus occlusive disease, otitic intracranial hyperten- there are two orthogonal planes (axial and coronal). sion (otitic hydrocephalus), facial nerve involvement, Previously, we referred to the aditus ad antrum, an inher- labyrinthitis, and petrous apicitis. Occasionally, these com- ently narrow communication between the epitympanum plications may occur superimposed upon chronic otitis (attic) and the mastoid antrum. Swollen mucosa may media. Such superinfection is especially dangerous when block the aditus, which traps secretions in the peripheral CH is present. In these cases, careful study of the tegmen mastoid with subsequent development of AOM. Effective tympani and sigmoid sinus plate is required for reasons therapy is crucial at this juncture. that will be described in subsequent sections of this chap- AOM is most often caused by bacterial infection. Strep- ter. When this type of bony defect is present, evaluation tococcus pneumoniae (pneumococcus) and Haemophilus with MRI (and MR angiography [MRA]) is strongly recom- influenzae account for 65 to 80% of cases.93 The latter agent mended.106,107 is less common but more aggressive and associated with a higher incidence of meningitis.88 Proteus and Pseudomonas Coalescent Mastoiditis species are less common culprits.94 The development of antibiotics, of course, resulted in a remarkable decline Fortunately, the vast majority of patients with acute in the incidence of the complications of this disorder. otomastoiditis are cured after a course of antibiotics, and Recently, however, there has been somewhat of an upsurge no imaging procedures are necessary.11 Should CT or MRI ch03.qxd 9/23/08 11:36 AM Page 81

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Fig. 3.32 Tuberculous otomastoiditis with parenchymal abscess. (A) Axial and (B) coronal computed tomography images reveal a destructive process sparing the inner ear. (C) Contrast-enhanced T1-weighted magnetic resonance image reveals a thick rind of enhancement surrounding the mastoid debris (single arrow) as well as a mature abscess in the periphery of the cerebellar hemi- C sphere (double arrows).

be performed at this time, nonspecific debris would be acidosis, and subsequent calcium dissolution.84,92 The di- identified, typically associated with several fluid levels agnosis of coalescent mastoiditis often requires the demon- (Fig. 3.33). CT will demonstrate the integrity of the mas- stration of subtle bony changes, which must be carefully toid septa, ossicular chain, and the internal and external sought in all AOM patients; therefore, high-resolution mastoid cortex.108 The turning point for these patients is CT is the best imaging modality available during this when mucoperiosteal disease becomes bone disease with interval (Fig. 3.34, Fig. 3.35, and Fig. 3.36). Subtle evidence enzymatic resorption of mastoid septa and the develop- of alternations of these mastoid septations may be clini- ment of an intramastoid empyema. This is referred to as cally significant and reflect antibiotic failure. Often a com- coalescent mastoiditis.109,110 Osteoclastic dissolution of the parison to the opposite side is needed in this regard pneumatic cell walls is likely a result of hyperemia, local (despite the fact that mastoid pneumatization is not always ch03.qxd 9/23/08 11:36 AM Page 82

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A B

Fig. 3.33 Uncomplicated acute otomastoiditis. (A) Axial and (B) coronal computed tomography images. There is diffuse debris throughout the mastoid. Note the preservation of the integrity of the mastoid septations as well as the internal and external mastoid cortices.

symmetric). Fortunately, coalescence is usually not subtle, Subperiosteal Abscess and the diagnosis will be obvious. Importantly, when coa- In addition to evaluating the status of the mastoid septa, lescent disease is the result of aditus obstruction or perhaps the internal mastoid cortex and external mastoid cortex attic blockade (isthmus obstruction), the TM and middle must be carefully examined. A subperiosteal abscess typi- ear may appear normal otoscopically. This is referred to as cally develops via direct extension of the inflammatory latent mastoiditis due to the paucity of clinical clues.92 debris through a defect in the external mastoid cortex. Such collections are often palpable (Fig. 3.37 and Fig. 3.38). They are usually postauricular due to the thin trabecular bone in this region (Macewen’s triangle).11 Abscess formation should not be confused with the edema, which occurs in this location secondary to thrombosis of mastoid emissary veins (Griesinger’s sign). Preauricular abscess formation is possible if the infection preferentially spreads along the zygomatic root. Even more rare is the Luc’s abscess which develops deep to the temporalis muscle.

Bezold Abscess The Bezold abscess is analogous to the superiosteal abscess occurring when the bony defect is seen at the mastoid tip (instead of the external mastoid cortex) medial to the insertion of the posterior belly of the digastric (digastric groove) and sternocleidomastoid muscle. This results in inflammatory debris extending inferiorly along the soft tissues of the neck, often with formation of an abscess (Fig. 3.39).111,112 ,113 Importantly, the inflammatory lesion most commonly lies within the posterior cervical space deep to the sternocleidomastoid muscle, resulting in the absence of a clinically palpable fluctuance.113 Pneumatiza- Fig. 3.34 Acute coalescent mastoiditis. Magnified axial computed tomography image reveals diffuse mastoid debris with fluid level tion of the mastoid tip is a predisposing factor (also anal- (arrow). All of the septations are thin and irregular. There is a sigmoid ogous to petrous apicitis in this regard, vide infra); therefore, sinus plate defect (outlined arrows), which must be viewed with suspicion. this process is more common in adults than children. For ch03.qxd 9/23/08 11:36 AM Page 83

Chapter 3 The Middle Ear and Mastoid 83

Fig. 3.35 Coalescent mastoiditis. (A) Axial computed tomography image reveals diffuse mastoid debris with extensive coalescent changes in mastoid septations (arrows). (B) Axial T2-weighted MRI confirms debris but not the changes in the bony septations. (C) Coronal-enhanced C T1-weighted MRI reveals that debris enhances.

these reasons, temporal bone CT is recommended for extracerebral (perisinus) abscess formation, and meningi- unexplained neck abscesses. The potential exists for this tis can occur via direct extension, hematogenous dissemi- abscess to extend inferiorly as far as the mediastinum. nation, or retrograde thrombophlebitis.114 The latter is considered to be the most common mode of spread. An abscess is a collection of pus lined by a fibrous cap- Meningitis, Abscess, and Empyema sule. When it occurs in the subdural or epidural compart- Defects in the internal mastoid cortex are of obvious con- ment, it must be distinguished from empyema, which cern, as this leaves the underlying dura adjacent to the spreads out over a wider area. Individuals with a subdural sigmoid sinus and cerebellum directly exposed to the empyema (SDE) typically have meningitis as well. SDE is a inflammatory process. Dangerous intracranial complica- much more likely complication of sinusitis than otomas- tions such as sigmoid sinus thrombosis, intracerebral or toiditis.115 Sterile subdural collections (hygroma) are also ch03.qxd 9/23/08 11:36 AM Page 84

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A B Fig. 3.36 Coalescent mastoiditis, left ear. (A) Magnifed axial computed the left ear demonstrates debris (*) in the peripheral mastoid in a patient tomography (CT) image of the normal right ear. Note the normal with otalgia and fever. Note the loss of mastoid septations, confirming pneumatization and well-defined septations. (B) Magnified axial CT of coalescent disease. The internal and external mastoid cortex is intact.

associated with meningitis in the absence of abscess for- the sigmoid sinus plate and the sigmoid sinus (Fig. 3.32, mation. Rarely, spread of inflammatory disease to the Fig. 3.40, and Fig. 3.41).92 meninges occurs along normal anatomical structures such Unexplained episodes of meningitis especially in chil- as the petrosquamous suture and petromastoid canal dren typically provoke a search for a parameningeal focus, (subarcuate artery).11 Proteus, Pseudomonas, and Staphylo- and history/findings compatible with otitis media are care- coccus species are often isolated in these advanced fully sought in this context. Detailed CT investigation of the cases.116 Abscesses may occur in the middle cranial fossa, bony margins of the temporal bone is required. Congenital but are much more common in the posterior fossa due to fistulas, often associated with inner ear malformations, osseous destruction in the Trautmann triangle between may be present (see Chapter 5). These patients typically

A B Fig. 3.37 Coalescent mastoiditis, subperiosteal abscess. (A) Axial com- side). Focal defect in external mastoid cortex (arrow). (B) Axial CT puted tomography (CT) image. Debris throughout mastoid with thin- image, postcontrast. Low-density mass representing subperiosteal ning and poor definition of mastoid septations (compare with opposite abscess. Note small air bubble (arrow). ch03.qxd 9/23/08 11:36 AM Page 85

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Fig. 3.38 Coalescent mastoiditis with subperiosteal phlegmon and lymphadenopathy. (A,B) Axial computed tomography (CT) images reveal diffusely eroded mastoid septations, indicating coalescent disease, with a large defect in the external mastoid cortex (arrow). (C) Corresponding axial CT image with soft tissue window reveals phlegmonous debris (arrow) rather than subperiosteal abscess, which typically occurs under these circumstances. (D) Axial CT image through C neck soft tissue reveals multiple pathologic lymph nodes (arrows).

have CSF otorhinorrhea. In several published reports, surgi- These defects are infralabyrinthine adjacent to the round cal investigation of focal cortical defects along the posterior window.118 Spontaneous CSF otorrhea may also be caused and middle fossa surfaces of the temporal bone has revealed by significantly larger defects and be associated with menin- arachnoid granulations as the cause of recurrent meningitis goencephalocele. These patients often present with CHD.119 in a significant number of cases117 (see Chapter 5). Hyrtl’s Meningitis is the most common intracranial complica- (tympanomeningeal) fissure normally closes at 24- to tion of acute otomastoiditis.120 Proteus, Pseudomonas, or 26-week gestation. If persistently patent, this structure Staphylococcus species are usually isolated. A brain may also be responsible for spontaneous CSF otorrhea. (parenchymal) abscess usually involves the temporal lobe ch03.qxd 9/23/08 11:36 AM Page 86

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A B

Fig. 3.39 Mastoiditis–Bezold abscess. (A) Axial computed tomography (CT) image reveals diffuse mastoid debris with a large sigmoid sinus plate defect (arrow). (B) More inferior image at the mastoid tip reveals a large area of erosion with a large lateral bony defect (arrow). (C) Axial CT image immediately subjacent to the mastoid tip C reveals a classic Bezold abscess (arrow).

and presents with symptoms of a mass lesion. Anaerobes may occur via direct extension or result from erosive such as Bacteroides and Fusobacterium may be the culprit. osteitis and retrograde thrombophlebitis via emissary Interestingly, a brain abscess is often a complication of veins. The majority are associated with epidural abscess. chronic rather than acute otitis. Epidural and subdural Perisinus inflammation may induce formation of mural abscess often occurs adjacent to the sigmoid sinus and is thrombus within the sinus lumen secondary to pressure strongly associated with bone erosion. Middle fossa effects, causing the adherence of fibrin and platelets.121,122 extraaxial collections often exhibit somewhat limited This mural thrombus becomes infected and propagates extension due to the firm attachment of the dura to the to form an obliterating thrombus.94 Some consider the arcuate eminence, a convexity corresponding to the site formation of a thrombus to be a protective mechanism of the superior semicircular canal.120 attempting to limit and localize the infection. Severe headaches, high spiking fevers, postauricular edema, sixth nerve palsy, and mental status changes herald the diagno- Dural Sinus Occlusive Disease sis clinically. Alterations of posture may be catastrophic Dural sinus occlusive disease (DSOD) is an extremely dan- for these patients. Antibiotic therapy is the cornerstone gerous and potentially fatal complication of AOM that of treatment.123 Anticoagulation is controversial. Surgical ch03.qxd 9/23/08 11:36 AM Page 87

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Fig. 3.40 Coalescent mastoiditis with temporal lobe parenchymal abscess. (A) Axial computed tomography (CT) image at bone window reveals diffuse middle ear debris sparing the inner ear. (B) Axial CT image at soft tissue window reveals a well-defined ring-enhancing mass in the middle cranial fossa, consistent with abscess (arrow). B

exploration is often needed. Aspiration of the clot may Due to anatomic proximity, involvement of the sigmoid/ yield the necessary restoration of flow, but incision into transverse sinus is most common. In many patients, a clot the sinus and removal of the clot may be necessary. Liga- may propagate antegrade into the internal jugular vein tion of the sinus is rarely needed, but it has been used to or retrograde to the torcula and superior sagittal sinus.124 control septic emboli.120 Extension along emissary veins to the subcutaneous tissues

A B Fig. 3.41 Acute otomastoiditis, cerebritis. (A) Axial and (B) coronal contrast-enhanced T1-weighted magnetic resonance images reveal mastoid debris with a heterogeneous intensely enhancing area (arrow) in the adjacent temporal lobe. ch03.qxd 9/23/08 11:36 AM Page 88

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A B Fig. 3.42 Mastoiditis. sigmoid sinus occlusive disease. (A) Axial contrast- hypersignal (arrow) in the expected location of the sigmoid sinus and enhanced T2-weighted MRI and (B) T1-weighted MRI reveals enhancing (B) an area of nonenhancement (arrow) centrally within the sigmoid sinus debris throughout mastoid in a patient with spiking fevers. (A) Abnormal representing a thrombus.

may also occur. Furthermore, the reader should be aware may be confusing as a result of dose-related issues and of the anatomic proximity of the superior and inferior due to thrombus enhancement, which occurs consis- petrosal sinuses, which drain the cavernous sinus. Clot tently in chronic cases, presumably secondary to the propagation retrograde could thus have further dire clinical conversion of the clot into vascularized connective tissue.127 consequences. Systemic septic emboli and pulmonary Enhancement with gadolinium also occurs commonly in thromboembolic disease also have grave implications.119 ,12 5 normal cases due to physiological slow flow. DSOD remains a difficult imaging diagnosis despite When considering this diagnosis, the observer must the advent of MRI (Fig. 3.42, Fig. 3.43, and Fig. 3.44). take into account indirect factors such as absent flow void Clinical suspicion is the single most important diagnostic on spin echo images and absent FRE on gradient echo element.126 If examination of conventional spin echo im- sequences. These findings are nonspecific, but should spark ages reveals a flow void in the typical anatomic location suspicion under certain clinical circumstances. On occa- of the sigmoid sinus, the diagnosis of occlusive disease sion, signal characteristics allow for direct visualization of is effectively excluded. Similarly, bright signal repre- the clot within the lumen of the sinus. This is perhaps most senting flow-related enhancement (FRE) on gradient effective in the case of the acute clot (initial stage) on spin echo pulse sequences also lessens the likelihood of this echo pulse sequences as the hypointensity elicited by diagnosis. Findings on spin echo images can be particu- deoxyhemoglobin can ordinarily be distinguished from the larly perplexing due to the vagaries of flow phenomena. signal void produced by rapidly flowing blood. Slightly In addition, gadolinium-enhanced T1-weighted images greater intensity of the clot may be appreciated on the first

Fig. 3.43 Acute otomastoiditis, sigmoid sinus thrombosis. (A) Axial con- MRI reveals hyperintense mastoid debris with a hypointense area in the trast-enhanced computed tomography (CT) image reveals mastoid debris vicinity of sigmoid sinus (arrow), representing an acute clot. (E) Sagittal with a “vacant” nonenhancing sigmoid sinus (arrow). (B) Magnified axial contrast-enhanced T1-weighted MRI reveals a nonenhancing area CT, left ear, reveals coalescent disease (arrow) with thinning of the sigmoid (arrow), representing thrombosis. (F) Magnetic resonance venography sinus plate (arrow). (C) Axial contrast-enhanced CT image reveals lym- confirms absent flow in the sigmoid sinus and internal jugular vein phadenopathy (arrows), more noticeable on the left. (D) Axial T2-weighted (arrow). (Courtesy of Deborah Shatzkes, MD.) ch03.qxd 9/23/08 11:36 AM Page 89

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A B

C D

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Fig. 3.44 Mastoiditis, sigmoid sinus occlusive disease. (A) Axial contrast-enhanced T1-weighted magnetic resonance image (T1WI) reveals nonspecific enhancing debris throughout the middle ear cleft with absent sigmoid sinus signal void replaced by enhancement (arrow). (B) Coronal contrast-enhanced T1WI reveals confirms abnormal enhancement (arrow) in the region of the expected location of the sigmoid sinus. (C) Magnetic resonance venography reveals absent flow in the transverse (arrow) and sigmoid sinus. C

echo (proton density), and this provides corroborative Presently, the combination of pre- and postcontrast evidence of the presence of the acute clot. Subacute clot MRI and MRA is the state of the art for evaluation of this (intermediate stage) is hyperintense on all spin echo dangerous clinical condition (Fig. 3.44). Two-dimensional pulse sequences and may result in confusion with normal time-of-flight MRA technique is used for screening, but slow flow characteristics; however, subacute clot visuali- phase contrast technique is often needed, as information zation has been reported in the sagittal sinus, torcula, and regarding the direction of flow may be crucial. The satura- sigmoid/transverse sinus complex.124 tion pulse is reversed to gain information about the ch03.qxd 9/23/08 11:36 AM Page 91

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venous side of the circulation. Recall that dural arteriove- to dural sinus thrombosis presumably due to impaired nous fistulas (DAVF) are associated with occlusive intracranial venous drainage.11 Actual hydrocephalus is in disease. As such, transosseous vessels (collaterals) and fact rare. Instead, most use this term to describe increased an increased number and size of extracranial vessels intracranial pressure occurring secondary to DSOD in the should be viewed with suspicion (see Chapter 4). context of complicated AOM. Some reserve this term for a The observer must be cautious when evaluating pseudotumor cerebri-like condition unassociated with MRI/MRA examinations, as there are numerous normal demonstrable clot.119 ,12 4 Others have suggested that OIH is variations. Most important of these is asymmetry, which a vasomotor reflex phenomenon originating from the is extremely common and may be dramatic. This is most thrombosis rather than mechanical obstruction. often related to the preferential drainage of the superior sagittal sinus into the right transverse sinus. Slow flow is Facial Nerve Involvement especially common in large veins. Arachnoid granulations Facial nerve involvement may occur as a complication of may result in focal defects within the walls of the dural AOM or COM (Fig. 3.45).130 The spread of inflammation is sinuses, and clinical correlation is obviously critical.128 CT facilitated by the common occurrence of developmental findings are much less specific. Intense rim enhancement dehiscences (perhaps 55%), which have the potential to of the sigmoid sinus with lack of internal enhancement allow passage of inflammatory by-products. Infections is the basis for CT diagnosis (empty delta sign), and this may also spread via the canaliculi, which transmit the remains a diagnostic mainstay, although its reliability has neural supply of the chorda tympani and stapedial mus- been questioned.129 In fact, CT may be the only modality culature. The tiny arteries that provide blood supply to used to follow these seriously ill patients. Intraluminal the nerve may also be involved. Toxins produced by bacteria gas bubbles may imply formation of an abscess.125 may result in facial nerve demyelination.

Otitic Intracranial Hypertension Labyrinthitis Historically, the term otitic hydrocephalus (otitic intracra- Labyrinthitis is also a potential complication of acute nial hypertension [OIH]) has been used to describe the otomastoiditis. Access to the labyrinth is typically via the circumstance in which hydrocephalus develops secondary round window or oval window (tympanogenic labyrinthitis,

A B Fig. 3.45 Mastoiditis, acute and chronic, facial nerve involvement. contrast-enhanced T1-weighted magnetic resonance image reveals (A) Axial computed tomography image reveals diffuse mastoid disease abnormal enhancement of the first genu as well as the intracanalicular with coalescence involving the mastoid antrum (*) (no surgery). New segment of the facial nerve (white arrow). (With permission Radiologic bone formation is noted in the attic (arrow). There is erosion near the Society of North America, 2003.) (See Color Plate Fig. 3.45.) first genu of the facial nerve canal (white arrow). (B) Corresponding axial ch03.qxd 9/23/08 11:36 AM Page 92

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secondary to perilymphatic fistula, 76% had documented otitis media.132

Petrous Apicitis The etiology of petrous apicitis (apical petrositis) has historically been a matter of debate.133 A minority of observers favor an osteomyelitis and consider the petrous apex to be an anatomically distinct and functionally separate portion of the temporal bone. As such, the infection would theoretically spread via retrograde thrombophlebitis along the venous plexus of the petrous ICA. However, the majority of observers considers petrous apicitis to be an osteitis that develops only in individuals with a pneumatized petrous Fig. 3.46 Acute otomastoiditis, labyrinthitis. Coronal contrast-enhanced apex. Communication of these air cells with the mastoid T1-weighted magnetic resonance image reveals abnormal enhance- and middle ear is well documented. CT scans in this cir- ment of the fluid-filled spaces of the labyrinth (arrows), consistent with cumstance reveal debris within the petrous apex air cells labyrinthitis. and lysis of bony septa (Fig. 3.47, Fig. 3.48, Fig. 3.49, and Fig. 3.50). As such, petrous apicitis is analogous to coalescent see Chapter 5). Exotoxins have also been implicated in the mastoiditis. Disruption of the anterior or posterior bony development of labyrinthitis in these patients, suggesting cortex may occur and result in fulminant intracranial com- hematogenous dissemination. The classic imaging finding plications, such as meningitis, empyema, cranial neuropa- is pathologic contrast enhancement within the normally thy, and various other cavernous sinus symptoms. The fluid-filled spaces of the labyrinth on T1-weighted gadolin- initial diagnosis of petrous apex inflammatory disease is ium-enhanced studies (Fig. 3.46).131 This phenomenon best made with high-resolution CT; however, after the will be considered in much greater detail in Chapter 5. diagnosis is made, MRI becomes important for evaluation These patients often develop sensorineural hearing loss of intracranial complications. Typical MR findings in these and vertigo. If the hearing loss is fluctuating, perilym- cases include pathologic enhancement at the periphery phatic fistula should be considered, especially in children. of the defect, presumably within the meninges, possibly In a series of 37 children with sensorineural hearing loss extending to the gasserian ganglion (Meckel’s cave) and

A B Fig. 3.47 Petrous apicitis. (A) Axial and (B) coronal computed tomography images demonstrate diffuse opacification localized to the petrous apex with loss of septations (arrows), indicating coalescent disease. ch03.qxd 9/23/08 11:36 AM Page 93

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C D Fig. 3.47 (Continued) (C) Axial precontrast T1-weighted magnetic reso- is manifest most notably by enhancement of the facial and superior nance image (T1WI) reveals petrous apex disease (arrow). (D) Axial post- vestibular nerves within the internal auditory canal (arrow). contrast T1WI reveals intensely enhancing debris. Leptomeningeal disease

cavernous sinus.134 The clinical findings in patients with Petrous apex lesions are considered in detail in Chap- complicated petrous apicitis are well documented. The ter 8. At this juncture, it is important to understand that classic Gradenigo triad (otomastoiditis, sixth nerve palsy, benign debris is very common in the asymptomatic and pain in the distribution of the fifth nerve) is actually patient. In particular, trapped fluid occurs commonly as an rarely present; however, the patient may present with any incidental finding on both CT and MRI and should not be one or more of these clinical entities. confused with clinically significant disease (Fig. 3.51 and

A B Fig. 3.48 Petrous apicitis. (A) Axial computed tomography (CT) image. detected. CT differential diagnoses include petrous apicitis and cholesterol There is diffuse debris throughout the right mastoid with multiple fluid granuloma, as well as recurrent cholesteatoma. (B) Axial noncontrast levels. Well-marginated erosion at the right petrous apex (arrow) is T1-weighted magnetic resonance image (T1WI). (Continued on page 94) ch03.qxd 9/23/08 11:36 AM Page 94

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Fig. 3.48 (Continued)(C) Axial postcontrast T1WI. There is enhancement of the meninges (arrows) adjacent to the nonenhancing low C signal intensity lesion in this patient with full Gradenigo syndrome.

Fig. 3.52).135 The imaging appearance of petrous apicitis finding. Meningocele and arachnoid cyst both fall under is nonspecific, and the diagnosis must be based on clini- this umbrella.136 cal symptomatology and patient history. Differential diagnosis includes trapped fluid, mucocele, CH, cholesterol granuloma, and cephalocele. The latter, petrous Chronic Otomastoiditis and Complications apex cephalocele, represents a protrusion of meninges As the name implies, chronic otomastoiditis is an unre- and CSF from Meckel’s cave and is typically an incidental solved inflammatory process of the middle ear and mastoid

A B Fig. 3.49 Petrous apicitis. (A) Precontrast axial T1-weighted magnetic displacement of the cavernous carotid (arrow, A,B). Differential diagnosis resonance image (T1WI). (B) Postcontrast axial T1WI. There is diffuse sig- includes aggressive neoplasms (including rhabdomyosarcoma). Clinical nal aberration involving the entire mastoid with obvious extent to the symptomatology (sixth and eighth nerve involvement) abated, and mag- petrous apex. There is remarkable intense enhancement. There is anterior netic resonance findings regressed after antibiotic treatment. ch03.qxd 9/23/08 11:36 AM Page 95

Chapter 3 The Middle Ear and Mastoid 95

A B Fig. 3.50 Petrous apex infection. Abscess. (A) Coronal CT reveals debris reveals a mature abscess within the temporal lobe (arrow). Note the un- at the left petrous apex with subtle evidence of bony erosion/permeation derlying enhancement at the petrous apex and diffuse debris throughout (arrow). (B) Corresponding coronal contrast-enhanced T1-weighted MRI the mastoid.

A B

Fig. 3.51 Benign “trapped” fluid in the petrous apex. (A) Axial CT reveals debris (arrow) at the petrous apex, which is well corticated. (B,C) Axial T1-weighted MRI and T2-weighted MRI demonstrate homogeneous fluid C intensity (arrows). ch03.qxd 9/23/08 11:36 AM Page 96

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ossicular fixation. TM perforations and various forms of myringitis will only receive passive reference because they are obvious otoscopically (in the absence of external canal occlusive disease) and can only be indirectly appreciated on CT.

Middle Ear Effusion Middle ear effusion (MEE) is commonly associated with both AOM and COM, and the discussion in this section is arbitrary. In fact, MEE often occurs in the absence of clinically apparent inflammation especially in children due to the relatively horizontal orientation of the eustachian tube and the presence of adenoidal tissue. Adenoidal tissue may harbor various microorganisms, which predisposes the patient to superimposed inflammation via eustachian tube propagation. CT is usually not needed, as uncomplicated serous otitis can be moni- tored otoscopically while it is being treated medically or with tympanostomy tubes.142 Decreased intratympanic pressure secondary to eustachian tube dysfunction is Fig. 3.52 Effusion, petrous apex. Axial computed tomography reveals opacification of petrous apex air cells (arrow) as an incidental finding the accepted etiology (Fig. 3.53, Fig. 3.54, Fig. 3.55, in an asymptomatic patient. Note the normal foramen ovale (o), fora- Fig. 3.56, Fig. 3.57, Fig. 3.58, and Fig. 3.59).142,149 men spinosum (s), carotid canal (c), jugular foramen (j), and mas- The reader should be aware that 38% of individuals toid segment facial nerve (f). with untreated nasopharyngeal carcinoma have MEE. Auditory symptoms are the presenting complaint in 18% of these patients.150 This is presumably due to eustachian tube displacement or invasion. Tensor veli palatini inva- associated with active and quiescent periods. TM perfo- sion has been suggested as a specific functional cause.150 ration is quite commonly associated. Virtually all of Therefore, unexplained middle ear effusion in an adult these patients have long-standing eustachian tube dys- must be scrutinized, as it is a classic initial manifestation function, and subsequent decreased intratympanic pres- of nasopharyngeal neoplasm.142,151 These neoplasms often sure is most likely the basic predisposing factor for this originate in the posterolateral recess (fossa of Rosen- variety of disease processes. Pseudomonas aeruginosa müller) (Fig. 3.60 and Fig. 3.61). Trotter’s syndrome and Staphylococcus aureus are the most common organ- (unilateral deafness, trigeminal neuralgia, and soft palate isms involved and are typically -lactamase-producing immobility) may develop if there is associated perineural (penicillin-resistant).110,137–142 invasion.152 The nasopharynx is always in the field of view All manifestations of COM, including CH, are unknown in when the middle ear is examined. This provides the imaging subhuman primates. It has been postulated that the upright specialist with a unique opportunity to make the initial position and the enlargement of the skull in humans have diagnosis. altered the skull base so that the eustachian tube and tym- Effusions localized to the epitympanum (attic), mastoid panic bone assume a more vulnerable vertical position.143 antrum, and/or mastoid air cells (sparing the middle ear The contralateral ear is very often abnormal in cases of cavity proper) may be due to a selective decrease in long-standing COM, with estimates as high as 63%.14 4 intratympanic pressure in this area (“attic block”), that is, The vast majority of these patients have a poorly obstruction to ventilation of the attic, antrum, and mastoid pneumatized mastoid, a consistent manifestation of air cells due to compromise of the anterior and posterior eustachian tube dysfunction. There are numerous clini- tympanic isthmi (see the Anatomy and Normal Variations cal manifestations of chronic otomastoiditis, many section). This most commonly occurs in individuals with a of which are both visible and diagnosable with current developmentally small middle ear cavity and a poorly imaging criteria.145–148 In this section, the following pneumatized middle ear cleft. The presence of a large entities are reviewed and updated: middle ear effusion, Koerner septum (petrosquamosal lamina) also predisposes granulation tissue (including cholesterol granuloma), mid- to this condition (Fig. 3.57).12,46,86,153 The reader should be dle ear atelectasis (TM retraction), acquired CH, non- aware that attic block may also result from the presence of cholesteatomatous ossicular erosions, and postinflammatory a mass lesion (see also Fig. 3.25). ch03.qxd 9/23/08 11:36 AM Page 97

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A B

Fig. 3.53 Middle ear effusion. (A,B) Axial and (C) coronal computed C tomography images reveal multiple fluid levels (arrows).

Middle ear effusions are diagnosed at CT by the pres- (Fig. 3.62).92,149 A variety of materials are used, including ence of dependent radiopacity (see Fig. 3.53, Fig. 3.54, various types of plastics and stainless steel.154,155 There are Fig. 3.55, Fig. 3.56, Fig. 3.57, Fig. 3.58, and Fig. 3.59).10 countless shapes and sizes produced by several manufac- Effusions can also be appreciated with MRI, although turers. Many of these have a bobbin shape, but some fluid levels are of less significance as MRI is extremely surgeons prefer a simple intratympanic phalange. The sensitive and quite often findings are of no clinical CT appearance of these devices is characteristic in significance. most circumstances (Fig. 3.63, Fig. 3.64, Fig. 3.65, and The purposes of surgically placed tympanostomy tubes Fig. 3.66).156,157 Identification may be hindered when are to normalize intratympanic pressure and limit the there is surrounding fluid or when the tube is in an atypi- potential for developing superimposed bacterial infections cal location. These tubes must not be misidentified as a ch03.qxd 9/23/08 11:37 AM Page 98

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A B Fig. 3.54 Middle ear effusion. (A,B) Axial computed tomography images reveal well-defined fluid levels (arrows).

foreign body, dislocated ossicle, or inflammatory mass.156 Granulation Tissue (Typical and Cholesterol Granuloma) Tympanostomy tubes may become dislodged and extrude The development of granulation tissue (GNT) in the mid- into the external canal or may actually migrate into the dle ear is extremely common, both as an isolated phenom- middle ear (Fig. 3.67). enon and in conjunction with other middle ear maladies,

A B Fig. 3.55 Middle ear effusion. Coronal CTs reveal (A) fluid levels (arrow) and (B) a tympanostomy tube (arrows). ch03.qxd 9/23/08 11:37 AM Page 99

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Fig. 3.56 Middle ear effusion. (A,C) Multiple axial computed tomography images reveal fluid levels (arrows). There is debris in the oval window niche surrounding the stapes superstructure (arrow, B), also a combina- C tion of granulation/fluid.

such as effusion and CH.158 From an imaging point of view, differentiation of CH from cholesterol granuloma (CG has one should consider granulation tissue as either typical or bright signal on all pulse sequences).162,163 Enhancing cholesterol granuloma. Both types appear at CT as nonspe- (typical) granulation tissue is significantly more common cific, nondependent radiopacity, although a few fluid levels than CH or cholesterol granuloma (Fig. 3.68 and Fig. 3.69). may be present. Typical GNT is vascularized and enhances The presence of typical GNT can often be inferred indirectly intensely with gadolinium on T1-weighted MR images. in a patient with nonerosive middle ear debris appreciated This is an extremely common entity. Cholesterol granu- on CT as CH will not usually result in at least some bone loma (CG), however, is far less common and has a distinct erosion (Fig. 3.70, Fig. 3.71, and Fig. 3.72). tendency to bleed, causing hemotympanum.158–161 As such, Cholesterol granuloma is a cause of idiopathic hemo- evaluation of enhanced T1-weighted MR images allows tympanum.16 4 CG is a foreign body, giant cell reaction to differentiation of typical GNT from CH (no enhancement cholesterol deposits with associated fibrosis and vascular with CH), and unenhanced T1-weighted MR images allow proliferation. Pathologic examination reveals brownish ch03.qxd 9/23/08 11:37 AM Page 100

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A B Fig. 3.57 Middle ear effusion. (A) Coronal computed tomography (CT) thick Koerner’s septum (outlined arrow). There is also an incidental fluid image reveals a fluid level in the middle ear (arrow). (B) Axial CT image level within Prussak’s space (white arrow). reveals a fluid level in the mastoid antrum associated with an unusually

A B Fig. 3.58 Middle ear effusion. (A,B) Axial CTs reveal numerous fluid levels (arrows). ch03.qxd 9/23/08 11:37 AM Page 101

Chapter 3 The Middle Ear and Mastoid 101

C D Fig. 3.58 (Continued) (C,D) Coronal CTs reveal numerous fluid levels (arrows).

A B Fig. 3.59 Mastoid antrum effusion. (A) Axial and (B) coronal computed tomography images reveal well-defined fluid levels (arrows) within the mastoid antrum. ch03.qxd 9/23/08 11:37 AM Page 102

Fig. 3.60 Middle ear effusion, nasopharyngeal carcinoma. (A) Axial computed tomography image of a patient with clinically unexplained middle ear effusion. Debris is seen throughout the left mastoid (thick black arrow). Note erosive changes involving the floor of the middle cranial fossa on the ipsilateral side (outlined arrows). (B,C) Axial and coronal enhanced T1-weighted magnetic resonance images reveal an enhancing nasopharyngeal mass (*). Erosive changes at the floor of the middle cranial fossa C are appreciated on the coronal image (white arrows).

A B Fig. 3.61 Dermoid obstructing eustachian tube. (A) Axial computed T1-weighted MRI reveals a high signal intensity mass (arrows) within tomography image. Diffuse nonerosive debris is seen throughout the nasopharyngeal portion of the eustachian tube. (Case courtesy of the left middle ear in a patient with a sclerotic mastoid. (B) Axial William P. Dillon, MD.) ch03.qxd 9/23/08 11:37 AM Page 103

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Fig. 3.62 Tympanostomy tube placement. (Used with permission, Salt Lake City ENT Associates.) (See Color Plate Fig. 3.62.)

fluid containing cholesterol crystals.160,165–168 Multinucle- drainage. Red blood cell breakdown leads to further for- ated giant cells are also apparent microscopically, as are mation of the cholesterol crystals, which continue the cy- red blood cells and hemosiderin. The cholesterol crystals cle of granulomatous reaction. Important for the novice and subsequent foreign body response are likely responsi- observer, cholesterol granuloma should never be confused ble for most histopathologic manifestations.169 Associated with CH. CG and its variants are all lined by fibrous con- hemorrhage aggravates the circumstance, leading to addi- nective tissue in contradistinction to CH, which is lined by tional neovascularity and continuing hemorrhage.16 8 keratinizing stratified squamous epithelium. Eustachian tube dysfunction (occlusion of the air cell sys- Cholesterol granuloma is usually preceded by chronic tem) with secondary mucosal edema and blood vessel MEE. Superimposed bacterial infection may or may not rupture is considered the most likely etiology. Stagnation be present. Causes are rarely erosive or destructive in of these hemorrhagic contents occurs due to the lack of most patients when they are isolated to the middle ear

A B Fig. 3.63 Tympanostomy tube, anteriorly positioned. (A) Axial and (B) coronal computed tomography images. Tympanostomy tube is in place, but positioned more anteriorly than we typically see (arrows). Pressure equalization is usually still effective under these circumstances. ch03.qxd 9/23/08 11:37 AM Page 104

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A B Fig. 3.64 Tympanostomy tube. (A) Axial and (B) coronal computed tomography images reveal phalange-shaped tympanostomy tube (arrows).

(Fig. 3.73). There has been one reported case of inner ear Importantly, CG limited to the middle ear may masquer- involvement secondary to middle ear CG.170 This is in ade otoscopically as a vascular mass, and the clinician may contradistinction to CG of the petrous apex, which has initially suspect paraganglioma (glomus tympanicum), the tendency to be extremely erosive and may compro- aberrant ICA, or dehiscent internal jugular vein. The mise the carotid canal and cavernous sinus anteriorly or, history of COM is usually the “tip-off” in this regard, and less commonly, the cerebellopontine angle posteriorly. imaging will be diagnostic.

Fig. 3.65 Tympanostomy tubes (arrow). Coronal computed tomography Fig. 3.66 Tympanostomy tubes (arrows). Coronal computed tomogra- image, nonmetallic bobbin-type tube. phy image, nonmetallic device, right ear. ch03.qxd 9/23/08 11:37 AM Page 105

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A B

Fig. 3.67 Tympanostomy tubes, dislocated. (A) Axial and (B) coronal CTs. Tube (arrows) has migrated through the tympanic membrane into the middle ear. (C) Different patient, axial CT image. Tube has extruded into C the external canal (arrow).

Similar to petrous apicitis, the risk of petrous apex CG encroachment on crucial structures, particularly the cra- is theoretically limited to only those 30% of patients who nial nerves. Many patients have retrocochlear symptoma- have a pneumatized petrous apex. Petrous apex CG is not tology due to involvement of the internal auditory canal. common, yet the incidence is 10 times more common Others have headaches due to traction on the adjacent than CH in this region and 40 times more common than middle cranial fossa dura or facial pain due to the mucocele. By contrast, schwannoma of CN VIII (acoustic involvement of the posterior cranial fossa dura. Facial neuroma) is 30 times more common than CG.171 Petrous nerve involvement is rare. Surgical treatment is drainage apex CG tends to remain clinically silent until there is and establishment of permanent aeration. Unlike CH, ch03.qxd 9/23/08 11:37 AM Page 106

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A B

C D Fig. 3.68 Granulation tissue, typical (A) axial T2-weighted MRI reveals MRI (T1WI) confirms disease. (C) Axial and (D) coronal contrast-enhanced diffuse nonerosive (CT confirmed) hypersignal throughout the middle ear T1WIs reveal intense enhancement throughout, consistent with inflam- and mastoid extending to petrous apex (arrows). (B) Axial T1-weighted matory granulation tissue.

there is no true epithelial lining; therefore, complete exci- blue-dome cyst, and giant cholesterol cyst.147,16 5 ,173 ,174 Giant sion is not necessary.172 Drainage is translabyrinthine in cholesterol cyst is a term used to describe the identical those with a “dead” ear and infralabyrinthine in others. histopathologic lesion when it arises at the petrous apex Yearly surveillance is recommended to limit recurrences. in patients with a well-pneumatized middle ear and Some confusing terminology is used in describing CG. mastoid and no history of chronic otitis.173 ,17 5 Cranial These lesions are variously referred to as chocolate cyst, neuropathies are particularly common with this variant ch03.qxd 9/23/08 11:37 AM Page 107

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C D Fig. 3.69 Erosive debris, attic. (A) Coronal computed tomography (CT) (C,D) Coronal pre- and postcontrast T1-weighted magnetic resonance image reveals soft tissue abnormality within the attic (arrow) eroding images reveal enhancement (arrow, D), indicating granulation tissue the malleus. The scutum is normal. (B) Axial CT image reveals a lesion rather than cholesteatoma. There was no surgery. eroding ossicles in the vicinity of the malleoincudal articulation (arrow).

A B Fig. 3.70 Granulation tissue. Coronal computed tomography images granulation tissue. These findings are nonspecific, and glomus tympan- through the (A) anterior cochlear turns and (B) vestibule demonstrate icum paraganglioma can have this appearance. nonerosive, nonexpansile holotympanic debris consistent with benign ch03.qxd 9/23/08 11:37 AM Page 108

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A B Fig. 3.71 Granulation tissue. Axial computed tomography images reveal diffuse nonerosive debris throughout the middle ear cleft. The ossicular chain including the stapes (arrow, B) is entirely intact. There is perhaps some developing tympanosclerotic calcification in the lateral attic (arrow, A).

A B Fig. 3.72 Granulation tissue. (A,B) There is nonerosive debris throughout the middle ear cleft. The ossicular chain, including the stapes (arrow, B), is intact. ch03.qxd 9/23/08 11:37 AM Page 109

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A B

Fig. 3.73 Cholesterol granuloma, middle ear. (A) Coronal and (B) axial CTs. There is debris throughout the middle ear cleft. Note: Intact ossicles and retracted tympanic membrane indicate that this is very unlikely to represent cholesteatoma. (C) Coronal nonenhanced T1-weighted MRI. Bright signal is present, indicating methemoglobin (identical on T2-weighted MRI) and C establishing diagnosis. See text beginning on page 98.

(see Chapter 8). 17 5 Jackler and Cho have recently pro- MRI is extremely helpful and in conjunction with CT is posed a hypothesis for the development of petrous apex virtually diagnostic for CG (Fig. 3.74 and Fig. 3.75). With CG in this context.176 They propose that these individuals few exceptions these lesions are bright on all spin echo have an inherently deficient bony partition between the sequences, which differentiates them from CH; CH petrous apex air cell system and the adjacent marrow will usually have relatively long T1 and T2 relaxation compartment. Hemorrhage from exposed marrow coagu- times.147,165,174 Differentiation from normal marrow should lates within mucosal cells and occludes outflow path- not be difficult because fat demonstrates less intense ways. Sustained hemorrhage results in cyst expansion. signal as the repetition time (TR) is increased. Partial sat- The terms chocolate cyst and blue-dome cyst refer to the uration gradient recalled echo sequences (GRASS), a tech- identical histological entity occurring in a mastoidectomy nique that is sensitive to magnetic field inhomogeneities, cavity. may demonstrate a peripheral ring of low signal intensity ch03.qxd 9/23/08 11:37 AM Page 110

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A B

Fig. 3.74 Cholesterol granuloma, left middle ear. (A) Magnified axial CT, left ear. Debris is seen in the mesotympanic space (arrow). (B) Corresponding magnified axial noncontrast T1-weighted MRI. Debris is diffusely hyperintense (arrow). (C) Corresponding magnified axial T2-weighted MRI. Debris is hyperintense on this sequence as well (arrow). Findings are consistent with the presence of extracellular methemoglobin. C

that is almost certainly indicative of hemosiderin-laden neoplasm, or atypical neuroma. A potential stumbling macrophages in the fibrous wall. Proton chemical shift block in the differential diagnosis is the rare hydrated imaging may reveal a cyclic pattern of signal intensity mucocele. The signal characteristics of these rare lesions centrally, reflecting the presence of lipid and cholesterol may be very similar, presumably due to the high protein crystals within the lesion.165 These additional sequences content (Fig. 3.76). may help to differentiate the hyperintense cholesterol Petrous apex/cerebellopontine angle CG should not be granuloma from thrombosed aneurysm, hemorrhagic confused with epidermoid congenital CH despite their ch03.qxd 9/23/08 11:37 AM Page 111

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A B Fig. 3.75 Cholesterol granuloma, right ear. (A) Magnified coronal noncontrast T1-weighted MRI, right ear. (B) Magnified coronal T2-weighted MRI, right ear. Diffuse hyperintense debris throughout the middle ear space is virtually diagnostic of cholesterol granuloma.

smoothly expansile nature.16 6 MR signal characteristics in Treatment of CG is effective surgical drainage. Such most cases are quite different from cholesterol granu- devices are well seen with CT (Fig. 3.85). MRI is also helpful loma/cholesterol cyst in that T1 and T2 relaxation times in the postoperative evaluation of cholesterol granuloma. are both quite long. Petrous apex CG is not uncommon Successful surgical intervention will result in a dramatic and has the classic appearance of a destructive lesion decrease in T1 signal.165 with MR characteristics of subacute/chronic blood (Fig. 3.77, Fig. 3.78, and Fig. 3.79). Differentiation of Central Nervous System Complications petrous apex CG from both trapped fluid and simple asymmetric pneumatization is a common clinical/imaging Central nervous system (CNS) complications are associ- issue. Trapped fluid is very common and is easily differen- ated with acute otomastoiditis, as described earlier. CNS tiated from petrous apex CG; it is nondestructive and complications are also associated with chronic otitis is characterized by long T1 and T2 relaxation times media even in the absence of CH.180 There are three main (Fig. 3.51 and Fig. 3.52). Asymmetric pneumatization categories: (1) abscesses and meningitis, (2) dural herni- may result in some confusion, as fatty marrow on the ations and encephaloceles, and (3) CSF leaks. The pres- nonpneumatized side has similar hyperintensity to chronic ence of either category 2 or 3, of course, predisposes to hematoma (Fig. 3.80 and Fig. 3.81). Again, CT is confirma- category 1. Dural herniations and encephaloceles are well tory, as there is no bony alteration. visualized with CT/MRI (Fig. 3.86). These are most com- Destructive petrous apex lesions may be subtle but monly associated with prior mastoidectomy (vide infra), extremely significant, as metastatic disease has a strong but they may also occur spontaneously often in associa- propensity to develop in this location due to the presence tion with long-standing COM. Labyrinthine fistula and of vascular blood marrow (Fig. 3.82 and Fig. 3.83). facial nerve involvement are commonly encountered. CSF Petrous apex arachnoid cysts may appear identical to leaks may or may not be present. Most can be surgically CH by both CT and MR criteria.177 Petrous apex mucocele corrected using a simple transmastoid repair. Idiopathic is typically associated with long T1 and T2 relaxation encephaloceles (without any predisposing condition) are times and perhaps very modest peripheral contrast rarely reported.181 enhancement (Fig. 3.84).17 8 Obliteration of the communicating cell tracts from the middle ear space is pre- Middle Ear Atelectasis sumed causative. At CT, an expansile lesion with erosive margins may be present.17 9 A history of chronic otitis is Although easily identified otoscopically, CT verification variable. of TM retractions is usually simple, particularly when ch03.qxd 9/23/08 11:37 AM Page 112

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A B

Fig. 3.76 Hemorrhagic granulation tissue. (A) Axial computed tomography (CT). Nonexpanded petrous apex contains debris (arrow). Air cells are developed. (B,C) Axial and coronal T1-weighted magnetic resonance images. Mixed intensity lesion with bright signal periphery (arrow). Patient had sensorineural hearing loss (cause unknown) and a mild fifth nerve palsy. At surgery, only “brownish thin fluid” was found; there were no C cholesterol crystals.

the membrane itself is thickened (Fig. 3.87 and Fig. 3.88). ruling out small (or even large) CHs that may be hidden TM retractions may arise in either the pars flaccida or from the examiner’s view.14 8 the pars tensa and are described clinically as mobile or Pars tensa retractions are more common and may fixed.182,183 Pars flaccida (attic) retractions are of particu- predicate the development of ossicular erosions, partic- lar diagnostic importance due to the propensity for ularly in the vicinity of the incus long process (Fig. 3.91 developing associated acquired attic CH (Fig. 3.89 and and Fig. 3.92).11,13 ,187 Severe retractions extend to the Fig. 3.90).184–186 Many observers believe that this type of cochlear promontory and in complicated cases may retraction may be due in whole, or in part, to associated cause an ossicular discontinuity such that the TM obstruction of the anterior and posterior tympanic becomes adherent to the capitulum of the stapes. This is isthmi, which are responsible for ventilation of the attic, referred to as nature’s myringostapediopexy due to its the antrum, and the remainder of the mastoid. Others physiological similarity with surgically performed type dispute this concept.58 Although the retractions them- 3 tympanoplasty. In these patients there is typically very selves were well visualized, CT is mainly ordered for little audiometric air/bone gap (conductive hearing will ch03.qxd 9/23/08 11:37 AM Page 113

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Fig. 3.77 Petrous apex cholesterol granuloma. (A) Axial computed tomography image. Large erosive mass at the right petrous apex. There is erosion of the carotid canal. Note the normal left carotid canal (arrow). (B) Nonenhanced axial T1-weighted magnetic resonance image. The mass is diffusely hyperintense. (C) Axial T2-weighted magnetic resonance image. The mass is diffusely hyperintense on this sequence as well. The hemorrhagic nature of the mass is indicated by the signal characteristics A (extracellular methemoglobin). (Courtesy of Phillip S. Yussen, MD.)

B C

often be normal or near-normal) (Fig. 3.93). Middle ear obliterating mucosal surfaces (Fig. 3.94, Fig. 3.95, Fig. 3.96, effusions commonly coexist. and Fig. 3.97).188 Four clinical categories of TM retraction have been Another report describes a type I retraction (no contact), described: (I) retraction, (II) retraction with incus con- type II retraction (contact with incudostapedial joint), type III tact, (III) middle ear atelectasis, and (IV) adhesive otitis retraction (contact with promontory), and type IV retraction media.11 Adhesive otitis media refers to a condition in (involvement of facial recess and sinus tympani). These which the middle ear space is totally obliterated and the observers recommend tympanoplasty for those with type II TM adheres to the ossicular chain and promontory, thereby and type IV retractions.189 ch03.qxd 9/23/08 11:37 AM Page 114

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Fig. 3.78 Cholesterol granuloma, petrous apex. (A) Axial CT reveals an expansile lesion of the petrous apex (arrows). (B) Axial T1WI reveals that the lesion is diffusely hyperintense (arrow). Axial T2WI also reveals hyperintensity, indicating chronic hemorrhage (extracellular methemoglobin). There is also a peripheral rim of T2-weighted hyposignal diagnostic of hemosiderin deposition. Note that the mastoid is well pneumatized. These lesions may arise spontaneously or because of long-standing chronic otitis. (Courtesy of Patricia Hudgins, MD.) A

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Fig. 3.79 Petrous apex cholesterol granuloma. (A) Axial and (B) sagittal T1-weighted MRIs (T1WIs), and (C) axial T2-weighted MRI reveal a hyperintense mass consistent with the hemorrhagic by-products visualized in this A lesion. (Courtesy of Dave Yousem, MD.)

B C

extensive mastoid pneumatization.191 The pars flaccida Acquired Cholesteatoma and Complications variety of CH is especially aggressive in children, although CH (“skin in the wrong place”) is an expansile lesion of there is a relatively smaller incidence of this type com- the middle ear or other pneumatized area of the petrous pared with the adult. Both congenital and acquired CHs bone lined by keratinizing stratified squamous epithe- are more common in males. lium.141 CH is actually a misnomer because this lesion is not a neoplasm and may or may not contain cholesterol crystals. Many prefer keratoma, although this term has never been universally accepted.12,184 Table 3.6 Middle Ear Cholesteatoma CHs may be congenital (epidermoid) or acquired % (Table 3.6). About 98% of middle ear CHs are acquired. Congenital 2 Congenital CHs are considered later in this chapter. Acquired 98 Acquired CHs arise from either the pars flaccida or the pars tensa of the TM and may be subdivided into primary Pars flaccida, usually primary acquired 82 acquired (no history of otitis media) and secondary Pars tensa, usually secondary acquired 18 acquired. There is likely a hereditary predisposition, and Posterosuperior (sinus cholesteatoma) 78 individuals of all ages are affected. Often, they are more Anterior and inferior 22 invasive in young children, particularly when there is ch03.qxd 9/23/08 11:37 AM Page 116

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A B

Fig. 3.80 Asymmetric petrous apex pneumatization. (A) Axial computed tomography image reveals a single large right petrous apex air cell (arrow). (B,C) Axial pre- and postcontrast T1-weighted magnetic resonance images reveal fatty signal within the normal marrow of the left C petrous apex (arrows). (Courtesy of Ka-Khy Tze, MD.)

There is an increased incidence in patients with cleft in this latter location grows faster and normally continu- palate, presumably secondary to the anatomic and physi- ously migrates outward, with the cerumen produced in ological differences in these patients. Acquired CH is the lateral cartilaginous portion of the canal. Retraction commonly associated with fibrous dysplasia when the pockets may remain dormant for many years, provided external auditory canal is involved. Patients with bilateral that normal physiological skin migration can occur. CHs have a similar tendency toward recurrence as those The safety of these retractions depends on this normal with unilateral disease. Hearing preservation is often less successful in these patients.192 Table 3.7 Etiology of Acquired Cholesteatoma The etiology of acquired CH is a matter of ongoing de- Retraction bate. There are four major theories (Table 3.7): retraction, papillary proliferation, immigration, and metaplasia.193 Papillary proliferation The retraction theory suggests that CHs arise from Immigration retraction pockets. As already indicated, eustachian tube Metaplasia dysfunction with decreased intratympanic pressure is Source: From Sudhoff H, Tos M. Pathogenesis of attic 11 believed to be responsible for TM retraction. The skin lin- cholesteatoma: clinical and immunohistochemical support for ing the EAC is unique. It lies directly on the periosteum of combination of retraction theory and proliferation theory. Am J the EAC and on the external surface of the TM.141 The skin Otol 2000;21(6): 786–792. Reprinted with permission. ch03.qxd 9/23/08 11:37 AM Page 117

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tial hazard because these lesions provide an excellent medium for bacteria. Another proposed mechanism is papillary proliferation. This theory suggests that epithelial cones invade the subepithelial connective tissue via microscopic defects in the inner layers of the TM.11 This would explain why middle ear CH occasionally occurs without a clinically apparent defect in the TM or result in a secondary perforation. When the TM appears normal, these CHs are presumed by the clinician to be congenital in nature. In practice, it may not be possible to differentiate an acquired from a congenital CH in this context. Recent evidence suggests that neither retraction nor papillary proliferation alone is a likely cause of the majority of acquired CH; presumably, the etiology in a majority of patients is a composite of these two theories.193 Proponents of the immigration theory believe that acquired CH results when keratinized stratified squamous epithelium from the surface of the TM invades Fig. 3.81 Nonpneumatized petrous apex. Axial T1-weighted mag- the middle ear via a TM perforation.11,19 4 These patients netic resonance image. Uniform bright signal (normal bone marrow) have a history of repeated bouts of COM, which dam- is present at the left petrous apex (arrows). Note the absence of mass ages the internal mucosal lining of the TM, allowing effect. Computed tomography showed no air cell development. stimulation of the outer keratinized squamous epithelium to invade the middle ear space and generate CH. migration and physician cleansing.194 Otherwise, kera- There is much disagreement regarding the commonal- tinized debris accumulates, an encrusted plug forms, and ity of this process.59,193 subsequent moisture causes expansion with the develop- The epithelial cells (both squamous and cuboidal) of ment of CH. Superimposed bacterial infection is a poten- the middle ear are pleuripotential and as such may

A B Fig. 3.82 Petrous apex metastatic disease. (A) Axial computed tomography image reveals a subtle destructive lesion involving the petrous apex (arrow). (B) Axial T1-weighted magnetic resonance image with contrast reveals intense enhancement of this lesion (arrow). ch03.qxd 9/23/08 11:38 AM Page 118

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A B

C D Fig. 3.83 Petrous apex metastatic disease. (A,B) Axial computed contrast demonstrates soft tissue abnormality (arrow). (D) Axial T1WI tomography images reveal destructive bony changes at the petrous with contrast demonstrates intense enhancement of this lesion (arrow). apex. (C) Axial T1-weighted magnetic resonance image (T1WI) without

undergo squamous metaplasia to keratinized squamous This space opens posteriorly into the epitympanum. epithelium when stimulated by an inflammatory process.11 There is often medial displacement of the ossicular chain Although interesting laboratory substantiation of metaplasia as the Prussak’s CH expands.182 Most commonly, the mass as a cause for CH has been documented, there are few extends posteriorly via the superior incudal space to the who espouse this theory. posterolateral attic and subsequently further posteriorly Most acquired CHs have typical growth patterns that through the aditus ad antrum into the mastoid antrum depend on their site of origin. These pathways are and central mastoid tract. A less common mode of exten- strongly influenced embryologically by the four endothe- sion is inferiorly via the inferior incudal space to the pos- lial lined sacs previously described (see the Embryology terior tympanic recesses. This latter pathway is more section above). common in children. Direct superior extension is ordinar- Pars flaccida (attic) CHs begin in Prussak’s space ily limited by the lateral malleal ligament. Rarely, exten- (Fig. 3.98, Fig. 3.99, Fig. 3.100, Fig. 3.101, Fig. 3.102, sion is anteriorly and inferiorly into the protympanum, Fig. 3.103, Fig. 3.104, Fig. 3.105, Fig. 3.106, and Fig. 3.107). although the tensor tympani tendon is limiting in this ch03.qxd 9/23/08 11:38 AM Page 119

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B A

Fig. 3.84 Petrous apex mucocele. (A) Axial T2-weighted image reveals diffuse nonspecific bilateral middle ear debris. A hyperintense lesion is present at the left petrous apex (arrows). (B) Axial and (C) coronal enhanced T1-weighted images reveal intense enhancement along the C periphery of the lesion (arrows). (Case courtesy of Dave Yousem, MD.)

A B Fig. 3.85 Cholesterol granuloma, postexploration, drainage. (A) Axial and (B) coronal computed tomography images. Middle ear exploration revealed cholesterol granuloma within the anterior tympanic cavity. A drainage device (arrows) is in place, and there is no evidence of recurrence. ch03.qxd 9/23/08 11:38 AM Page 120

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A B Fig. 3.86 Meningoencephalocele, tegmen tympani defect. (A) Coronal the middle ear. The tegmen is intact of the left (thin black arrow, B). T1-weighted MRI and (B) coronal T2-weighted MRI reveal a tegmen de- There was a long history of bilateral chronic otitis but no history of fect (thin white arrows). A portion of the temporal lobe and accompany- trauma. ing meninges (thick, outline arrows) protrude through the defect into

regard. In fact, the mode of extension of attic CHs de- is also a problem.197 Extension of these lesions is toward pends on the precise embryologic pneumatization of the mastoid antrum via the aditus. Many CHs arising in Prussak’s space, which is quite variable.9,12,195 the pars tensa grow medial to the bulk of the ossicular CHs arising from the pars tensa are usually due to chain and displace these structures laterally (Fig. 3.113).198 posterosuperior retraction pockets (Fig. 3.108, Fig. 3.109, This is in direct contrast to Prussak (pars flaccida) CHs Fig. 3.110, and Fig. 3.111). These lesions will therefore be- (described above), which typically pass lateral to the os- gin in the posterior tympanum and commonly involve sicular mass and displace it medially. CHs extending into the posterior recesses, initially the more lateral facial re- the antrum consistently widen the aditus, often provid- cess and subsequently the more medial sinus tympani.196 ing an important clue to diagnosis.198 CHs confined to the When this medial extension occurs, they are often referred middle ear can give rise to chronic mastoid infection by to as sinus cholesteatomas. Determination of the extent of inhibition of ventilation of the epitympanum secondary these lesions is difficult to visualize otoscopically, but to occlusion of the anterior and posterior tympanic fortunately it is relatively simple with CT, particularly on isthmi. One of the surgical goals in this circumstance is to examination of axial sections (Fig. 3.112). Surgical visibility lyse these adhesions to bring about normal ventilation of

A B Fig. 3.87 Tympanic membrane retraction, pars tensa. (A) Axial and (B) coronal images reveal thickening and retraction of the pars tensa portion of the tympanic membrane (arrows). ch03.qxd 9/23/08 11:38 AM Page 121

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A B Fig. 3.88 Tympanic membrane retraction with thickening. (A) Axial and (B) coronal images reveal substantial thickening and retraction of the tympanic membrane (arrows). No middle ear debris is seen. The mastoid is somewhat sclerotic.

Fig. 3.89 Tympanic membrane retraction, pars flaccida. Coronal com- Fig. 3.90 Pars flaccida retraction. Coronal computed tomography im- puted tomography image reveals a retraction involving the pars flac- age reveals retraction of the pars flaccida portion of the tympanic cida portion of the tympanic membrane (arrow). This patient also has membrane (white arrow). Note the tympanostomy tube (arrow) is a tympanostomy tube within a retracted pars tensa. anteriorly positioned. ch03.qxd 9/23/08 11:38 AM Page 122

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Fig. 3.91 Pars tensa retraction. Axial computed tomography image reveals broad retraction of the pars tensa portion of the tympanic membrane. Note the anteriorly positioned tympanostomy tube (arrow). Fig. 3.92 Tympanic membrane retraction. There is broad retraction of the tympanic membrane (arrows) in this patient with long-standing chronic otitis. The ossicles are intact.

A B Fig. 3.93 Myringostapediopexy. (A) Coronal and (B) axial computed tomography images. There is broad retraction of the tympanic membrane (white arrows) to the head of the stapes. The long process of the incus is absent. ch03.qxd 9/23/08 11:38 AM Page 123

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the entire mastoid. Rarely, CHs may develop anterior to the malleus head in the epitympanum (anterior epitympanic space). Facial nerve involvement at the level of the geniculate ganglion is quite common in this circumstance (Fig. 3.114).45 Petrosal CH, defined as CH medial to the otic capsule, may be congenital or acquired.199 This distinction is aca- demic, as the behavior is identical. There are five subgroups: supralabyrinthine, infralabyrinthine, massive labyrinthine, apical, and infralabyrinthine-apical.200 The term petrosal is preferred to petrous apex, as it encompasses both petrous apex and meatolabyrinthine lesions. There is a strong tendency to recur after surgery, particularly in the region of the intrapetrous carotid artery. Facial nerve morbidity is also quite common (Fig. 3.115). High-resolution CT allows for exquisite delineation of virtually all middle ear and mastoid CHs. The extent of the soft tissue mass and commonly associated complications are easily visualized. The diagnosis is dependent on the identification of bone destruction, a finding typically not present with uncomplicated granulation tis- Fig. 3.94 Severe tympanic membrane retraction (“nature’s myringostapediopexy”). There is retraction of the tympanic membrane to the sue. Small lesions in Prussak’s space or the facial recess stapes head (long arrow). There was no conductive deficit. There is are apparent prior to bony change. In these cases, the perhaps some erosion of the long process of the incus (short arrow). diagnosis is based primarily on location (and clinical There has been no surgery. There was no conductive deficit in this findings).145,201 case. See text on page 112.

A B Fig. 3.95 Chronic otitis media, tympanic membrane retraction. (A) Axial computed tomography image reveals debris throughout the middle ear cleft. The distal incus is poorly seen (arrow) and probably eroded. (B) Axial CT image. (Continued on page 124) ch03.qxd 9/23/08 11:38 AM Page 124

124 Imaging of the Temporal Bone

Fig. 3.95 (Continued) (C) Coronal CT image reveals pronounced retraction of the tympanic membrane (arrows) to the level of the promontory. Findings are difficult to distinguish from perforation on the coronal CT image.

MRI plays a valuable role when defects at the level of nerve involvement and unexplained sensorineural hear- the tegmen tympani or sinus plate are visualized with CT. ing loss.203 If clinically necessary, enhanced MRI can be MRI clearly delineates any epidural extension of CH. Simi- used to distinguish enhancing granulation tissue from larly, protrusion of intracranial contents into the middle nonenhancing CH.162 ear is easily appreciated and crucial to identify (Fig. 3.116, Virtually all complications of CHs are related to bony Fig. 3.117, Fig. 3.118, Fig. 3.119, Fig. 3.120, Fig. 3.121, erosion (Fig. 3.123, Fig. 3.124, Fig. 3.125, Fig. 3.126, and Fig. 3.122).202 Other indications for MRI are facial Fig. 3.127, Fig. 3.128, Fig. 3.129, Fig. 3.130, Fig. 3.131,

A B Fig. 3.96 Tympanic membrane retraction, granulation. (A) Coronal CT reveals retraction of the tympanic membrane (arrows) to the promontory. There is abnormal soft tissue debris. (B) Axial CT image confirms abnormal soft tissue (arrow), representing granulation. ch03.qxd 9/23/08 11:38 AM Page 125

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A B Fig. 3.97 Adhesive otitis media, tympanic membrane retraction. (A) Axial (B) Coronal CT image reveals retraction of the tympanic membrane (arrows) computed tomography (CT) image reveals nonerosive debris throughout to the level of the promontory in this patient with chronic eustachian tube the middle ear. The ossicular chain, including the stapes (arrow), is intact. dysfunction. There are indications of erosion of the incus long process.

Fig. 3.132, Fig. 3.133, and Fig. 3.134). The pathogenesis of (Fig. 3.125, Fig. 3.126, and Fig. 3.127). The ossicles are in- this bony destruction is a subject of controversy. Factors intact in only 10% of pars tensa CHs.196 The long process of volved are mechanical, biochemical, and cellular.1 The sim- the incus and the stapes superstructure are classically plest concept is that of mechanical pressure caused by the eroded first as the lesion extends to the oval window direct effect of the expansion of keratin and associated niche. Pars tensa CHs can invest and resorb the malleus debris.194 Those who believe that stratified squamous ep- handle.207 CT evidence of ossicular erosion has been ap- ithelium by itself cannot erode bone postulate biochemical parent in only approximately one half of our CH cases. The agents such as endotoxins (from regional bacteria) and in- reason for this discrepancy is not clear, but it may be due flammatory granulation tissue result in fibroblast elabora- to early diagnosis, as all of our surgeons are well educated tion of collagenase and acid hydrolase. Other factors include regarding the value of CT. Ossicular erosion occurs roughly highly invasive fibroblasts, enzymatic lysis, and an osteo- twice as often in COM when there is associated CH. 208 clast stimulator. Numerous cytokines and growth factors Labyrinthine fistula is a serious complication of CH are also thought to play a role.184,204–206 Cellular elements and is associated with considerable morbidity. Fistula are associated with osteoclast activity. The bone destruc- without CH in the context of COM is also not rare.209,210 tion/erosion associated with CH quite possibly may be due to the simultaneous effects of all three of these factors. This tendency for bony erosion leads to remodeling of the middle ear cleft as well as associated complications such as ossicular erosion, labyrinthine fistula, facial nerve Table 3.8 Complications of Cholesteatoma canal involvement, petrous apex extension, total hearing Ossicular erosion loss, and automastoidectomy (Table 3.8). Facial nerve invasion The type of ossicular destruction caused by acquired Labyrinthine fistula CH depends on the origin and mode of extension.21,22 The ossicular chain is intact in less than 30% of pars flaccida Petrous apex growth (usually postoperative) CHs. The long process of the incus is the most common site Total hearing loss of involvement, followed by the incus body and malleus Intracranial complications (tegmen/sinus plate defects) head. The classic large pars flaccida lesion amputates the Automastoidectomy latter two structures from the rest of the ossicular chain ch03.qxd 9/23/08 11:38 AM Page 126

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A B Fig. 3.98 Pars flaccida cholesteatoma. (A) Axial computed tomogra- (white arrow) and subtle scutum erosion (black arrow). Incidentally phy image demonstrates soft tissue lesion of Prussak’s space (arrow). noted is the superior malleal ligament (white arrow, B). (B) Coronal CT image reveals mass presenting as an “aural polyp”

A B Fig. 3.99 Acquired cholesteatoma, pars flaccida. (A) Axial and (B) coro- demonstrable retraction pocket. The scutum remains intact. There is a nal computed tomography images reveal a tiny soft tissue mass (single low-lying middle cranial fossa dura (black arrows, B) with absent arrow) located in Prussak’s space that arises within an otoscopically tegmental air cell above the external auditory canal. ch03.qxd 9/23/08 11:38 AM Page 127

Chapter 3 The Middle Ear and Mastoid 127

A B Fig. 3.100 Acquired cholesteatoma, pars flaccida. (A) Axial and malleus head is displaced medially (white arrow, B), but at this time (B) coronal computed tomography images reveal a soft tissue mass in there is no ossicular erosion. Prussak’s space (*) with erosion of the scutum (black arrow, B). The

Fig. 3.101 Acquired cholesteatoma, pars flaccida. Magnified axial computed tomography image, left ear, demonstrates a soft tissue Fig. 3.102 Acquired cholesteatoma, pars flaccida. Axial image reveals mass (arrow) interposed between the ossicular mass and the lateral a soft tissue mass in Prussak’s space (black arrow). There is subtle ero- attic wall without evidence of bone remodeling at this time. sion of the scutum (white arrow). ch03.qxd 9/23/08 11:38 AM Page 128

128 Imaging of the Temporal Bone

A B Fig. 3.103 Chronic otitis, granulation tissue. (A) Axial and (B) coronal where. The pars flaccida (PF, arrow) and the lateral malleal ligament (LML) computed tomography images reveal a soft tissue abnormality within the are intact, and the scutum is normal (white arrow, B). This essentially elimi- attic beyond otoscopic view (black arrows) and patchy debris diffusely else- nates classic pars flaccida cholesteatoma as a possible diagnosis.

COM associated with episodic vertigo, especially notice- Fig. 3.133, and Fig. 3.134).209,211 Associated facial nerve in- able upon otoscopic manipulation, should alert the clini- volvement is reported as high as 29%, defined as either cian to this disorder. A 5 to 10% incidence of fistula in facial canal erosion or preoperative facial weakness. Fistula patients operated for CH is noted by most authors staging may be performed simply by measuring the diame- (Fig. 3.128, Fig. 3.129, Fig. 3.130, Fig. 3.131, Fig. 3.132, ter of the fistula itself. Others categorize by severity of otic

A–C Fig. 3.104 Prussak cholesteatoma, invagination theory. (A) Coronal diagram. Retraction of pars flaccida (arrow). (B) Otoscopic view, diagram. Retraction identified (arrow). (C) Coronal diagram. Cholesteatomatous debris appreciated in sac (arrow). ch03.qxd 9/23/08 11:38 AM Page 129

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A B Fig. 3.105 Cholesteatoma, pars flaccida type, diagrammatical. (arrows). (From Swartz JD. Cholesteatomas of the middle ear. Radiol (A) Otoscopic view (diagram); stippled mass within the pars flaccida Clin Am 1984;22:15–35. Reprinted with permission.) retraction pocket. (B) Sagittal diagram; various modes of spread

capsule destruction. In the preliminary stage there is bone intact. In stage 2, the perilymphatic space is open, and the erosion without disruption of the fluid-filled spaces CH matrix is in contact with the membranous labyrinth. In (perilymphatic/endolymphatic) of the labyrinth.209 In stage 3, there is direct involvement of the membranous stage 1, the endosteal membrane is exposed but remains labyrinth. This staging is of value for the imaging specialist, as awareness of such staging is important for good communication with the surgeon. The most common site of fistula is the lateral semicircular canal (LSCC) due to its proximity in cases of atticoantral CH. The LSCC should be carefully studied in both the coronal and axial planes. Most observers rely on the coronal plane, but in actuality a more complete view of the canal is available on axial imaging; therefore, the observer should rely more on the axial plane if difficulties arise.14 8 The other semicircular canals are involved much less commonly.211 Even less common are cochlear fistulas. These are usually located at the level of the promontory between the round and oval windows and are often the result of posterior tympanic (pars tensa) CH212 (Fig. 3.130 and Fig. 3.131). Determination of the position of the stapes is crucial to the diagnosis of oval window fistula. When a fragment is displaced into the vestibule, the diagnosis is virtually certain.213 There is controversy regarding the surgical management of CH- induced LSCC fistulas, as aggressive removal could result in a perilymphatic fistula, which may be quite difficult to manage.214 Manipulation of the LSCC is believed to be an unlikely cause of cochlear damage, as the utriculoen- Fig. 3.106 Atticoantral cholesteatoma, granulation. Enhanced (Gd-DTPA) axial magnetic resonance image. Thin rind of contrast dolymphatic valve forms a protective barrier between the enhancement in periphery (arrows). Granulation tissue was present in pars superior (semicircular canals, utricle) and the pars this location surrounding the cholesteotoma. inferior (cochlear duct, saccule).215,216 Most observers ch03.qxd 9/23/08 11:38 AM Page 130

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A B Fig. 3.107 Acquired Prussak cholesteatoma. (A) Coronal computed Soft tissue mass in Prussak’s space displaces the ossicular mass medially. tomography (CT) image. There is a soft tissue mass in Prussak’s space There is remodeling of the lateral attic wall (arrow). (triple arrows). The scutum is blunted (single arrow). (B) Axial CT image.

recommend meticulous complete removal in the case of nerve or compression atrophy and is not dependent on small fistulas, but leaving the CH matrix in place within bone destruction.217,218 Inflammatory neuroma is a rare larger fistulas. complication.217 Facial nerve paresis occurs in 1% of CH Facial nerve dysfunction may occur as a complication of patients preoperatively and in this context is often due to acute or chronic otitis media (Fig. 3.115 and Fig. 3.135). This erosion of the intratemporal facial nerve canal, such an ero- may be secondary to direct inflammatory effects on the sion is not uncommon at the level of the anterior tympanic

A B Fig. 3.108 Cholesteatoma, facial recess. (A) Artist’s rendering of poste- vicinity (arrows). (From Swartz JD. Cholesteatomas of the middle ear. rior tympanic cholesteatoma: otoscopic view of mass in posterosuperior Radiol Clin Am 1984;22:15–35. Reprinted with permission.) retraction. (B) Sagittal depiction. Note possible extent of mass from this ch03.qxd 9/23/08 11:38 AM Page 131

Chapter 3 The Middle Ear and Mastoid 131

A B Fig. 3.109 Acquired cholesteatoma, pars tensa. (A) Axial computed tomography (CT) image reveals small soft tissue mass (arrows). (B) Axial CT image (more superior) confirms mass resting on the surface of the pyramidal eminence.

segment.24 Facial nerve paresis is more likely to occur when is poor. Secondary facial nerve dehiscence due to bony ero- there is a congenital facial nerve canal dehiscence. This is sion from the CH is an under-recognized entity.219 This pre- most common at the level of the mid-tympanic segment, disposes the nerve to damage during surgery. within the oval window niche.218 Gradual onset of facial Embryologically, most acquired CHs, particularly the weakness is the typical clinical presentation, and prognosis epitympanic variety, follow the course of the saccus

A B Fig. 3.110 Acquired cholesteatoma, pars tensa. (A) Axial image reveals a soft tissue mass (arrow) in the facial recess. (B) Coronal image confirms the mass (arrow). ch03.qxd 9/23/08 11:39 AM Page 132

132 Imaging of the Temporal Bone

A B Fig. 3.111 Acquired cholesteatoma, pars tensa. (A) Axial computed is absent (arrow), and there is some abnormal soft tissue. At surgery, tomography (CT) image through the middle ear reveals a soft tissue some of the cholesteatoma matrix had drained externally (see text on mass (arrow). The stapedial crura are intact (arrowheads). (B) Axial CT automastoidectomy on page 136). image through the attic reveals an intact malleus head. The incus body

A B Fig. 3.112 Acquired cholesteatoma, pars tensa. (A) Axial computed (CT) tomography image reveals a soft tissue mass with its epicenter in the facial recess (arrow). (B) Coronal CT image at the level of the vestibule reveals intact ossicles (right angle). ch03.qxd 9/23/08 11:39 AM Page 133

Chapter 3 The Middle Ear and Mastoid 133

Fig. 3.112 (Continued) (C) Coronal CT image (more posterior) reveals a soft tissue mass. The sinus tympani (black arrow) and round window niche (outlined arrow) are spared.

medius. When the anterior saccule of the saccus medius enlarging CH has easy access to the first genu. In this develops slowly, the anterior portion of the epitympanum circumstance, the cholesteatomatous mass will be medial is pneumatized by the saccus anticus. Under these to the ossicular chain rather than in its typical location lat- circumstances, the tensor tympani fold is absent, and the erally.204 The anterior epitympanic recess (AER) (supratubal recess) is referred to earlier in the chapter and is typically separated from the attic proper by a bony or fibrous band referred to as the cog. Importantly, this recess is in direct apposition to the proximal tympanic segment of the facial nerve canal. Cholesteatomatous involvement of the AER increases the likelihood of facial nerve symptoms (Fig. 3.136). Other conditions predisposing to facial canal involvement are previous intact canal wall mastoidectomy (posterior epitympanum contiguous with mastoid bowl) and bony occlusion of the aditus ad antrum. CT provides the most highly accurate demonstration of the bony confines of the facial nerve canal; however, in questionable cases, contrast-enhanced MRI may be of great value because inflammatory changes in the involved segment or segments may demonstrate greater than expected enhancement.220 CHs have nonspecific signal intensities. In general, lesions are isointense on T1-weighting and become moderately hyperintense as the TR is lengthened (Fig. 3.106, Fig. 3.115, and Fig. 3.119). Lesions that invade the facial nerve canal may masquerade as schwannoma. Debris elsewhere in the mastoid or the presence of a mastoidectomy cavity will usually lead the observer to the correct diagnosis. Aggressive migration of CH to the petrous apex is also Fig. 3.113 Acquired cholesteatoma. Axial computed tomography image. Localized expansion involving the anterior epitympanic recess a function of the pneumatization pattern, which allows (large arrow) leaves cholesteatoma in direct apposition to the proximal for growth along planes of least resistance (Fig. 3.137 and tympanic segment of the facial nerve canal (long, thin arrow). Fig. 3.138). These patients often have severe headaches ch03.qxd 9/23/08 11:39 AM Page 134

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Fig. 3.114 Cholesteatoma, facial nerve canal invasion. (A) Axial computed tomography image. Mass (*) invades first genu as it courses toward the petrous apex. There is cortical disruption superiorly and anteriorly (arrows). (B) Coronal T1-weighted magnetic resonance image (T1WI). Mass (*) has modest epidural component (arrows). (C) Axial T1WI. Mass (*) is identified (arrows). Compare with the opposite side. The lesion was moderately hyperintense on T2-weighted magnetic resonance C imaging.

as part of their symptom complex possibly due to aspect) of the IAC and is associated with sensorineural meningeal traction.221 Such migration may be infra- hearing deficit. Direct erosion of the cochlear capsule is labyrinthine, anterosuperior, and posterosuperior.206,222 rare, but it does occur on occasion when the CH is espe- The infralabyrinthine route, inferior to the cochlea and IAC, is cially aggressive. Perineural growth along the facial nerve associated with involvement of the clivus and sphenoid is another mode of petrous apex extension.213 Extension sinus. The anterosuperior route is above the cochlea and of acquired CH to the petrous apex is sufficiently unusual IAC, thereby resulting in direct apposition to the middle that often alternative diagnoses are entertained despite cranial fossa (MCF) dura. The posterosuperior route the clinical history. The use of MRI in this circumstance between the limbs of the superior SCC results in should be quite helpful most of the time, as enhance- cholesteatomatous involvement of the fundus (lateral ment of CHs with gadolinium is virtually nonexistent and ch03.qxd 9/23/08 11:39 AM Page 135

A B

Fig. 3.115 Petrosal cholesteatoma. (A) Axial computed tomography image reveals a lobulated destructive mass eroding the cochlear apex as well as the facial nerve canal at the first genu. There is medial extension to the fundus of the IAC (thick black arrow). Note that the mastoid is sclerotic. The lesion erodes the head of the malleus (thin black arrow). (B) Axial T1-weighted magnetic resonance image (T1WI) demonstrates that the lesion is somewhat hyperintense (unexplained). (C) Axial T1WI postcontrast reveals faint enhancement, indicating associated granulation tissue. Note invasion of the cochlea (arrow). (D,E) Axial T2-weighted magnetic resonance image confirms the extent of the lesion as well as cochlear invasion (arrows). (Case courtesy of Deb Shatzkes, MD.) E ch03.qxd 9/23/08 11:39 AM Page 136

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A B Fig. 3.116 Acquired cholesteatoma. (A) Magnified coronal computed basilar turn of the cochlea reveals that the mass extends to the superior- tomography (CT) image of the right ear at the level of the anterior turns most aspect of the attic. The tegmen tympani is thin (double arrows). of the cochlea demonstrates a soft tissue mass (arrow) in Prussak’s The ossicles are intact at this time. Perhaps the cortex over the lateral space. (B) Magnified coronal CT image of the right ear at the level of the semicircular canal is thin (single arrow).

occurs only at the periphery of the lesion. By contrast, images should always be viewed with clinical suspicion in aggressive tumors typically enhance intensely. this regard, as this would place the CH matrix in direct ap- CT is highly useful in guiding the surgical approach position to the dura along the floor of the middle cranial to the aggressive CH. Middle fossa/geniculate involve- fossa. MRI is always recommended in this circumstance. ment dictates a combined transmastoid-MCF approach. Anomalous venous connections between the superficial Translabyrinthine surgery is used when there is involve- middle cerebral vein and the petrosal system may occur in ment of the labyrinth, IAC, posterior fossa, or jugular bulb. this region, potentially complicating surgery.227 A transcochlear approach is needed when extensive As noted previously, the most common CT appearance disease with involvement of the carotid canal and cochlea for acquired CH is that of a homogeneous soft tissue den- is diagnosed.223 sity originating in the attic or facial recess. These are lined Total hearing loss can occur due to petrous apex ex- by keratinizing squamous epithelium that contains vari- tension, labyrinthine fistula, or round window invasion ous by-products associated with bony erosion. Rarely, the with subsequent labyrinthitis.224 The oval window is typ- contents of the interior of the CH may drain and empty ically quite resistant to such invasion. Enhancement of externally, leaving only this aggressive membrane. The the membranous labyrinth with gadolinium is the earli- extensive bony remodeling in the absence of a soft tissue est imaging manifestation of labyrinthitis. There are no mass is strongly reminiscent of mastoidectomy (automas- associated CT findings at this stage. Replacement of the toidectomy). This is often referred to as mural cholesteatoma membranous labyrinth by fibrous or ossific tissue may or, alternatively, as unusual cholesteatoma shell (Fig. 3.139, eventually occur in complicated or untreated cases. CT is Fig. 3.140, Fig. 3.141, see also Fig. 3.111).228 diagnostic in the ossific stage (labyrinthine ossification) (see Chapter 5). Postinflammatory Noncholesteatomatous The serious and potentially fatal complications that Conductive Hearing Loss have been associated with CH prior to the antibiotic era have diminished remarkably. Currently, intracranial com- Most patients with CHD and COM do not have CH. Confir- plications such as meningitis, abscesses, and lateral sinus mation of this fact has probably been the single most thrombosis have been reduced to less than 0.3%.160,225,226 notable contribution of CT and MRI for these patients. The CT has reduced these complications even further by observer must be cognizant of the appearance of the nor- allowing early diagnosis, and we recommend MRI when mal ossicular chain to diagnose focal ossicular erosions such complications are suspected111,112 Associated erosion and postinflammatory ossicular fixation in these patients of the tegmen tympani identified on direct coronal (Table 3.9). ch03.qxd 9/23/08 11:39 AM Page 137

Chapter 3 The Middle Ear and Mastoid 137

Fig. 3.117 Attic cholesteatoma, tegmen defect. (A) Coronal computed tomography (CT) image reveals a soft tissue lesion within the attic beyond otoscopic view. There is erosion of the tegmen tympani (arrow) leaving the lesion in direct apposition to overlying middle cranial fossa dura. (B) Coronal CT image (more posterior) confirms the well- marginated mass (arrow). (C) Axial CT image confirms the mass and associated tegmen defect (arrow) and incidental fluid level (outlined arrow). Magnetic resonance imaging is indicated in these cases as meningoencephalocele must be excluded. A

B C

Ossicular Erosions Fig. 3.149).21,22 Several theories for this bony destruction have been proposed, and histochemical analysis has Ossicular erosion is a well-known consequence of otitis revealed numerous substances capable of bony lysis.25 media both with and without CH (Fig. 3.142, Fig. 3.143, Currently, most researchers believe that multinucleate Fig. 3.144, Fig. 3.145, Fig. 3.146, Fig. 3.147, Fig. 3.148, and osteoclasts or mononuclear histiocytes are primarily 7 Table 3.9 Noncholesteatomatous Conductive Hearing Deficit responsible for these erosions. Other possible mediators are prostaglandins, lipopolysaccharides, and acid phos- Ossicular erosions phatase. The latter enzyme is a well-known marker for Ossicular fixation (misnomer: tympanosclerosis) lysosomal activity. Such lysosomes are likely released Fibrous tissue from mature mononuclear histiocytes.20,229 Capillary Hyalinization of collagen (true tympanosclerosis) proliferation and subsequent high oxygen tension further facilitate bone resorption and enhance the inflammatory New bone formation stimulus and foreign body reaction. ch03.qxd 9/23/08 11:39 AM Page 138

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A B Fig. 3.118 Acquired cholesteatoma. (A) Coronal image reveals an expansile mass in the attic with malleus destruction and blunting of the scutum (arrow). (B) Coronal image (more posterior) reveals erosion of the tegmen tympani (arrows).

The distal incus is clearly the most vulnerable segment the distal incus that would explain such erosion in indi- of the ossicular chain (Fig. 3.142). This has been docu- viduals with COM and resulting mucosal disruption.11 mented in otolaryngologic and radiologic literature. The Importantly, ossicular erosions can be discovered in nature of middle ear vascularity is at least partially either a draining or “dry” ear. At the time of CT study, the responsible. There is a well-known watershed region near middle ear and mastoid may be free of debris; however,

Fig. 3.119 Acquired cholesteatoma, magnetic resonance appearance. (A) Magnified coronal T1-weighted MRI, left ear, reveals an inhomogeneous A mass (*). ch03.qxd 9/23/08 11:39 AM Page 139

Chapter 3 The Middle Ear and Mastoid 139

B C Fig. 3.119 (Continued) (B) Sagittal T1WI reveals mass (*). Intact tegmen (arrow). Well-depicted second genu of the facial nerve canal (double arrows). (C) Coronal T2-weighted MRI reveals a bright signal mass (*). The dura subjacent to the temporal lobe is well visualized (arrow).

the ossicular defects may be well appreciated. A pronounced CHD is usually present.25 Clinically, fenestral otosclerosis may be suspected if the TM is entirely healed.230 The imaging specialist is able to play a very significant role in these cases. As already indicated, there is a distinct propensity for involvement of the long process and lenticular process of the incus. We have encountered erosions of the stapes as well. Defects in the malleus head or incus body are less common. CT recognition of these erosions is important, and the observer must be thoroughly familiar with the normal appearance of the ossicular chain in both the axial and coronal projections to recognize them. On occasion, the normal incudostapedial joint may be replaced by a fibrous band that is usually a poor conductor of sound. In this situation, the incudostapedial articulation as visualized on the axial view may appear unusually wide or even subluxed (Fig. 3.143, Fig. 3.144, and Fig. 3.145).25 Diagnosis of the extent of involvement of the ossicular chain may aid the otologic surgeon in planning the Fig. 3.120 Acquired cholesteatoma, sinus plate destruction. Axial appropriate surgical procedure. The surgeon may select computed tomography image reveals a large destructive mass involv- homograft implantation, incus interposition, or possibly ing the middle ear and mastoid with erosion of the sigmoid sinus plate (double arrows), leaving the lesion in direct apposition to the dura on placement of a total or partial ossicular replacement the surface of the sigmoid sinus. Magnetic resonance venography is prosthesis. These will be discussed in a separate section recommended under these circumstances. of this chapter. ch03.qxd 9/23/08 11:39 AM Page 140

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A B

Fig. 3.121 Acquired cholesteatoma, aggressive. (A) Axial computed tomography (CT) image reveals a massive atticoantral lesion, which has amputated the head of the malleus (black arrow) and the eroded incus body/short process (double black arrows). The cortex over the lateral semicircular canal is intact (white arrow). (B) Coronal CT image reveals obvious destruction of the scutum (arrow) and remodeling of the tegmen (double arrows). (C) More inferior axial image reveals involvement of the mastoid antrum with erosion of the sigmoid sinus plate (arrow). C

Review of the axial CT images at and immediately Ossicular Fixation below the level of the oval window is crucial in these patients due to the propensity for involvement of Postinflammatory ossicular fixation may also develop as a the distal ossicular chain. At this level, two parallel lines consequence of otitis media and result in CHD in the are seen in the normal person. The line most anterior absence of CH.231,232 There are numerous theories that is formed by the tensor tympani tendon and the attempt to explain the pathogenesis of these conditions, malleus neck, and the more posterior line by the lentic- many of which are beyond the scope of this text. ular process of the incus, the incudostapedial articula- Superimposed bacterial invasion results in hyperemia, tion, and the stapes superstructure. Defects in the edema, and cellular infiltration of the mucoperiosteum of “posterior line” are common in these patients (Fig. 3.144, the middle ear. Most cases of AOM resolve; however, with Fig. 3.146, and Fig. 3.147). persistent eustachian tube dysfunction and subsequent ch03.qxd 9/23/08 11:39 AM Page 141

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progression to COM, there is associated columnar metaplasia and goblet cell formation. If the underlying mucoperiosteum is destroyed, polypoid granulation tissue may develop. This granulation tissue may be responsible for noncholesteatomatous erosion (described above). As this granulation tissue regresses, a fibrous, calcific, or bony restriction to ossicular movement may ensue.232,233 Such postinflammatory ossicular fixation has been described by Kinney232 as taking three pathological forms: fibrous tissue fixation (often resulting from adhesive COM), hyalinization of collagen (true tympanosclerosis), and fibroosseous sclerosis (new bone formation).234 The term tympanosclerosis is imprecisely but commonly used for all three of these entities. Fibrous tissue fixation may be generalized or circumscribed. The extent of organization of the exudate and the ability of the middle ear and mastoid to be repneuma- tized constitute the two primary factors that contribute to the degree of fibrosis. As the inflammatory process Fig. 3.122 Acquired cholesteatoma. Expansile soft tissue mass within becomes more protracted, the adhesions may become the mastoid. There is a surgical defect laterally (white arrow). Impor- dense and more permanent. There is a predisposition tantly, there is a defect in the sigmoid sinus plate (black arrow). Mag- for fibrous tissue to develop in the anterosuperior oval netic resonance imaging is useful under these circumstances. window region with subsequent stapes fixation (peristapedial tent). Invasion of the round window may predispose the patient to the development of sensorineural

A B Fig. 3.123 Acquired cholesteatoma, aggressive. (A) Axial computed rotic changes in the vicinity of the malleus head (white arrow). The cortex of tomography (CT) image through the attic reveals a massive lesion (*). There the lateral semicircular canal is intact (double arrows). (B) Axial CT image, are incidental findings most consistent with superimposed tympanoscle- more inferior to (A). The incus body (arrow) is essentially intact.

(Continued on page 142) ch03.qxd 9/23/08 11:39 AM Page 142

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C D Fig. 3.123 (Continued) (C) Coronal CT image reveals destruction of (arrow). (D) Axial CT image through the middle ear reveals an intact not only the scutum but also the entire lateral attic wall (*). The tym- stapes (arrow). panosclerotic changes near the malleus head are again demonstrated

hearing loss (SNHL) due to localized release of toxins ligament of the oval window may result in secondary (serous labyrinthitis).158,232 Involvement of Prussak’s space stapes fixation.239 Repair of this latter process involves may also occur, resulting in lateral fixation of the malleus stapedectomy with prosthesis placement similar to the head and neck. At CT, fibrous tissue within Prussak’s procedure involved for fenestral otosclerosis. Unfortu- space may be identical to early CH.31 The associated con- nately, tympanosclerosis of the annular ligament is ductive hearing loss (CHL) will usually be more severe. associated with the higher incidence of poor surgical Fibrous tissue in the middle ear appears as noncalcific, results.238 Tympanosclerosis of the TM is especially com- nondependent soft tissue debris. Encasement of the ossic- mon.236 CHL is variable in this circumstance. If manubrial ular chain results in CHL. The observer should suspect the fixation is present, movement of the entire ossicular presence of fibrous tissue, as opposed to CH or granula- chain may be restricted. tion tissue when middle ear soft tissue is associated with The CT appearance of true tympanosclerosis is that disproportionate conductive deficit (Fig. 3.148, Fig. 3.149, of unifocal or multifocal punctate or web-like calcific and Fig. 3.150). The TM will often be retracted in these densities in the middle ear cavity, epitympanum, or cases, clearly differentiating the process from CH or neo- tympanum membrane (Fig. 3.151, Fig. 3.152, Fig. 3.153, plasm, which would cause TM bulging. Fig. 3.154, Fig. 3.155, and Fig. 3.156).240 It is important Hyalinization of collagen within the tympanic cavity to remember that this debris may occur without CHD if represents true tympanosclerosis.235,236 Deposition of cal- the debris is not in a position to compromise the ossic- cium and phosphate crystals occurs following fibroblastic ular chain. The observer must be familiar with the invasion of the submucosal layers of the middle ear. The normal anatomic appearance of the suspensory liga- layers of submucosa subsequently thicken and fuse into a ments and tendons to be able to diagnosis abnormal homogeneous mass. Another theory suggests that plaques calcifications (Fig. 3.157, Fig. 3.158, and Fig. 3.159). develop from organized inflammatory exudates originally Tympanosclerosis of the annular ligament or stapes lying free within the tympanic cavity rather than submu- footplate may be difficult to differentiate from atypical cosal tissue reaction.237 The suspensory ligaments and fenestral otosclerosis (Fig. 3.160, Fig. 3.161, Fig. 3.162, tendons of the ossicles may degenerate and subsequently Fig. 3.163, Fig. 3.164, and Fig. 3.165).240 These patients calcify or ossify.238 Ossicular movement becomes restricted. usually have a long history of COM. Ossification of the These calcific secondary unions may be due to osteitis stapedius tendon may be congenital or result from involving the ossicular chain. Involvement of the annular tympanosclerosis. ch03.qxd 9/23/08 11:39 AM Page 143

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A B

Fig. 3.124 Acquired cholesteatoma. (A) Axial computed tomography (CT) image through the attic reveals a soft tissue abnormality within the lateral aspect of the attic (outlined arrow). The ossicular mass (malleus head, incus body/short process) is intact. The lesion extends through the aditus (arrow) into the mastoid antrum (*). (B) Axial CT image through the middle ear reveals that the stapes superstructure (white arrow) is intact. There is an incidental posterior fossa mass related to the vestibular aqueduct (black arrow), quite possibly a calci- fied meningioma or an endolymphatic sac tumor. (C) Coronal CT image confirms the attic lesion. The scutum is blunted (arrow). C

The final pathological category of postinflammatory the epitympanum may be extensive in protracted and ossicular fixation is that of new bone formation. This is neglected cases. also termed fibro-osseous sclerosis.232 This is much All of these pathological entities are characterized by more common in the epitympanum than elsewhere the lack of active drainage. Clinical differentiation from (Fig. 3.166, Fig. 3.167, and Fig. 3.168). Lamellar new fenestral otosclerosis may be difficult if the TM is healed. bone is formed due to the deposition of osteoblasts. This CT is diagnostic in this circumstance. In fact, in the pres- is the least common manifestation of postinflammatory ence of a normal TM, postinflammatory ossicular fixation ossicular fixation. On occasion, fibroosseous sclerosis of has been (clinically) termed pseudootosclerosis.230,241 ch03.qxd 9/23/08 11:39 AM Page 144

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A B Fig. 3.125 Acquired cholesteatoma. (A) Axial image reveals a soft tissue (black arrows) despite the fact that the cog is either absent or destroyed. mass in the attic, which has amputated the head of the malleus (white (B) Coronal CT image reveals that the mass has resulted in thinning of arrow). The cortex over the first genu of the facial nerve is preserved the tegmen tympani (arrow).

Under very rare circumstances, a protruding, dehiscent Surgical Treatment of Inflammatory Disease facial nerve (tympanic segment) can compromise the distal ossicular chain in the oval window niche. The CT Mastoidectomy findings may be confusing and suggest a facial nerve mass The type and extent of middle ear and mastoid surgery (Fig. 3.169). Such a protrusion is not rare and is an often performed for chronic inflammatory disease depend on described hazard of prosthetic stapedectomy. the amount of disease encountered. Each case is therefore

A B Fig. 3.126 Acquired cholesteatoma. (A) Axial computed tomography (double black arrows). (B) Coronal CT image reveals that the attic is image reveals a diffuse atticoantral mass, which has eroded the incus remodeled (double black arrows).The scutum is intact (white arrow). body (white arrow). The cortex over the lateral semicircular canal is intact ch03.qxd 9/23/08 11:39 AM Page 145

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Fig. 3.126 (Continued) (C) Coronal CT image through the antrum reveals the erosion of Koerner’s septum (arrow).

individualized. The object of the procedure is to remove (intact canal wall) mastoidectomy. Simple mastoidectomy all diseased tissue while preserving as much of the nor- was used extensively in the past but has fallen into mal structure as possible. Specifically, an attempt is made disrepute as a treatment for COM except under certain to preserve the bony wall of the external auditory canal circumstances. (EAC) and the ossicular chain (Table 3.10).122,226,242 The canal-wall-up procedure (also referred to as the Mastoidectomy may be categorized into closed cavity facial recess approach) spares the posterior external canal (external auditory canal wall preserved) and open cavity wall with removal of the mastoid air cells, lateral mastoid types (Table 3.11).122,190,242–244 Closed cavity procedures cortex, and Koerner’s septum, and thus creates commu- include simple (cortical) mastoidectomy and canal-wall-up nication of the surgically produced cavity (“mastoid bowl”)

A B Fig. 3.127 Atticoantral cholesteatoma. (A) Magnified axial computed antrum. There is erosion of the incus body. (B) Coronal CT image reveals tomography (CT) image, right ear. There is a soft tissue mass extending that the mass (*) extends into the middle ear cavity proper. The cortex from the attic through the aditus (arrow) into the proximal mastoid over the lateral semicircular canal is intact (arrow). ch03.qxd 9/23/08 11:39 AM Page 146

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A B Fig. 3.128 Acquired cholesteatoma, lateral semicircular canal fistula. diagnostic for labyrinthine fistula. (B) Axial (CT) image confirms a large (A) Coronal computed tomography image reveals a large destructive destructive mass (*), which destroys the cortex of the lateral semicircu- mass (*) destroying the cortex of the lateral semicircular canal (arrow), lar canal (arrow), diagnostic for labyrinthine fistula.

with the attic and antrum (Fig. 3.170, Fig. 3.171, adults) described as high as 50%; however, healing time Fig. 3.172, Fig. 3.173, Fig. 3.174, and Fig. 3.175).245 This is faster and long-term care is easier.243,247 This procedure allows inspection of middle ear contents and is a useful is technically more difficult and residual disease is harder procedure for CH in children with well-pneumatized to detect. For some observers, recurrent CH has been a mastoids.246 Canal-wall-up techniques avoid creation of a much less significant problem.248 Transcanal anterior potentially troublesome tympanomastoidectomy cavity; atticotomy is useful when CH is limited to the attic. An however, this is accomplished at the expense of de- endaural incision is utilized to remove the scutum and creased surgical exposure and recurrence rates (for obliterate the aditus (Fig. 3.176).

A B Fig. 3.129 Acquired cholesteatoma, labyrinthine fistula. (A) Axial and (B) This must be reported to the referring physician. Note the anteriorly coronal images reveal a holotympanic mass with erosion of the cortex positioned sigmoid sinus (S). over the lateral semicircular canal (arrows), indicating impending fistula. ch03.qxd 9/23/08 11:39 AM Page 147

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A B

Fig. 3.130 Acquired cholesteatoma, round window fistula. (A) Axial computed tomography (CT) image reveals an expansile mass with destruction of the ossicular chain. (B) Axial CT image reveals involvement of the round window niche with subtle bone erosion (arrow). (C) Axial CT image (opposite side) for comparison (arrow). C

Table 3.11 Value of Postoperative Imaging of Mastoidectomy Cavity* Table 3.10 Mastoidectomy (Simplified) Assessment of recurrent/residual debris (CT; MRI helpful for Mastoid External Ossicles differential diagnosis) Air Cells Canal Wall (Except Stapes) Determination of type of surgery performed (CT) Intact canal wall X (canal wall up) Status of facial nerve canal (CT; especially mastoid segment) Modified radical X X Assessment of bony margins (CT; tegmen tympani, sinus plate)* (canal wall down) *MRI recommended for meningoencephalocele, epidural Radical X X X cholesteatoma, and sigmoid sinus compromise. (canal wall down) Abbreviations: CT, computed tomography; MRI, magnetic resonance imaging. ch03.qxd 9/23/08 11:39 AM Page 148

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A B

Fig. 3.131 Acquired cholesteatoma, cochlear fistula. (A) Coronal computed tomography image reveals a mass with erosion of the malleus (arrow). (B) Coronal CT image through vestibule reveals focal erosion of C promontory (arrow). (C) Axial CT image confirms erosion (arrow).

Automastoidectomy was discussed in an earlier section With the open cavity (canal-wall-down) procedure, of this chapter. This refers to the nonoperated patient in the posterior wall of the external auditory canal (includ- whom the contents of the CH have drained, leaving only the ing the scutum) is removed, as is the superior attach- outer membrane. Please be aware that an automastoidec- ment of the TM (tympanic annulus). Surgical removal of tomy defect does not necessarily involve the entire mastoid the scutum allows inspection of the attic (epitympa- and may simulate only an atticotomy (“auto-atticotomy”) num). This results in one large cavity corresponding to (Fig. 3.111, Fig. 3.177, and Fig. 3.178). the mastoid, mastoid antrum, epitympanum, and meso- Canal-wall-up procedures are also used to provide tympanum (Fig. 3.182, Fig. 3.183, and Fig. 3.184).244,245 access to the cochlea for cochlear implant, facial nerve The middle ear orifice of the eustachian tube is often decompression, and endolymphatic sac decompression obliterated to prevent exposure of the surgically created (Fig. 3.179, Fig. 3.180, and Fig. 3.181). cavity to the nasopharynx. Canal-wall-down procedures ch03.qxd 9/23/08 11:39 AM Page 149

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allow sufficient exposure for ossicular reconstruction (if required). When the ossicular chain is preserved in a canal-wall-down procedure, it is often referred to as a modified radical mastoidectomy (Fig. 3.182 and Fig. 3.183). This procedure is advocated particularly in the presence of CH localized to the attic and antrum.204,208 Recurrent CH has been reported to occur in as few as 6% of patients. There is continued controversy regarding the use of open and closed techniques. Some surgeons may prefer to take down the EAC with reconstruction by a flexible hydroxyapatite sheet. The CT appearance is reminiscent of a normal EAC wall when correctly osseointegrated.249 Radical mastoidectomy is a more extensive canal-wall- down procedure, which is necessary when there is holo- Fig. 3.132 Extensive middle ear cholesteatoma. Axial computed tomog- tympanic disease.190,250 Further exposure results from raphy image. Diffuse erosive soft tissue mass throughout the left middle careful dissection (skeletonization) of the mastoid ear space extends into a deep sinus tympani (short arrow) beyond surgical inspection. Also note the normal, although extraordinarily deep, segment of the facial nerve canal and removal of diseased sinus tympani (shorter arrow) and the more lateral facial recess (longer ossicles, preferably with the exception of the stapes arrow) with the intervening pyramidal eminence on the right side.

A B

Fig. 3.133 Acquired attic cholesteatoma. (A) Magnified coronal computed tomography (CT) image, right ear, reveals an erosive expansile attic mass resulting in irregularity of the lateral attic wall (arrow) and disruption of the scutum. The malleus is medially displaced. (B) Coronal CT image at level of the vestibule. Saucerization of the lateral semicircular canal is seen with the mass in direct apposition to the membranous labyrinth (arrowhead). Note the extensive expansile mass. (C) Axial CT image. The C fistula is evident (arrow). ch03.qxd 9/23/08 11:39 AM Page 150

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tympanoplasty, can be performed much more easily if such aeration is maintained. Such atelectatic change would be especially dangerous if the TM was adherent to the facial nerve. The CT attenuation and MRI signal characteristics of virtually all debris in the mastoidectomy cavity are nonspecific (long T1 and T2). Granulation tissue cannot be differentiated from recurrent CH with CT. Contrast- enhanced MRI may be useful in this circumstance, as granulation tissue enhances and CH does not. T2-weighted MRI hypointensity may result from hemorrhage or con- cretions resulting from superinfection (Fig. 3.185). Recent reports have indicated that diffusion-weighted imaging may be useful. CH is very bright with DWI due to a combination of restricted diffusion and “T2 shine through.”251 Regardless of the histopathologic diagnosis, the most Fig. 3.134 Large erosive cholesteatoma with extensive fistula. Coronal common location for recurrent debris within the mastoid computed tomography image, left ear, reveals a diffuse erosive/expansile bowl is posterosuperiorly (Fig. 3.12). mass with fistulization into both the superior and lateral semicircular Granulation tissue appears in this context far more canals (arrows). Note that the tegmen is diffusely thinned and irregular. commonly than any other abnormality. On occasion, Magnetic resonance imaging was recommended in this case. cholesterol granuloma (chocolate cyst) is encountered. On CT, this entity appears more well defined in contrast to the irregular jagged margins often caused by other debris.16 8,173 (Fig. 3.184). Some surgeons obliterate the mastoid bowl With MRI, the characteristically short T1 relaxation time with fat to control any potential complications more of this hemorrhagic lesion is of great help in differentiat- effectively. ing this lesion from recurrent CH or simple granulation These procedures may be performed in two stages. tissue (see previous section).147,165 As noted above, some The cavity is created in the first stage, and a Silastic surgeons pack the mastoid bowl with fat, and the bright (Dow Corning, Midland, MI) device is inserted to main- signal encountered on non-fat-suppressed T1-weighted tain aeration and prevent atelectasis with TM retraction MR images can be confused with cholesterol granuloma if (Fig. 3.172 and Fig. 3.175). The second stage, which includes this surgical history is not available (Fig. 3.186).

A B Fig. 3.135 Radical mastoidectomy, recurrent cholesteatoma. (A) Axial undergone prior radical mastoidectomy. Differential diagnosis includes and (B) coronal computed tomography images reveal a well-marginated cholesterol granuloma and perhaps mucocele. lesion (arrows) anterosuperior to the cochlear apex in a patient who has ch03.qxd 9/23/08 11:39 AM Page 151

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A B Fig. 3.136 Acquired cholesteatoma. (A) Axial computed tomography epitympanic recess. See text on page 133. (B) Axial CT image. Oppo- (CT) image. Mass remodels the attic and destroys the ossicular chain, site ear for comparison. “Cog” (arrow); GSPN (within facial hiatus) but it respects the “cog” (arrow) and does not invade anterior (double arrows).

Although not completely specific in a histopathologic amount of soft tissue debris in the middle ear cavity sense, imaging of the postmastoidectomy ear provides proper (particularly in the posterior recesses) are also of other information of greater value.55,245 The type of great interest to the operating surgeon and are easily debris in the cavity matters less than the extent, and identified with good quality CT examination. The ob- careful CT evaluation reveals this information easily server must conduct a careful search for possible fistula (Fig. 3.187, Fig. 3.188, Fig. 3.189, and Fig. 3.190).64 The formation, which may complicate the postoperative status of the bony margin of the mastoid bowl and the course (Fig. 3.190, Fig. 3.191, and Fig. 3.192).

A B Fig. 3.137 Recurrent cholesteatoma extending to the petrous apex. contrast-enhanced T1-weighted image. Enhancement of granulation (A) Coronal computed tomography image. Radical mastoidectomy with tissue in mastoid bowl (single arrow), but no enhancement of the debris in the mastoidectomy cavity but an intact tegmen (arrow). cholesteatoma extending to the petrous apex (double arrows). (Case Erosive changes involving the petrous apex (double arrows). (B) Axial used with permission of the Radiologic Society of North America.) ch03.qxd 9/23/08 11:39 AM Page 152

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A B Fig. 3.138 Aggressive acquired cholesteatoma, left ear. (A) Coronal computed tomography (CT) image. (B) Axial CT image. Mass (*) invades the cochlea (reminiscent of otospongiosis).

Imaging specialists must be aware of the importance of toid surgery. Importantly, this condition can develop in indi- correctly diagnosing encephaloceles. Usually these protrude viduals with a long history of COM without prior surgery. For through tegmen defects and may or may not be associated this reason, study of the tegmen (tympani and mastoideum) with CSF leaks.202,252 Discussion of these entities is included is an important part of the CT examination in all patients here because 80% of these patients have a history of mas- with a surgical history. CH is not necessarily associated.

A B Fig. 3.139 Cholesteatoma, automastoidectomy. (A) Coronal computed The entire mastoid is lined by a paper-thin cholesteatomatous sac. Some tomography (CT) image. The appearance of the middle ear is reminis- bulk is seen in the attic. There is erosion of the lateral semicircular canal cent of a radical mastoidectomy cavity. No surgery has been performed. (arrow). (B) Axial CT image. The fistula is clearly demonstrated (arrow). ch03.qxd 9/23/08 11:40 AM Page 153

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defects are not uncommon in the absence of encephalocele. The dura is a very competent barrier in most individuals. We have identified several tegmen defects in our postoperative case material (Fig. 3.193 and Fig. 3.194). MRI is very useful when such tegmen defects are identified on CT imaging (Fig. 3.195). Coronal imaging is particularly useful in this regard, but often axial images are helpful. Axial CT will also demonstrate the status of the sigmoid sinus plate (Fig. 3.196). If defective, MRI is recommended to evaluate the adjacent cerebellum and sigmoid sinus.253 Identification of the residual ossicular chain (particularly the stapes) and underlying labyrinth is quite useful when reoperation is being considered for inflammatory disease. This is easily accomplished with CT. CT evaluation will also reveal the type and extent of previous mastoid surgery, which is of obvious importance if past medical records are unavailable. Such information may not be immediately apparent even upon clinical inspection of the Fig. 3.140 Cholesteatoma, automastoidectomy. Coronal computed cavity. The surgeon will need to know if any attempt was tomography image. Findings suggest radical mastoidectomy cavity. No surgery has been performed. The entire mastoid was lined by a made at ossicular reconstruction. thin cholesteatomatous membrane. No soft tissue bulk is seen. The status of the facial nerve canal, particularly the mastoid segment, should be addressed when evaluating these scans. If bone has been aggressively removed such that further intervention might compromise this seg- Treatment is surgical and usually intradural when the ment of the nerve, the surgeon should be warned. This encephalocele is large. Temporalis fascia is often suitable for evaluation may have medicolegal complications as well if closure, but some vascularized tissue is needed when CSF a facial palsy is present (Fig. 3.197, Fig. 3.198, Fig. 3.199, leak is a problem. The reader should be aware that tegmen and Fig. 3.200).

Fig. 3.142 Postinflammatory ossicular erosion. Coronal computed tomography image reveals a thickened and retracted tympanic mem- Fig. 3.141 Automastoidectomy. There has been no surgery in this brane. Note that the long process of the incus is absent (double case. The appearance is remniscent of a mastoidectomy (white arrow), arrows). The lenticular process of the incus (and possibly the head of and there is a lateral semicircular canal fistula (black arrow). the stapes) is intact (single arrow). ch03.qxd 9/23/08 11:40 AM Page 154

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tympanosquamous suture). Herniation of the TMJ into the EAC may be spontaneous as the result of trauma, infection, or neoplasia (Fig. 3.201).254 Many reported cases are secondary to otologic surgery performed on patients with chronic otitis media. Interestingly, these patients have few symptoms directly relating to the TMJ; instead, they typically have a fluctuating meatal stenosis. Individuals with congenital persistence of the foramen of Huschke within the tympanic bone may be predisposed to develop this condition.

Tympanoplasty This is a procedure designed to preserve or reestablish conductive hearing function.190,242 There are five basic types, which are classified by the degree of ossicular bypass. Type I tympanoplasty is performed most often for TM perforations in the presence of a normal ossicular chain. CT evaluation of such a procedure is of limited value and is rarely performed, although preoperative Fig. 3.143 Noncholesteatomatous ossicular erosion. Coronal com- study may be useful to exclude underlying middle ear puted tomography image, left ear, reveals retraction of the tympanic abnormality, especially in those individuals with long- membrane and a notch defect in the long process of the incus (arrow) standing COM. Within the first few weeks after the proce- in a patient with conductive hearing deficit. dure, the new TM will appear somewhat thick, but it eventually appears normal.157 The boundaries of this tym- The anterior wall, roof, and part of the posterior wall of panoplasty are the same as those of a normal TM. In a the temporomandibular joint (TMJ) are formed by the type II tympanoplasty the malleus is bypassed, and the squamous portion of the temporal bone. The remainder of graft connects directly to the body of the incus. In a type the posterior wall is formed by the tympanic bone (and III tympanoplasty, the graft attaches to the capitulum

A B Fig. 3.144 Noncholesteatomatous ossicular erosion, incus. (A) Axial The stapes (B, short, thick arrow) is intact. There is no evidence of and (B) coronal computed tomography images reveal absence of the cholesteatoma. Patchy middle ear debris is noted. There was a 40 dB long (B, long arrow) and lenticular (A, long arrow) processes of the incus. conductive deficit and a long history of chronic otitis. ch03.qxd 9/23/08 11:40 AM Page 155

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(head) of the stapes; in a type IV tympanoplasty, to the footplate of the stapes; and in a type V tympanoplasty, the graft attaches to the oval window.122,190,242 The anatomy of these procedures is often definable with CT; however, subtle discrepancies at the attachments may not be apparent. The coronal projection has been most suitable in this regard. CT findings may still have significant clinical import (Fig. 3.202).157

Ossicular Reconstructions Ossicular chain reconstruction is the rebuilding of the middle ear ossicular chain, which has been disrupted or destroyed through the use of some interpositioned device. These procedures are intended to regain the original mechanics of the ossicular chain and convert this mechanical energy into the electrical impulse produced by the cochlea.255

MRI Safety of Prostheses and Implants MRI safety of the stapes prostheses and various other otologic implants is a constant source of concern in day- to-day radiology practice. There are numerous publications on this subject, such as Reference Manual for Fig. 3.145 Noncholesteatomatous ossicular disruption. Artist’s Magnetic Resonance Safety, Implants and Devices by F. G. rendering of ossicular changes. See text on page 139. Shellock.256 For specific inquiries, the reader is referred to

A B Fig. 3.146 Noncholesteatomatous ossicular erosion. (A) Axial computed tomography image reveals absence of the distal incus (thick arrow). (B) More inferior axial CT image reveals a tympanostomy tube (thin arrow). ch03.qxd 9/23/08 11:40 AM Page 156

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Fig. 3.149 Fibrous tissue fixation. Coronal computed tomography image reveals holotympanic debris with retraction of the tympanic membrane (arrows). There was maximal conductive hearing deficit, which differenti- Fig. 3.147 Ossicular erosion. Coronal computed tomography image ates this debris from typical granulation tissue. There is no evidence of al- reveals erosion of the long process of the incus (arrow) in this patient teration of the ossicles or bony margins of the tympanic cavity. with conductive hearing loss and a long history of chronic otitis media (same patient as Fig. 3.88). if specifications are included regarding the field strength in which the testing was performed. The observer should this publication. Anecdotally, there have been reports of be aware that one recent study revealed that virtually MRI safe (nonferromagnetic) devices causing problems as all of these prostheses are nonferromagnetic, whereas well as reports of numerous devices believed to be ferro- another revealed that all stainless steel devices exhibited magnetic actually causing no problems at all. The use of some degree of ferromagnetism at 4.7T.257–259 Both stud- terms such as MRI safe or MRI compatible is only helpful ies concluded, however, that MRI is safe “if performed with caution.” The exception may be those patients who underwent surgery many years before with a device not tested in this study.260 In this medicolegal environment, this is as far as anyone seems willing to go. One of these communications has also recommended a practical way to evaluate a prosthesis using a sterile handheld pace- maker magnet. The reader should keep in mind that movement ex vivo does not necessarily imply movement in vivo as the prosthesis is fixed in vivo three-dimensionally, certainly making movement less likely. Induced magnetism from previous exposure is of concern but is also probably not a factor. Concern about heating of the prosthesis has been lessened over time due to the small size of these devices.

Stapes Prostheses Numerous surgical procedures have been developed to diminish the audiometric air–bone gap in patients with Fig. 3.148 Fibrous tissue fixation. Axial computed tomography image conductive hearing loss. In individuals with stapes immo- reveals holotympanic debris. There was maximal conductive hearing deficit, which differentiates this debris from typical granulation tissue. bility due to otosclerosis, trauma, or postinflammatory There is no evidence of alteration of the ossicles or bony margins of ossicular fixation, this most often involves a stapedec- the tympanic cavity. tomy with insertion of a Teflon (DuPont, Wilmington, DE), ch03.qxd 9/23/08 11:40 AM Page 157

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A B Fig. 3.150 Tympanosclerosis. (A) Axial and (B) coronal computed tomography images reveal diffuse amorphous nonspace-taking debris (arrows), with multiple punctate calcifications appreciated on the axial CT image.

wire, Silastic (Dow Corning, Midland MI), or stainless steel There are numerous possible attendant complications prosthesis (prosthetic stapedectomy). Rarely, labyrinthine of the surgical procedure, including damage to the bone homograft or cadaveric ossicle may be utilized. TM and postoperative otitis media.263–265 The imaging Alternatively, stapedotomy may be performed in which specialist must be familiar with these complications the stapes superstructure (head and crura) are resected, because there is increased risk associated with revision but the footplate is preserved. A prosthesis is then inserted stapedectomy. via a small hole drilled in the footplate of the stapes. This CH formation has been reported as a poststapedec- technique reduced some the complications of stapedectomy risk.266 Round window rupture is an additional tomy, including vertigo and postoperative granuloma. reported complication, although this appears to have no Partial stapedectomy has also been described in which consistent imaging manifestation.267,268 Other poor the footplate and anterior crus, is resected, leaving only surgical results are persistent or recurrent conductive the posterior crus, which is placed over a perichondral deficit, vertigo, and SNHL. Recurrent CHD may result graft.261 In most cases, the lateral aspect of the prosthesis from incus necrosis, prosthesis subluxation, granuloma attaches to the long process of the incus. If the prosthesis development, or postoperative tympanic fibrosis.269 is too long, attachment to the malleus handle is also pos- Postprocedural vertigo is especially problematic and may sible. All of these devices have a characteristic CT appear- result from incorrect position of the prosthesis, perilym- ance (Fig. 3.203, Fig. 3.204, and Fig. 3.205).262 Stainless phatic fistula, and incus necrosis with secondary pros- steel devices are easily appreciated in both the coronal thesis dislocation. and axial projections (Fig. 3.206 and Fig. 3.207). Pressure necrosis may occur within the long process at Both subluxation and graft lateralization can thus be read- the site of prosthesis attachment. Elderly patients appear ily identified (Fig. 3.208, Fig. 3.209, Fig. 3.210, and Fig. 3.211). more predisposed.265,270–272 The focal defect in the long Most prostheses are far more easily recognized in the axial process can only be appreciated on direct coronal images.262 projection utilizing overlapping sections, similar to the CT A wire prosthesis may also slip inferiorly along its incus procedure performed for the evaluation of fenestral oto- attachment (loose wire syndrome). Interestingly, there may sclerosis (see Chapter 5). Our findings have indicated that be temporary improvement in hearing in these patients the prosthesis need not be centrally located within the oval after middle ear inflation due to pressure generated through window to be effective; however, identification of the tip the eustachian tube, which “pushes” the wire superiorly. of the prosthesis superficial or deep to the oval window Prosthesis subluxation is the most common repairable membrane should be viewed with suspicion.262 cause of prosthetic failure and is seen in 50 to 60% of patients ch03.qxd 9/23/08 11:40 AM Page 158

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A B

Fig. 3.151 Tympanosclerosis. (A) Axial and (B,C) coronal computed tomography images reveal a sclerotic mastoid, indicating chronic eustachian tube dysfunction. There is amorphous, nonspace-taking debris throughout C the middle ear cleft with numerous areas of calcification (arrows).

who present with recurrent conductive deficit. This subluxation is usually posterior and inferior.64,263,273 This is best appreciated with axial CT when the wire prosthesis has been used. Subluxation of a bulkier prosthesis may also be appreciated in the coronal projection.262 Adjacent soft tissue reaction typically makes the prosthesis less visible. Malleoincudal dislocation may occur, particularly when there is regrowth of otosclerotic bone about the oval window. This is relatively easy to diagnose by CT criteria.31 Secondary torsional stresses are believed to be responsible.273 The appearance may be identical to that which occurs secondary to trauma (see Chapter 6). Our findings indicate that no postoperative soft tissue Fig. 3.152 Tympanosclerosis, ossicular fixation. Magnified axial com- debris should persist near the oval window after 4 to puted tomography image of the left ear demonstrates debris within the lateral aspect of the attic and throughout the mastoid antrum. There is 6 weeks. When such an abnormality is discerned on CT in an area of calcification interposed between the incus body and the lat- the presence of a persistent or recurrent CHL, granuloma eral attic wall (arrow). formation or tympanic fibrosis may have intervened. ch03.qxd 9/23/08 11:40 AM Page 159

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A B Fig. 3.153 Atticotomy defect, tympanosclerosis. (A) Axial and (B) coronal present with areas of calcification (smaller arrows), consistent with true computed tomography images reveal that the patient is postatticotomy tympanosclerosis. The stapes superstructure appears to be at least (white arrow) for Prussak cholesteatoma. Residual middle ear debris is mostly intact.

These complications may result from immunologic sensi- or SNHL.263,264,271 The symptoms are usually self-limited. tivity or surgical trauma to the mucoperiosteum.263,264,271 When symptomatology of this type is persistent or recurring, Serous labyrinthitis is relatively common in the immedi- perilymphatic fistula, a more serious complication, should ate postoperative period and may result in transient vertigo be suspected (see Chapter 5).274,275 In this circumstance,

A B Fig. 3.154 Tympanosclerosis, middle ear effusion. (A) Magnified axial dal complex. (B) Magnified coronal CT image of the left ear confirms ossi- computed tomography (CT) image of the left ear reveals an area of ossifi- fication (thick arrow). The distal incus is also absent (thin arrow; same cation along the lateral attic wall (arrow), which was fixing the malleoincu- patient as Fig. 3.59). ch03.qxd 9/23/08 11:40 AM Page 160

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A B Fig. 3.155 Intact canal wall mastoidectomy, tympanosclerosis. (A) Axial appears less distinct due to tympanosclerotic infiltration. The distal incus and (B) coronal computed tomography (CT) images reveal an intact is destroyed (arrow, B). canal wall mastoidectomy. On the axial CT image, the ossicular mass

there is an abnormal communication between the inner ear middle ear, depending on the pressure dynamics within the (utricle or saccule within the vestibule) and the middle ear. vestibule itself.271 Such a fluid level is obviously nonspecific, This may result from contraction of aging fibrous tissue or although it must be viewed with suspicion in the appropri- barotrauma. The hearing loss may be mixed or predomi- ate clinical circumstance. Alternatively, a pneumolabyrinth nantly sensorineural. Vertigo and dizziness are associated. may result.278 Air bubbles at the tip of the prosthesis repre- Symptoms typically fluctuate. Meningitis may rarely develop sent an indirect sign of perilymphatic fistula.57 as a secondary complication.276,277 CT diagnosis is difficult. Similar symptomatology may result from abnormal Fluid (perilymph) may present as a fluid level within the protrusion of the prosthesis into the vestibule with resultant

A B Fig. 3.156 Cholesteatoma, tympanosclerosis. (A,B) Axial computed tomography (CT) images reveal an aggressive mass (*). There is tympanosclerotic encasement of the ossicular mass (arrow, A). Intact stapes superstructure (small arrow, B). ch03.qxd 9/23/08 11:40 AM Page 161

Chapter 3 The Middle Ear and Mastoid 161

Fig. 3.156 (Continued) (C) Coronal CT image confirms ossicular encasement (arrow). Note the tympanostomy tube (same patient as Fig. 3.123).

penetration of the utriculosaccular organ. CT in this cir- Postoperative labyrinthitis in its early stages also is cumstance can be diagnostic (Fig. 3.212). devoid of CT manifestations; however, if this persists for a Poststapedectomy dizziness may also result from en- long period, labyrinthine replacement may develop. Such dolymphatic hydrops and fibrous adhesions within the replacement is initially fibrous, but it eventually becomes vestibule. These may have no imaging manifestations. ossific. CT in this circumstance is diagnostic when this

Fig. 3.158 Tympanosclerosis, labyrinthine fistula. Axial computed tomography section, left ear. There is debris throughout the entire middle ear cleft with multiple calcifications indicating tympanosclero- Fig. 3.157 Magnified axial computed tomography image of the left ear sis (small arrows). There is obvious erosion of the cortex of the lateral demonstrates calcification of the anterior mallear ligament (arrow). semicircular canal (outlined arrow). ch03.qxd 9/23/08 11:40 AM Page 162

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historic interest. Perhaps the most commonly encountered of these is fenestration of the lateral semicircular canal.279,280 This entity must not be confused with acquired fistula formation.

Ossiculoplasty Long-standing inflammatory disease with or without CH may result in extensive compromise/destruction of the ossicular chain, necessitating ossiculoplasty. Homo- graft ossicular implants are available in donor banks. These are obtained from cadavers or from patients who have undergone labyrinthectomy. Cadaveric materials are used much less frequently today due to the threat of AIDS. Alternatively, the surgeon may wish to resculpt the exist- ing ossicles. The most common of these procedures is the incus interposition.122,138,281,282 Provided that the majority of the incus is preserved in an individual with an undam- aged stapes, the incus may be disarticulated from the malleus and altered by drilling a depression on the under- Fig. 3.159 Tympansclerosis. Magnified axial computed tomography surface of its body or upper surface of the short process in image of the left ear demonstrates thickening and calcification of the such a way that the stapes capitulum (head) fits into a stapedius tendon (arrow). depression adjacent to the short process. The modified and repositioned incus transmits sound directly from the replacement has progressed to the ossific stage (see manubrium of the malleus to the stapes. A homograft Chapter 5). MRI may demonstrate fibrous replacement incus may be used in the same manner. Overall, this proce- and has been proven useful in patients with subacute dure is used much less frequently; however, it remains labyrinthitis (enhancement of the membranous labyrinth, extremely important for the observer to be aware of the see Chapter 5). appearance of the incus interposition graft. In these Other types of surgery for otosclerosis have been patients, the CT appearance is indistinguishable from a dis- developed prior to prosthetic stapedectomy, which are of located incus occurring secondary to trauma (Fig. 3.213

A B Fig. 3.160 New bone formation, postinflammatory fixation. (A) Axial and (B) coronal computed tomography images. Ossification coats the surface of the lateral semicircular canal (arrow, B) and encases the ossicular mass (arrow, A). ch03.qxd 9/23/08 11:40 AM Page 163

Chapter 3 The Middle Ear and Mastoid 163

A B Fig. 3.161 Tympanosclerosis, oval window. (A) Axial and (B) coronal images reveal nonerosive, nonexpansile holotympanic debris and intact ossicles. Note the ossific occlusion of the oval window (arrows).

and Fig. 3.214).31,157,270 These grafts may therefore result in depicted with CT (Fig. 3.215, Fig. 3.216, and Fig. 3.217). considerable confusion to the uninitiated, and clinical Two variants on this procedure have been described over correlation is critical. CT is ideally suited for visualization the last 10 years.282 The first is the “notched incus with short of the graft, but obviously it cannot guarantee a function- process” procedure, which is used when the stapes super- ing interface or determine the clinical success or failure of structure is intact. The long process of the incus is this procedure. Encased and dislocated grafts are also well removed, and a small cup is formed to fit the head of the

A B Fig. 3.162 Tympanosclerosis, oval window. (A) Axial and (B) coronal computed tomography images reveal nonerosive, nonexpansile holotympanic debris and intact ossicles. Note ossific disease within the oval window niche (arrows) surrounding the stapes superstructure. ch03.qxd 9/23/08 11:40 AM Page 164

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Fig. 3.165 Postinflammatory ossicular erosion, tympanosclerosis. Coronal computed tomography image, right ear, at the level of the vestibule reveals the absence of the long and lenticular process of the incus (larger arrow) in a patient with conductive deficit and a long his- Fig. 3.163 New bone formation, attic and tympanosclerosis, oval tory of chronic otitis. Tympanosclerotic thickening of the stapes foot- window. Coronal computed tomography image in a patient with a plate (smaller arrow) is also noted. long history of chronic otitis media and severe conductive deficit reveals ossific encasement of the attic (multiple arrows) and occlusion of the oval window (single arrow).

stapes. The “notched incus with long process” procedure Synthetic materials are currently extremely popular. is used when the stapes superstructure is absent. In this Research by biomedical engineers resulted in the develop- case, the lenticular process of the incus is removed, and ment of a biocompatible polytetrafluoroethylene-vitreous the long process is articulated with the footplate. carbon (Proplast; Dow Corning, Midland, MI) and a high-density polyethylene sponge (Plasti-Pore; Smith & Nephew plc, London, UK). Plasti-Pore is much more commonly used. A polymer of hydroxyapatite and polyethylene (HAPEX; Smith & Nephew) has also been developed. These substances can be tooled to a variety of shapes and are referred to as total and partial ossicular reconstructive prosthesis (TORP and PORP, respectively). The TORP conducts sound directly from the newly formed TM to the oval window. A PORP is used in an individual in whom the stapes superstructure is maintained. The device is placed between the TM (less commonly the incus long process) and the stapes head (capitulum). Failure rates are generally less than 10%, depending on the surgical criteria. Such fail- ures are caused by extrusion, cartilage resorption with graft lateralization, and fibrous adhesions.269,283–285 These grafts are obliquely placed, and visualization in a single CT section is often not possible. They are thicker and of lower density than the normal incus. TORPs and PORPs consist of a head and a shaft. The head is composed of hydroxyapatite, a calcium phosphate polymer that has the capacity to form bonds with living bone and efficiently conducts vibratory energy.286 Hydroxyapatite is biocompatible, allowing TM contact without the use of requisite tissue graft. The shape of the Fig. 3.164 Tympanosclerosis, oval window. Axial computed tomography image reveals nonerosive debris throughout the middle ear. Note prosthetic head depends upon the presence or absence of calcification in the oval window niche surrounding the stapes super- the manubrium of the malleus. If the manubrium is present, structure (arrow). There was a 40 dB conductive hearing deficit. the head of the prosthesis will have a notch to support ch03.qxd 9/23/08 11:40 AM Page 165

Chapter 3 The Middle Ear and Mastoid 165

A B Fig. 3.166 Ossicular fixation, lateral attic wall. (A) Axial and (B) coronal computed tomography images reveal ossific debris (arrows) along the lateral attic wall, resulting in ossicular fixation and conductive deficit.

the manubrium, which helps to prevent subluxation. The Applebaum prosthesis is designed to correct con- If the manubrium is absent, the head of the prosthesis ductive deficit resulting from incudostapedial disruption will be flat or egg-shaped to maximize TM contact. The caused by trauma or chronic otitis media. This prosthesis shaft of the prosthesis is usually made of Plasti-Pore or forms a bridge between the incus long process and the various polymers. These materials are easily trimmed and head (capitulum) of the stapes. The prosthesis is L-shaped, cut to a variety of shapes and sizes to suit the anatomy of with depressions to fit the incus long process at one end each patient. CT appearances are varied and depend upon and the stapes head at the other. This prosthesis has a the type of device and the surgical technique (Fig. 3.218, characteristic appearance (Fig. 3.219). Fig. 3.219, Fig. 3.220, Fig. 3.221, Fig. 3.222, Fig. 3.223, Fig. 3.224, Fig. 3.225, Fig. 3.226, Fig. 3.227, Fig. 3.228, Fig. 3.229, Fig. 3.230, Fig. 3.231, Fig. 3.232, Fig. 3.233, Fig. 3.234, Fig. 3.235, and Fig. 3.236). The reader should be aware of the most commonly used prostheses. These include the Applebaum, Black Oval-Top, Richards, and Goldenberg.

Fig. 3.168 New bone formation. Coronal computed tomography image. Fig. 3.167 Postinflammatory ossicular fixation (arrows). Magnified Bony mass in the round window niche (arrow). Patient status postradical coronal computed tomography image, left ear. mastoidectomy. ch03.qxd 9/23/08 11:40 AM Page 166

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Fig. 3.171 Canal wall-up mastoidectomy (facial recess approach). Axial computed tomography image reveals a canal wall-up mastoidectomy Fig. 3.169 Facial nerve dehiscence, conductive deficit, coronal com- cavity (*) performed for facial recess (arrow) exploration and excision puted tomography image. There is obvious inferior protrusion (arrow) of cholesteatoma. of the facial nerve (tympanic segment) into the oval window niche. This should not be confused with postinflammatory debris (compare Fig. 3.28).

not only is unstable but also obstructs the surgeon’s view The Black Oval-Top prosthesis has a horseshoe shape of the shaft. Extrusion rates are in the 3–7% range and oc- that bypasses the malleus.286 Although many patients cur most commonly in those patients with inadequate have benefited from the use of this device, there are sev- middle ear ventilation. eral problems with the design that have limited its use There are several versions of the Richards prosthesis (Fig. 3.218, and Fig. 3.236). The articulation with the TM (Fig. 3.231, Fig. 3.234, and Fig. 3.235). The flat head may be centered or off-centered. The shaft is hollow, allowing for its characteristic appearance. Encasement of the prosthesis by recurrent CH or granulation tissue results in dampening of sound transmission. The Goldenberg prosthesis also has a flat head, but unlike the Richards device, the shaft is off-centered, which is often preferred by the surgeon because it allows increased visibility. This off-center design, however, results in a somewhat increased risk of subluxation. Retraction of the TM results in a tendency of the prosthesis to angle and migrate (Fig. 3.220, Fig. 3.221, Fig. 3.222, and Fig. 3.233). Surgeons are less concerned with the manufacturer than the usefulness of the specific device. The prosthesis is usually selected at the time of surgery after viewing the exposed middle ear cavity with the operating microscope. CT is also the study of choice for the evaluation of the patient with recurrent symptomatology. Dislocated, extruded, lateralized, and encased prostheses are all well visualized with high-resolution CT techniques (Fig. 3.223 to Fig. 3.236). Frank dislocations are usually easy to diag- Fig. 3.170 Intact canal wall (canal wall-up) mastoidectomy. Axial com- nose, particularly with the TORP. Fibrous adhesions are puted tomography image reveals a well-demarcated mastoid cavity (*) without evidence of recurrent disease. The external auditory canal also well visualized but may paradoxically impede iden- wall (white arrows) is preserved. tification of the device itself.285 ch03.qxd 9/23/08 11:40 AM Page 167

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described below if otitis media and mass lesion have been ruled out. As we will discuss in Chapter 5, CHD in a young adult in the absence of a mass lesion or a history of chronic otitis is quite possibly caused by otosclerosis.

Oval Window Atresia/Congenital Stapes Fixation Most observers believe that oval window atresia (congenital oval window nondevelopment, congenital absence of the oval window) occurs when the primitive stapes fails to fuse with the primitive vestibule during the seventh week of gestation and results in absence of the cleavage plane between the lateral semicircular canal above and the cochlear promontory below.287,288 Another theory is that during the fifth to sixth week of gestation, the developing facial nerve is displaced and interposed between the primitive stapes and the otic capsule, resulting in lack of contact between these structures and oval window Fig. 3.172 Canal wall-up mastoidectomy (facial recess approach), developmental failure. Silastic implant. Axial computed tomography image reveals a canal Regardless of etiology, the stapes and incus lenticular wall-up (intact canal wall) mastoidectomy (*). There is a Silastic implant (arrows) in place to prevent adhesions prior to a second look and process are anomalous, and the facial nerve is malposi- tympanoplasty. tioned (inferomedially).287–289 Importantly, the external auditory canal is entirely normal. These patients present with maximal conductive deficit and typically have no sig- Nonneoplastic Congenital Conductive nificant history of otitis media (Fig. 3.237, Fig. 3.238, and Hearing Deficit Fig. 3.239). Surgery (vestibulotomy with TORP or stapes prosthesis) is difficult, as there are few landmarks for the In this section, we consider CHD unassociated with mass vestibule, and the location of the facial nerve creates a lesion. As such, this section will include discussion of oval significant obstacle. Oval window atresia is rare and may window atresia, isolated congenital ossicular anomalies and occur bilaterally in 40% of patients.290–292 CT diagnosis of CHDs associated with a named syndrome. CHD diagnosed this entity is best made in the coronal projection. The round early in life is quite likely caused by one of the conditions window is also best seen in this manner. Detailed evaluation of the remainder of the ossicular chain, particularly the stapes, necessitates overlapping axial sections as well. Oval window atresia should not be confused with congenital stapes fixation (vide infra). Recall that the normal oval window consists of the stapes footplate and the annular ligament. Congenital stapes fixation results when the stapes forms normally, but the annular ligament does not develop.288 This results from the lack of differentiation of the lamina stapedialis into the annular ligament with subsequent footplate ankylosis.293 CHL diagnosed early in life is far more likely to represent congenital stapes fixation than otosclerosis, which is rare in this age group. A definitive CT diagnosis of congenital fixation may not be possible because the footplate itself cannot be discerned from the adjacent annular ligament. CT diagnosis is only possible when the structures are physically thickened. We have had occasion to see several cases in which stapes fixation was found at surgery and the CT scan appeared completely normal (Fig. 3.240). It is our recommendation Fig. 3.173 Canal wall-down mastoidectomy, tissue collapse. There has been an open-cavity procedure (canal wall down). Mastoid debris is actu- that such a diagnosis be suggested in the appropriate ally a collapse of overlying soft tissue to fill a cavity (*) rather than recur- clinical circumstance (unexplained documented congeni- rent/residual debris. The graft extends to the stapes head (arrow). tal CHD) in the presence of a normal CT scan. Associated ch03.qxd 9/23/08 11:40 AM Page 168

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A B

Fig. 3.174 Intact canal wall (canal wall-up) mastoidectomy. (A) Axial and (C) coronal computed tomography images reveal a mastoidectomy defect (*) with an intact external auditory canal wall (arrows). (B) Axial CT image through the attic confirms an intact malleus head and incus C body. There is no evidence of residual cholesteatoma.

developmental arrest of the adjacent stapedial anlage considered in Chapter 2. Congenital ossicular anomalies would produce deformity of the crura themselves (stapes (COA) without accompanying external ear malformation superstructure). This is well defined on CT. Congenital are much less common.296 CHD is the predominant symp- stapes deformity is associated with salivary choristomas of tom, and fenestral otosclerosis is usually the major differen- 294 the middle ear. Stapedial fixation has also been associ- tial diagnostic consideration in the adult patient. The lack 295 ated with aberrant ICA and persistent stapedial artery. of progression of the hearing loss and an early age at diagnosis represent clinical clues in favor of COA. CT may thus be quite enlightening when performed preoperatively. Isolated Congenital Ossicular Anomalies When bilateral, these anomalies are probably inherited Ossicular deformities and resulting conductive deficit are via autosomal dominant transmission. When unilateral, commonly associated with EAC dysplasia and as such are they are typically sporadic and isolated.297 ch03.qxd 9/23/08 11:40 AM Page 169

Chapter 3 The Middle Ear and Mastoid 169

A B Fig. 3.175 Mastoidectomy, Silastic tube. (A) Coronal and (B) axial computed tomography images reveal a canal wall-up mastoidectomy. A Silastic tube (arrows) has been inserted as part of the first step of a two-step tympanoplasty procedure. (Courtesy of Timothy L. Larson, MD.)

Congenital ossicular anomalies (without associated fixation.301 The former is more common and may be external canal dysplasia) are classified as follows: isolated due to failure of annular ligament development or due stapedial ankylosis (class I), stapedial ankylosis with to annular ligament ossification. The latter is more easily other ossicular anomalies (class II), ossicular anomalies demonstrable at CT. with a mobile stapes (class III), and oval/round dysplasia Incudostapedial disconnections are the most common (class IV).82,271,298,299 Class III defects (mobile stapes) are isolated congenital ossicular deformity both in the litera- often associated with epitympanic fixation.300 ture and in our experience (Fig. 3.241, Fig. 3.242, Fig. 3.243, Isolated congenital stapes ankylosis (class I) may be and Fig. 3.244).82,138,282,302,303 The long process of the incus is subdivided as either footplate fixation or suprastructure absent or appears elongated and more posteriorly oriented

A B Fig. 3.176 Recurrent cholesteatoma, atticotomy defect. (A) Coronal (B) Axial image reveals soft tissue mass (*; recurrent cholesteatoma) computed tomography image reveals an atticotomy defect (arrow) eroding the lateral attic wall and anterior portion of tegmen (long, thin after removal of the scutum. There is abnormal soft tissue along the arrow). superolateral attic wall with thinning of the tegmen (long, thin arrow). ch03.qxd 9/23/08 11:40 AM Page 170

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as the stapedial anlage cells appear around the primitive stapedial artery (see Chapter 4). The articulation is formed when the anlage of the long process swings toward the stapedial ring to fuse with the future capitulum (head) of the stapes. Congenital nonunion of the incus and stapes occurs due to improper development of the long process of the incus rather than lack of development of the head of the stapes. There is a common association of abnormalities of the long process with anomalies (including absence) of the stapes superstructure. The status of the stapes must be carefully evaluated preoperatively due to the implications for surgical reconstruction. Because the stapes footplate cannot be distinguished from the annular ligament on CT, careful attention must be paid to relative oval window thickness. The malleus will usually be normal in this group of patients. CT in both the coronal and axial projections is required for diagnosis.82,83 The least common category of COA is that which includes malleus and incus fixations (Fig. 3.245 and Fig. 3.246). Although these anomalies are common when associated with EAC dysplasia (see Chapter 2), they occur Fig. 3.177 Automastoidectomy. Coronal computed tomography image reveals erosion of the scutum and some abnormal soft tissue medially. only uncommonly on an isolated basis. The malleus bar is The lateral attic wall appears vacant (*).The malleus is also eroded and a rare cause of congenital conductive deficit.305 This has displaced medially (arrow). There has been no surgery in this case. At been described interposed between the malleus neck and surgery, there was an extensive cholesteatoma membrane, which had the posterior tympanic wall. Differentiation from postin- drained externally (automastoidectomy, “auto-atticotomy”). flammatory fixation may be difficult in the individual case, particularly if the ossification is in the approximate than normal with respect to the oval window. The incud- location of a tendon or ligament.138 Ankylosis of the incus, ostapedial articulation develops between the sixth and the scutum, and the tegmen has been reported.306 Under eighth weeks of fetal life entirely from the second arch.304 normal circumstances, the malleus and incus become The formation of the stapedial ring occurs by the sixth week separated while in their precartilaginous stage when a

A B Fig. 3.178 Cholesteatoma. There had been no surgery in this case. (A) (arrow). Surgical exploration revealed erosive cholesteatoma lining the Coronal computed tomography image reveals that the scutum is membrane; however, the squamous contents had drained externally absent (arrow). (B) Axial CT image reveals erosion of the incus body (autoatticotomy). ch03.qxd 9/23/08 11:40 AM Page 171

Chapter 3 The Middle Ear and Mastoid 171

Fig. 3.178 (Continued) (C) Axial CT image reveals that the lateral attic wall has been remodeled (arrow).

zone of undifferentiated mesenchyme is interposed.304 genital incudomallear ankylosis is sufficiently rare that The malleoincudal articulation forms in this manner. Fail- concomitant associated otosclerosis or chronic otitis ure of this separation would obviously result in fusion. media should always be considered.307 The axial CT projection would be the most valuable for When the diagnosis of congenital stapes fixation is diagnosis, as it is when the anomaly is associated with suspected, the inner ear must be very carefully studied deformity of the external auditory canal.83 Isolated con- with CT. When inner ear anomalies are encountered, the

A B Fig. 3.179 Canal wall-up mastoidectomy, endolymphatic sac decom- There is a surgical defect in the posterior wall of the cavity (arrow, A). pression. (A,B) Axial computed tomography images reveal a canal A portion of the shunt device is noted (arrow, B). (Courtesy Timothy wall-up mastoidectomy defect (*). This was performed for the purposes L. Larson, M.D.) of endolymphatic sac decompression in a patient with Meniere’s disease. ch03.qxd 9/23/08 11:40 AM Page 172

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A B

Fig. 3.180 Canal wall-up mastoidectomy, labyrinthectomy, cochlear image through the middle ear reveals an intact canal wall, labyrinthec- otosclerosis. (A) Axial computed tomography image through the attic tomy defect (thick white arrow), and cochlear otosclerosis (short black reveals a mastoidectomy and surgical labyrinthectomy defect (thick arrows). (Courtesy of Timothy L. Larson, MD.) white arrow) as well as cochlear otosclerosis (short black arrows). (B) Axial

surgeon must be cautioned against stapes surgery due deformity has an X-linked mode of inheritance. A similar to the high associated incidence of profuse perilymph deformity (stapes, IAC) was described with otopalatodigi- flow upon surgical manipulation, the perilymphatic tal syndrome.293 Concurrent SNHL may serve as an effec- “gusher.”308,309,310 The “bulbous” IAC with nondevelopment tive clinical warning. Deformity of the cochlear aqueduct of lateral bony margin has been demonstrated to be strongly has fallen into disrepute as a potential cause of gusher, de- associated with this surgical hazard (see Chapter 5). This spite the fact that the cochlear aqueduct is widely patent at 13 weeks of gestation at the time of differentiation of the lamina stapedialis. Congenital stapes deformity is associated with perilymphatic fistula (see Chapter 5).311 We have a few examples of a “monopod” stapes having only one demonstrable crus (Fig. 3.247 and Fig. 3.248; see also Fig. 3.239). This deformity may or may not be associated with CHD and other stapes anomalies. Congenital ossification of the stapedius tendon is a rare, often bilateral anomaly associated with CHD.312 Clinically, fenestral otosclerosis or true ossicular deformity might be expected. Axial CT demonstrates subtle pathological thickening and hyperdensity of the tendon as it courses from the pyramidal eminence to the stapes. Normally, only a thin soft tissue density is seen. Anomalies of the stapes such as absent obturator foramen (monopod stapes) and defective footplate are associated. Congenital conductive deficit is rarely caused by a persistent stapedial artery, which may occur with or without an aberrant ICA (see Chapter 4). 313,314 The isolated per- Fig. 3.181 Mastoid cavity, labyrinthectomy. This mastoid cavity (*) was created for the purposes of labyrinthine obliteration (thick white sistent stapedial artery is manifest as a small vascular arrows) in a patient with intractable vertigo. The ossicular mass is channel passing between the stapes crura. Of course, tin- intact. Note normal anterior mallear ligament (short black arrow). nitus is a more common presenting symptom. ch03.qxd 9/23/08 11:41 AM Page 173

Chapter 3 The Middle Ear and Mastoid 173

A B Fig. 3.182 Modified radical (canal wall-down) mastoidectomy. (A) Axial body, A) (malleus head, neck, manubrium, B) and absence of the and (B) coronal computed tomography images reveal a mastoidectomy external auditory canal wall. This is a modified radical (canal wall-down) defect (*) characterized by an intact ossicular chain (malleus head, incus mastoidectomy.

Syndromal Congenital Conductive Hearing Deficit fusion of two or more cervical vertebrae, resulting in diminished range of motion. Hearing loss may be sen- There are several syndromes associated with congenital sorineural, conductive, or mixed. The CHDs are explained CHD. Klippel–Feil syndrome has received some attention by the high incidence of ossicular derangement in these in this regard.315 This is classically manifested by the

A B Fig. 3.183 Modified radical mastoidectomy, recurrent cholesteatoma. cholesteatoma (*). The ossicles are intact, including the stapes super- (A) Axial and (B) coronal computed tomography images.There has been structure (arrows). a modfied radical mastoidectomy (canal wall-down). There is recurrent ch03.qxd 9/23/08 11:41 AM Page 174

A B

Fig. 3.184 Radical mastoidectomy, adhesive debris, tympanosclerosis. (A) Axial and (B,C) coronal computed tomography images reveal a radical mastoidectomy defect (*). Adhesive debris persists in the middle ear, best appreciated in the region of the oval window (arrow, C). Calcifica- C tions (arrows, B,C) are manifestations of tympanosclerosis.

Fig. 3.185 Mastoidectomy, fat packing. Axial T1-weighted magnetic resonance image (T1WI) demonstrates a mastoidectomy, which was performed for the purpose of translabyrinthine resection of a cerebellopontine angle mass. The cavity has been packed with fat, creating the diffusely increased T1WI signal. This appearance must not be confused with cholesterol granuloma (chocolate cyst). ch03.qxd 9/23/08 11:41 AM Page 175

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Fig. 3.186 Recurrent cholesteatoma, superinfected. (A) Axial computed tomography image reveals a mass filling the mastoid bowl (*). Note the lateral semicircular canal fistula (arrow). (B,C) Axial pre- and postcontrast T1WI reveal a mild degree of heterogeneous contrast enhancement. (D,E) Axial and coronal T2WI demonstrate a remarkable degree of hypointensity within the center of the lesion likely due to hemorrhage. At surgery, a recurrent cholesteatoma was diagnosed that was hemorrhagic and superinfected with Pseudomonas bacteria.

B C

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A B Fig. 3.187 Modified radical (canal wall-down) mastoidectomy, recurrent disease. There has been a modified radical (canal wall-down) mastoidectomy. The ossicular chain is intact. There is debris (cholesteatoma and granulation tissue) (*) is mastoid bowl. Note the intact stapes superstructure (arrow).

patients. Deformities of the incudostapedial articulation air–bone gap in patients with incudostapedial deformity secondary to anomalies of the distal incus are particularly than in those with stapes fixation. common. The stapes is often abnormal, ranging from Wildervanck’s syndrome (cervico-ocular-acoustic complete absence to fixation with otherwise normal con- dysplasia) consists of a triad of Klippel–Feil deformity of figuration. Surgeons have had more success reducing the the cervical spine, congenital hearing loss, and an ocular motility disturbance known as Duane’s retraction syndrome.316 There is a strong female predominance. A diffuse ossicular ankylosis is typical. Inner ear deformity is associated. Miscellaneous ossicular deformities have been found in individuals with Madelung’s dyschondroosteosis, otopalatodigital syndrome, and Pyle’s craniometaphyseal dysplasia. Stapes fixation has been described with acrocephalosyndactyly (Apert’s syndrome), Beckwith– Wiedemann, and Mayer–Rokitansky–Küster–Hauser syndromes.317,318 Oculoauriculovertebral dysplasia (OAVD) encompasses a diverse group of entities, including the original cases described by Goldenhar.319 These entities are believed to result from poor blood supply in the vicinity of the first and second branchial arches (Fig. 3.249). External canal deformity in association with OAVD is discusssed in Chapter 2. Various ossicular deformities are associated. Individuals with craniometaphyseal dysplasia, a genetic bone disorder characterized by dysplastic scle- Fig. 3.188 Tympanosclerosis, mastoidectomy. Axial computed tomography image reveals a mastoidectomy (*), canal wall down. There is rotic involvement of the cranium and long bones, often 320 adhesive debris within the middle ear space with calcification (arrows) have attic fixation as well as stapedial ankylosis. SNHL consistent with tympanosclerosis. (Courtesy of Deborah Shatzkes, MD.) secondary to IAC stenosis is also described. ch03.qxd 9/23/08 11:41 AM Page 177

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A B

C D Fig. 3.189 Mastoidectomy, recurrent cholesteatoma, atypical tym- arrow). (B) Axial CT image also reveals a mass (*) as well as residual intact panosclerosis. (A) Axial computed tomography image reveals mastoidec- incus body (arrow). (C) Coronal image confirms deformed ossicle is a tym- tomy defect with some residual air cells posteriorly (thin arrows). There is panosclerotic replacement of the malleus head (arrow). (D) Axial image extensive debris representing recurrent cholesteatoma (*). Deformed through the hypotympanum demonstrates a tympanostomy tube ossicle is a tympanosclerotic replacement of the malleus head (large (arrow).

Various ossicular deformities are described in clei- severe cranial base deformity. Because the otic capsule, docranial dysplasia.321 The key to this diagnosis is the petrous ridge, and ossicular chain are derived entirely presence of associated wormian bones often related to from cartilage, one would expect that these structures the peripheral sutures. might be abnormal in these patients.322 In fact, ossicular Achondroplasia is a congenital disorder of endochon- deformity is extremely rare. These patients often have an dral ossification and as such is associated with a variably unusual upward angulation of the petrous apex relative to ch03.qxd 9/23/08 11:41 AM Page 178

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A B Fig. 3.190 Atticotomy, recurrent cholesteatoma. (A) Coronal computed (B) Axial CT image reveals a recurrent lesion that is eroding the incus tomography image reveals that the scutum has been surgically removed body (arrow) and extending posteriorly into the mastoid antrum. (arrow) for the purposes of attic exploration and cholesteatoma removal.

the EAC. This type of deformity is also seen in Paget’s dis- Neoplasia and Pseudoneoplasia ease, osteomalacia, and occasionally as a development variation in individuals with no known syndrome. These Paraganglioma and congenital CH are the two most patients characteristically have poorly developed mas- common noninflammatory primary middle ear masses, toids and foreshortened carotid canals. and each has distinguishing clinical and imaging characteristics. Other lesions are substantially less common.

A B Fig. 3.191 Canal wall-down mastoidectomy. Recurrent cholesteatoma, diagnostic of a labyrinthine fistula. Recurrent cholesteatoma (*) is also lateral semicircular canal fistula. (A) Axial computed tomography image presented. (B) Axial CT image through the middle ear reveals incidental reveals a large defect in the lateral semicircular canal (white arrow), fenestral otosclerosis (outlined white arrow). ch03.qxd 9/23/08 11:41 AM Page 179

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Fig. 3.194 Recurrent cholesteatoma. Radical mastoidectomy, bone defects. Radical mastoidectomy, tegmen defect. Coronal computed tomography image, right ear. Large defect in the tegmen (arrow) is Fig. 3.192 Recurrent cholesteatoma mimicking encephalocele, supe- seen in a patient who has undergone radical mastoidectomy. Such rior semicircular canal fistula. Coronal computed tomography image defects must be viewed with suspicion, as an encephalocele may be reveals a surgical defect with absence of a long segment of the present. Correlation with magnetic resonance imaging was recom- tegmen tympani (double black arrows). Mass (*) in cavity could have mended. Incidental note is made of diffuse debris in the oval window been an encephalocele, but it proved to be recurrent cholesteatoma niche. (magnetic resonance image not available). There is a labyrinthine fistula (white arrow) involving the superior semicircular canal. Paraganglioma

Masses that originate outside the middle ear (jugular Paraganglioma of the middle ear (glomus tympanicum) is foramen, carotid canal, etc.) and involve the middle ear the most common primary tumor of the middle ear and and mastoid secondarily are considered elsewhere in this the second most common tumor of the temporal bone volume. (after schwannoma of CN VIII). This entity is extensively discussed in Chapter 4. These lesions are visualized as otoscopically vascular through an intact TM and enhance

Fig. 3.193 Mastoidectomy, tegmen reconstruction, encephalocele. Fig. 3.195 Encephalocele. Patient has undergone radical mastoidec- Coronal computed tomography image reveals mastoidectomy. The tomy but now presents with a mass bulging into the mastoid bowl. tegmen was reconstructed with hydroxyapatite graft (white arrows). Coronal T1-weighted magnetic resonance image. Large tegmen Subsequent dehiscence of the graft resulted in meningoencephalo- defect (small arrows) with meningoencephalocele (*) is seen in the cele (black arrow). (Courtesy of Timothy L. Larson, MD.) mastoid bowl. (Courtesy of Kent B. Remley, MD.) ch03.qxd 9/23/08 11:41 AM Page 180

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arise from glomus bodies associated with the tympanic branch of the glossopharyngeal nerve, which courses along the surface of the promontory after entrance into the middle ear via the inferior tympanic canaliculus. Im- portantly, paragangliomas may occur anywhere within the middle ear cavity or even the eustachian tube.323,324 Larger lesions ( 1.5 cm) may contain signal voids usually most easily visualized on T2-weighted thin section MRIs (Fig. 3.252). Often, holotympanic lesions have the tendency to encase rather than destroy the ossicular chain, a factor that helps to distinguish paraganglioma from CH on CT.

Congenital Cholesteatoma A CH found behind an intact TM in a patient with no history of middle ear/mastoid surgery, otitis media, or otorrhea is presumed to be congenital.325–328 Congenital CH of the middle ear is far less common than the acquired variety, perhaps representing 2% of the total.184 Congenital CHs generally have a thinner and flatter Fig. 3.196 Recurrent cholesteatoma, radical mastoidectomy, bone matrix when they lie in direct apposition to an intact TM defects. Axial computed tomography image, right ear. There is a recurrent expansile mass within the mastoidectomy cavity (small (pressure effect). Congenital CH is most often unilateral; arrows). Importantly, the sigmoid sinus plate is preserved (large however, a few bilateral cases have been reported.329,330 curved arrow). Because many of these patients have a well-pneumatized mastoid, these lesions may grow for years without being discovered.331 intensely with gadolinium. One of the main purposes of Congenital CH (epidermoid, primary cholesteatoma) imaging is to distinguish the glomus tympanicum from usually presents with CHD. Others are incidentally dis- the tympanic portion of a much larger glomus jugulare covered by the primary care physician during otoscopy as (Fig. 3.250 and Fig. 3.251). Origination in the vicinity of part of a routine physical examination. The reader should the promontory is classic, as paragangliomas typically be aware that congenital CH may form medial to a bony

A B Fig. 3.197 Recurrent cholesteatoma, petrous apex. (A) Axial and (B) has undergone prior radical mastoidectomy. Magnetic resonance imag- coronal computed tomography images reveal a well-marginated lesion ing would be confirmatory. Differential would include cholesterol gran- superior and anterior to the anterior cochlear turns (*) in a patient who uloma and perhaps mucocele. ch03.qxd 9/23/08 11:41 AM Page 181

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Fig. 3.198 Mastoidectomy, facial paralysis. Axial computed tomogra- Fig. 3.199 Radical mastoidectomy, dehiscent facial nerve. There has phy image reveals a mastoidectomy defect and residual debris (*). The been a radical mastoidectomy. Residual/recurrent debris (*) is identi- posterior genu was violated (arrow), resulting in facial paralysis. fied. Total ossicular replacement prosthesis placement was precluded, (Courtesy of Timothy L. Larson, MD.) as the abnormal soft tissue in the oval window niche (arrow) was a dehiscent facial nerve. (Courtesy of Timothy L. Larson, MD.)

external auditory canal atresia plate or proliferate in the squamous epidermal cells, the epidermoid formation (EF) presence of fibrous dysplasia.326 (Fig. 3.253, Fig. 3.254, and Fig. 3.255).332 The EF is situ- There is a distinct propensity for occurrence in the ated at the point of epithelial transformation between the anterosuperior quadrant of the middle ear adjacent to the tympanic cavity and eustachian tube.333 In fetal life, the EF eustachian tube and anterior tympanic ring at the precise acts as an “organizer” in the development of the TM and location of a constant well-documented rest of stratified middle ear. As many as 89% of these lesions have been

A B Fig. 3.200 Postsurgical defect, second genu facial nerve canal removed) (arrows). (B) Coronal CT image. Mastoid cavity is in direct (postoperative facial palsy). (A) Axial computed tomography (CT) image. apposition with the canal along the proximal mastoid segment (white The posterior tympanic recesses and ridges are absent (surgically arrow). ch03.qxd 9/23/08 11:41 AM Page 182

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A B

Fig. 3.201 Mastoidectomy, otalgia, temporomandibular joint dysfunction. (A) Axial and (B) coronal computed tomography images reveal mastoidectomy defect. There is absence of bone at the posteromedial wall of the glenoid fossa (arrows) with abnormal soft tissue from the joint space (*) extending into the hypotympanum. (C) Corresponding axial T2-weighted magnetic resonance image also reveals abnormal C middle ear debris (arrow).

reported to arise in this location from this structure, as intracranial sites, whereas the junction of the calvar- which normally regresses at 33 weeks’ gestation.327 ium with the cranial base (membranous–cartilaginous Although compelling, the EF theory is not unifying, and junction) is the most likely site of the intradiploic many other etiologies for congenital CH have been sug- lesion.334,336 gested. Some observers believe that they arise from aber- Several authors have suggested that middle ear con- rant epithelial embryonic rests left at the time of closure genital CHs reflect an abnormal migration of external of the neural tube between the third and fifth week of fe- canal ectoderm beyond the tympanic ring (site of devel- tal life and are thus identical to both the intracranial and oping TM). The tympanic ring provides an inhibitory intradiploic variety in this regard.61,334,335 The cerebello- function in this regard.337 Recently, observers have pro- pontine angle (CPA) and suprasellar cistern predominate vided evidence that lesions presumed to be congenital ch03.qxd 9/23/08 11:41 AM Page 183

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A B Fig. 3.202 Radical mastoidectomy, type lll tympanoplasty. (A) Magnified coronal and (B) magnified axial computed tomography images, left ear, radical mastoidectomy cavity. There is a tympanoplasty in direct apposition to the head of the stapes (arrows).

may actually be acquired and arise from a resolved retrac- between the middle ear cavity proper and the attic (see the tion of the pars tensa portion of the TM.338 first section, Anatomy). These isthmi represent the embry- The peristapedial region and posterior tympanum are ological termination of the first branchial pouch between additional relatively common sites of origin for congenital the first and second branchial arches (Fig. 3.256 and CH.339 This is in the approximate location of the base of Fig. 3.257).340 These more posterior lesions are often asso- the tympanic isthmi, which are responsible for contiguity ciated with recidivism and more extensive disease.197,341

A B Fig. 3.203 Stapes prosthesis, wire. (A) Axial computed tomography wire stapes prosthesis. Note that the tip (arrow) is well seated within the (CT) image reveals that the tip of the prosthesis (arrows) is well seated oval window membrane, although somewhat posteriorly positioned. within the oval window. (B) Magnified axial CT image, left ear, reveals a ch03.qxd 9/23/08 11:41 AM Page 184

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A B Fig. 3.204 Stapes prosthesis, graft lateralization. (A) Axial computed reveals separation between the tip of the prosthesis (white arrow) and the tomography (CT) image, left ear, shows a large plaque of otosclerosis in oval window membrane (black arrow). There was recurrent conductive the anterior oval window (arrow). The tip of the wire prosthesis (P, arrow) is hearing deficit. well seated centrally within the oval window. (B) Magnified axial CT image

They are also more often associated with CHD than con- sites, such as the IAC (Seessel epipharyngeal pouch) and genital CH elsewhere due to their proximity to the ossicu- geniculate ganglion (epibranchial placode).342,343 lar chain. The rare congenital CH originating within the attic Numerous theories have been advanced to explain the may be beyond otoscopic view. Because these patients development of congenital CH at unusual temporal bone may present with only progressive CHD, fenestral

A B Fig. 3.205 Stapes prosthesis, Kurz K piston. (A) Axial computed tomography (CT) image reveals the device to best advantage (arrow). (B) Coronal CT image reveals that the device is only faintly appreciated (arrows). ch03.qxd 9/23/08 11:41 AM Page 185

Chapter 3 The Middle Ear and Mastoid 185

Fig. 3.205 (Continued) (C) Photograph of the device. This device extends from the malleus handle (instead of the incus long process) to the oval window.

otosclerosis or congenital deformity may be suspected and as such are virtually impossible to excise in their clinically (Fig. 3.258).82 entirety. Facial nerve morbidity is common. Petrous apex Petrosal CHs are medial to the otic capsule and involve CH must be differentiated from cephalocele and trapped either the petrous apex or meato-labyrinthine region.344,345 fluid, which are more smoothly marginated processes They may be congenital or acquired. These are destructive requiring no surgical intervention. These latter lesions are lesions, which have a strong tendency to recur after sur- discussed in more detail elsewhere in this volume. gery, as they are often found adherent to vital structures Congenital CHs may rarely originate within the mastoid (Fig. 3.259). As this is certainly the least common site of origin within the temporal bone, diagnosis is difficult.346,347 These probably arise from epidermal rests. CT attenuation characteristics of congenital and acquired CH are identical. Clinical and imaging diagnosis of the congenital variety hinges on the otoscopically intact TM.82 Other circumstances that aid in diagnosing the congenital variety include origination within the middle ear cavity proper (as opposed to the attic) and the presence of a well- pneumatized mastoid.68 TM defects do heal, and aggressive congenital lesions may disrupt the TM secondarily. There- fore, the etiology for some CHs will never be elucidated. CT remains the mainstay for diagnosis, although MRI is useful in complicated cases, particularly in the presence of tegmen defects. The MRI of congenital CH is consistent. Vir- tually all congenital (and acquired) CHs have nonspecific low to intermediate T1-weighted signal and bright T2-weighted signal (Fig. 3.260). As with the acquired variety, there is little if any contrast enhancement with gadolinium (Table 3.12).335

Schwannoma Fig. 3.206 Stapes prosthesis. The tip of this prosthesis is well seated centrally within the oval window (arrow). There is an anteriorly Schwannoma must also be considered in the patient with a positioned otosclerotic plaque (smaller arrow). mass behind the intact TM.325 Congenital CH, paraganglioma ch03.qxd 9/23/08 11:41 AM Page 186

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A B Fig. 3.207 Metallic stapes prosthesis, normal position. (A) Magnified coronal and (B) magnified axial computed tomography images, right ear. Prosthesis is in an excellent position centrally within the oval window (arrow). v, vestibule.

and schwannoma may have an identical CT appearance; ganglioma and schwannoma can be distinguished from however, schwannomas usually arise from the facial congenital CH at MRI, as they enhance with gadolinium at nerve, and their specific location within the middle ear MRI (Fig. 3.261 and Fig. 3.262). Importantly, schwanno- often suggests the diagnosis (see Chapter 7). Both para- mas of the middle ear (and facial schwannomas elsewhere

Fig. 3.208 Dislocated stainless steel stapes prosthesis. Axial com- Fig. 3.209 Stapes prosthesis, graft lateralization. Magnified axial puted tomography image reveals that the tip of the prosthesis (arrow) computed tomography image reveals separation between the tip of is positioned remote from the oval window posteriorly, inferiorly, and the prosthesis (white arrow) and the oval window membrane (black laterally. arrow). There was recurrent conductive hearing deficit. ch03.qxd 9/23/08 11:41 AM Page 187

Chapter 3 The Middle Ear and Mastoid 187

A B Fig. 3.210 Stapes prosthesis, graft lateralization. (A) Axial and (B) coronal computed tomography images reveal that the tip of the prosthesis (arrow) is located superficial to the oval window (smaller arrows) in this patient with recurrent conductive hearing deficit.

within the temporal bone) often do not present with incidentally during the otoscopic portion of a routine facial palsy.348 Schwannomas are usually well circum- physical exam. Although usually arising from the facial scribed and arise from the main trunk of the facial nerve, nerve or its branches, schwannomas originating within although chorda tympani origin has been described. the middle ear may also arise from the tympanic branch As with congenital CH, the mass is often discovered of the glossopharyngeal nerve (nerve of Jacobson).349 Jacobson’s nerve arises from the inferior ganglion of the glossopharyngeal nerve and enters the middle ear via the inferior tympanic canaliculus (ITC). Clues to such an origin include widening of the ITC and erosion of the cochlear promontory. The normal ITC is consistently seen on coronal CT images between the carotid canal anteriorly and the jugular fossa posteriorly (Fig. 3.3b).

Rhabdomyosarcoma Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma and the second most common head and neck malignancy in children after neuroblastoma.350–355

Table 3.12 Uses of Magnetic Resonance Imaging in Middle Ear Disease Hemorrhagic lesions (cholesterol granuloma) Tegmen or sinus plate defects (encephalocele, epidural cholesteatoma, sigmoid sinus thrombophlebitis) Fig. 3.211 Stapes prosthesis, subluxation. Axial computed tomography image reveals posterior subluxation of a stapes prosthesis (long, Intracranial complications thick arrow). There is regrowth of otosclerosis within the oval window Suspected facial nerve involvement (short outlined arrow). ch03.qxd 9/23/08 11:41 AM Page 188

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A B Fig. 3.212 Medially subluxed metallic piston prosthesis. (A) Magnified coronal and (B) magnified axial computed tomography images, left ear. The metallic piston prosthesis has migrated well into the vestibule (arrow) and as such is almost certainly compressing the saccule.

About 30 to 50% of RMS cases occur in the head and more frequently than those of other races, and there is a neck.348 This is a highly malignant neoplasm thought to slight male predominance.358 arise from primitive mesenchymal cells committed to Head and neck RMSs are classified as cranial para- skeletal muscle differentiation (rhabdomyoblasts).356,357 meningeal, orbital, and nonorbital parameningeal.359 There Fortunately, they are extremely uncommon (Fig. 3.263, are three pathological forms: embryonal, alveolar, and Fig. 3.264, and Fig. 3.265). White children are involved pleomorphic. The embryonal type is by far the most common

A B Fig. 3.213 Incus interposition, normal function. (A) Axial computed (white arrow). (B) Coronal CT image confirms incus interposition (black tomography (CT) image reveals the patient’s resculpted incus (black arrow), tympanic membrane (small white arrows), and stapes (long white arrow) interposed between the tympanic membrane and the stapes arrow). ch03.qxd 9/23/08 11:41 AM Page 189

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Only 7% of RMSs develop within the middle ear. Origi- nation from the orbit, paranasal sinuses, or nasopharynx is far more common, yet RMS is the most common primary middle ear malignancy in children.254,353 Clinical symptomatology usually includes otalgia and painless bloody otorrhea. Unfortunately, most cases masquerade as chronic otitis media until they have progressed to the nonresectable stage.254,356 About 30% have neurological deficits at the time of diagnosis. Facial palsy and symptomatology involving other cranial nerves are common, and when these symptoms occur in conjunction with a draining ear, the clinician should be alerted. The facial canal may be involved by direct invasion or via retrograde spread. Positron emission tomography (PET) is an important staging tool. CT and MRI are complementary in evaluation of this lesion. CT demonstration of extensive indiscriminate bony destruction is the key to the diagnosis in contrast to the Fig. 3.214 Incus interposition graft. The graft (black arrow) is identi- much more predictable patterns associated with CH. The fied within the middle ear and articulates exquisitely (white arrow) extent of the soft tissue mass is easier to distinguish with with the stapes head. (Courtesy Timothy L. Larson, MD.) MRI, particularly when the intracranial compartment is involved.41 MRI signal characteristics are nonspecific histological variety in the head and neck. Prognosis of this intermediate T1-weighted signal and bright T2-weighted lesion depends on the specific site of origin. Superficially signal. Intense enhancement with gadolinium is the located lesions (orbital) have survival rates reaching 90%. rule.356 Invasion may be lateral into the EAC, medial into Deeply located lesions (parameningeal) require more the IAC, cephalad into the MCF, posterior into the PCF, or intense therapy and have lower survival rates in the 50% inferior/anterior into the TMJ or neurovascular compart- range. Middle ear RMS is classified as parameningeal. ments. From an imaging standpoint, these lesions may be

A B Fig. 3.215 Incus interposition, encased, poorly functioning. (A) Axial through the middle ear reveals the patient’s resculpted incus (arrow) computed tomography (CT) image reveals that the incus has been re- encased by debris, which limits mobility and function. moved from its normal position in the attic (arrow). (B) Axial CT image (Continued on page 190) ch03.qxd 9/23/08 11:41 AM Page 190

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Fig. 3.215 (Continued) (C) Coronal CT image confirms a graft (arrow) interposed between the tympanic membrane and the stapes.

impossible to differentiate from Langerhans cell histiocy- viral, bacterial, traumatic, metabolic, and not truly neo- tosis and other aggressive entities, including adenocarci- plastic, this entity is considered here due to the imaging noma and squamous cell carcinoma. The age of the patient similarities with the previously mentioned lesions is a useful distinguishing feature. (Fig. 3.266, Fig. 3.267, and Fig. 3.268). This disease is characterized by multisystem proliferation of benign-appearing histiocytes associated with the presence of the Langerhans Cell Histiocytosis immunoreactive Langerhans cell, which is derived from dendritic histiocytes normally found only within the The etiology of Langerhans cell histiocytosis (LCH) is dermis of the skin.357,360,361 The presence of T cell disputed. Although it has been variously described as dysfunction in these patients implies an autoimmune etiology. Origination along the posterior petrous surface within or adjacent to the endolymphatic sac has been reported, which is interesting due to the immunologic role of this structure.361 Electron microscopy discloses the characteristic Birbeck granules adhering to the cytoplasmic membrane, which permits differentiation from lymphoma.362 Three major categories have been described. The infantile (Letterer–Siwe) form, referred to as histiocytosis type 1, is unassociated with temporal bone disease. Temporal bone involvement does occur with the Hand–Schüller–Christian and eosinophilic granuloma (EG) varieties, collectively referred to as histiocytosis type 2.7,363–365 All types are more common in males. EG is a milder form that is often unifocal and monostotic and may occur at any age.363 Approximately 70 to 80% of patients with LCH have head and neck involvement. The cranial vault is the most common site (42%).362 Cervical lymph node enlargement Fig. 3.216 Dislocated incus interposition graft, mastoidectomy. Axial computed tomography image reveals an incus interposition graft (thin is also common. Sixty-eight percent of patients are under 366 white arrows), which is anteriorly subluxed. The oval window (thick 10 years of age at onset; 20 to 30% of patients have black arrow) and stapes are visualized. temporal bone involvement.362 This occurs most often ch03.qxd 9/23/08 11:42 AM Page 191

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A B

C D Fig. 3.217 Incus interposition graft. (A) Axial computed tomography patient, incus interposition, complicated. Magnified axial CT image, left (CT) image, attic level. Malleus head remains (arrow), incus body ear, partially eroded and somewhat poorly positioned incus interposi- absent. (B) Axial CT image (more inferior). Graft (arrow) identified and tion graft (arrow) surrounded by diffuse recurrent cholesteatoma. surrounded by debris. (C) Coronal CT image. Graft (arrow). (D) Different

in children with multisystemic disease. Five to 25% of external auditory canal meatal skin involvement with patients have otologic symptoms and no other findings.367 granulation tissue and posterior canal wall erosion are Temporal bone involvement is often bilateral (30%). common clinically.7,368,369 There is a strong propensity for As with RMS, LCH patients often present with a drain- involvement of the hypothalamic–pituitary–axis leading ing ear masquerading as otitis media, which classically to diabetes insipidus. Infundibular stalk thickening is results in treatment delay. Periauricular eczema and noted more commonly than atrophy. These radiosensitive ch03.qxd 9/23/08 11:42 AM Page 192

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Petrous apex involvement is unusual and distinctive.367 LCH lesions in the vicinity of the anterior (first) facial genu are treated conservatively at many centers, as most of the morbidity associated with LCH is the result of major organ involvement rather than head and neck disease per se. Origination along the posterior petrous surface may be difficult to differentiate from endolymphatic sac tumor.361 CT examination often reveals indistinctly marginated lytic lesions involving the mastoid associated with contrast-enhancing soft tissue masses.367 MRI findings are nonspecific with low to intermediate T1-weighted signal and bright T2-weighted signal. The presence of enhancement (although typically not intense) helps to differentiate these lesions from CH. Facial nerve paralysis is unusual, since Langerhans cells do not directly invade neural tissue.368,369 Otic capsule involvement may occur but is uncommon. Cranial nerve involvement suggests brainstem or cerebellopontine angle disease. MRI examination reveals heterogeneously enhancing lesions characterized by solid and cystic components. Importantly, hemorrhagic by-products may be present and are a help- Fig. 3.218 Black oval-top total ossicular replacement prosthesis (TORP). 366 Coronal computed tomography (CT) image reveals a well-positioned ful distinguishing characteristic. Black oval-top TORP with a hydroxyapatite head (white arrow) and Plasti-Pore shaft (smaller outlined arrows). Giant Cell Tumor Giant cell tumors account for 5% of all primary bone tu- lesions are further characterized by a relative lack of mors. They are histologically benign but are locally cranial nerve involvement despite extensive destruction invasive and potentially metastatic.371 This is a rare lesion that may extend deep into the mastoid or medially to the of the temporal bone, which may extend to the middle ear petrous apex. The cure rate following radiotherapy is and infratemporal fossa (nasopharyngeal masticator excellent. Recurrences may require chemotherapy.370 space)68 and has a tendency to become quite large.372 There

A B Fig. 3.219 Applebaum prosthesis. (A) Axial computed tomography to chronic otitis. This prosthesis is characterized by a notch (arrowhead) image demonstrates a typical appearance of an Applebaum prosthesis for incus long-process insertion. Intact stapes (curved arrows). (B) Drawing (arrow), used for correcting conductive hearing deficits in patients with of same. (Courtesy of the Radiologic Society of North America.) erosion of the distal incus and incusostapedial articulation secondary ch03.qxd 9/23/08 11:42 AM Page 193

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peculiar destructive lesion of the temporal bone under these clinical circumstances should bring this entity to mind (Fig. 3.269). There is a strong tendency for recurrence after surgery.373 Fractionated radiotherapy has proved to be an excellent alternative to surgery.371,374,375 Individuals diagnosed with giant cell tumor should perhaps be evaluated for hypercalcemia/hyperparathyroidism, as brown tumor is histopathologically identical. Giant cell granuloma is a distinct pathologic entity with a similar appearance, occurring in a similar age group.376 This lesion is believed to develop as a reparative process secondary to prior trauma and intraosseous hemorrhage.

Aneurysmal Bone Cyst Aneurysmal bone cysts (ABCs) are benign fibroosseous expansile lesions that most commonly occur in long bones similar to GCTs. Approximately 20 cases have been reported involving the temporal bone.377–380 Patients often Fig. 3.220 Coronal computed tomography image reveals a canal present with facial asymmetry and hearing loss. They are wall-up mastoidectomy defect. A Goldenberg partial ossicular replacement prosthesis is clearly identified (arrow). histologically benign but locally aggressive, containing multiple thin-walled, blood-filled cystic cavities. Regard- less of location, they occur predominantly in the first three decades of life. ABC is typically a multiloculated, are three histologic grades.370 Grade I is benign, grade II is “bubbly,” expansile lesion, containing several fluid/fluid locally aggressive, and grade III is prone to metastasis and levels, and a thick, well-defined hypointense rim is consis- sarcomatous degeneration. As with these lesions else- tently visualized on MRI.380 Both giant cell tumor and the where, particularly in long bones, the age range is 20 to 40 cystic form of fibrous dysplasia could conceivably have a years, and there is a female predominance. Therefore, a similar imaging appearance (see Chapter 5).

A B Fig. 3.221 Goldenberg partial ossicular replacement prosthesis (PORP). There is a mastoidectomy defect with residual debris (*) (granulation (A) Axial and (B) coronal computed tomography images reveal that versus recurrent cholesteatoma). PORP (arrows) articulates with the intact stapes head (small arrows). ch03.qxd 9/23/08 11:42 AM Page 194

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A B Fig. 3.222 Goldenberg partial ossicular replacement prosthesis (PORP). (A) Axial and (B) coronal computed tomography images reveal that PORP (arrows) articulates with the intact stapes head (small arrows).

A B Fig. 3.223 Mastoidectomy, recurrent cholesteatoma, total ossicular in the oval window. (B) Coronal CT image (more posterior) reveals the replacement prosthesis (TORP). (A) Coronal computed tomography recurrent cholesteatoma (*) to best advantage. (CT) image reveals a mastoidectomy cavity. TORP (arrow) is well seated ch03.qxd 9/23/08 11:42 AM Page 195

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A B

Fig. 3.224 Total ossicular replacement prosthesis (TORP), radical mastoidectomy, recurrent cholesteatoma. (A) Axial and (B) coronal computed tomography images reveal a well-seated device (arrows). There has been a radical mastoidectomy. There is recurrent cholesteatoma (*) best seen on the axial CT image. (C) Drawing of same. (Courtesy of the Radio- C logic Society of North America [286].)

Squamous Cell Carcinoma Middle Ear Adenoma Squamous cell carcinoma (SCCA) and basal cell carci- Middle ear adenomas (MEAs) are rare, benign, indolent noma are quite rare and may be associated with a epithelial tumors that arise from the modified respira- history of chronic otitis media, similar to their counter- tory mucosa of the middle ear.387,388 They have received parts in the external auditory canal.352,365,381–384 Bone considerable attention in the clinical and imaging literature destruction is typically rather extensive, much more due to widely divergent pathologic classifications.389,390 than one would expect from simple chronic otitis.385 They rarely invade bone and do not metastasize. Several Therapy may involve temporal bone resection. Squa- specific entities are included under this category mucosal mous cell carcinomas have a definite male preponder- adenoma, papillary adenoma, inverting papilloma, and ance. Middle ear lesions are believed to originate carcinoid. Each has distinguishing microscopic characteris- in most patients from the tympanic mucosa. More com- tics. Mucosal adenoma contains cuboidal and low colum- monly, SCCA originates within the external canal, from nar cells. Papillary adenoma is more aggressive than which it often demonstrates a multidirectional pattern mucosal adenoma and is characterized by local invasion. of growth.386 Inverting papilloma of the temporal bone is exceedingly ch03.qxd 9/23/08 11:42 AM Page 196

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Fig. 3.225 Total ossicular replacement prosthesis (TORP), partial subluxation. There has been a mastoidectomy (*). A portion of the canal wall remains (arrow, B,C). Residual debris noted (*, B,C). A TORP is identified, quite possibly a Richards centered device with a hydroxyapatite head and HAPEX (hydroxyapatite polyethylene composite;) shaft. The tip of the shaft (thick arrow, C) is anteriorly and laterally subluxed and no longer C seated within the oval window membrane (arrows).

rare and is identical to that which arises in the nasal usually reveal enhancement with gadolinium, an impor- cavity; carcinoid tumors contain argentaffin cells identi- tant differentiating point (Fig. 3.270 and Fig. 3.271). cal to those found in the intestine.391–394 Angiographic blush is unusual, but when present it creates All are pinkish soft tissue masses associated with an difficulty in differentiating MEA from glomus tympan- intact TM and typically present with conductive hearing icum paraganglioma. loss. The mean age at presentation is 45 years. Lesions Despite the name similarity, MEA should not be con- which should not be confused with MEA include cerumi- fused with endolymphatic sac tumors (ELSTs). The latter are noma, which is an external canal lesion (the middle ear aggressive papillary lesions, which are considered in detail has no apocrine glands), and choristoma (see below). in Chapter 4. They arise from the endolymphatic sac along Imaging characteristics are variable. Most are indis- the posterior petrous surface and invade the middle ear tinguishable from congenital CH on CT. MR scans secondarily. They are highly invasive and dangerous.394–398 ch03.qxd 9/23/08 11:42 AM Page 197

Chapter 3 The Middle Ear and Mastoid 197

Fig. 3.227 Total ossicular replacement prosthesis (TORP). Coronal computed tomography image reveals a normally functionng TORP. The head (thick white arrow), shaft (thin white arrow), and articulation with the oval window (black arrow) are clearly defined. Fig. 3.226 Total ossicular replacement prosthesis (TORP). Coronal computed tomography image reveals a well-seated TORP extending from the tympanic membrane (black arrow) to the oval window (white arrow)

Adenocarcinomas may develop from the mucosal Choristoma lining of the middle ear. They are strongly associated with Choristomas are histologically normal tissue in an organ chronic long-standing otitis media, but are less common where it is not normally located. By contrast, hamartomas in this respect than SCCA.370 Some benign adenomas and are malformations of normal tissue occurring within the malignant adenocarcinomas probably arise from ectopic organ of origin, and heterotopia is a term used for normal salivary tissue of the middle ear.

A B Fig. 3.228 Partial ossicular replacement prosthesis (PORP), residual debris. (A) Axial computed tomography (CT) image through the attic reveals debris throughout the attic and antrum. The incus body is absent (arrow). (B) Axial CT image through the middle ear and (Continued on page 198) ch03.qxd 9/23/08 11:42 AM Page 198

198 Imaging of the Temporal Bone

C D Fig. 3.228 (Continued) (C) coronal image reveals a Goldenberg PORP (arrow). Residual debris also demonstrated (B,C). (D) Drawing of same. (Courtesy of the Radiologic Society of North America.)

tissue aberrantly positioned within the organ of origin.399,400 salivary tissue surrounded by a fibrous tissue capsule. Choristoma is a misnomer, as it is not tumor tissue. A better They represent a developmental error and probably occur term might be simply “ectopic tissue”. Salivary choristoma when salivary tissue is trapped within the middle ear as of the middle ear is the most common type involving the tympanic ring fuses.401,402 Branchial arch anomalies, the temporal bone. They are rests of histologically normal especially incus deformity, are commonly associated, and

Fig. 3.229 Total ossicular replacement prosthesis (TORP), subluxation. Coronal image reveals a canal wall up mastoidectomy. The TORP Fig. 3.230 Extruded partial ossicular replacement prosthesis (PORP). (small white arrows) is dislocated inferiorly relative to the oval window Coronal computed tomography image reveals the lateralized graft (single thick arrow). (arrows). (Courtesy of Timothy L. Larson, MD.) ch03.qxd 9/23/08 11:42 AM Page 199

Chapter 3 The Middle Ear and Mastoid 199

Fig. 3.232 Partial ossicular replacement prosthesis (PORP), lateralized. The PORP is subluxed laterally (arrows). Fig. 3.231 Canal wall-down, lateralized partial ossicular replacement prosthesis (PORP). Coronal computed tomography image reveals a thickened tympanic membrane (double arrows). The Richards PORP (single white arrow) is dislocated (lateralized) far from the oval window (thin black arrow).

patients generally have a CHD.328 Dehiscence and an anom- Teratoma and Dermoid alous course of the facial nerve are also quite common. Teratomas are derived from all three germinal layers and Patients usually present with CHL and a mass behind an in- are almost always benign, especially in children.403,404 tact TM. Choristomas may also involve other cranial nerves.400 The most common site of origin in the head and neck is Von Hippel–Lindau disease may also be associated.394

A B Fig. 3.233 Partial ossicular replacement prosthesis (PORP), recurrent conductive hearing deficit. (A) Axial and (B) coronal computed tomography images reveal that the Goldenberg device (arrow) has been encased by debris, limiting its effectiveness. Note patchy peripheral mastoid debris. ch03.qxd 9/23/08 11:42 AM Page 200

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A B

C D Fig. 3.234 Richards centered prosthesis (partial ossicular replacement reveals a well-positioned Richards centered prosthesis (arrow) fash- prosthesis [PORP]), encasing debris. (A) Magnified axial computed ioned as a PORP, which is encased by debris. The stapes (small arrows) is tomography (CT) image through the attic reveals that the incus body is intact. (C) Drawing of same. (D) Miscellaneous Richards devices. (C,D absent (arrow). (B) Magnified axial CT image through the middle ear Courtesy of the Radiologic Society of North America.)

the nasopharynx. Teratomas of the middle ear have been mon than teratoma and often extend into the eustachian reported rarely and are typically destructive lesions, tube. which generally do not recur after surgical excision. They are described as mature (well-differentiated Metastasis components) or immature (Fig. 3.272). Dermoids are composed only of ectoderm and mesoderm.405 The most Metastasis involving the middle ear and mastoid usually common site for dermoid in the head and neck is the extends from elsewhere, particularly the petrous apex orbit. Dermoids discovered within the middle ear are (Fig. 3.273 and Fig. 3.274).68 The process may spread in a also quite rare (24 reported cases), but are more com- perineural, hematogenous, or leptomeningeal fashion.406 ch03.qxd 9/23/08 11:42 AM Page 201

Chapter 3 The Middle Ear and Mastoid 201

A B Fig. 3.235 Encased total ossicular replacement prosthesis (TORP). (A) Axial and (B) coronal computed tomography images reveal the head and shaft of a well-positioned Richards centered TORP, which is encased by debris. (Courtesy of Deb Shatzkes, MD.)

Primary sites in order of frequency are breast, lung, kid- A temporal bone metastasis from a cardiac myxoma ney, prostate, head and neck squamous neoplasms, and featuring calcifications and both a destructive and an ex- stomach. Perineural metastasis may rarely present as a pansile nature was demonstrated with CT.408 Metastases middle ear mass.407 This extension may be posteriorly that disseminate hematogenously are often associated along the facial hiatus (greater superficial petrosal nerve) with diffuse metastatic disease in other locations. Bone or superiorly via the stylomastoid foramen (facial nerve). marrow involvement due to sluggish flow in sinusoids is

A B Fig. 3.236 Dislocated total ossicular replacement prosthesis (TORP). (A) Axial and (B) coronal computed tomography images reveal the head (small arrows) and shaft (large arrow) of a black TORP, which is completely dislocated into the hypotympanum. (Courtesy of Deb Shatzkes, MD.) ch03.qxd 9/23/08 11:42 AM Page 202

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A B

C D Fig. 3.237 Congenital oval window atresia. (A) Axial and (B) coronal no history of chronic otitis, and the tympanic membrane was normal. computed tomography (CT) images of the right ear. (C) Axial and The oval window is small and ossified (arrow). No distinct facial nerve (D) coronal CT images of the normal left ear for comparison. There was anomaly is seen in this case.

believed to be the etiologic factor. These lesions may (meningeal metastasis, carcinomatous meningitis) is not be osteoblastic or osteolytic, similar to those that appear uncommon. Involvement of the inner ear is not unusual elsewhere in the skeleton. The endochondral bone in this circumstance, but middle ear or mastoid disease of the labyrinth is resistant to such invasion.409 One would be exceptional.406 should suspect metastasis in an adult patient when Direct extension from external canal, parotid gland, bone destruction is indiscriminate and atypical for CH. and nasopharyngeal tumors may masquerade as a pri- Leptomeningeal spread via the internal auditory canal mary middle ear tumor.410 Importantly, primary middle ch03.qxd 9/23/08 11:42 AM Page 203

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A B

C D Fig. 3.238 Bilateral oval window atresia. (A) Axial and (B) coronal com- (C) Axial and (D) coronal CT images of the left ear also reveal oval puted tomography (CT) images of the right ear reveal absence of the window nondevelopment (black arrow). Stapes deformity (single white oval window (black arrow) and an anomalous facial nerve (white arrow). arrow) and facial nerve deformity (double white arrows) are also noted.

ear, mastoid, and external canal lesions may infiltrate and aspergillosis may be difficult to distinguish from the parotid gland. The site of origin of an advanced malignancy.410 lesion may therefore be difficult to determine due to reciprocal roots of extension.411 Lymphatic spread of Granulocytic Sarcoma primary middle ear neoplasms to the preauricular and retropharyngeal nodes is unusual but may occur; Granulocytic sarcoma (chloroma) is an extramedullary hematogenous propagation is exceptional. Aggressive collection of leukemic cells usually occurring in individu- infections such as malignant external otitis, tuberculosis, als with acute myelogenous leukemia (AML) or represent ch03.qxd 9/23/08 11:42 AM Page 204

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Fig. 3.239 Oval window atresia, monopod stapes. (A) Axial and (C) coronal computed tomography (CT) images reveal congenital nondevelopment of the oval window annular ligament/stapes footplate replaced by an area of calcification/ossification (arrow). (B) Axial CT image also C demonstrates a monopod stapes (white arrow).

conversion of chronic myelogenous leukemia to AML. Osteomas The lesion is important to recognize as resolution after Osteomas have been reported within all portions of the chemotherapy is common. Recently, a lesion has been temporal bone, most notably the EAC. They are also well described infiltrating the petrous apex.412 documented within the mastoid.414,415 They are classified under the umbrella of fibroosseous lesions (with fibrous Extramedullary Hematopoiesis dysplasia and ossifying fibroma). There are two histologic Extramedullary hematopoiesis may present as nonerosive types: compact osteoma (mature bone) and osteoma middle ear debris.413 This occurs in patients with chronic cancellare (immature bone with fibrous elements). They anemic states, particularly sickle cell anemia and thal- are often discovered as palpable lesions protruding from assemia. In this circumstance, peripheral bone marrow is the posterolateral mastoid near the occipitomastoid recruited to bolster insufficient erythrocyte production. suture.416 At CT, there is a well-demarcated dense The majority of patients have findings consistent with outgrowth (Fig. 3.275 and Fig. 3.276). Surgery is usually extramedullary hematopoiesis elsewhere in the cranial reserved for cosmetic deformity. External canal osteo- base within the field of view manifest by a wide trabecu- mas are of greater significance and are considered in lar bone pattern. Chapter 2. ch03.qxd 9/23/08 11:42 AM Page 205

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A B Fig. 3.240 Congenital stapes fixation. (A) Coronal (reversed) and was present at surgery. (From Swartz JD, Glazer AU, Faerber EN, et al. (B) axial computed tomography images. The stapes footplate/annular Congenital middle ear deafness: CT study. Radiology 1986;159:187–190. ligament complex appears entirely normal (arrows). The patient had a Reprinted with permission.) 50 dB conductive hearing deficit. A “fixed” immobile stapes footplate

An osteoma of the malleus manubrium causing con- canals. The etiology is often never established; however, ductive deficit was recently reported.417 Compact osteo- there are reports of osteomas occurring in response to mas are composed of mature bone with histologically trauma or therapeutic irradiation. They are typically demonstrable dense lamellae and mature haversian asymptomatic and remain stable for years.

A B Fig. 3.241 Congenital ossicular deformity. (A) Axial computed tomogra- (B,C) Axial CT images through the middle ear proper reveal absence of phy (CT) image through the attic reveals a well-pneumatized mastoid and the incus long and lenticular processes with only faint delineation of the a normal malleus head/incus body (arrows) (normal first branchial arch). stapes (arrow) (abnormal second branchial arch). (Continued on page 206) ch03.qxd 9/23/08 11:42 AM Page 206

206 Imaging of the Temporal Bone

Fig. 3.241 (Continued)

A B Fig. 3.242 Absent incus, probably postinflammatory. (A) Axial com- that the mastoid is well pneumatized, this still most likely represents puted tomography (CT) image through the attic reveals that the incus postinflammatory erosion, as the involvement includes structures sub- body and short process are absent (arrow). (B) Axial CT image through tended by the first (incus body, short process) and second (incus long, the middle ear reveals that the distal incus is absent. Despite the fact lenticular process) branchial arch. ch03.qxd 9/23/08 11:42 AM Page 207

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A B Fig. 3.243 Congenital ossicular deformity. (A) Axial computed tomog- that the distal incus and stapes (arrow) are intact. This disorder involves raphy (CT) image through the attic reveals an anomalous malleus head only the first branchial arch and is presumed to be a congenital ossicular and incus body (arrow). (B) Axial CT image through the middle ear reveals deformity.

An osteoblastoma (see below) is most commonly found are divided into three groups, grade I, grade II, and in the spine, but a few have been reported in the temporal grade III, with the latter demonstrating the most aggres- bone, usually the peripheral mastoid.418 Patients usually sive features. These highly vascular lesions typically present with pain and swelling. CT typically demonstrates a have a honeycomb configuration with trabeculation calcific matrix. MRI findings are nonspecific. reminiscent of the much more common calvarial hemangioma. MRI signal characteristics are mixed and nonspecific. Intense contrast enhancement is the Hemangioendothelioma rule.420 Angiographic blush is variable. Hemangioma or Hemangioendothelioma is a rare vascular tumor com- paraganglioma is typically the clinical preoperative posed of endothelial cells.419 Histopathologically, they diagnosis. Ossifying hemangiomas within the middle ear

A B Fig. 3.244 Congenital conductive loss, bony mass. (A) Magnified coronal facial nerve canal (outlined arrow). The ossicles are deformed, and there is and (B) magnified axial computed tomography images, right ear. Bony fibrous tissue identified within the oval window niche. The oval window mass near the cochleariform process on the right and extending along the (solid arrow, B) is occluded by soft tissue and some bony debris. ch03.qxd 9/23/08 11:42 AM Page 208

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A B

Fig. 3.245 Congenital malleus fixation. (A) Coronal computed tomography (CT) image reveals abnormal soft tissue density (arrow) representing fibrous tissue fixation of the malleus head to the tegmen tympani. Axial CT images of (B) the right ear and (C) the left ear reveal ossification of the C anterior malleal ligament (arrow), significance unknown.

demonstrate the characteristic CT pattern of ossific bone infection, trauma, or osteodystrophy. MFH is typically spiculation (Fig. 3.277). They are believed to arise from an aggressive transcranial process, often reminiscent of the facial nerve (see Chapter 7). atypical meningioma.421

Malignant Fibrous Histiocytoma Pseudotumor Malignant fibrous histiocytoma (MFH) is a rare lesion con- Inflammatory pseudotumor occurs most commonly in sisting of fibroblastic and histiocytic cells that usually arises the lung/pleura. A nonpulmonary lesion that occurs at in damaged bone often as a consequence of irradiation, various locations is variously referred to as plasma cell ch03.qxd 9/23/08 11:42 AM Page 209

Chapter 3 The Middle Ear and Mastoid 209

A B Fig. 3.246 Congenital attic fixation. (A) Axial and (B) coronal computed tomography images reveal ossific debris along the lateral attic wall (arrow). There was no history of chronic otitis, and the tympanic membrane was normal.

granuloma, xanthomatous pseudotumor, inflammatory T2-weighted MRIs due to the relative lack of mobile myofibroblastic tumor, and inflammatory histiocytic protons within these fibrotic lesions. Enhancement with proliferation.422–424 Head and neck lesions are most gadolinium is homogeneous. As such, they masquerade often found in the orbit. This is an aggressive process, as malignancy. Facial nerve involvement is common. An and temporal bone lesions typically demonstrate sub- autoimmune etiology has been suggested. Many stantial bone destruction at CT examination. Temporal patients report previous surgery, trauma, or inflamma- bone lesions most commonly involve the middle ear tory disease. Avascular osteonecrosis has also been and mastoid; however, involvement of inner ear struc- reported to result in a destructive lesion mimicking tures has been reported. Dural thickening and enhance- neoplasm.425 This destruction involved not only the ment may occur. Lesions are typically hypointense on inner ear, but also the middle ear and mastoid. The

A B Fig. 3.247 Congenital oval window atresia with stapes deformity. Axial computed tomography (CT) image, right ear. (A) There is absence of the normal oval window cleavage plane (black arrow) and a monopod stapes (white arrow). (B) Axial CT image, left ear. Normal side for comparison. ch03.qxd 9/23/08 11:42 AM Page 210

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Fibroinflammatory pseudotumor is a destructive benign lesion that may be confused with malignant neoplasms. Infection may be a contributing factor and results in a delay in diagnosis.426

Xanthoma Xanthomas develop because of lipid leakage into the surrounding tissues, where macrophages subsequently phagocytize these lipids.427,428 An inflammatory reaction ensues with giant cells and fibrosis. Systemic xanthomas most commonly occur along tendons and exposed skin surfaces. Intracranial xanthomas have been reported rarely among patients with hyperlipidemia, most commonly type II. Intracranial, extraaxial xanthomas have been described as occurring in the Fig. 3.248 Congenital oval window atresia with stapes deformity. temporal bone, the skull base, and over the cerebral Axial computed tomography (CT) image reveals atresia of the oval window (black arrow) and a monopod stapes deformity (white arrow). convexities. Because of their slow progression, they tend to present in middle-aged and elderly patients, patient in question was noted to have elevated plasma although they have been reported in young patients. homocysteine, a condition strongly related to the devel- Clinical presentation may include severe headaches, opment of spontaneous thromboembolism. otorrhea, cranial nerve palsies, tinnitus, otitis media,

Fig. 3.249 Goldenhar’s syndrome. (A) Axial computed tomography (CT) image through the middle ear reveals external auditory canal atresia and absent ossicles. Abnormal middle ear soft tissue (*) may represent cholesteatoma. The cochlea appears normal. (B) Axial CT image reveals corresponding mandibular deformity (arrow). B ch03.qxd 9/23/08 11:42 AM Page 211

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reflects their high lipid content as well as associated inflammatory reaction. On unenhanced T1-weighted MRIs, most are hyperintense, with corresponding heterogeneous low-signal intensity on T2-weighted MRIs. These lesions typically display only moderate enhancement.

Complications of Therapeutic Radiation Temporal bone complications of therapeutic radiation are highly variable. Uncomplicated otomastoiditis is by far the most common manifestation.357 These patients develop mucosal thickening in the EAC, middle ear, and mastoid and commonly have middle ear effusions as well (Fig. 3.279 and Fig. 3.280). CHL is commonly associated.429,430 Complicated otomastoiditis may ensue, leading to coalescent disease, which may appear identical to that which Fig. 3.250 Paraganglioma (glomus tympanicum). Axial computed to- occurs secondary to other varieties of AOM (Fig. 3.281). mography image reveals a soft tissue mass along the surface of the Focal injury may involve the EAC and appear identical to promontory (arrow). malignant external otitis. The least common but the most dangerous complication is osteoradionecrosis. This results in diffuse moth-eaten demineralization involving the otic and otalgia. Intracranial xanthomas are usually hypo- capsule and often the entire cranial base (Fig. 3.282). dense to brain on unenhanced CT scans. Osseous abnor- Osteoradionecrosis is a well-documented, potentially malities include bony destruction and remodeling. lethal complication presumably resulting from a combi- Because cholesterol is not degraded, they tend to have a nation of damage to the vascular supply and direct injury “bubbly appearance” (Fig. 3.278). The MRI appearance to osteoblasts/osteoclasts.431,432 Healing and resistance to

A B Fig. 3.251 Paraganglioma (glomus tympanicum). (A) Axial and (B) coronal computed tomography images reveal a well-marginated mass along the surface of the promontory (white arrows). Note the sublabyrinthine infiltration (small black arrows). ch03.qxd 9/23/08 11:43 AM Page 212

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A B Fig. 3.252 Glomus tympanicum, MRI. (A) Enhanced T1-weighted MRI reveals intense enhancement of the lesion (arrow). (B) Coronal T2-weighted MRI reveals signal voids reflecting the vascular channels. Note fluid in the attic and mastoid secondary to “attic block” (arrow).

infection are both impaired. Aseptic necrosis, mucosal Petrous carotid pseudoaneurysms have been reported and inflammation, and subsequent fibrosis are common may result in severe epistaxis.433 sequelae possibly leading to the development of a poten- Mastoid surgery is important in the overall manage- tially fatal meningitis.430 Presenting symptoms include ment of this disorder and may prevent intracranial otalgia, aural drainage, hearing loss, and meningismus. complications.434 Subtotal petrosectomy and hyperbaric

A B Fig. 3.253 Congenital cholesteatoma. (A) Axial and (B) coronal computed tomography images reveal a soft tissue mass in the anterior tympanic cavity (arrow). Note the normal incudostapedial articulation (small white arrow, A) and the lateral malleal ligament (small white arrow, B). ch03.qxd 9/23/08 11:43 AM Page 213

Chapter 3 The Middle Ear and Mastoid 213

A Fig. 3.254 Congenital cholesteatoma. (A) Axial and (B) coronal computed tomography images reveal a soft tissue mass in the anterior tympanic cavity (black arrow). The mastoid is well pneumatized. A tympanostomy tube was placed (white arrow, B).

A B Fig. 3.255 Congenital cholesteatoma. (A) Coronal computed tomography (CT) image, right ear, reveals a nondependent soft tissue mass (arrow). The tympanic membrane was intact. (B) More anterior CT image reveals a tympanostomy tube (arrow). ch03.qxd 9/23/08 11:43 AM Page 214

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A B Fig. 3.256 Congenital cholesteatoma. (A) Axial and (B) coronal computed tomography images reveal a holotympanic lesion with bulging of the tympanic membrane (arrow). There is debris throughout the mastoid secondary to the “attic block.”

oxygen therapy are among the treatment options.433,435 from mucosal hyperplasia, loss of ciliary function, and Extensive fibrosis can result in a tumor-like condition. eustachian tube obstruction. These changes are best appre- Numerous, nonosteitic complications may also occur.430 ciated with CT. Bone marrow–containing regions are well Cholesteatomatous involvement of the middle or external evaluated with MRI, and changes in these locations may be ear may complicate severe otitis media, which itself results demonstrated earlier in the course of treatment.

A B Fig. 3.257 Congenital cholesteatoma. (A) Axial and (B) coronal computed tomography images; nondependent irregularly marginated soft tissue mass (*) within the middle ear cavity proper. The distal ossicular chain is eroded, and the mass abuts the oval window niche (arrow). ch03.qxd 9/23/08 11:43 AM Page 215

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Fig. 3.258 Congenital conductive hearing deficit. (A,B) Axial and (C) coronal computed tomography images reveal an ossific mass (arrow) in the attic. Surgery revealed findings most consistent with atypical congenital cholesteatoma. The ossicles are absent and presumed eroded. C

Sensorineural hearing loss is an additional complication Meningocele, Meningoencephalocele, and of therapeutic radiation, which may occur in the absence of Heterotopic Brain bony findings. This may be secondary to necrosis of the organ of Corti or vasculopathy. There is a predilection for On rare occasions, exploration of the middle ear may the basilar turn of the cochlea. reveal brain or meninges. When the “mass” is contigu- Radiation-induced neoplasms are highly aggressive ous with a tegmen defect, particularly after mas- but fortunately rare.433 Ostogenic sarcoma and fibrosar- toidectomy, the diagnosis should not be difficult. coma are the most common. The average latency period is Arguably, all patients with tegmen (or sinus plate) 15 years, and virtually all patients receive 5,000 cGy of defects demonstrated on CT should undergo MRI radiation to their primary tumor. examination. ch03.qxd 9/23/08 11:43 AM Page 216

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A B

Fig. 3.259 Congenital cholesteatoma of the mastoid. (A) Noncontrast axial T1-weighted magnetic resonance image. (B) Axial T2-weighted magnetic resonance image. (C) Axial computed tomography (CT) image. Cholesteatoma (C) is identified with intermediate signal characteristics. There was no enhancement with gadolinium. Note the smooth C expansile nature appreciated with CT.

Petrous apex cephalocele is a protrusion of meninges more difficult.437 These lesions are composed of normal and CSF from Meckel’s cave.136,177 This term encompasses glial cells interconnected by a thin fibrous stroma. both arachnoid cyst and meningocele, depending upon the Heterotopic brain occurring at other sites (nasopharynx, precise contents of the lesion. Communicating and non- soft palate) is somewhat easier to explain on a develop- communicating varieties have been described. They are mental basis due to their midline location. The MRI usually incidental, but are associated with spontaneous appearance of this lesion has not been reported. CSF otorrhea. They are low density (CT) and fluid intense (MRI) expansile lesions, which have sharply defined Miscellaneous Lesions margins similar to CH. Trigeminal notch erosion is diagnostic and allows successful differentiation. Bilaterality is Punctate calcifications within a smoothly marginated mass not rare. suggests chondroblastoma (Fig. 3.283).435 These lesions are A spontaneous meningocele may develop adjacent to isointense on T1-weighted spin echo images and on mixed the tegmen or facial nerve canal (first genu).436 These T2-weighted signal.436 Contrast enhancement is common. lesions may masquerade as several different entities on Temporal bone chondroblastomas occur in a slightly older CT; however, CSF intensity on MRI is diagnostic. These age group than the typical epiphyseal lesion. They are more patients may have chronically increased intracranial pres- common in males, arise from endochondral rests, and may sure and are at risk for the development of CSF fistula and occur at numerous locations within the temporal bone, meningitis. These lesions often present in adulthood. including the squamous portion.438 Although development at the tegmen or facial canal Physaliphorous and chondroid chordomas may appear is most typical, there is a propensity for occurrence in similar to chondroblastoma.439–442 The petrous apex is the petromastoid canal and adjacent to giant apical preferentially involved, as these notochordal derivatives air cells. are classically midline entities.443,444 Heterotopic brain has been reported occurring within Chondrosarcoma is a more common cartilaginous an apparently intact middle ear, and diagnosis is therefore lesion than chondroma. It tends to arise more laterally, ch03.qxd 9/23/08 11:43 AM Page 217

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A B

Fig. 3.260 Invasive cholesteatoma. (A,B) Coronal computed tomography images. Expansile attic mass (*) erodes the tegmen tympani (small arrows) and cortex over the lateral semicircular canal (white arrow), resulting in a fistula. (C) Coronal T2-weighted magnetic resonance image. Lesion is hyperintense and impinges on the floor of the middle cranial fossa. C

and the majority has multiple cranial neuropathies Often, there is a history of trauma. T1- and T2-weighted at the time of diagnosis. Speckled calcifications are relaxation times are nonspecific, and enhancement with common. gadolinium is faint. Giant cell reparative granuloma is most common in Wegener’s granulomatosis of the head and neck is rarely the mandible, but it has been reported in the temporal isolated to the temporal bone, although some form of bone as a lytic lesion of the petrosquamous junction and otologic involvement is not uncommon in the presence as such may involve the antrum, attic, or external audi- of systemic disease.370 The CT findings of nondestructive tory canal.445,446 Such granulomas may be difficult to dis- middle ear and mastoid opacification is nonspecific. tinguish from giant cell tumors and other lesions with a Cytoplasmic antineutrophil and cytoplasmic antibody test- histological marker of multinucleated giant cells.370,373 ing is highly sensitive and specific.447 ch03.qxd 9/23/08 11:43 AM Page 218

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A B

C D

Fig. 3.261 Middle ear schwannoma, second genu. (A) Axial computed tomography image reveals an expansile mass (arrow) involving the posterior tympanic cavity. (B,C) Axial pre- and postcontrast T1-weighted magnetic resonance images (T1WIs) reveal an intensely enhancing mass (arrow). (D,E) Sagittal pre- and postcontrast T1WIs confirm same E (arrow). ch03.qxd 9/23/08 11:43 AM Page 219

Chapter 3 The Middle Ear and Mastoid 219

Fig. 3.262 Middle ear schwannoma. (A) Axial and (B) coronal computed tomography images reveal a soft tissue mass (*) within a well- developed mastoid. (C) Axial postcontrast T1-weighted magnetic resonance image demonstrates intense enhancement. The absence of flow voids (arrow) is suggestive of the diagnosis. C

A B Fig. 3.263 Rhabdomyosarcoma. (A) Axial and (B) coronal computed tomography (CT) images reveal a middle ear mass with permeative bone destruction (arrows). (Continued on page 220) ch03.qxd 9/23/08 11:43 AM Page 220

220 Imaging of the Temporal Bone

Fig. 3.263 (Continued) (C) Axial contrast-enhanced CT image reveals intense enhancement of the clinically palpable component.

Fibrous dysplasia commonly results in a tumor-like Occurrence in young women is not uncommon, and hor- lesion (see Chapter 5). It contains varying degrees of sclero- monal influences on the growth of this lesion have been sis and cyst formation and is often difficult to differentiate strongly implied. Such lesions are characteristically from ossifying fibroma (Fig. 3.284) (see Chapter 5). expansile and locally invasive. Many arise from the squa- Ossifying myxoma is a rare lesion characterized by vari- mous portion of the temporal bone and extend into the able amounts of fibrous tissue and calcifications within mastoid. myxomatous matrix.448 It may be quite aggressive. There is Osteoblastomas are most commonly found in the spine, a predisposition for the facial bones. but a few have been reported in the temporal bone, usually Desmoplastic fibroma most commonly occurs in the the peripheral mastoid.418,444 Patients usually present with mandible but has been reported in the temporal bone.449 pain and swelling. CT typically demonstrates a calcific

A B Fig. 3.264 Rhabdomyosarcoma. (A) Coronal and (B) axial images, on axial images with poor definition of the ossicular chain. This pattern left ear. Diffuse erosive/destructive middle ear mass is identified. of destruction would be atypical for cholesteatoma. Note disruption of the anterior wall of the tympanum (arrows) as seen ch03.qxd 9/23/08 11:43 AM Page 221

C D Fig. 3.264 (Continued) (C) Magnified contrast-enhanced axial T1-weighted MRI; intense enhancement of mass (arrows). (D) Magnified axial T2-weighted MRI. The mass (arrow) is relatively hypointense, probably reflecting dense cellularity.

Fig. 3.265 Rhabdomysarcoma. (A) Axial and (B) coronal computed tomography (CT) images reveal a destructive lesion. (C) Enhanced axial CT image at the soft tissue window reveals the mass (*) more distinctly. C ch03.qxd 9/23/08 11:43 AM Page 222

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Fig. 3.266 Langerhans cell histiocytosis. Axial computed tomography image, right ear, reveals a mass in the posterior tympanic cavity (*), resulting in irregular bone destruction. The mastoid segment of the facial nerve canal is intact (arrow). (Courtesy of Deborah Shatzkes, MD.)

A B Fig. 3.267 Langerhans cell histiocytosis. (A) Axial precontrast and medial and lateral cortical disruption. The mass clearly impinges upon the (B) postcontrast T1-weighted magnetic resonance images reveal an area of the sigmoid sinus (arrow). intensely enhancing destructive mass throughout the middle ear with ch03.qxd 9/23/08 11:43 AM Page 223

Chapter 3 The Middle Ear and Mastoid 223

Fig. 3.268 Langerhans cell histiocytosis. Axial computed tomography image reveals debris throughout the middle ear associated with obvious bone destruction (arrows). (Courtesy of Paul Caruso, MD.)

A B Fig. 3.269 Giant cell tumor. (A) Magnified coronal computed tomogra- (B) Enhanced coronal T1-weighted magnetic resonance image. Lesion phy image, right ear. There is a soft tissue lesion within the attic and enhances intensely and impinges on the floor of the middle cranial fossa tegmental air cells with diffuse disruption of the tegmen tympani (arrow). (arrow). ch03.qxd 9/23/08 11:43 AM Page 224

224 Imaging of the Temporal Bone

A B Fig. 3.270 Middle ear adenoma. (A) Axial computed tomography im- resonance image confirms the mass and reveals intense contrast age reveals a soft tissue mass within the middle ear in a patient with a enhancement excluding the diagnosis of cholesteatoma. (Courtesy of well-pneumatized mastoid. (B) Axial postcontrast T1-weighted magnetic H. Ric Harnsberger, MD, and Amirsys, Inc.)

A B Fig. 3.271 Middle ear adenoma. (A) Axial computed tomography postcontrast T1-weighted magnetic resonance image confirms the image reveals a soft tissue mass within the middle ear in a patient with mass and reveals intense contrast enhancement, excluding the diagno- a well-pneumatized mastoid. There are destructive changes in the pos- sis of cholesteatoma. (Courtesy of H. Ric Harnsberger, MD, and Amirsys, terior tympanum (arrows), indicating an aggressive process. (B) Axial Inc.) ch03.qxd 9/23/08 11:43 AM Page 225

A B Fig. 3.272 Teratoma. (A) Axial and (B) coronal computed tomography images reveal an ossific mass within the middle ear. At surgery, there was a well-formed tooth as well as additional debris.

A B

Fig. 3.273 Metastasis, petrous apex. (A) Axial computed tomography (CT) image reveals a subtle destructive lesion on the left (black arrow). (B,C) Axial pre- and postcontrast T1-weighted magnetic resonance images reveal an enhancing lesion corresponding to the area of destruc- C tion at CT (white arrow). ch03.qxd 9/23/08 11:43 AM Page 226

226 Imaging of the Temporal Bone

A B

Fig. 3.274 Metastasis, petrous apex. (A) Axial computed tomography image reveals subtle evidence of an erosive lesion (arrow). (B,C) Pre- and postcontrast T1-weighted magnetic resonance images reveal an enhancing lesion (arrow). C ch03.qxd 9/23/08 11:43 AM Page 227

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Fig. 3.275 Osteoma of the mastoid. Coronal computed tomography Fig. 3.276 Osteoma, malleus manubrium. Axial computed tomogra- image of osteoma (O). Compare with opposite side. phy image reveals a homogeneously dense middle ear mass (arrow). Osteoma confirmed surgically. (Courtesy of Chuck Schatz, MD.)

A B Fig. 3.277 Ossifiying hemangioma. (A) Axial and (B) coronal computed tomography images reveal a middle ear mass with a “honeycomb” appearance diagnostic of ossifying hemangioma (arrow). ch03.qxd 9/23/08 11:43 AM Page 228

228 Imaging of the Temporal Bone

Fig. 3.278 Mastoid xanthoma. (A) Magnified axial computed tomography image, right ear. Diffuse expansile/erosive mass (arrows) involving the mastoid and extending anteriorly into the mastoid antrum. (B) Noncontrast axial T1-weighted magnetic resonance image (T1WI). (C) Contrast-enhancing axial T1WI. Heterogeneous enhancement of the mass. There was a history of type 11 hyper-cholesterolemia. (Case courtesy of Walter Rose, MD.)

B C ch03.qxd 9/23/08 11:43 AM Page 229

Chapter 3 The Middle Ear and Mastoid 229

A B Fig. 3.279 Postirradiation mastoiditis, external canal debris. (A) Axial computed tomography (CT) image through the attic reveals patchy mastoid debris. Note coalescent changes (arrow). (B) Axial CT image through the external auditory canal reveals a nonspecific soft tissue abnormality (arrow).

A B Fig. 3.280 Postirradiation changes, mastoid and external canal. (A) Axial coalescent disease (arrow). (B) Coronal CT image, right ear. There is a lesion computed tomography (CT) image, right ear. There is diffuse mastoid in the external canal with some expansion and several internal flecks of debris with erosion of multiple mastoid septations consistent with ossification.

(Continued on page 230) ch03.qxd 9/23/08 11:43 AM Page 230

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C D Fig. 3.280 (Continued) (C) Precontrast axial and (D) postcontrast coronal magnetic resonance images reveal that much of the mastoid disease enhances with gadolinium (arrows). Note pachymeningeal enhancement.

A B

Fig. 3.281 Postirradiation change, coalescent mastoiditis. (A–C) Magnified mastoid septate erosion (arrows) consistent with coalescent disease. Fluid axial computed tomography (CT) images, right ear, reveal patchy debris levels are also appreciated (outline arrows). throughout the middle ear and mastoid with clearly definable areas of ch03.qxd 9/23/08 11:43 AM Page 231

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Fig. 3.281 (Continued) (D–F) Corresponding normal CT images of the left ear for comparison. F ch03.qxd 9/23/08 11:43 AM Page 232

232 Imaging of the Temporal Bone

C D

Fig. 3.282 Postirradiation osteitis, facial palsy. (A) Axial computed tomography (CT) image through the cranial base reveals diffuse permeative erosive changes in the marrow (arrows). Patient has undergone mastoidectomy in an attempt to control disease. Diffuse debris in the surgical cavity is noted (*). (B) Magnified axial CT image through the right ear reveals erosive changes involving the labyrinth at the cochlear apex (arrow). (C–E) Magnified axial CT images through the left ear reveal erosive changes involving the first genu of the facial canal and supragenicu- E late air cells (arrows). Labyrinthine erosion is also noted (arrow, C). ch03.qxd 9/23/08 11:43 AM Page 233

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A B

Fig. 3.283 Chondrogenic tumor. (A) Sagittal T1-weighted magnetic resonance image (T1WI; pregadolinium [PRE Gd]). Note obvious expansion of the middle ear and the mastoid as well as the squamous portion of the temporal bone. (B) Sagittal T1WI (postgadolinium [POST Gd]). Patchy enhancement is identified throughout. (C) Coronal T1WI postgadolinium (POST Gd). Mass is identified in the middle ear and mastoid. The tegmen (double arrows) appears to be intact. Computed tomography demonstrated numerous calcifications within the matrix. Multiple pathologists C were unable to agree on a diagnosis. ch03.qxd 9/23/08 11:43 AM Page 234

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A B

Fig. 3.284 Fibrous dysplasia, middle ear. (A) Axial computed tomography (CT) image reveals typical findings consistent with sclerotic fibrous dysplasia involving the orbit (larger black arrow) with a calcific mass in the attic (black arrow). (B) Magnified axial CT [same slice as (A)] confirms a lesion (arrow). (C) Magnified axial CT through the middle ear also confirms C a mass (arrow). There was no history of chronic otitis in this patient.

matrix. The lesion is characterized by extensive signal and is difficult to differentiate histologically from void on MRI with heterogeneous parenchymal and dural teratomas. enhancement.444 Extramedullary plasmacytoma is common in the The CT appearance of Ewing sarcoma has been head and neck, but only seven cases have been reported described.450 Perpendicular spicula of new bone formation in the middle ear and mastoid.452,453 These lesions provides a classic appearance. Verrucous carcinoma was are radiosensitive and of variable histologic grade. CT reported in an elderly patient with a long history of chronic appearance is nonspecific. Enhancement with gadolin- otitis and a destructive mass demonstrated at CT.370 ium is the rule. Hamartomas are malformations composed of more Elevated plasma homocysteine and subsequent increased or less normal tissue indigenous to the site in which risk of thrombosis have been reported to result in a destruc- it is discovered.451 Middle ear origin is, of course, rare tive temporal bone lesion due to avascular osteonecrosis.454 ch03.qxd 9/23/08 11:43 AM Page 235

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424. Gasparotti R, Zanetti D, Bolzoni A, Gamba P, Morassi ML, 439. Tanohata K, Noda M, Katoh H, et al. Chondroblastoma of Ungari M. Inflammatory myofibroblastic tumor of the the temporal bone. Neuroradiology 1986;28:367–370 temporal bone. AJNR Am J Neuroradiol 2003;24(10): 440. Muntane A, Valls C, Angeles de Miquel M, Pons LC. 2092–2096 Chondroblastoma of the temporal bone: CT and MR ap- 425. Bonding P, Skriver E, Helin P, Qvortrup K. Destructive, pearance. AJNR Am J Neuroradiol 1993;14:70–71 granulating lesion in the temporal bone after elevated 441. Flowers CH, Rodriguez J, Naseem M, et al. MR of benign plasma homocysteine. Otol Neurotol 2004;25(4): chondroblastoma of the temporal bone. AJNR Am J 610–615 Neuroradiol 1995;16:414–416 426. Mulder JJ, Cremers WR, Joosten F, et al. Fibroinflammatory 442. Varvares MA, Cheyney ML, Goodman ML, Cheisler pseudotumor of the ear. A locally destructive benign E, Montgomery WW. Chondroblastoma of the temporal lesion. Arch Otolaryngol Head Neck Surg 1995;121: bone: case report and literature review. Ann Otol Rhinol 930–933 Laryngol 1992;101:763–769 427. Bonhomme GR, Loevner LA, Yen DM, Deems DA, 443. Meyers SP, Hirsch WL, Curtin HD, et al. Chordomas of Bigelow DC, Mirza N. Extensive intracranial xanthoma the skull base: MR features. AJNR Am J Neuroradiol associated with type II hyperlipidemia. AJNR Am J 1992; 13:1627–1636 Neuroradiol 2000;21(2):353–355 444. Tsuchida T, Nagao S. Benign osteoblastoma of the tem- 428. Jackler RK, Brackmann DE. Xanthoma of the temporal poral bone. Neuroradiology 1995;37:326–327 bone and skull base. Am J Otol 1987;8(2):111–115 445. Kim HJ, Lee HK, Suh DC, et al. Giant cell reparative 429. Kveton JF, Sotelo-Avila C. Osteoradionecrosis of the granuloma of the temporal bone: MR findings with ossicular chain. Am J Otol 1986;7:446–448 pathologic correlation. AJNR Am J Neuroradiol 2003;24: 430. Smouha EE, Karmody CS. Non-osteitic complications of 1136–1138 therapeutic radiation to the temporal bone. Am J Otol 446. Lewis ML, Weber AL, McKenna MJ. Reparative cell gran- 1995;16:83–87 uloma of the temporal bone. Ann Otol Rhinol Laryngol 431. Ma KH, Fagan PA. Osteoradionecrosis of the temporal 1994;103:826–828 bone: a surgical technique of treatment. Laryngoscope 447. Lane SK, And Gravel JW. Clinical utility of common 1988;98:554–556 serum rheumatologic tests. Am Fam Physician 432. Tartaglino LM, Rao VM, Markiewicz PA. Imaging of radi- 2002;65:1073–1080 ation changes in the head and neck. Semin Roentgenol 448. Knox GW, Roth M, Salem H, Stiles W. A unique temporal 1994;29:81–91 bone lesion resembling juvenile active ossifying myx- 433. Auyeung KM, Lui WM, Chow LC, Chan FL. Massive epis- oma. Am J Otol 1996;17:297–300 taxis related to petrous carotid artery pseudoaneurysm 449. Pensak ML, Nestok BR, Van Loveren H, Shumrick KA. after radiation therapy: emergency treatment with cov- Desmoplastic fibroma of the temporal bone. Am J Otol ered stent in two cases. AJNR Am J Neuroradiol 2003; 1997;18(5):627–631 24(7):1449–1452 450. Carroll R, Miketic L. Ewing sarcoma of the temporal 434. Leonetti JP, Origitano T, Anderson D, Melian E, Severtson bone: CT appearance. J Comput Assist Tomogr 1987;11: M. Intracranial complications of temporal bone osteora- 362–363 dionecrosis. Am J Otol 1997;18(2):223–228 451. Baget S, Francois A, Andrieu-Guitrancourt J, Marie JP, 435. Lustig LR, Jackler RK, Lanser MJ. Radiation-induced tumors Dehesdin D. Hamartoma of the middle ear: a case of the temporal bone. Am J Otol 1997;18(2):230–235 study. Int J Pediatr Otorhinolaryngol 2003;67(3): 436. Gray BG, Willinsky RA, Rutka JA, et al. Spontaneous 287–291 meningocoele, a rare middle ear mass. AJNR Am J Neuro- 452. Panosian MS, Roberts JK. Plasmacytoma of the middle radiol 1995;16:203–207 ear and mastoid. Am J Otol 1994;15:264–267 437. Ashamalla HL, Thom SR, Goldwein JW. Hyperbaric 453. Kandiloros DC, Nikolopoulos TP, Ferekidis EA, oxygen therapy for the treatment of radiation induced Adamopoulos GK. Histologic diagnosis and surgical sequelae in children: the University of Pennsylvania management of primary extramedullary plasmacytoma experience. Cancer 1996;77:2407–2412 in the middle ear cavity. Am J Otol 1996;17(3):498 438. Klein MV, Schwaighofer BW, Sobel DF, et al. Heterotopic 454. Bonding P, Skriver E, Helin P, Qvortrup K. Destructive, brain in the middle ear: CT findings. J Comput Assist granulating lesion in the temporal bone after elevated Tomogr 1989;13(6):1058–1060 plasma homocysteine. Otol Neurotol 2004;25: 610–615 ch04.qxd 9/19/08 11:17 AM Page 247

Temporal Bone Vascular Anatomy, 4 Anomalies, and Disease, with an Emphasis on Pulsatile Tinnitus Gul Moonis, Ann Kim, Douglas Bigelow, and Laurie A. Loevner

The temporal bone is the bony framework within which a normal vascular asymmetry, vascular variants, and patho- complex array of anatomic relationships exists. These logical vascular conditions. anatomic relationships involve important vascular structures, including the sigmoid sinus, internal jugular bulb/vein, and petrous segment of the internal carotid Normal Venous Anatomy artery (ICA) and the closely associated nervous structures. The sigmoid sinus and jugular bulb/vein are the major In this chapter, we will focus on the normal vascular venous structures intimately associated with the tem- anatomy of the temporal bone, including normal variants poral bone (Fig. 4.1 to Fig. 4.10). The sigmoid sinus is and congenital vascular anomalies, as well as acquired the most distal dural venous sinus and serves to connect vascular lesions related to the temporal bone. Essential to the transverse sinus to the internal jugular vein at the the discussion of vascular lesions are those related to pul- level of the jugular bulb (Fig. 4.1A). At its junction with satile tinnitus (PT) and vascular tympanic membranes the transverse sinus, the sigmoid sinus drains the vein (TMs); we will conclude with a comprehensive review of of Labbé (Fig. 4.1B) and, slightly more distally, the supe- these topics. rior petrosal sinus.1 From here, the sigmoid sinus courses inferiorly and medially in a gentle S-shaped curve, carving out the sigmoid sulcus along the intracra- Normal Vascular Anatomy nial surface of the mastoid portion of the temporal bone (Fig. 4.5 and Fig. 4.6).1, 2 As the sigmoid sinus passes in Knowledge of the normal appearance of the major venous, the sigmoid sulcus along the medial border of the mas- arterial, and neural structures within and adjacent to the toid air cells, it defines a bony interface described as the temporal bone is critical to the correct identification of sigmoid plate (Fig. 4.6). The sigmoid sinus then proceeds

A B Fig. 4.1 Normal venous anatomy: magnetic resonance venography (MRV). (A) Axial MRV maximal intensity projection (MIP) image (TS, transverse sinus; SS, sigmoid sinus; JB, jugular bulb). (B) Coronal MRV MIP image (SSS, superior sagittal sinus; LAB, vein of Labbé; IJV, internal jugular vein). 247 ch04.qxd 9/19/08 11:17 AM Page 248

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Fig. 4.3 Normal anatomy: axial postgadolinium T1-weighted magnetic resonance image. The horizontal segment of the petrous internal Fig. 4.2 Normal anatomy: axial postgadolinium T1-weighted magnetic carotid artery (★) is at/above the level of the cochlea (IAC, internal audi- resonance image (MRI). Sigmoid sinus (SS) becomes continuous with tory canal; TS, transverse sinus; MAST, mastoid air cells). the jugular bulb (JB). The petrous internal carotid artery (CC) is anterior to the jugular bulb.

anteromedially to become continuous with the jugular The jugular bulb represents the prominent cephalad bulb situated within the bony jugular foramen. The sig- dilation of the internal jugular vein in the roof of the moid sinuses may be symmetric or very asymmetric in jugular foramen (Fig. 4.1, Fig. 4.2, and Fig. 4.4). In the size, such that the absence of one sinus can represent a coronal plane, the jugular bulb is seen lying immedi- normal anatomic variant and not a pathologic process ately beneath the vestibule in the posterior hypotympa- (Fig. 4.11). num (Fig. 4.9).3,4

A B Fig. 4.4 Normal anatomy: sagittal magnetic resonance image. (A) to its most cephalad point, the jugular bulb (JB), which drains the sig- Sagittal postgadolinium T1-weighted multiplanar reformatting (MPR) moid sinus (SS). (B) Anterior to the internal jugular vein (*) is the image demonstrates the normal course of the internal jugular vein (*) internal carotid artery (ICA). ch04.qxd 9/19/08 11:17 AM Page 249

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Fig. 4.5 Normal anatomy: unenhanced axial computed tomography (CT) image. The sigmoid sulcus (SS) carrying the sigmoid sinus insinuates along the medial border of the mastoid segment of the temporal bone to become continuous with the jugular bulb within the jugular foramen (JF) formed by the occipital bone (OCC) and temporal bone. The caroticojugular spine (CJS) separates the JF from the carotid canal (CC) containing the internal carotid canal. Also at this level, the hypoglossal canal (HGC) is formed by the clivus (CL) and the occipital bone (OCC).

Fig. 4.6 Normal anatomy: unenhanced axial computed tomography (CT) image. At a slightly higher level, the jugular foramen is separated into the pars nervosa (PN) anteriorly and the pars vascularis (PV) posterolaterally by the jugular spine (JS) and, more commonly, a fibrous septum, not visualized on imaging. The horizontal segment of the internal carotid canal within the horizontal carotid canal (not shown) courses toward the foramen lacerum (FL) and forms part of its roof. The inferior petrosal sinus drains the cavernous sinus and travels within the petrooccipital fissure (★), then within the pars nervosa before draining into the internal jugular vein. Well depicted in this image is the course of the sigmoid sinus as it carves out the sigmoid sulcus (SS) along the medial border of the mastoid temporal bone. The sigmoid plate (SP) defines the bony border between the sigmoid sinus and the mastoid air cells. The course of the eustachian tube (ET) parallels that of the horizontal carotid canal and the horizontal segment of the facial nerve but is located more inferiorly. The vascular structures of the temporal bone are intimately associated with other important structures, including the vidian canal (VC), foramen ovale (FO) containing the mandibular segment of CN V (V3), and the foramen spinosum (FS) containing the middle meningeal artery. The descending segment of the facial nerve (DFN) travels within the mastoid temporal bone before exiting through the stylomastoid foramen.

Fig. 4.7 Normal anatomy: unenhanced axial computed tomography (CT) image. The petrous internal carotid artery ascends vertically through the petrous temporal bone to the level of the cochlea (COCH), where it makes a sharp bend (posterior genu of the internal carotid artery) to course anteromedially in the horizontal carotid canal (HCC), ending just cephalad to the foramen lacerum. The tensor tympani muscle (TTM) parallels the course of the horizontal carotid canal. ch04.qxd 9/19/08 11:17 AM Page 250

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Fig. 4.9 Normal anatomy: a coronal reformatted CT image of the tem- Fig. 4.8 Normal anatomy: coronal computed tomography (CT) image. poral bone. The superior and inferior divisions of the vestibular nerve A coronal reformatted image on unenhanced CT of the temporal bone. course in the internal auditory canal (IAC) and are separated by the At the level of the cochlea (COCH) and malleus, the vertical segment of crista falciformis (CF). LSCC, lateral semicircular canal; CN VII, tympanic the petrous internal carotid artery (ICA) can be found medial to the tym- segment of the facial nerve; SSCC, superior semicircular canal; VEST, panic cavity. Superolateral to the cochlea, the distal aspect of the hori- vestibule; JF, jugular foramen. zontal segment of the facial nerve (CN VII) is visualized. Above the cochlea is the internal auditory canal (IAC). Visualized in this image is the anterosuperior IAC segment above the crista falciformis, through which the labyrinthine segment of the facial nerve courses. EAC, external auditory canal; SSCC, superior semicircular canal.

The jugular foramen is the bony channel in which the IX expands, forming the superior glossopharyngeal gan- sigmoid sinus connects to the internal jugular vein at the glion, then proceeds inferiorly along the medial aspect of level of the nasopharyngeal carotid space. This foramen the jugular bulb within the pars nervosa of the jugular courses anteriorly, laterally, and inferiorly as it insinuates foramen.6,8 Before CN IX completely exits the skull base, itself between the medial petrous temporal bone and the its tympanic branch (nerve of Jacobson) usually emerges occipital bone.3,4 The endocranial opening of the jugular from the inferior glossopharyngeal ganglion, also located foramen is usually divided by a fibrous (more common) within the jugular foramen, enters the inferior tympanic or bony septum into two compartments, the smaller canaliculus located in the caroticojugular spine (between anteromedial pars nervosa and the larger posterolateral pars the ICA and internal jugular vein), and reaches the middle vascularis (Fig. 4.6 and Table 4.1). Although these names ear along with the inferior tympanic artery, where it suggest otherwise, the pars nervosa and pars vascularis ascends along the medial wall of the cochlear promon- both contain important vascular and neural structures. tory. It supplies the main sensory fibers to the mucosa of The pars nervosa contains both the inferior petrosal sinus the mesotympanum and the eustachian tube and joins and the glossopharyngeal (IX) nerve. The inferior petrosal the caroticotympanic nerve to form the lesser superficial sinus drains the cavernous sinus and courses in the petro- petrosal nerve.6,9 The inferior tympanic canaliculus is occipital fissure adjacent to the clivus prior to its exit occasionally seen on CT in cross section at the level of the through the pars nervosa and subsequent drainage into caroticojugular spine.5,10 the internal jugular vein just beneath the jugular foramen The pars vascularis of the jugular foramen contains the (Fig. 4.6).4,5 After emerging from the lateral aspect of the jugular bulb and the vagus (X) and spinal accessory (XI) medulla as multiple rootlets, cranial nerve (CN) IX forms a cranial nerves (Fig. 4.6).4,11 Similar to CN IX, the vagus single bundle that courses a short distance before making nerve also has a superior ganglion within the jugular fora- a sharp bend at its genu lodged just below the external men; it yields an auricular (Arnold’s) branch (cutaneous opening of the cochlear aqueduct.6,7 At this level, the CN to the external ear), which travels through the mastoid ch04.qxd 9/19/08 11:17 AM Page 251

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Fig. 4.11 Asymmetric sigmoid sinus. Axial enhanced computed tomography image through the temporal bones shows asymmetry in size of the venous sinuses, the right sigmoid sinus (★) larger than the left (arrow). This is a normal variant and should not be confused with pathology, as the cortices are smooth without bony destruction. Eval- uation of the remainder of the venous system (not shown) reveals that the entire right side was larger than the left.

canaliculus on the lateral wall of the jugular foramen to reach the descending canal of the facial nerve (Fig. 4.6 and Fig. 4.10).6 The nerves of Jacobson and Arnold contain glomus formations that can give rise to paragangliomas.5 The cranial nerves within the jugular foramen have been identified as filling defects on normal contrast-enhanced high-resolution computed tomography (CT) scans and linear structures of soft intensity on magnetic resonance Fig. 4.10 Coronal reformatted image through the temporal bone on unenhanced CT. The descending segment of the facial nerve (CN VII) imaging (MRI) when appropriate angulation and technique courses vertically through the mastoid bone before exiting through are utilized.11,12 the stylomastoid foramen. Emphasized here is the close anatomic The CT and MRI appearance of the jugular foramen relationship of the facial nerve with the jugular foramen (JF), the depends on the level and angulation of the study. Detailed vestibule (VEST), and the antrum of the mastoid air cells. CT anatomy is best appreciated on axial sections (Fig. 4.5, Fig. 4.6, and Fig. 4.7).5,11 Vascular anatomy is best seen on MRI in the axial and sagittal planes (Fig. 4.2, Fig. 4.3, and Fig. 4.4). There is often considerable variation in the size and symmetry of the normal jugular foramen, with the right side usually larger than the left.5,13 The bony margin, not the size of the foramen, should guide diagnostic eval- Table 4.1 Contents of the Jugular Foramen uation. One should not confuse an extremely large normal Pars Nervosa (smaller anteromedial portion) foramen with a pathological process, as a normal foramen will always be well corticated (Fig. 4.12). An exception to Inferior petrosal sinus the rule may be a long-standing endocranial arteriove- CN IX (glossopharyngeal nerve) nous anomaly that drains by way of the jugular foramen. Proximal portion of the tympanic branch of IX (Jacobson’s nerve) This may cause nonerosive well-corticated pathological Pars Vascularis (larger posterolateral portion) enlargement. “Normal” measurements are available but are impractical in day-to-day evaluation. Irregular, jagged Jugular bulb margins are never normal. CN X (vagus nerve) Auricular branch of X (Arnold’s nerve) Associated posterior jugular paraganglion Normal Arterial Anatomy Distal portion of Jacobson’s nerve The petrous portion of the ICA courses through the temporal Associated posterior jugular paraganglion bone in a bony tunnel termed the carotid canal (Fig. 4.5, Fig. 4.6, and Fig. 4.7). It is accompanied by the periarterial CN XI (spinal accessory nerve) sympathetic plexus, which forms the deep petrosal nerve. ch04.qxd 9/19/08 11:17 AM Page 252

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A B Fig. 4.12 Asymmetrically enlarged jugular foramen. (A) Asymmetric T1-weighted magnetic resonance image shows an asymmetrically enlargement of the jugular foramen (arrow) is a common anatomic variant enlarged right jugular bulb. This normal anatomic variant can appear like that occurs more commonly on the right, as depicted here. The smooth, a mass, particularly on a single image. Careful evaluation of all of the well-corticated margins of the jugular foramen on CT indicate that the images will reveal its continuation with the sigmoid sinus and internal asymmetry is not due to a pathologic process. (B) Axial postgadolinium jugular vein.

Because of this anatomic relationship, injury to the carotid artery in this area, such as occurs in dissection, will often present as an incomplete Horner’s syndrome (miosis, ptosis, but not anhidrosis). This kind of incomplete Horner’s syndrome is also referred to as oculosympathetic palsy.14 Incomplete Horner’s syndrome occurs due to sparing of sudomotor fibers to the face that travel along the external carotid artery (ECA), whereas the pupillomotor fibers travel along the ICA after synapsing in the superior sympathetic ganglion. According to the classification system described by Bouthillier et al,15 there are three segments to the petrous ICA – a vertical or ascending segment, a genu (posterior loop of the ICA), and a horizontal segment (Fig. 4.13).16,17 The ICA enters the skull base through the carotid canal, ascending vertically in the petrous temporal bone to the level of the cochlea (Fig. 4.5, Fig. 4.6, and Fig. 4.7). At this level, the canal and artery make an anteromedial bend of ~90 degrees, coursing horizontally in an anteromedial direction, ending at the apex of the petrous pyramid, just cephalad to the foramen lacerum (Fig. 4.6 and Fig. 4.7). A small branch, the caroticotympanic artery, arises from the petrous ICA near its genu and perforates the bony plate of the carotid canal to enter the posteromedial tympanic cavity.18 This vessel will become important in the discussion of the origins of Fig. 4.13 Magnetic resonance angiography of the internal carotid the aberrant carotid artery. artery (ICA). Maximal intensity projection image of the ICA in the The petrous ICA vertical segment can be identified on lateral projection demonstrates the normal anatomy of its petrous segment. There are three segments of the petrous ICA, the vertical both axial and coronal CT and MR images. On axial segment (V) that courses through the petrous temporal bone, the section (Fig. 4.5 and Fig. 4.6), the vertical segment is posterior genu (G) that bends anterolateral to the cochlea, and the located anterior to the jugular bulb, separated by the horizontal segment (H). ch04.qxd 9/19/08 11:17 AM Page 253

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caroticojugular spine. On coronal CT images (Fig. 4.8), Pathology the vertical segment is located inferior to the cochlea and medial to the head of the malleus in the tympanic Vascular Lesions of the Temporal Bone cavity.15 The petrous ICA horizontal segment is best seen on The vascular structures of the temporal bone course axial MR or CT sections (Fig. 4.3 and Fig. 4.7). At the between different compartments of the head and neck; genu of the horizontal and vertical portions, the canal is hence, they can serve as conduits for the spread of disease, separated from the posterolateral middle ear cavity by a particularly neoplastic and infectious processes. relatively thin bony plate.16 Its course then parallels the Tumors from the nasopharyngeal mucosal area (squa- more anterolateral eustachian tube and tensor tympani mous cell carcinoma, non-Hodgkin’s lymphoma, minor sali- muscle toward the petrous apex, forming the roof of the vary gland malignancies) and adjacent deep facial spaces foramen lacerum before ascending into the cavernous will spread along paths of least resistance, following a sinus. Superficial and just lateral to the horizontal seg- perivascular course through the skull base along the carotid ment of the petrous ICA, the greater and lesser superfi- canal (Fig. 4.14). These tumors will often encase and narrow cial petrosal nerves, respectively, course within their the ICA, but they rarely result in complete occlusion. own distinctive grooves.15 The CT appearance of the Infections of the nasopharyngeal carotid space may horizontal segment of the carotid canal is relatively affect the vertical portion of the petrous ICA (Fig. 4.15), constant. Conventional unenhanced spin echo MRI, whereas apical petrositis will more commonly involve the however, does not effectively demonstrate the petrous more distal horizontal petrous ICA. ICA because the low signal of flowing arterial blood next to the low signal of bone makes identification of the Venous Sinus Thrombosis normal artery difficult. The combination of source images and reprojection images found in MR angiography Venous structures of the temporal bone, including the (MRA) has vastly improved the ability of MRI to identify transverse sinus, sigmoid sinus, and internal jugular bulb/ the normal and diseased petrous ICA (Fig. 4.13). vein, are subject to thrombophlebitis and thrombosis. The

A B Fig. 4.14 Perivascular spread of nasopharyngeal cancer. A 53-year-old of the petrous internal carotid artery (arrow) and also extending into the man presented with known nasopharyngeal squamous cell carcinoma jugular foramen (arrowhead). (B) Slightly higher level shows that the for radiation treatment. (A) Axial enhanced T1-weighted MR image enhancing nasopharyngeal tumor travels along the carotid canal and obtained on a 3.0 Tesla unit shows a large enhancing mass arising from the continues to encase the horizontal segment of the right petrous internal lateral wall of the right nasopharynx (*) encasing the vertical segment carotid artery (arrow). ch04.qxd 9/19/08 11:17 AM Page 254

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jugular vein may occur (Fig. 4.16). When this occurs, severe intracerebral complications may ensue.19,20 Venous infarction of the temporal lobe is one of the more common complications seen in this setting as the vein of Labbé drains the posterolateral temporal lobe directly into the junction of the transverse and sigmoid sinuses (Fig. 4.1B).19,21 MRI and MR venography (MRV) can be very helpful in diagnosing transverse and sigmoid sinus thrombosis in its early phase, prompting therapy before more serious sequelae appear. Care must be taken with this diagnosis, however, because asymmetry in the size of the transverse/ sigmoid sinuses and jugular bulb is a common anatomic variant. Whereas the hypoplastic side may mimic sinus thrombosis due to its small size (Fig. 4.17D), the more prominent contralateral side may demonstrate slow or turbulent flow that can also mimic thrombosis on conventional MRIs (Fig. 4.17).12,22 The diagnosis of venous sinus thrombosis can be made only after studying all available Fig. 4.15 Skull base osteomyelitis causing narrowing of the petrous MRI sequences and confirming abnormal signal within internal carotid artery in a 45-year-old woman with a retropharyngeal the venous sinuses on all images (Fig. 4.18). infection and skull base osteomyelitis. Axial enhanced CT image Conventional angiography can be used to confirm shows inflammatory in mass the retropharyngeal and prevertebral diagnosis suspected on cross-sectional imaging and pro- spaces causing erosion of the clivus and temporal bone (black arrowheads), and narrowing of the left vertical petrous internal carotid vide a means for endovascular thrombolysis. artery (white arrow). The normal caliber right internal carotid artery is shown for comparison (white arrowhead). Infectious etiology was proven on pathologic examination. Lesions of the Jugular Foramen The jugular foramen as a distinct anatomic site in the inferomedial temporal bone, like the petrous apex, com- proximity of the mastoid air cells makes the sigmoid mands its own site-specific differential diagnosis list sinus particularly vulnerable to inflammatory processes (Table 4.2). Because of the complex surgical issues for a involving the mastoids. When infection affects these air lesion of the jugular foramen, both axial and coronal CT cells, secondary thrombosis of the sigmoid sinus and (using soft tissue and bone algorithm) and enhanced MR adjacent transverse sinus or jugular bulb and internal imaging are usually employed for presurgical planning.

A B Fig. 4.16 Mastoiditis causing dural sinus thrombosis. A 12-year-old within the left mastoid air cells (arrow). (B) Axial T2-weighted MRI child presented with persisting fever, left ear pain, and drainage, demonstrates inflammatory debris within the left mastoid air cells with despite completing a course of antibiotics. (A) Axial postgadolinium heterogeneous signal (arrow) and loss of flow void within the left T1-weighted magnetic resonance image (MRI) demonstrates a filling sigmoid sinus. defect in the left sigmoid sinus, indicating thrombus with enhancement ch04.qxd 9/19/08 11:17 AM Page 255

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Fig. 4.16 (Continued) (C) Axial diffusion weighted MRI shows restricted diffusion within the left mastoid air cells and sigmoid sinus compatible with abscess formation. (D) MR venography reformatted in the coronal plane demonstrates nonvisualization of the sigmoid sinus (arrow) and internal jugular vein (arrowheads), confirming extensive thrombosis. Filling defect in the left transverse sinus is compatible with partial thrombus. (Images courtesy of Michael Jay, MD.) D

Although it is not always possible to suggest the histologi- bony jugular foramen and the jugular bulb may be nor- cal diagnosis from CT and/or MR images, many of the mally quite asymmetric in size (Fig. 4.12). Flow-related lesions that involve the jugular foramen either primarily artifacts on MRI (Fig. 4.17A) can occasionally mimic, and or secondarily have distinctive radiological features. thus must be differentiated from venous thrombosis When confronted by an abnormality of the jugular (Fig. 4.18A) or schwannoma (Fig. 4.22). Once these “do foramen on CT or MRI, the radiologist must first decide if not touch” lesions have been excluded, the radiologist the lesion is real or one of the “do not touch” lesions may proceed with an attempt to differentiate the group of found in this area (Table 4.2). As described previously, the real mass lesions of the jugular foramen.

A B Fig. 4.17 Asymmetric dural sinuses mimicking thrombus. (A) Unen- flight magnetic resonance venogram (2D TOF MRV) source image shows hanced axial T1-weighted magnetic resonance image demonstrates a hy- flow-related enhancement in the area of question, confirming normal flow perintense focus (arrow) in the region of the right jugular bulb, which may through this area. mimic a mass or venous thrombus. (B) Axial two-dimesional (2D) time-of- (Continued on page 256) ch04.qxd 9/19/08 11:17 AM Page 256

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C D

Fig. 4.17 (Continued) (C) More superiorly, axial 2D TOF MRV shows that the hyperintense focus is contiguous with the sigmoid sinus (SIG), consistent with a normal jugular bulb (JB) relative to the hypoplastic left venous system. T1-weighted hyperintensity in Fig. 4.18A was likely related to flow alterations in the enlarged jugular bulb. (D) Axial MRV maximal intensity projection (MIP) image demonstrates apparently complete absence of the left transverse and sigmoid sinuses and jugular bulb (arrows). The imager must be diligent in reviewing all images to ensure that this appearance is not due to a hypoplastic venous system, as in this case, in which the entire ipsilateral venous system is small. Note the nearly identical appearance of this image with the ones of pathologic thrombosis (Fig. 4.16D and Fig. 4.18B). (E) Enhanced computed tomography (CT) image of the head in bone window can better define bony anatomy. This CT image shows that the left jugular foramen is very small (arrow) compared with the right, consistent with developmental E hypoplasia. The sigmoid sinus (arrowhead), as expected, is also hypoplastic.

Although multiple potential lesions of the jugular The combination of extreme tumor vascularity and per- foramen are listed in Table 4.2, statistically speaking meative margins is highly suggestive of the diagnosis of paraganglioma, schwannoma, and meningioma make up paraganglioma.24,25 On T1-weighted images (T1WI), MRI the vast majority of the tumors found within this struc- most commonly demonstrates hypointense flow voids ture. Of these three, paraganglioma (glomus jugulare or within the tumor (pepper) parenchyma, whereas hyperin- glomus jugulotympanicum) is the most common and tense foci of methemoglobin within the tumor inter- will be discussed in detail in the Pulsatile Tinnitus sec- stices (salt) is seen far less commonly (Fig. 4.20).26 tion of this chapter. Schwannomas of the jugular foramen usually origi- Paragangliomas, schwannomas, and meningiomas nate from CN IX. CN IX deficits, however, are unusual un- have specific characteristics, including different growth less a significant portion of the schwannoma is below patterns and effects on the surrounding bone, that can the skull base.27 Most patients present with decreased be helpful in differentiating them on imaging. Paragan- hearing and, less often, vertigo and ataxia likely related gliomas typically extend from the jugular foramen in a to compressive effects of the mass on CN VIII.27,28 superolateral direction to involve the medial hypotym- Schwannomas follow the course of CN IX and typically panum.23 CT shows a permeative destructive pattern demonstrate a superomedial vector of growth toward with erosion of the jugular spine and foramen (Fig. 4.19). the lateral aspect of the brainstem.23 As schwannomas ch04.qxd 9/19/08 11:17 AM Page 257

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A B Fig. 4.18 Right transverse and sigmoid sinus and internal jugular vein pulse sequences to correctly distinguish normal anatomic variance in thrombosis. (A) Axial T2-weighted magnetic resonance image shows size of the sinuses versus true thrombosis. (B) Two-dimensional time-of- loss of normal flow void within the right transverse and sigmoid sinuses flight magnetic resonance venogram maximal intensity projection and proximal right internal jugular vein (arrows), which should raise the image in the coronal plane confirms thrombus in the right transverse imager’s suspicion for thrombus. It is imperative to evaluate all of the and sigmoid sinuses (arrows) and internal jugular vein.

rarely grow into the middle ear cavity, otoscopic evaluation is most commonly negative in these patients.29 On CT, these lesions are usually isodense to brain parenchyma and cause enlargement of the jugular foramen with sharp, rounded, and thin sclerotic rims (Fig. 4.21).23,27,29 When the lesion projects downward

Table 4.2 Lesions of the Jugular Foramen “Do Not Touch” Lesions Asymmetrically enlarged jugular bulb (MRI)* Asymmetrically enlarged jugular foramen (CT)* Slow or turbulent flow in large or high jugular bulb (MRI)* Vascular Lesions Sigmoid sinus, jugular bulb, internal jugular vein thrombosis* Arteriovenous fistula or malformation (enlarged jugular bulb) Tumors Glomus jugulare or jugulotympanicum paraganglioma* Schwannoma (CN IX, X, XI)* Neurofibroma (CN IX, X, XI) Meningioma Lateral clival chordoma Fig. 4.19 Permeative destruction of glomus jugulotympanicum. Axial unenhanced computed tomography image through the right tempo- Metastasis ral bone demonstrates permeative destruction of the right jugular Chondrosarcoma (petro-occipital synchondrosis) foramen with loss of normal cortex (arrows). A soft tissue mass is seen extending into the middle ear cavity and external auditory canal. This Invasive nasopharyngeal carcinoma appearance is typical of paragangliomas. *Most common lesions ch04.qxd 9/19/08 11:17 AM Page 258

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Fig. 4.20 Axial T2 weighted MR image demonstrates a glomus jugulare (white arrow). There are punctate areas of T2 hypointensity representing flow voids from areas of high blood flow in this vascular tumor.

Fig. 4.21 Smooth remodeling of schwannoma. Axial unenhanced computed tomography image demonstrates a mass causing smooth expansion of the left jugular foramen (arrows). Note the bony margins into the nasopharyngeal carotid space or upward into remain sharp with thin sclerotic rims. the basal cisterns, it becomes characteristically dumbbell-shaped (Fig. 4.22).30 MRI typically demonstrates low T1- and high T2-weighted signal with uniform enhancement, but cystic components may be seen, par- adults between the ages of 20 and 60 years. Although they ticularly in larger lesions (Fig. 4.23).29 Unlike paragan- are most commonly found in a parafalcine location or over gliomas, flow voids within the lesion are conspicuously the cerebral convexity, 33% arise from the meninges asso- absent. Schwannomas are also less likely to infiltrate and ciated with the skull base.34 Because the arachnoidal cells insinuate into surrounding structures and are thus tech- may be found anywhere along the meninges, meningiomas nically easier to remove surgically, but they are less can be found on any of the meningeal-lined surfaces of the responsive to radiation than paragangliomas. They are temporal bone. Clinical presentation is similar to schwan- also slower growing and are less likely to exhibit malignant nomas with hearing loss and cranial neuropathies (CN V behavior.30,31 through XII) being common. Unlike schwannomas, however, The jugular foramen is a rare location for meningioma, meningiomas can present as a vascular tympanic mass, as accounting for 4% of posterior fossa meningiomas in the they may secondarily extend into the middle ear cavity.35 largest neurosurgery series.32,33 These tumors arise from Meningiomas of the jugular foramen can be either pri- arachnoidal cells of the meninges and usually occur in mary or secondary.36 Posterior fossa meningiomas with

A B Fig. 4.22 Dumbbell-shaped schwannoma. A 48-year-old woman pre- enhancing, dumbbell-shaped mass (arrow) that extends through the sented with dizziness. (A) Coronal unenhanced and (B) postgadolinium jugular foramen into the basilar cisterns. T1-weighted magnetic resonance images demonstrate a diffusely ch04.qxd 9/19/08 11:17 AM Page 259

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C D Fig. 4.22 (Continued) (C) The mass is hypointense relative to CSF (arrow) (D) Axial postgadolinium T1-weighted MR image shows the enhancing on this T2-weighted MR image, and has no flow voids, a finding that can mass in the right jugular foramen and cerebello-medullary angle (arrows). be helpful in distinguishing a schwannoma from a paraganglioma.

secondary extension into the jugular foramen have imag- of erosive and sclerotic changes. The hyperostotic bony ing characteristics similar to meningiomas elsewhere. response characteristic of meningiomas in other locations They are solid, well-circumscribed, extraaxial, dural-based is not typical for primary jugular foramen meningiomas. masses often showing an en plaque pattern of growth Treatment of jugular foramen meningiomas is surgical (Fig. 4.24). Strong uniform enhancement is seen, often resection, but these lesions have the highest likelihood of with a dural tail at its margin. Primary jugular foramen recurrence after surgery compared with paragangliomas meningiomas, on the other hand, are characterized by and schwannomas. extensive skull base infiltration and a “centrifugal” pattern Primary cholesteatoma (epidermoid) is a benign of growth.23 This includes growth into the middle ear cavity congenital neoplasm made of epithelial rests of exfoli- laterally, the jugular tubercle, hypoglossal canal, occipital ated keratin that can produce a smoothly marginated condyle, and clivus medially, and the nasopharyngeal lesion of the jugular foramen on CT. Locally aggressive carotid space inferiorly. The skull base infiltration has a features are usually not seen unless large. These lesions “permeative-sclerotic” appearance on CT; the margins of occur in the immediate vicinity of the jugular foramen, the jugular foramen are irregular with a combination usually emanating from the petrous apex or middle ear

A B Fig. 4.23 Schwannoma with cystic changes. (A) Axial T2-weighted jugular vein. (B) Coronal postcontrast magnetic resonance image magnetic resonance image demonstrates a large mass hyperintense shows peripheral areas of enhancement and nonenhancing cystic portions relative to CSF in the right carotid space (arrows) between the anteri- (arrows). Larger schwannomas, such as depicted here, can undergo orly displaced internal carotid artery and posteriorly displaced internal cystic degeneration. ch04.qxd 9/19/08 11:17 AM Page 260

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they may be indistinguishable. There is often a rapid onset of clinical symptoms, especially cranial nerve palsies, as well as pain, which is usually not seen with schwannomas and paragangliomas. The spread of these lesions is indiscriminate with respect to the characteristic routes often followed by paragangliomas. Many metastases are vascular and may produce similar angiographic findings to those of paragangliomas. Renal and thyroid metastases are notorious in this regard.

Patient Evaluation of Pulsatile Tinnitus and/or Vascular Retrotympanic Mass Fig. 4.24 Secondary jugular foramen meningioma. Axial postcontrast One of the major indications for radiologic evaluation of T1-weighted multiplanar reformatting magnetic resonance image the temporal bone in adults is for further assessment through the posterior fossa demonstrates a large, homogeneously 37–39 enhancing extraaxial mass (M) that extends into the jugular foramen of tinnitus and/or a vascular retrotympanic mass. Tin- (arrowheads). This was a pathologically confirmed meningioma. nitus can be characterized as nonpulsatile or pulsatile. The term pulsatile tinnitus (PT) refers to the patient who perceives a rhythmic sound thought to be pulse-synchronous. PT may be further subcategorized into arterial and venous types. Arterial PT rises in systole and does cavity. On MRI, primary cholesteatomas are hypointense not disappear with light pressure on the ipsilateral jugu- to isointense on T1WIs with occasional peripheral en- lar vein. Venous PT is heard as a continuous bruit around hancement. the ear accentuated in systole but is abolished by light Other tumors that have infiltrating, destructive margins pressure on the ipsilateral jugular vein.40–42 When PT is that involve the jugular foramen seen on CT are chordoma, perceived only by the patient, it is referred to as subjec- chondrosarcoma, hematogenous metastases, and direct in- tive PT; when audible to the examining physician as vasion from aggressive regional malignancies, particularly, well, it is objective PT. PT may be associated with both squamous cell carcinoma of the nasopharynx.30,39 Metas- normal vascular variants of the temporal bone and a tases may be much more aggressive and destructive than wide variety of pathologic processes affecting this area paragangliomas (Fig. 4.25), although in their earlier stages (Table 4.3).25,37,38,43

A B Fig. 4.25 Breast cancer metastatic to the jugular foramen. Forty-seven- foramen (★), indicating an aggressive process. Biopsy revealed year-old woman with known breast cancer presented with new pain in metastatic disease. (B) Corresponding axial postgadolinium magnetic the right occipital region. Bone scan demonstrated increased activity at resonance image demonstrates an ill-defined, heterogeneously enhanc- the right posterior base of skull concerning for metastatic disease. ing mass extending through the jugular foramen (arrows) and involving (A) Coronal unenhanced computed tomography image in bone algo- the right cerebellar hemisphere and surrounding dura (arrowhead). rithm demonstrates permeative bony destruction of the jugular ch04.qxd 9/19/08 11:17 AM Page 261

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Table 4.3 Differential Diagnosis of Pulsatile Tinnitus Table 4.4 Pulsatile Tinnitus Etiologies: Grouped by Mechanism Normal Vascular Variants Arterial Causes Venous variants Congenital Asymmetric jugular bulb* Aberrant internal carotid artery High, nondehiscent jugular bulb* Persistent stapedial artery Dehiscent jugular bulb Laterally displaced internal carotid artery Jugular bulb diverticulum Acquired Arterial variants Atherosclerotic stenosis, turbulence Aberrant internal carotid artery Fibromuscular dysplasia Lateralized internal carotid artery Internal carotid artery dissection Persistent stapedial artery Petrous internal carotid artery aneurysm Tumors Arteriovenous High-Flow Causes Paraganglioma Vascular Glomus tympanicum paraganglioma* Transverse-sigmoid dural sinus arteriovenous fistula Glomus jugulotympanicum paraganglioma* Direct, extracranial arteriovenous fistula Glomus jugulare paraganglioma* Paratemporal bone cerebral arteriovenous malformation Glomus vagale paraganglioma Tumor Meningioma Glomus tympanicum, jugulotympanicum, jugulare paraganglioma Endolymphatic sac adenomatous tumors Paratemporal bone meningioma Vascular metastasis (renal, thyroid, etc.) Endolymphatic sac adenomatous tumor Acquired Vascular Lesions Miscellaneous Dural arteriovenous fistula* Active phase, cochlear otosclerosis Extracranial direct arteriovenous fistula Paget’s disease of temporal bone area Atherosclerotic carotid artery stenosis Venous Causes Fibromuscular dysplasia Congenital Internal carotid artery dissection Jugular bulb diverticulum Petrous internal carotid aneurysm High, dehiscent jugular bulb Transverse sinus stenosis Acquired Large vessel arteritis Transverse-sigmoid dural sinus stenosis Miscellaneous Causes Benign intracranial hypertension (pseudotumor cerebri) Otomastoiditis Systemic conditions with hyperdynamic systemic circulation Paget’s disease of the temporal bone Chronic anemia Osteolytic phase of otosclerosis Thyrotoxicosis Idiopathic or benign intracranial hypertension (pseudotumor cerebri) Pregnancy *More common lesions

Another way of grouping the causes of PT is to con- conditions of the middle ear (Table 4.5). It is often im- sider the three underlying mechanisms for the creation possible for the clinician to distinguish between these of a pulse-synchronous sound: arterial jetting, arteriove- entities on otoscopic examination.39,44 Because misiden- nous shunting, and venous turbulent flow (Table 4.4).42 tification of normal vascular variants as pathological Vascular tympanic membrane is the term used to describe lesions may lead to serious complications if biopsy is the red or blue appearance of the TM on otoscopic exam- attempted, pretreatment radiological evaluation and diag- ination as a result of a vascular retrotympanic mass.37–39 nosis is essential. A vascular TM can be seen with normal vascular vari- Given the anatomic complexity of the temporal bone ants, paragangliomas, and certain chronic inflammatory and the varying imaging modalities and protocols available, ch04.qxd 9/19/08 11:18 AM Page 262

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Table 4.5 Differential Diagnosis of the Vascular-Appearing Tympanic Membrane Arterial Causes Aberrant internal carotid artery* Lateralized internal carotid artery Petrous internal carotid artery aneurysm (with dehiscent carotid plate) Venous Causes Dehiscent jugular bulb* Infectious Inflammatory Causes Cholesterol granuloma* Otomastoiditis with hemorrhage Tumors Glomus tympanicum paraganglioma* Glomus jugulotympanicum paraganglioma* Large meningioma *Most common lesions Fig. 4.26 Imaging algorithm for the work-up of a patient with non-PT. MRV, magnetic resonance venography; MRA, magnetic resonance angiography; CTA, computed tomography angiography; ICA, internal the radiologist’s task of ruling out a vascular temporal carotid artery; DAVF, dural arteriovenous fistula; gad, gadolinium. bone lesion may be quite formidable. Radiological evalua- (Adapted from Weissman JL, Hirsch BE. Imaging of tinnitus: a review. tion can be simplified and made more cost-effective if the Radiology 2000;216(2):342–349. Reprinted with permission.) type of tinnitus (objective versus subjective, arterial versus venous) and the appearance of the TM are known prior to radiological evaluation. Utilizing this information, evaluating patients with PT but no retrotympanic mass an algorithmic approach can be used to direct the choice may obviate the need for multiple examinations for diag- of initial study (Fig. 4.26).37–39 Contrast-enhanced high- nosing and planning treatment for PT, as this examination resolution CT of the temporal bone has become the study can accurately diagnose the bony, neoplastic, and vascular of choice for the initial evaluation of both objective and etiologies of PT. In their study, the CTA and CTV were per- subjective types of PT, particularly in the presence of a formed simultaneously with a single acquisition of im- retrotympanic mass.40 Because the most common causes ages after a fixed delay that allowed imaging of both the of PT are vascular abnormalities within the middle ear arterial and venous structures. The images were also re- and otic capsule, CT offers an advantage over MRI in eval- viewed in bone windows, allowing excellent evaluation of uating temporal bone anatomy, structures embedded the temporal bones in multiple planes. If a dural AVF was within bone, and the effects of a lesion on its bony sur- suspected, however, conventional angiography remained roundings (i.e., erosion, remodeling, hyperostosis).40 the gold standard for the evaluation of this entity. Whereas CT is used as the first line of diagnostic problem- The four broad categories for PT and retrotympanic solving, MRI has a complementary role in further delin- masses are vascular variants and congenital anomalies, eating the soft tissue characteristics and extent of a lesion. acquired vascular lesions, neoplasms, and chronic inflam- In the setting of objective PT and normal CT and MRI matory lesions of the middle ear cavity. Table 4.3 lists the examinations, angiography is recommended as the next processes that generally cause subjective and objective imaging study to exclude the presence of dural arteriove- tinnitus. The causes of a vascular-appearing TM are listed nous fistulas (DAVFs), as these lesions are notoriously dif- in Table 4.5. ficult to appreciate on cross-sectional imaging. To ensure a complete evaluation, it is imperative that both the anterior (external and internal carotid artery) and posterior Etiology (vertebral artery) circulations are studied. Vascular Variants and Congenital Anomalies If atherosclerotic disease is the suspected etiology, CTA of the head and neck can be performed primarily or Particular variations and anomalies in vascular anatomy in secondarily.45 Recently, Krishnan et al46 proposed that the temporal bone are a frequent cause of PT and a vascular- employing CTA and CTV as the single initial study for appearing TM. These include the jugular bulb variants/ ch04.qxd 9/19/08 11:18 AM Page 263

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anomalies (high jugular bulb, dehiscent jugular bulb, and asymmetry in the size of the jugular foramen with jugular bulb diverticulum), aberrant ICA, and the rare preservation of the jugular spine and all cortical margins persistent stapedial artery.4,47–49 When these vascular (Fig. 4.12A). The transverse and sigmoid sinuses as well as anomalies present with PT and a vascular TM, differentia- the internal jugular vein are enlarged on the side of the tion from neoplasms becomes crucial prior to biopsy. enlarged jugular bulb. Venous flow alterations occurring in Contrast-enhanced high-resolution CT of the temporal a large, asymmetric jugular bulb at times may mimic bone is the principal imaging tool used to diagnose these thrombosis or jugular foramen schwannoma, especially on normal vascular variants and congenital anomalies, as the postcontrast T1WIs (Fig. 4.12B and Fig. 4.22D). Careful bony detail is better delineated on CT than on MRI. evaluation of all of the pulse sequences should, however, make it clear that this appearance represents an asymmetrically enlarged jugular bulb rather than a mass. Addition- Jugular Bulb Variants ally, MRV either with standard two-dimensional (2D) When a patient presents with venous PT or a vascular time-of-flight (TOF) technique or with phase contrast retrotympanic mass, jugular bulb variants may frequently technique can clear up the confusion (Fig. 4.18). be difficult to clinically differentiate from paragan- A high-riding jugular bulb is defined when the supe- gliomas.44 Just as often, however, these normal venous rior margin of the bulb reaches or rises above the floor of variants can be seen on CT and MRI performed for other the internal auditory canal. The bulb is considered nonde- reasons as completely incidental findings. Recognition of hiscent if the bone between the jugular bulb and middle these normal variants prevents misdiagnosis and unnec- ear cavity is intact. On enhanced T1WI, this normal vari- essary intervention. ant appears as an enhancing focus in the medial temporal The major jugular bulb variants include the asymmetri- bone, which can be mistaken for tumor. However, on CT, cally large jugular bulb, high-riding jugular bulb without or the bony margins will always be well corticated, differen- with dehiscence, and jugular bulb diverticulum. The first of tiating this normal variant from a pathological process these, the asymmetrically large jugular bulb, is a common (Fig. 4.27).24 normal vascular variant, which only becomes an imaging When the high-riding jugular bulb is dehiscent (Fig. 4.28), problem when the radiologist discovers it in the search for it usually presents as a vascular retrotympanic “mass.”50 a cause of PT. By itself, the asymmetrically large jugular The dehiscent vessel is most commonly seen behind the bulb is generally not felt to be a cause of venous PT. posteroinferior quadrant of the tympanic membrane,42 The jugular bulb is asymmetrically larger on the right side and its size depends on the size of the deficiency in the twice as often as it is on the left side.13,40,41 CT demonstrates sigmoid plate.51 This normal venous variant is best diagnosed

A B Fig. 4.27 High riding jugular bulb without dehiscence. (A) Axial (B) Coronal image shows that the JB is not dehiscent, as the bone unenhanced computed tomography image shows a high-riding jugu- (arrow) maintains its integrity between the jugular foramen and ear lar bulb (JB) extending to the floor of the internal auditory canal (IAC). cavity. ch04.qxd 9/19/08 11:18 AM Page 264

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A B Fig. 4.28 High-riding jugular bulb, dehiscent. (A) Axial unenhanced cavity (arrow). (B) Coronal image again demonstrates a high riding computed tomography image through the temporal bone shows a jugular bulb (★) with bony dehiscence and minimal protrusion into high-riding jugular bulb extending to the level of the internal auditory the middle ear cavity. canal (not shown) and lacks a bony separation from the middle ear

on coronal CT (Fig. 4.29). The jugular bulb is seen directly A jugular bulb diverticulum is considered a true venous contiguous with the middle ear mass across the dehis- anomaly and is an outpouching of the jugular bulb extend- cence, confirming its origin. MRI does not readily demon- ing superiorly, medially, and posteriorly in the petrous bone strate the presence or absence of dehiscence because of the (Fig. 4.29).52 The jugular bulb may be high or normal in posi- lack of fine bone detail inherent to MRI. Dehiscence, how- tion. The TMs are normal in appearance in these patients, as ever, can be inferred by the presence of a lateral lobula- the middle ear cavity is not breached. Venous pulsatile tinni- tion on the coronal MR image. tus may be present if turbulence of venous flow occurs.39,42

Fig. 4.29 Jugular diverticulum. (A) Coronal postgadolinium T1-weighted magnetic resonance image demonstrates a focal outpouching of the jugular bulb extending superiorly, consistent with a jugular bulb diverticulum. This was an incidental finding. Note that the outpouching is oriented superiorly (arrow), unlike the lateral projection seen in a dehiscent jugular bulb. (B) Coronal computed tomography image in bone window in a different patient with a jugular diverticulum demonstrates a superior lobulation (arrow) emanating from the jugular bulb. ([A] Courtesy of A Michael Jay, MD.) ch04.qxd 9/19/08 11:18 AM Page 265

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B Fig. 4.30 Sigmoid sinus diverticulum. This 68-year-old woman presented to the emergency department for mental status changes. (A) Axial and (B) coronal reformatted unenhanced computed tomography images in bone window demonstrate a lateral diverticulum of the right sigmoid sinus (arrows) that causes an outpouching in the mastoid temporal bone. There is a thin bony plate remaining without frank dehiscence. The normal A left side is shown for comparison (arrowheads).

PT can also be caused by a sigmoid sinus diverticu- important that the clinical-radiologic evaluation differenti- lum.53 This may present as an enhancing, expansile mass ates between these two lesions, as a mistake in diagnosis in the petrous bone (Fig. 4.30). with resultant surgical intervention can be disastrous.55 The CT appearance of aberrant ICA is characteristic (Fig. 4.32).17,42,56,57 The reduced caliber aberrant ICA enters Aberrant Internal Carotid Artery the tympanic cavity through an enlarged inferior tym- Aberrant ICA is a collateral pathway that develops as a result panic canaliculus in the caroticojugular spine, posterior of agenesis of the first embryonic (C1) segment of the ICA and lateral to the normal location of the vertical segment (Fig. 4.31). It may be associated with a persistent stapedial of the ICA. It courses anteriorly across the cochlear artery. To maintain intracranial blood flow, blood is promontory to join the horizontal portion of the petrous rerouted through the inferior tympanic artery branch of carotid canal through a dehiscence in the carotid plate. the ascending pharyngeal artery, which anastomoses with The vertical portion of the carotid canal may be hypoplas- the caroticotympanic branch of the petrous ICA and ulti- tic or absent. If there is stenosis at the point where the mately connects to the horizontal segment of the petrous aberrant artery rejoins the horizontal internal carotid ICA. This collateral pathway, also known as an aberrant artery, objective PT may occur. ICA, enlarges these otherwise tiny vessels due to the new On coronal CT sections, the aberrant ICA appears as a vascular demands, and thereby also enlarges the inferior round soft tissue density within the middle ear. On a tympanic canaliculus at the skull base, through which the single image, the artery has a striking resemblance to a inferior tympanic artery normally enters the cranium.44,45 glomus tympanicum paraganglioma. The recognition of Because the C1 segment of the ICA never forms, the normal the tubular nature on sequential coronal images accom- endocranial opening of the carotid canal is absent. Instead, panied by the absence of the normal-appearing vertical the enlarged inferior tympanic canaliculus serves as the segment of the carotid canal permits its correct identifica- endocranial opening of the aberrant ICA, resulting in a tion as an aberrant ICA.17 Although not necessary for diag- more posteriorly and laterally positioned anomalous verti- nosis, the aberrant ICA also shows characteristic features cal petrous carotid canal. Because the inferior tympanic ar- with angiography.58 tery and caroticotympanic artery normally course through MRA is more sensitive than conventional MRI for a reli- the middle ear cavity, the aberrant vessel also travels along able diagnosis of aberrant ICA (Fig. 4.32E).59–62 MRA find- the cochlear promontory in the middle ear before anasto- ings of aberrant ICA include a lateral and superior location mosing with the horizontal petrous ICA through a dehis- of the carotid genu in the middle ear on the anteroposte- cence in the carotid plate. This results in the vascular rior (AP) projection and a posterior and superior location retrotympanic mass seen on otoscopic examination. This on the lateral projection.59 A combination of MRI/MRA and rare anomaly may present with objective or subjective pul- high-resolution CT may be required for reliable identifica- satile tinnitus and/or conductive hearing loss, but most tion of this anomaly.63 patients have relatively minor symptoms that do not Although not considered a cause of PT, a laterally dis- require treatment.42,44,54 Aberrant ICA has historically been placed ICA is included in this section because at first confused with a middle ear paraganglioma because both glance, this normal variant can appear similar to an aber- have very similar clinical presentations, and both can pres- rant ICA (Fig. 4.33).64 The laterally displaced ICA swings ent with a vascular retrotympanic mass. It is extremely more posterior and lateral than expected due to a bony ch04.qxd 9/19/08 11:18 AM Page 266

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A B Fig. 4.31 Schematic representation of aberrant internal carotid artery larger than normal. The aberrant ICA has a more lateral and posterior (ICA). (A) Schematic representation of the normal anatomy of the cer- cervical course, passes through the posterior hypotympanum, and en- vical and petrous ICA. (B) Schematic representation of an aberrant ters the posterolateral margin of the horizontal petrous ICA canal ICA. When the cervical (C1) portion of the ICA fails to develop, the (large arrow), bypassing the absent vertical carotid canal. (From Lo inferior tympanic artery enlarges, redirecting the flow through the WW, Solti-Bohman LG, McElveen JT Jr. Aberrant carotid artery: radio- normally small anastomosis with the caroticotympanic artery (now logic diagnosis with emphasis on high-resolution computed tomogra- referred to as the hyoid artery). This new arterial circuit is called the phy. Radiographics 1985;5(6):985–993. Reprinted with permission.) aberrant ICA. The inferior tympanic canaliculus, as expected, is much

dehiscence at the genu between the petrous ICA vertical Basic knowledge of the embryogenesis of this area helps and horizontal segments, allowing protrusion of the ICA to understand this congenital vascular variant (Fig. 4.34). into the anterior middle ear cavity.49 Close inspection of The development of the branchial system produces six the images will reveal that the ICA penetrates the floor paired aortic arches. The first arch gives rise to the fetal of the middle ear cavity anterolateral to the cochlea, not mandibular artery, which regresses. The second arch gives through an enlarged inferior tympanic canaliculus, as rise to the hyoid artery, which normally persists as the seen in aberrant ICA. caroticotympanic branch that arises from the petrous ICA near its genu. The stapedial artery arises from the hyoid artery near its origin and divides into a dorsal branch Persistent Stapedial Artery (future middle meningeal artery) and a ventral branch The persistent stapedial artery is a very rare vascular (future maxillary and mandibular arteries). The stapedial anomaly. A symptomatic persistent stapedial artery is artery then regresses, fully disappearing by the third even less common. Most are found incidentally at the fetal month. When it persists, the stapedial artery arises time of middle ear surgical exploration or radiologic from the vertical petrous ICA and enters the anteromedial work-up of an aberrant ICA. It may occur with or without hypotympanum in an osseous canal. It then courses upward an aberrant ICA.65,66 through the stapedial obturator foramen, where it enters ch04.qxd 9/19/08 11:18 AM Page 267

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A B

C D Fig. 4.32 Aberrant internal carotid artery (ICA). (A) Axial postcontrast image demonstrates the abnormal appearance of the aberrant vertical computed tomography (CT) image shows the abnormally small right aber- segment of the petrous ICA (long arrow), which enters the skull base rant ICA (arrow) that is more posterolaterally positioned than the normal through an abnormally enlarged inferior tympanic canaliculus (between left ICA (arrowhead). (B) Axial postcontrast CT in bone algorithm through short arrows). (D) Anteroposterior projection from magnetic resonance the temporal bone demonstrates an aberrant course of the right ICA as it angiogram MIP of the intracranial vasculature shows the lateral course of passes anteriorly across the cochlear promontory (arrow) to join the hori- the aberrant right internal carotid (arrowheads) compared to the normal zontal portion of the petrous ICA (arrowheads) through a dehiscence in the left side. carotid plate. (C) Coronal reformatted maximal intensity projection (MIP) ch04.qxd 9/19/08 11:18 AM Page 268

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A B Fig. 4.33 Laterally displaced internal carotid artery (ICA). (A) Axial mag- (arrows), allowing a more lateral position. Inspection of the remainder of netic resonance angiograph demonstrates a slightly laterally displaced the study will demonstrate that the ICA penetrates the floor of the mid- right petrous internal carotid artery when compared with the left. dle ear cavity anterolateral to the cochlea and that the inferior tympanic (B) There is a dehiscence of the carotid plate at the genu of the ICA canaliculus and vertical carotid canal are normal in appearance.

Fig. 4.34 Developmental anatomy of persistent stapedial artery. (A) caroticotympanic artery (remnant of the embryonic hyoid artery). Schematic representation of the normal anatomy of the internal carotid Alternatively, the inferior tympanic artery may form the inferior segment artery (ICA) and part of the tympanic arterial plexus. (B) Schematic of the PSA. In the latter case, enlargement of the inferior tympanic representation of a persistent stapedial artery not associated with an canaliculus is expected. There is no foramen spinosum in either situation. aberrant ICA. The persistent stapedial artery arises from an enlarged ch04.qxd 9/19/08 11:18 AM Page 269

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and enlarges the tympanic or horizontal facial nerve canal Acquired Vascular Lesions through a bony dehiscence. It leaves the facial canal 2 mm Acquired vascular lesions are an important cause of objec- behind the geniculate ganglion and travels anteriorly and tive or subjective types of PT and may be overlooked cephalad in the extradural space of the middle cranial because CT and conventional MRI of the temporal bone fossa to form the middle meningeal artery.65,67 may be normal.37–39 The otoscopic examination is also Persistent stapedial artery is probably beyond the resolu- usually normal. Pathology in this group includes DAVFs, tion of even the most sophisticated MRA techniques. How- extracranial AVFs, stenotic lesions of the internal carotid ever, the CT findings of persistent stapedial artery are char- artery, vertebrobasilar dolichoectasia, aneurysm of the acteristic (Fig. 4.35).56,67,68 It appears as a tubular structure petrous ICA, and stenosis of dural venous sinuses.45,69–77 arising at the junction of the vertical and horizontal petrous ICA, entering the hypotympanum where it travels along the cochlear promontory. The artery then enters the obturator Dural Arteriovenous Fistula foramen of the stapes where it is seen as a rounded density. Subsequently, the artery travels along the tympanic segment DAVF is one of the major causes of PT, especially the objec- of the facial nerve which is enlarged. Additionally, the fora- tive form.37–39,78,79 If this entity presents with typical objec- men spinosum on the ipsilateral side is absent reflecting tive PT, angiography is performed in the setting of a negative supply of the middle meningeal artery from the persistent contrast-enhanced CT and/or MRI scan and high suspicion stapedial artery, rather than its normal origin from the max- for a DAVF, with embolic treatment employed at that time illary branch of the ECA. In most cases, the diagnosis is made as appropriate. If the patient has significant neurological retrospectively at the time of middle ear exploration. symptoms that supersede complaints of PT, such as headache, cerebral ischemic/hemorrhagic events, or chronic increased intracranial pressure, the initial imaging study Other Vascular Anomalies should be MRI with MRA and MRV rather than CT.39,80 Unilateral agenesis or hypoplasia of the ICA has been Although conventional angiography is the gold standard for reported both in the presence of the persistent stapedial the evaluation of DAVFs, there are characteristic MRI find- artery and in its absence. In the latter situation, the only ings associated with this entity that the radiologist should anomaly identified by CT would be absence or hypopla- be able to recognize (Fig. 4.39, Fig. 4.40, and Fig. 4.41). sia of the normal carotid canal (Fig. 4.36). MRI/MRA can The pathogenesis of DAVF is debated, but is felt to be be helpful in these cases to confirm the diagnosis by acquired in most cases.71,81,82 Probably the most common delineating the mature collaterals that develop in mechanism of formation is recanalization of thrombosed response to the absence of the ICA. Unilateral agenesis transverse and sigmoid sinuses. Thrombosis may be of the ICA has a left-sided predilection and is associated spontaneous or secondary to trauma, surgery, or hyper- with intracranial aneurysms.66 Bilateral agenesis of the coagulable states. Recanalization may lead to direct arte- ICAs is exceedingly rare. riovenous connections between the meningeal branches

A B Fig. 4.35 Persistent stapedial artery (PSA). (A) Coronal reformatted and traveling along the anteromedial aspect of the hypotympanum. computed tomography (CT) image at the level of the basilar turn of (B) Axial unenhanced CT image through the cochlear promontory the cochlea (black arrow) demonstrates the persistent stapedial shows the anomalous bony canal coursing through the cochlear artery (white arrows) arising from the petrous internal carotid artery promontory (arrow). (Continued on page 270) ch04.qxd 9/19/08 11:18 AM Page 270

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C D

Fig. 4.35 (Continued) (C) As the persistent stapedial artery ascends, it courses through the obturator foramen (arrow). (D) Then the PSA enters into the horizontal facial canal (arrow) to travel with the facial nerve. Note how the horizontal facial canal is widened. Internal auditory canal (★). (E) Because the middle meningeal artery does not have its normal origin from the internal maxillary artery, the foramen spinosum is absent E (arrow). Foramen ovale (★).

of the external carotid artery and the recanalized dural intraarterial embolization to reduce flow and venous venous sinus.83 hypertension. When retrograde cortical venous drainage was Dural fistulas are classified by their venous drainage identified on angiography, intraparenchymal hemorrhage pattern.84 Type I DAVFs exclusively drain into a cerebral and focal neurological deficits occurred. Occlusion of the sinus; type II DAVFs drain into both a cerebral sinus and cortical venous drainage by intraarterial embolic tech- cortical veins; type III DAVFs drain exclusively into corti- niques is essential in such cases. If intravascular tech- cal veins. DAVFs of the sigmoid sinus occur predomi- niques fail in such patients, surgical resection of the sinus nantly in middle-aged women, presenting with unilateral may be necessary. Finally, in type III DAVF with direct cor- PT and an audible bruit on retroauricular auscultation.77 tical venous drainage, the chances of hemorrhage into the Venous drainage patterns as delineated by angiography brain are very high, and all treatment options should be can predict the clinical course of these lesions. In a study exhausted in the quest to disconnect this circuit.81,85 by Cognard et al,81 those patients shown to have antegrade DAVFs are notoriously difficult to identify on conven- dural sinus flow (Fig. 4.37) did not develop significant tional MRI, but there are multiple diagnostic clues that can neurological symptoms and were considered benign. suggest their presence.39,80,86 Conventional MR pulse These patients were treated only if the pulsatile tinnitus sequences may identify abnormally high signal within the was debilitating. However, when retrograde dural sinus transverse and sigmoid sinuses on T1WIs but are often flow was present, nearly 30% developed intracranial unrevealing (Fig. 4.39).87 Abnormally dilated leptomeningeal hypertension (Fig. 4.38). This group was treated with vessels manifesting as enlarged cortically based flow voids ch04.qxd 9/19/08 11:18 AM Page 271

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Fig. 4.36 Isolated absent internal carotid artery. Axial postcontrast computed tomography (CT) image demonstrates a normal left petrous internal carotid artery (★) within the horizontal segment of the petrous carotid canal. However, inspection of the expected location of the right horizontal canal (arrows) demonstrates no normal appearing horizontal carotid canal or internal carotid artery.

on T2WIs are suggestive of a more aggressive DAVF and Fig. 4.37 Type I dural arteriovenous fistula (DAVF). Left common 88 may reflect retrograde drainage of the lesion. With these carotid artery injection in the lateral projection demonstrates a DAVF more aggressive types of DAVFs, posterior fossa ischemic fed by the occipital branch of the external carotid artery (arrows) with events with or without hemorrhage may also be present early antegrade drainage into the transverse and sigmoid sinuses. (Fig. 4.40). With regard to MRA, it has been observed that the source images are better than the maximal-intensity may show the entirety of the DAVF to a better advantage projection (MIP) images in depicting the multiple high- (Fig. 4.41B). Whereas high-resolution CT (HRCT) is much intensity curvilinear or nodular structures adjacent to the less sensitive for the detection of DAVFs, the associated sinus wall and the transosseous collaterals present in this transosseous collaterals have been described to “scallop” lesion (Fig. 4.41A).87 However, the reprojected MRA images the inner cortex on HRCT images, which may be a helpful diagnostic clue if present.89 In the small, strategically placed lesion, even the most detailed MRI may fail to make the diagnosis. Therefore, in patients with equivocal or definite objective PT, a negative contrast-enhanced CT and/or MR with MRA and MRV should be followed by conventional angiography.39,90 Angiographic findings in DAVF vary with the severity of the lesion.81,83,85 In the less severe, more common form where dural sinus flow is antegrade, enlarged internal or external carotid artery branches are seen rapidly draining into the transverse and sigmoid sinuses in an antegrade direction (Fig. 4.39E). More serious lesions will show retrograde flow in the sinuses, with the worst form of DAVF draining directly into engorged cortical veins. Drainage into the vertebral venous plexus can also occur (Fig. 4.42). Conventional angiography remains the gold standard for the evaluation of DAVFs; however, the often nebulous presenting symptomatology, the invasiveness of the pro- Fig. 4.38 Type II dural arteriovenous fistula (DAVF). Lateral projection cedure, and the exposure of the patient to ionizing radia- of the left common carotid artery in the early arterial phase demonstrates enlarged external carotid artery branches, most prominently tion can contribute to delayed evaluation and subsequent the occipital artery (white arrows), feeding numerous DAVF vessels in treatment of the patient with this modality. Thus, ongoing the occipital region. There is antegrade flow in the faintly seen right efforts are in place to better delineate findings on nonin- transverse sinus and internal jugular vein (★); the left transverse sinus vasive imaging so that appropriate evaluation and treat- was occluded. Retrograde flow was seen into the straight sinus (black ment can occur earlier within the course. Specifically, arrowhead), superior sagittal sinus (black arrows), and numerous cortical veins (white arrowheads). This type of DAVF is associated with an within the last decade, there has been the emergence of increased risk of intracranial hypertension and intraparenchymal dynamic MRA imaging to address the lack of temporal res- hemorrhage. olution in conventional TOF MRA imaging. Initial studies ch04.qxd 9/19/08 11:18 AM Page 272

D Fig. 4.39 Dural arteriovenous fistula (DAVF). Sixty-two-year-old man presented with left-sided pulsatile tinnitus after undergoing resection of a left cerebellar gangliocytoma 4 years prior. (A) Unenhanced axial T1-weighted magnetic resonance image (T1WI) demonstrates abnormal signal in the left posterior fossa, including subtle serpentine areas of increased T1 signal, suggesting abnormal vessels (arrows). (B) Axial T2-weighted magnetic resonance image demonstrates a few serpentine flow voids (arrows) in the left posterior fossa that correlate with the abnormality seen on the T1WI. These findings are suggestive of a vascular abnormality but can often be difficult to see. (C,D) Axial three-dimensional time-of-flight source image from the magnetic resonance angiogram (MRA) (C) and axial MRA maximal intensity projection image (D) clearly demonstrate abnormal vascularity with numer- E ous small vessels (arrows) with faint visualization of the left sigmoid sinus. (E) Angiography is the gold standard in the evaluation of DAVFs. Lateral projection of left common carotid artery (★) in the early arterial phase demonstrates an enlarged occipital artery (arrows) feeding the DAVF with abnormal early antegrade drainage into the left sigmoid sinus (arrowheads). ch04.qxd 9/19/08 11:18 AM Page 273

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Fig. 4.40 Dural arteriovenous fistula (DAVF) with subacute infarct. (A) Axial postgadolinium T1-weighted magnetic resonance image shows numerous enhancing serpentine vessels representing enlarged feeding arteries and draining veins. Axial fluid attenuated inversion recovery (B) and axial gradient echo (C) images demonstrate hemorrhage in the right cerebellum. C

Direct Arteriovenous Fistula used 2D MR digital subtraction angiography techniques in which the intracranial circulation was repeatedly imaged Direct arteriovenous fistula may be intracranial or extracra- after the intravenous administration of a contrast bolus for nial involving either the carotid or vertebral artery. Intracra- each anatomic plane acquired. The contrast images were nial direct AVFs are, by far, most commonly located in the then subtracted from a previously acquired mask in the cavernous sinus, but can occur anywhere (Fig. 4.43). corresponding plane to produce angiographic images that Carotid-cavernous fistulas (CCFs) (Fig. 4.44) are usually would demonstrate the flow of contrast as a function of posttraumatic fistulous connections between the cavernous time, much like conventional angiography.91–93 The main portion of the internal carotid artery and the cavernous disadvantages with this technique, however, were the sinus. Pulsatile exophthalmos is the most common present- decreased spatial resolution relative to conventional TOF ing sign in this lesion, but pulsatile tinnitus may be an MRA and conventional angiography and the necessity to important diagnostic clue to its presence when venous flow rebolus the patient with each projection acquired. Recently, is not directed significantly into the superior ophthalmic there has been the evolution of more sophisticated tech- vein of the orbit. niques using three-dimensional (3D) parallel imaging that Extracranial direct AV shunts most often involve the results in higher spatial resolution images and the ability vertebral artery, but the extracranial internal or external to generate a 3D volume set that can be viewed in any carotid artery may also be involved. These lesions are obliquity after a single contrast bolus.94–96 Continued linked to a traumatic event in many circumstances but research aimed at fine-tuning time-resolved MRA with are considered to be spontaneous when the trauma is parallel imaging techniques will undoubtedly result in a minor or no history of trauma exists.97,98 In the case of a widely used and important tool in the noninvasive evalua- vertebral AVF, trauma to the neck and/or cervical spine tion of intracranial arteriovenous malformations. can injure the vertebral artery along its course through ch04.qxd 9/19/08 11:18 AM Page 274

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Fig. 4.41 Dural arteriovenous fistula (DAVF) with transosseous collaterals. (A) Three-dimensional time-of-flight magnetic resonance angiography axial source image demonstrates transosseous collaterals (arrow) that traverse the left hypoglossal canal. (B) Postprocessed maximal intensity projection MRA of the posterior circulation reveals the corresponding abnormal tangle of vessels (arrows) in the left posterior fossa. B

the foramen transversarium from C6 to C2 (Fig. 4.45). In of the ICA, encapsulation of the extravasated blood by the this area, the vertebral artery is intimately associated carotid sheath creates a perivascular hematoma, leading with a venous plexus. This close association makes this to a pseudoaneurysm. Although less common, sponta- segment of the vertebral artery especially susceptible to neous ICA dissection that does not result in stenosis has development of a direct AVF. At angiography, high-flow also been shown to present with PT.76 direct connections between the vertebral artery and MRI has long been the imaging modality of choice for venous plexus are observed. the evaluation of arterial dissection102; however, recent studies suggest that multidetector row CTA is emerging as an alternative study.104 Axial T1-weighted fat satu- Stenotic Vascular Disease rated MRI from the carotid bifurcation to the pituitary Stenotic arterial disease secondary to atherosclerosis sella is a very sensitive pulse sequence for diagnosing (Fig. 4.46), fibromuscular dysplasia (Fig. 4.47), dissection arterial dissection (Fig. 4.48A). Crescentic T1-hyperintensity (Fig. 4.48 and Fig. 4.49), and arteritis represents a group from the subacute intramural hematoma is readily of potentially treatable lesions causing PT.76,99–102 The PT apparent on this sequence, with the residual lumen is usually objective, as it results from arterial jetting and seen as an adjacent focal low signal area.103 Little or no turbulence in the vicinity of the temporal bone. A bruit flow may be present in the vertical and horizontal seg- may be heard in the neck over the stenotic vessel if the ments of the petrous ICA. MRA demonstrates luminal diseased vessel is proximal. Stenosis of the ICA can be changes, intimal flaps, and pseudoaneurysms to advan- diagnosed by MRA or CTA. tage (Fig. 4.48B).99,103,105,106 ICA dissection can occur spontaneously, but it is more As CTA has gained more widespread use in the evalua- commonly secondary to trauma and may result in nar- tion of vascular lesions, it has also been instrumental in rowing or occlusion of the ICA. Depending on the degree the identification of arterial dissection, particularly in the of ICA narrowing, ICA dissection may present clinically acute setting when MRI may not be as easily available. with a range of diverse symptoms and signs from neck The most common finding on CTA is mural thickening and face pain, anterior unilateral headache, and incom- with irregularity and/or narrowing of the lumen.104 In the plete Horner’s syndrome through transient ischemic acute phase, a smooth tapering of a short segment of the attack to frank stroke (10%).99,103 If there is associated rupture artery is typical; however, a spectrum of manifestations ch04.qxd 9/19/08 11:18 AM Page 275

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Fig. 4.43 Intracranial direct arteriovenous fistula (AVF). This 21-year- old man presented with a long history of severe headaches. There was no history of trauma. Axial maximal intensity projection magnetic resonance angiogram demonstrates a very large direct AVF with a direct connection from an enlarged right posterior cerebral artery (arrow) to a markedly enlarged transverse sinus (★). Enlarged right medial cerebral artery branches were suspicious for contributing inflow to the AVF.

Aneurysm of the Petrous Internal Carotid Artery Petrous ICA aneurysm is much less common than the Fig. 4.42 Dural arteriovenous fistula (DAVF) draining into the vertebral venous plexus. Lateral view of a left common carotid injection other vascular lesions previously discussed and typi- demonstrates a skull base DAVF supplied primarily by an enlarged cally represents a posttraumatic pseudoaneurysm rather ascending pharyngeal artery with venous drainage into the vertebral than a true aneurysm.72,107 The aneurysm may present venous plexus (arrows). with a vascular TM if it has eroded through the carotid plate and protruded into the tympanic cavity. CT demonstrates an expansile petrous bone mass with smooth cortical margins (Fig. 4.50A). MRA is usually diagnostic, exists including formation of pseudoaneurysms to com- although the conventional MRI appearance of the plete occlusion.104 Although less common, the presence of pseudoaneurysm may mimic cholesterol granuloma or an intimal flap between the true and false lumens of the a mucocele.108 Conventional angiography remains the artery is diagnostic (Fig. 4.49).104 reference standard for diagnosing the lesion (Fig. 4.50B). Angiography demonstrates the stenosis or occlusion of Petrous ICA pseudoaneurysms are very difficult to the ICA, classically beginning 2 cm above the origin of treat by open surgical methods and are usually treated the ICA at the carotid bifurcation. The dissection generally endovascularly.107 terminates at the level of the entrance of the ICA into the vertical segment of the petrous ICA canal. Luminal irregu- Miscellaneous Acquired Vascular Causes larity and stenosis (“string sign”) may be accompanied by an intimal flap, arterial outpouching, or pseudoaneurysm. Some investigators believe that microvascular compres- Stenotic venous structures may also cause PT. Although sion of CN VIII can cause PT.109–111 Nowe et al110 hypothe- the paired dural venous sinuses can markedly differ in sized that vascular compression of the peripheral segment size and still be within the spectrum of normal variance, a of the nerve in the internal auditory canal resulted in PT focal stenosis may lead to turbulent flow within a sinus due to a resonance effect in the petrous bone transmitted and cause PT.45 to the cochlea. The anterior inferior cerebellar artery ch04.qxd 9/19/08 11:18 AM Page 276

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Fig. 4.44 Direct arteriovenous fistula: carotid-cavernous fistula. An 18-year-old woman with a remote history of head trauma secondary to a motor vehicle accident presented with pulsatile tinnitus in the left ear and pulsatile exophthalmos of the left eye. Magnetic resonance imaging (MRI) and conventional angiogram were performed. (A) Axial T1-weighted MR image (T1WI) through the cavernous sinus demonstrates multiple enlarged vascular flow voids in the left cavernous sinus (arrows). (B) Axial T1WI through the orbits demonstrates an enlarged left superior ophthalmic vein (arrowheads), which is often seen in carotid-cavernous fistulas due to increased pressure in the cavernous sinus preventing normal drainage of the superior ophthalmic vein. (C) Lateral projection of a selected left internal carotid artery injection demonstrates early filling of the cavernous sinus (★) and the left superior ophthalmic vein (white arrow). There is also early filling of the inferior petrosal sinus (black arrow). Note is also made of a pseudoaneurysm (arrowhead). C

(AICA) (Fig. 4.51) often makes a normal redundant loop glomus (“a ball”) bodies, or paraganglia, which are com- within the IAC without disrupting the CN VIII. However, if posed of chemoreceptor cells derived from the primitive its course results in compression and displacement of CN neural crest and are frequently located near nerves and ves- VIII, tinnitus may result. Less commonly, a dolichoectatic sels (Fig. 4.53).117 Nearly all head and neck paragangliomas vertebrobasilar system can also cause PT if the enlarged are nonchromaffin, that is, nonsecretory; however, very tortuous vessels impinge on CN VIII (Fig. 4.52). rarely these lesions are found to secrete epinephrine or norepinephrine similar to pheochromocytomas, which are the best-known chromaffin paragangliomas.105,106,118 Temporal Bone Tumors Paragangliomas are found where glomus formations are normally located (Fig. 4.53). The term glomus tym- Paragangliomas panicum paraganglioma is used to describe the paragan- Paragangliomas, also known as glomus tumors, are the most glioma that arises in glomus bodies situated on the common tumors causing PT and a vascular TM.37,38,112–114 promontory of the medial wall of the middle ear cavity Glomus tympanicum and jugulotympanicum paragangliomas (Fig. 4.54). These glomus bodies are associated with the are the most common tumors of the middle ear and second distal portion of Jacobson’s nerve (inferior tympanic only to acoustic schwannomas as the most common tumors branch of CN IX) as it bends around the basal turn of of the temporal bone.115 ,116 Paragangliomas arise from the cochlea to access the cochlear promontory itself ch04.qxd 9/19/08 11:18 AM Page 277

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Fig. 4.45 Extracranial direct arteriovenous fistula (AVF), status-post trauma. A 52-year-old man sustained head and neck trauma from a high-speed motor vehicle accident. (A) Axial T2-weighted magnetic resonance (MR) image demonstrates fracture of the C2 vertebral body (arrowheads) with abnormal flow voids in the region of the right vertebral artery (arrow). (B) Axial source image from his MR angiogram (MRA) confirms the abnormal vessels in the region of the right vertebral artery (arrow). Normal contralateral vertebral artery is shown for comparison (arrowhead). (C) Maximal intensity projection MRA image demonstrates early filling of the vertebral venous plexus C (arrows), consistent with direct AVF.

(Fig. 4.53C). However, these tumors may arise at various formations of Jacobson’s nerve or the auricular branch of locations in the medial wall of the middle ear, correspon- the vagus nerve (Arnold’s nerve) within the jugular fora- ding to locations of glomus bodies anywhere along the men (Fig. 4.53C). If they are confined within the glomus course of Jacobson’s nerve.119 Glomus jugulotympanicum formations of the adventitia of the jugular bulb, they tumors are distinct from glomus tympanicum tumors and are referred to as glomus jugulare paragangliomas are considered to belong to the glomus jugulare tumor (Fig. 4.56). Glomus vagale tumors (Fig. 4.57) arise from family. They are essentially glomus jugulare tumors that the intravagal glomus formations of the vagus nerve at its have grown into the middle ear cavity, thus involving inferior (nodosum) ganglion or superior (jugular) gan- both the jugular foramen and the middle ear (Fig. 4.55). glion. When located within the inferior ganglion, which Most of the jugulotympanic tumors arise in glomus is usually situated at the level of the nasopharyngeal ch04.qxd 9/19/08 11:18 AM Page 278

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Fig. 4.46 Internal carotid artery (ICA) stenosis causing pulsatile tinnitus (PT). Coronal multiplanar reformatting image from a computed tomography angiogram of the circle of Willis shows a tight stenosis (arrow) of the right supraclinoid ICA in this patient with right-sided PT. Also note the extensive arteriosclerotic vascular calcifications.

Fig. 4.47 Fibromuscular dysplasia. Lateral projection of a right com- carotid space, the tumor will displace the carotid vessels mon carotid artery injection during a conventional angiogram demonstrates the irregular beaded appearance of the internal carotid artery anteromedially (Fig. 4.58A). Tumors from the superior characteristic of fibromuscular dysplasia (arrows). vagal (jugular) ganglion usually are dumbbell-shaped with intracranial and cervical components. Finally, carotid body paragangliomas arise in glomus formations associated with the glossopharyngeal nerve at the neurofibromatosis II are some of the well-established carotid bifurcation and often cause the characteristic tumor syndromes that predispose individuals to develop- splaying of the internal and external carotid arteries ment of paragangliomas.127 (Fig. 4.59).117 The carotid body tumor represents the most Paragangliomas grow by local invasion along paths of common type of paraganglioma, followed by glomus least resistance, such as air cell tracts, fissures, foramina, jugulare and glomus jugulotympanicum.120 and vascular channels.115,122,128–131 Intracranial invasion is Glomus vagale and glomus jugulotympanicum tumors seen in 15 to 20% of skull base lesions.116 ,13 2 Malignant have a predilection for women, whereas there is no gen- behavior is most commonly seen in glomus vagale tumors der predilection for carotid body tumors.121–123 Although (16 to 19%), followed by carotid body tumors (6%) and sporadic cases are overwhelmingly more common, there glomus jugulotympanic tumors (2 to 4%).133 Malignant is a familial form that is characterized by autosomal transformation of a primary tumor cannot be predicted by dominance with incomplete penetrance.117 This familial histopathologic or immunohistochemical features, rather form is seen most commonly in the carotid body and in it is defined if there is tumor extension to regional lymph younger patients.123–125 An alteration in the long arm of nodes or distant metastases (Fig. 4.60).134,135 Distant chromosome 11 is postulated as the cause of the familial metastases are most frequently seen in bone, lung, and form (11q23 locus).126 Multicentricity has been reported in liver.136 Although the familial form of paragangliomas has 3 to 26% of cases, with a higher incidence of multicentric an increased incidence of multicentricity, it has a paragangliomas occurring in familial cases. If paragan- decreased incidence of malignant transformation.124 gliomas occur in multiple sites within the head and neck, Prevalence of local invasion and recurrence is estimated at a hereditary component is suggested. Multiple endocrine 40 to 50% for glomus jugulare tumors, 17% for glomus neoplasia type 2 (MEN2), von Hippel–Lindau disease, and vagale, and 10% for carotid body tumors.137 ch04.qxd 9/19/08 11:18 AM Page 279

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Fig. 4.48 Internal carotid artery dissection. (A) Axial fat-saturated T1- weighted magnetic resonance image (T1WI) demonstrates a hyperintense crescent-shaped signal in the right distal cervical internal carotid artery (arrow) compatible with a mural hematoma in this case of carotid dissection. Also note the luminal narrowing of the internal carotid artery adjacent to the mural hematoma. (B) Three-dimensional time-of-flight magnetic resonance angiogram demonstrates a significant narrowing of the lumen, of the internal carotid artery (arrows) corresponding to the area of abnormality on the axial T1WI. B

Clinical presentation in patients with paragangliomas depends on the specific primary site of involvement, combined with the individual route of spread of a given tumor. When paragangliomas involve the temporal bone, symptoms are related to tumor bulk (conductive hearing loss), tumor arteriovenous shunting (PT, bruit), or inner ear involvement (vertigo, sensorineural hearing loss).2,37,113,116,138 Numerous cranial nerves may be compromised due to involvement of the jugular foramen (CN IX, X, and XI), hypoglossal canal (CN XII), cavernous sinus and middle cranial fossa (CN IV, V, and VI), or IAC (CN VII and VIII). Cranial nerve VII symptoms, more commonly, are due to involvement of the mastoid segment (Fig. 4.61) and to a lesser extent the tympanic, labyrinthine, and canalicular segments of the facial nerve. Vagale paraganglioma usually presents as a slowly growing, painless lateral neck mass behind the angle of the mandible. Vagal nerve deficits are seen late in the course of these lesions because the nerve fibers are splayed over the tumor surface.139 A carotid body tumor presents as a lateral neck mass that transmits Fig. 4.49 Internal carotid artery (ICA) dissection: computed tomogra- pulsation and is often associated with a bruit.140 Glomus phy angiogram (CTA). Enhanced axial source from a CTA of the neck shows an intimal flap (arrow), which is also focally dilated. This appear- tympanicum paraganglioma tends to present early with ance is characteristic of an ICA dissection. PT, conductive hearing loss, and/or a vascular retrotympanic ch04.qxd 9/19/08 11:18 AM Page 280

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A B Fig. 4.50 Petrous internal carotid artery (ICA) aneurysm. (A) Axial unen- petrous temporal bone, which is slightly hyperdense on this unenhanced hanced computed tomography image of the right temporal bone in this study. (B) Lateral oblique image of a right common carotid injection patient with pulsatile tinnitus reveals an expansile mass (★) in the demonstrates the large lobulated aneurysm of the petrous ICA (arrows).

Fig. 4.52 Vertebrobasilar dolichoectasis. Axial source image from a Fig. 4.51 Vascular loop of anteroinferior cerebellar artery touching TOF study shows ectatic left vertebral and basilar arteries (arrow- nerves. Axial T2-weighted magnetic resonance image demonstrates heads) exerting mass effect on the brainstem and left cerebellum. a normal course of the left anteroinferior cerebellar artery (arrow) The left vertebral artery courses in the expected location of the looping into the internal auditory canal. When there is compression cisternal segments of the VII/VIII cranial nerve complex, which can of CN VIII (arrowhead), pulsatile tinnitus can result. result in tinnitus. ch04.qxd 9/19/08 11:18 AM Page 281

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Fig. 4.53 Schematic representation of the locations of the normal paraganglia. (A) Overview drawing of the major locations of glomus body paraganglia locations in the head and neck area with special attention to the carotid space, jugular foramen, and temporal bone locations. The carotid body, anterior jugular, and tympanic paraganglia are associated with the glossopharyngeal nerve (IX). The inferior laryngeal, superior laryngeal, vagale, and posterior jugular paraganglia are related to the vagus nerve (X). (B) Schematic of the glomus bodies located near the skull base. (C) Axial drawing through the jugular foramen. The inferior tympanic branch of CN IX, Jacobson’s nerve (J), arises from CN IX anterior to the internal jugular vein (JV) and continues anterior to the JV to the middle ear and cochlear promontory. The auricular branch of CN X, Arnold’s nerve, courses posteriorly to the JV toward the facial canal. In this drawing, the emphasis is on the anterior and posterior jugular paraganglia. Both these glomus bodies are found within the jugular foramen and can give rise to a glomus jugulare para- C ganglioma. When these paragangliomas grow to invade the middle ear cavity, they are referred to as glomus jugulotympanicum paragangliomas. The tympanic paraganglion on the cochlear promontory is the site of origin of the glomus tympanicum paraganglioma. ch04.qxd 9/19/08 11:18 AM Page 282

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A B

Fig. 4.54 Glomus tympanicum paraganglioma. (A) Axial and (B) coronal unenhanced computed tomography (CT) image in bone algorithm through the right temporal bone demonstrates a small soft tissue mass in the middle ear cavity, projecting along the cochlear promontory (arrow). There is no associated bony erosion. (C) Coronal postgadolinium T1-weighted magnetic resonance image demonstrates a small enhancing mass (arrow) corresponding to CT findings. Glomus tympanicum tumors arise from glomus bodies associated with the inferior C tympanic branch of CN IX (Jacobson’s nerve).

mass behind the posteroinferior quadrant of the tympanic embolization for hemostasis,141 whereas glomus tympan- membrane.37 In the patient presenting with PT and a icum tumors can be operated via a transtympanic mem- vascular retrotympanic mass, it is often impossible to brane approach without definitive need for preoperative clinically distinguish between glomus tympanicum and embolization. Furthermore, it may not be feasible to dis- glomus jugulotympanicum paragangliomas.37–39 It is im- tinguish between paragangliomas and normal vascular portant, however, for this distinction to be made preopera- variants by physical examination, particularly the aberrant tively because glomus jugulotympanicum tumors require ICA. Because inadequate surgical exposure of jugulotym- more extensive skull base surgery with preoperative panicum paraganglioma or biopsy of a normal vascular ch04.qxd 9/19/08 11:18 AM Page 283

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A B Fig. 4.55 Glomus jugulotympanicum paraganglioma. (A) Axial unen- involving the jugular bulb (★). (B) Slightly more superiorly, the lesion hanced computed tomography image of the temporal bone demon- erodes into the middle ear cavity (arrowhead). Imaging findings are strates permeative destructive lesion (arrows) of the temporal bone characteristic of glomus jugulotympanicum.

variant may result in serious complications, correct (Fig. 4.63). The Glasscock–Jackson classification for interpretation of the pretreatment CT or MR images is glomus tumors in the temporal bone uses the HRCT essential. appearance of the tumors to determine the best surgical Imaging characteristics of paragangliomas on HRCT approach (Table 4.6).142,112,132 of the temporal bone depend on their location. Glomus MRI of paragangliomas is best accomplished using con- jugulare tumors cause characteristic expansion and per- ventional T1WI without and with contrast in axial and meative erosion of the jugular foramen (Fig. 4.56D). If coronal planes and fat-saturated T2WI. Paragangliomas are the tumor grows superolaterally into the middle ear usually heterogeneously T2 hyperintense, avidly enhancing cavity to become a glomus jugulotympanicum, destruc- lesions. Postcontrast fat-saturated T1WIs maximally delin- tion of the ossicular chain is common.117 HRCT of a glo- eate the enhancing tumor in areas where soft tissue, fat, or mus tympanicum paraganglioma demonstrates a focal fatty marrow exist. In larger tumors ( 1 cm), the charac- mass on the cochlear promontory, extending out into teristic “salt and pepper” appearance may be appreciated the middle ear cavity to abut the inner margin of the on the unenhanced T1WIs (Fig. 4.20).26,143 The “salt” is tympanic membrane (Fig. 4.54).43,119,138 Unlike the glo- thought to be secondary to subacute hemorrhage within mus jugulare/jugulotympanicum paragangliomas, the the tumor and is seen much less frequently than the “pep- glomus tympanicum tumors generally spare the ossi- per,” which results from the prominent serpentine flow cles, even if they reach large sizes and fill most of the voids of the tumor vessels.26 MRV may provide additional middle ear cavity (Fig. 4.62). If the mass is large enough information regarding jugular vein invasion, occlusion, and to reach superiorly into the epitympanum, attic, or aditus collateral venous sinus drainage.14 4 ad antrum, blockage will result in fluid accumulation in High resolution axial and coronal CT with bone algo- the mastoid antrum and air cells. In such cases, the rithm provides the surgeon with important additional margins of the tumor may be impossible to judge on information regarding precise bony surgical land- CT alone. MRI with the use of contrast will clarify the marks.138,145,146 Tumor evaluation in the skull base and size and extent of the lesions for the otologic surgeon medial temporal bone still often requires both modalities ch04.qxd 9/19/08 11:18 AM Page 284

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A B

C D Fig. 4.56 Glomus jugulare paraganglioma. (A) Axial T2-weighted mag- mass intensely enhances (arrow). (D) Axial unenhanced computed netic resonance (MR) image demonstrates a heterogeneously hyperin- tomography image demonstrates permeative destruction of the left tense mass (arrow) within the jugular foramen. (B) Unenhanced axial jugular foramen (arrow), typical of these vascular tumors. T1-weighted and (C) axial postgadolinium MR images show that the

to fully prepare the surgeon to operate with the least anteroinferior cerebellar artery (AICA) may supply the amount of surgical complications. intradural component of glomus jugulare tumors. The The typical angiographic appearance of a paragan- inferior tympanic artery is the most common supply to glioma is that of a hypervascular mass with enlarged glomus tympanicum tumors.150,151 Angiography is per- arterial feeders, intense tumor blush, and early draining formed preoperatively in patients with glomus jugulare veins.147,14 8 Very rarely, avascular paragangliomas may and glomus jugulotympanicum to (1) provide a vascular occur.14 9 Vascular supply to temporal bone paragan- road map for the surgeon, (2) evaluate the collateral gliomas is predominantly from ECA branches (Fig. 4.58B). arterial and venous circulations of the brain should The most common feeders are branches of the ascending sacrifice of a major vessel become necessary, (3) search pharyngeal artery, which supply the inferomedial com- for multicentric tumors, and (4) preoperatively embolize partment of the tumor around the jugular foramen the tumor. and medial tympanic cavity. Posterior auricular, stylo- Nuclear imaging can be a useful adjunctive tool in the mastoid, and occipital arteries supply the posterolateral preoperative evaluation of paragangliomas, particularly compartment of the mastoid region.18 Branches from because it allows imaging of the entire body. Because the posteroinferior cerebellar artery (PICA) and the paragangliomas can secrete catecholamines, iodine ch04.qxd 9/19/08 11:18 AM Page 285

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A B Fig. 4.57 Glomus vagale paraganglioma. (A) Axial T2-weighted mag- (B) Axial postgadolinium T1-weighted MRI demonstrates the intense netic resonance (MRI) shows a hyperintense mass (arrow) below the enhancement characteristic of these vascular tumors (arrow). Internal jugular foramen posterior to the internal carotid artery (arrowhead). carotid artery (arrowhead).

A B Fig. 4.58 Glomus vagale paraganglioma. (A) Lateral view from a left anteriorly. (B) Lateral view of a selective left external carotid artery injec- common carotid artery injection shows dense tumor blush of the glomus tion (ECA) shows the tumor being fed by the ascending pharyngeal artery vagale tumor which displaces the internal and external carotid arteries (AscPH), a branch of the ECA. (Images courtesy of John Weigele, MD.) ch04.qxd 9/19/08 11:18 AM Page 286

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carotid canal involvement had previously been considered the limits of surgical resectability; however, with more advanced microsurgical techniques and newer surgical approaches, the currently accepted boundaries of nonre- sectability are the foramen magnum and cavernous sinus.112 ,15 6 Seventh cranial nerve rerouting may be necessary for larger tumors.112 With the advent of precise delivery systems for radiation treatment such as Gamma Knife and Cyber Knife surgery, radiation therapy as a single modality treatment is being used more often to control tumor growth in those patients who are poor surgical candidates or who are at very high risk of major postoperative morbidity from the loss of functional cranial nerves or other neural deficits.157,158 Successfully irradiated paragangliomas usually demonstrate residual mass on CT or MRI, the presence of which does not by itself indicate treatment failure.159 Stabiliza- tion or reduction in size, decreased enhancement, diminished flow voids, and reduced T2-weighted signal on MRIs after radiation therapy are indicative of local control. When recurrent paraganglioma is suspected, contrast- Fig. 4.59 Carotid body tumor. Lateral projection from a right com- enhanced fat-saturated MRI can be very helpful in mon carotid artery injection shows the characteristic splaying of the differentiating surgical change from recurrent tumor internal carotid artery (ICA) and the external carotid artery (ECA). (Fig. 4.65).143,159 Progression of bone invasion on CT im- This vascular tumor shows the characteristic arterial blush. ages may confirm the MRI suspicion. Octreotide scans have also been useful for detecting recurrent disease.153 In difficult cases, angiographic identification of tumor may be the only study that can definitively diagnose the tagged meta-iodobenzylguanidine (MIBG), an analog of recurrence. norepinephrine, can be used to localize tumors and search for multifocal tumors (Fig. 4.64). This norepineph- Other Temporal Bone Tumors rine analog is taken up by presynaptic adrenergic nerve endings and stored in neurosecretory granules.152 Al- There are other less common tumors of the temporal though MIBG allows for very tissue-specific evaluation of bone that may present with PT or a vascular retrotym- paragangliomas, the disadvantage in using MIBG in head panic mass, depending on their location. These include and neck paragangliomas is that most are nonsecretory hemangiomas,160 endolymphatic sac tumors, and vascular tumors; thus, the use of this radionuclide is generally metastases, such as renal cell and thyroid carcinoma.161 reserved for tumors known to secrete catecholamines. Tumors of the endolymphatic duct and sac (ELST) An alternative strategy is to exploit the high density of (Fig. 4.66) are distinctive, rare, slow growing papillary cys- somatostatin type 2 receptors on the cell surface of neu- tadenomas or low-grade adenocarcinomas generally roendocrine tumors like paragangliomas. Octreotide is a appearing histologically benign, however, they are highly somatostatin analog that, when coupled to a radioisotope, destructive and behave in an aggressive manner.162 produces a scintigraphic image of tumors expressing Patients most frequently present with sensorineural somatostatin type 2 receptors. Octreotide scintigraphy hearing loss, facial nerve palsy, pulsatile tinnitus, and appears to be a reliable test to detect paragangliomas and vertigo (Meniere symptomatology). Otorrhea is an unusual may be quite helpful in preoperative planning.153,154 presenting symptom indicating eustachian tube dys- There is general agreement that surgery is the treat- function or middle ear/mastoid destruction. ment of choice for glomus tympanicum tumors and Typically, endolymphatic sac tumors are unilateral and smaller paragangliomas. Larger glomus jugulare and sporadic however, there is a strong association with von glomus jugulotympanicum tumors may be treated with Hippel-Lindau (VHL) disease and in this context may be surgery, radiation therapy, or a combination of both to bilateral.163 The VHL gene regulates a vascular endothelial control tumor growth. Transcatheter embolization is fre- growth factor which promotes angiogenesis. Deletion or quently used prior to surgical intervention, especially in mutation of this gene results in the development of the the larger tumors.141,155 Intracranial involvement and vascular tumors typical of VHL disease.16 4 ch04.qxd 9/19/08 11:18 AM Page 287

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A B

C D Fig. 4.60 Malignant degeneration of glomus tumor. (A) Axial post- demonstrates a destructive lesion in the right petrous apex (arrow). gadolinium T1-weighted (T1WI) magnetic resonance image demon- This lesion was discontinuous from the initial lesion. (D) Axial post- strates a large, enhancing carotid body tumor (arrow), displacing the gadolinium T1WI demonstrates a new enhancing mass infiltrating the internal carotid artery medially (arrowhead). This mass stayed stable right petrous apex and clivus (arrow), correlating to CT findings. Pathology for years. (B) Axial unenhanced computed tomography (CT) image at revealed metastatic paraganglioma. In addition to this lesion, the the level of the petrous apices is normal without intracranial exten- patient had two lung masses that were initially thought to represent a sion of the tumor. (C) Routine follow-up imaging 6 years after initial primary lung cancer. However, on resection and pathologic analysis, diagnosis. Axial unenhanced CT at the level of the petrous apices now the lung masses were found to be metastatic paraganglioma.

At CT, ELSTs are characterized by permeative retro- there are foci of T1 hypersignal reflecting recent hemor- labyrinthine bone destruction.162 These lesions often have rhage and elevated protein concentration. The combina- multiple bony spicules and may be surrounded by a tion of this hyperintensity and signal voids (hypointensity) thin shell of reactive bone indicating that they expand is referred to as “salt and pepper.” Intralabyrinthine relatively slowly. Intratumoral calcifications have been hemorrhage has also been reported manifest by hypersig- described as “bone sequestra.” At MRI, lesions are charac- nal within the labyrinth on T1 weighted images (see terized by intense contrast enhancement and numerous Chapter 5).165 There is an intense blush at conventional signal voids reflecting vascular channels. On occasion angiography with supply from the posterior occipital and ch04.qxd 9/19/08 11:18 AM Page 288

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C D Fig. 4.61 Glomus jugulotympanicum involving CN VII. A 58-year-old the descending facial nerve canal can be seen as it exits the skull base woman with left-sided facial fasciculations. (A) Axial and (B) coronal through the stylomastoid foramen between the mastoid bone (M) and computed tomography images through the left temporal bone in bone the styloid. (C) Axial postcontrast T1-weighted magnetic resonance window demonstrates a permeative destructive lesion in the left tem- image (T1WI) shows the enhancing glomus tumor (arrowhead) between poral bone (arrowheads) involving the jugular foramen and the the jugular bulb (★) and sigmoid sinus posteromedial to it, which is nar- descending facial nerve canal (arrows), correlating with the patient’s rowed but patent. (D) Axial postgadolinium T1-weighted MR image presenting symptom of facial fasciculations. On the coronal image, shows that the tumor extends into the middle ear cavity (arrowheads).

ascending pharyngeal branches of the external carotid similar. The key to diagnosis is recognition of the epicen- artery as well as the caroticotympanic branch of the inter- ter of the lesion along the posterior petrous surface at the nal carotid artery. This often allows for successfully pre- level of the vestibular aqueduct in contradistinction to operative embolization. paraganglioma which is hypotympanic arising typically at ELST is often initially confused with the much more the jugular foramen.16 6 ELST may appear identical to vas- common paraganglioma as imaging characteristics are cular metastases such as those of thyroid or renal origin ch04.qxd 9/19/08 11:18 AM Page 289

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fortuitously arising in the vicinity of the vestibular aqueduct. Meningioma can mimic ELST; however, they typically have a dural “tail” and quite commonly exhibit uniform T2 hyposignal reflecting cellular homogeneity. The reader should be aware that arachnoid granulations may occur along the posterior petrous surface appearing as lobular erosions (Fig. 5.50). Contiguity with the cerebrospinal fluid space on T2-weighted images usually allows confi- dent differentiation.162,167 A destructive lesion along the posterior petrous surface in a child may be a manifestation of LCH (see Chapter 3).

Chronic Inflammatory Lesions Cholesterol granuloma is a process that may affect the middle ear. On otoscopy it is usually seen as a dark, greenish compressible mass, but can occasionally present as a vascular retrotympanic mass that is indistinguishable from a paraganglioma. Although cholesterol Fig. 4.62 Large glomus tympanicum. Axial unenhanced computed granuloma is classically thought of as petrous apex le- tomography image shows a glomus tympanicum tumor filling the middle ear cavity. Glomus tympanicum tumors usually do not cause bony sion, it actually occurs more commonly in the middle ear destruction of the ossicles, even when large and filling the middle ear cavity resulting from chronic infection and hemorrhage. cavity. Note the preservation of the ossicles (arrow). Grossly, it consists of greenish-brownish fluid containing

A B Fig. 4.63 Large glomus tympanicum paraganglioma that fills the mid- segments of the petrous internal carotid artery (C); air in the external dle ear cavity creating a secondary attic block. (A) Axial bone com- auditory canal (E). (B) Corresponding axial enhanced T1-weighted puted tomography (CT) image of the left ear shows opacification of the magnetic resonance image (T1WI) demonstrates the avidly enhancing middle and mastoid air cells. The tumor (T) density in the middle ear is tumor (T) in the middle ear, contrasting with nonenhancing low signal the same as the fluid density (F) in the mastoid air cells, making it diffi- intensity of the fluid (F) backed up behind the attic block in the mastoid cult to be sure of tumor margins. Genu of the vertical and horizontal air cells. (Continued on page 290) ch04.qxd 9/19/08 11:18 AM Page 290

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C D Fig. 4.63 (Continued) (C) Coronal bone CT of the middle of the left remains low in signal. External auditory canal (E). The ability of ear again shows no differentiation of tumor (T) from epitympanic enhanced MRI to sort out the precise tumor margins is essential in fluid (F). External auditory canal (E). (D) Coronal enhanced T1WI this case. CT alone does not answer the critical surgical question of demonstrates the enhancing tumor (T) obstructing the entrance to what is the true tumor extent. the attic (arrow). Fluid (F) in the epitympanum and mastoid air cells

Table 4.6 Glasscock–Jackson Classification for Glomus Tumors Glomus Tympanicum Type I Small mass limited to the promontory Type II Tumor completely filling middle ear space Type III Tumor filling middle ear and extending into mastoid process Type IV Tumor filling middle ear, extending into mastoid or through tympanic membrane to fill external auditory canal; may extend anterior to internal carotid artery Glomus Jugulare Type I Small tumor involving jugular bulb, middle ear, and mastoid process Type II Tumor extending under internal auditory canal; intracranial extension Type III Tumor extending into petrous apex; intracranial extension Type IV Tumor extending beyond petrous apex into clivus or infratemporal fossa; intracranial extension Source: Adapted from Glasscock ME, Jackson CG, Harris PF: Glomus tumors: diagnosis, classification, and management Fig. 4.64 I-123 meta-iodobenzylguanidine (MIBG) study for paragan- of large lesions. Arch Otolaryngol 108:401, 1982. glioma. I-123 MIBG study can be useful in identifying secretory paragangliomas. This 50-year-old woman received this study before resection of her known carotid body tumor to ensure that there were no additional lesions. Normal, physiologic uptake is seen in bilateral parotid glands (arrowheads). Abnormal uptake is seen in the left carotid body tumor. ch04.qxd 9/19/08 11:18 AM Page 291

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A B Fig. 4.65 Recurrent glomus jugulotympanicum. (A) Coronal enhanced puted tomography image, the mass (arrow) causes permeative T1-weighted magnetic resonance image shows a subtle enhancing destruction of the jugular foramen with soft tissue extension into mass in the left jugular foramen (arrow) in this patient with a history of the middle ear, suggestive of recurrent glomus jugulotympanicum. prior glomus jugulotympanicum resection. (B) On the coronal com- Recurrence was confirmed on pathology.

cholesterol crystals, whereas histopathologically, it is be- and cholesteatoma. CT shows a globular, nonenhancing lieved to be a form of specialized granulation tissue.16 8,169 mass in the middle ear cavity. MRI shows high-signal Although CT readily distinguishes cholesterol granuloma tissue in the middle ear cavity on T1WIs as a result of from normal vascular variants, it may not differentiate it the cholesterol and subacute blood that is found in from other middle ear masses, such as paraganglioma these lesions.16 8,170

A B Fig. 4.66 Endolymphatic sac tumor (ELST). (A) Unenhanced axial computed tomography image demonstrates a destructive lesion along the posterior margin of the left petrous temporal bone (arrow) in the region of the vestibular aqueduct. (B) Axial T2-weighted magnetic resonance (MR) and (Continued on page 292) ch04.qxd 9/19/08 11:18 AM Page 292

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C D

Fig. 4.66 (Continued) (C) axial fluid attenuated inversion recovery (FLAIR) images show hyperintensity within the mass lesion (arrow). Persisting hyperintensity on FLAIR images is an important finding to distinguish ELST from other lesions, such as prominent arachnoid granulations, which can also occur in this region. Note the marked hyperintensity of the vestibule anterior to the tumor on the (C) FLAIR and (D) unenhanced T1-weighted MR images (T1WIs). This likely reflects blood products, as these tumors are prone to microhemor- rhages. (D) Axial unenhanced and (E) enhanced T1-weighted images demonstrate T1 hypointensity and avid enhancement of the tumor, respectively (arrows). These findings are similar to those of a glomus jugulare paraganglioma except that the location of the lesion is over the endolymphatic sac rather than the jugular foramen. (Images courtesy of Alexander Mamourian, MD.) E

Hemorrhage in the middle ear cavity is nonspecific and show opacification of the middle ear with normal can be seen with any chronic inflammatory process. appearing ossicles and no evidence of bony erosion. When hemorrhage occurs, the TM will take on a “vascular T1WI will reveal high signal fluid within the same area, hue,” which may be confusing to the otoscopist. CT will again without evidence of bone or trabecular loss.

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Griffiths PD, Hoggard N, Warren DJ, Wilkinson ID, pression of the cochlear nerve in patients with severe Anderson B, Romanowski CA. Brain arteriovenous tinnitus. Preoperative findings and operative outcome malformations: assessment with dynamic MR digital in 22 patients. Neurol Res 1998;20(3):242–248 subtraction angiography. AJNR Am J Neuroradiol 2000; 110. Nowe V, De Ridder D, Van de Heyning PH, et al. Does the 21(10):1892–1899 location of a vascular loop in the cerebellopontine angle 93. Wang Y, Johnston DL, Breen JF, et al. Dynamic MR digital explain pulsatile and non-pulsatile tinnitus? Eur Radiol subtraction angiography using contrast enhancement, 2004;14(12):2282–2289 fast data acquisition, and complex subtraction. Magn 111. Moller MB, Moller AR, Jannetta PJ, Jho HD. Vascular Reson Med 1996;36(4):551–556 decompression surgery for severe tinnitus: selection 94. Gauvrit JY, Leclerc X, Oppenheim C, et al. Three- criteria and results. 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The Inner Ear and Otodystrophies 5 Joel D. Swartz and Suresh K. Mukherji

Phylogeny and Embryology cochlear turns is complete. The fetus is able to hear with maturation of the organ of Corti, which occurs by the 22nd The phylogeny of the human ear has been the subject of to 24th week of gestation. considerable study. In most aquatic organisms, there is The otic capsule develops as a cartilaginous condensa- only a water motion detection system.1 The initial evo- tion of mesenchyme around the otic vesicle between the lution into what we understand as the “ear” begins with fourth and eighth weeks of gestation. Growth of the otic the development of structures analogous to the phylo- capsule continues to the 16th gestational week. During genetically older utricle and semicircular canals (SCC; the growth of the otic capsule, vacuoles begin to arise in posterior and superior only). Later vertebrates evolved a the developing cartilaginous otic capsule. These vacuoles third (lateral) semicircular canal (LSCC) and a saccule. eventually coalesce to form the perilymphatic space. The A primitive cochlear duct, the lagena, further evolves as newly created perilymphatic space contains perilymph an outpouching of the saccule. The major alteration in fluid, which surrounds and bathes the membranous the evolutionary ladder occurs when these structures labyrinth. Ossification of the otic capsule occurs between become isolated from the external environment and weeks 16 and 24 via 14 ossification centers. The end result endolymph replaces seawater as the essential fluid. This is the bony labyrinth. occurs simultaneously with the formation of a distinct Otic capsule ossification is unique in that (1) there are tympanomastoid compartment, which itself represents a large number of ossification centers—14—considering the functional adaptation of the aquatic gill; the ossicu- the small size of the final product; (2) there is no epiphy- lar chain probably develops as seawater is no longer seal growth (centers fused directly); and (3) maturation is available at this stage to serve as a conductive medium.2 arrested in a primary state of ossification (i.e., endochon- A simplification of the embryological development of dral bone persists). the ear is a difficult task. The reader is referred to other The membranous part of the SCC system begins to textbooks for more detailed explanations of this process.3 develop as two fingerlike extensions from the utricular side 5 Suffice it to say that the maturation of the inner ear has of the otic vesicle at about the fourth week of gestation. three main phases: (1) development (3rd to 11th week), (2) growth (11th to 16th week), and (3) ossification (16th to 24th week). The development of the sensory epithelium Table 5.1 Inner Ear Embryology within the membranous labyrinth occurs simultaneously Primordium Week Complete with growth and ossification (8th to 24th week) (Table 5.1). Otic placode 3rd The inner ear arises from the otic placode, which is a Otic pit 4th thickening of the surface neuroectoderm located between the first branchial groove and the hindbrain. This process Otic vesicle (otocyst) 5th occurs early in the third gestational week. Each otic placode Ventral pouch of otocyst: invaginates and sinks below the surface neuroectoderm into the underlying mesenchyme. This results in formation Cochlear duct 8th of the otic pit. The edges of the otic pit fuse to form the otic Saccule 11th vesicle (otocyst).4 The otic vesicle is the precursor of the membranous labyrinth. Dorsal pouch of otocyst: The otic vesicle divides into a dorsal utricular portion, Endolymphatic duct 11th which forms the utricle, SCCs, and endolymphatic duct Utricle and semicircular ducts 11th (ELD), as well as a ventral saccular portion that gives rise to the saccule and cochlear duct. The cochlear duct completes Semicircular canals 19th–22nd one turn by the 8th week, and two turns by the 9th to 10th Labyrinthine ossification 23rd week. By the end of the 10th week, the entire membranous 1 3 Total development 26th labyrinth is identifiable and formation of the 2 /2 to 2 /4

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Between weeks 4 and 8, the membranous labyrinth has Perilymph is also the exclusive fluid content of the three subdivisions: the endolymphatic duct system (ELDS), cochlear aqueduct (CA). the saccule with the cochlear duct (pars inferior), and the utricle and its semicircular ducts (pars superior). The The Vestibule and Semicircular Canals primitive form of each semicircular duct is first filled by mesenchymal tissue and later establishes a lumen. The Anatomy superior, posterior, and, finally, horizontal ducts complete The vestibule is the largest cavity of the bony labyrinth, this development by week 8. After differentiation of mes- measuring 4 to 6 mm at maximal diameter. The medial enchyme to the cartilage that will later form the endochon- wall of the vestibule is unique in that it contains two dis- dral bone of the otic capsule, the membranous labyrinth tinct depressions—the elliptical recess posterosuperiorly reaches adult shape. Complete maturation of the SCCs and the spherical recess anteroinferiorly (Fig. 5.1A, occurs at about midgestation, with the superior semicircular Fig. 5.2B, Fig. 5.3B, and Fig. 5.4C).3,10,11 Between these two canal (SSCC) completed first, usually by week 19, and the concavities lies the vestibular crest, a ridge that divides horizontal SCC last, usually by week 22. posteriorly into two limbs bounding an additional depres- We have presented an overview of the development of sion, the cochlear recess, which is the most proximal the inner ear. A more detailed discussion of specific struc- portion of the cochlear apparatus leading to the scala tures will be included in the following sections. vestibuli (cochlea). These structures are not typically seen on routine imaging as of this writing. Anatomy and Function The utricle is firmly anchored within the elliptical recess by connective tissue and filaments of the utricular 12 Overview branch of the superior vestibular nerve. Similarly, the saccule is adherent to the spherical recess by fibrous The inner ear consists of a membranous (endolymphatic) tissue and the saccular branch of the inferior vestibular labyrinth containing the functional sensory epithelium nerve. surrounded by an osseous (bony) labyrinth with an inter- The utricle and saccule communicate with each other posed perilymphatic labyrinth (Fig. 5.1A, Fig. 5.1B; see via the utriculosaccular duct. The utricle also communi- color plates) (Table 5.2). cates with the endolymphatic sinus (as well as the SCCs) The membranous labyrinth consists of the utricle, sac- via the utricular duct. In addition to the communications cule, semicircular ducts, cochlear duct (scala media), and with the utricle, the saccule communicates with the endolymphatic duct and sac. All of these structures con- endolymphatic sinus (via the saccular duct) and the cochlea tain endolymph, the functional fluid of the inner ear that (via the ductus reuniens).3,4,6,13,14 bathes and nourishes the sensory epithelium. Endolymph On the posterior wall of the utricle reside five openings is rich in potassium and low in sodium, similar to intra- for the three semicircular ducts. Remember that when we cellular fluid (Fig. 5.1B).3,4,6–8 use the term ducts, we are referring to the functioning The osseous labyrinth is the bony shell that surrounds endolymph containing apparatus, and when we use the the membranous labyrinth. The utricle and saccule term canals, we are referring to the bony covering only, (membranous labyrinth) are housed within the vestibule which is separated from the ducts by perilymph. There (bony labyrinth), the semicircular ducts (membranous are five openings instead of six because the superior and labyrinth) within the semicircular canals (bony labyrinth), posterior semicircular ducts/canals have a common crus and the ELD (membranous labyrinth) within the proximal (Fig. 5.3C, Fig. 5.4C, Fig. 5.4E, and Fig. 5.4F). The osseous vestibular aqueduct (bony labyrinth) (Fig. 5.1A). superior border of the SSCC is responsible for a ridge The perilymphatic labyrinth is interposed between along the roof of the petrous bone known as the arcuate the membranous and bony labyrinth. Perilymph is rich eminence (Fig. 5.3D, Fig. 5.5A, and Fig. 5.5B). Bony dehis- in sodium and low in potassium. This composition is cence at this site may result in significant clinical sympto- similar to extracellular and cerebrospinal fluid. Peri- matology and is discussed in detail later in the chapter. lymph is located within the vestibule surrounding the The LSCC is 30 degrees off the horizontal plane and utricle and saccule, between the semicircular ducts and provides much of the anatomic medial wall of the walls of the SCCs, and within the vestibular aqueduct epitympanum (attic) and aditus ad antrum (Fig. 5.2B, surrounding the ELD.4,9–11 The scala vestibuli and scala Fig. 5.2C, Fig. 5.3B, Fig. 5.3C, and Fig. 5.3D). Each of the tympani are perilymph-containing structures within the semicircular ducts/canals is orthogonal with one another. cochlea that parallel the endolymph-containing cochlear The superior and lateral canals/ducts are innervated by duct (scala media) and are crucial to the sound conduc- the superior vestibular nerve, the posterior SCC/duct tion mechanism (Fig. 5.1C and Fig. 5.1D; see color plates). by the inferior vestibular nerve (singular nerve). ch05.qxd 9/23/08 11:54 AM Page 300

300 Imaging of the Temporal Bone

B Fig. 5.1 Artist renderings. Normal inner ear anatomy. (A) Bony labyrinth with emphasis on structure of posterior wall of vestibule (Color Plate 5.1A). (B) Membranous labyrinth and subtended neural structures (Color Plate 5.1B). ch05.qxd 9/23/08 11:54 AM Page 301

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D Fig. 5.1 (Continued) Artist renderings. Normal inner ear anatomy. (C) Cochlea (Color Plate 5.1C). (D) Movement of sound waves within the cochlea. See text and Color Plate 5.1D. ([A–D] Courtesy of David L. Daniels, MD, with permission.) ch05.qxd 9/23/08 11:54 AM Page 302

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Table 5.2 Inner Ear Terminology Function Membranous Labyrinth The utricle, saccule, and semicircular ducts are involved Bony Labyrinth (Endolymphatic) with balance and maintenance of a stable retinal image. Cochlea Cochlear duct The utricle and saccule are collectively referred to as the Vestibule Utricle and saccule static labyrinth as their function is to detect the position Vestibular aqueduct Endolymphatic duct/sac of the head relative to gravity. They each have a focal concentration of sensory receptors (maculae) located at right Semicircular canals Semicircular ducts angles to each other and consisting of ciliated hair cells

A B

C D Fig. 5.2 (A) Axial computed tomography (CT): curvilinear petromastoid nerve canal; PTS, proximal tympanic segment, facial nerve canal; LSC, canal (black arrows) courses through crura of the superior semicircular lateral semicircular canal; PSC, posterior semicircular canal; V, canal (white arrows). (B) Axial CT: lateral semicircular canal (short white vestibule). (D) Axial CT: apical turn (AT), middle turn (MT), and proximal arrow), posterior semicircular canal (outlined white arrow) (V, vestibule; basilar turn (BT) of the cochlea (CNA, cochlear nerve aperture; IVNA, in- SVN, aperture for superior vestibular nerve; FNC, proximal tympanic ferior vestibular nerve aperture; OW, oval window niche; PSC, posterior segment of facial nerve canal). (C) Axial T2-weighted magnetic reso- semicircular canal). Internal auditory canal (outlined black arrow), modi- nance image (T2WI), right ear (FN, facial nerve; SVN, superior vestibular olus (short white arrow), singular canal (singular nerve to posterior semi- nerve; LS, labyrinthine segment, facial nerve canal; FG, first genu, facial circular canal) (short thin arrow). ch05.qxd 9/23/08 11:54 AM Page 303

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E F

G H Fig. 5.2 (Continued) (E) Axial T2WI, right ear (CN, cochlear nerve; IVN, singular canal, singular nerve to posterior semicircular canal; CNA, inferior vestibular nerve; OSL, osseous spiral lamina; PSC, posterior cochlear nerve aperture; ISS, medial interscalar septum; ISS, partial, semicircular canal; V, vestibule) contains the cochlear duct (scala media) lateral interscalar septum [This is a normal variation compatible with and separates the scala vestibuli (SV) and scala tympani (ST). The inter- normal cochlear function and should not be confused with pathologic scalar septum (ISS) separates the apical turn from the middle turn. Note modiolar deficiency.]). (H) Axial CT (AT, apical turn of cochlea; MT, mid- that the modiolus (MOD) has a classic “trapezoid” shape. (F) Axial CT dle turn of the cochlea; BT, basilar turn of the cochlea; RW, round win- (IVN, canal for inferior vestibular nerve; V, vestibule; CNF, cochlear neu- dow; VAQ, vestibular aqueduct [and adjacent fovea harboring endolym- ral foramen; VAQ, vestibular aqueduct; RC, canal of Rosenthal [through phatic sac]; PSC, posterior semicircular canal; white arrow, promontory; which cochlear nerve fibers travel through the osseous spiral lamina CA, cochlear aqueduct [otic capsule segment]). from the modiolus]). (G) Axial CT (PSC, posterior semicircular canal; SC, (Continued on page 304) ch05.qxd 9/23/08 11:54 AM Page 304

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I J Fig. 5.2 (Continued) (I) Drawing emphasizing cochlear aqueduct. (From cochlea; VAQ, vestibular aqueduct; C, carotid canal, horizontal portion; Jackler RK, Hwang PH. Enlargement of the cochlear aqueduct: fact or fic- RWN, round window niche) promontory [bony covering of basilar turn of tion? Otolaryngol Head Neck Surg 1993;109:14–25. Used with permis- the cochlea] (outlined white arrow). sion.) (J) Axial CT (PSC, posterior semicircular canal; BT, basilar turn of the

and tiny crystals of calcium carbonate (otoliths) embed- cerebellar artery (PICA) branch of the vertebral artery as ded in a gelatinous mass. These otoliths respond to gravi- an AICA–PICA trunk. The posterior, superior, and lateral tational pull; therefore, changes in head position distort semicircular canals/ducts are supplied via the anterior and stimulate the hair cells. vestibular branch of the LB; the capsule and posterior The semicircular ducts are collectively referred to as semicircular canals/ducts receive nutrients via the poste- the kinetic labyrinth because they respond to rotational rior vestibular branch. or angular acceleration. Each of the semicircular ducts The petromastoid canal (PMC) is an anteriorly convex subtends two thirds of a circle and contains an ampulla conduit usually measuring 0.5 to 1.0 mm passing between for transmission of vestibular nerve fibers. These ampul- the SSCC and LSCC connecting the cranial cavity to the lae are analogous to the maculae of the utricle and sac- mastoid antrum, which should not be confused with frac- cule in that they contain hair cells. Endolymph flow in ture (Fig. 5.2A). There is an increase in the length of the response to angular head movements stimulates these PMC with increasing volume of perilabyrinthine pneuma- hair cells. Each semicircular duct responds to a different tization. It contains the subarcuate artery (branch of the rotational axis. AICA) and has the potential to transmit suppurative debris in either direction (similar to CA). These vessels sup- Vascular Supply ply the otic capsule of the semicircular canals as well as part of the vestibule, facial canal, and mastoid mucosa. The arterial supply to the vestibule and semicircular The subarcuate fossa (SAF) is the medial orifice of the canals/ducts arises from the labyrinthine branch (LB) of PMC. A wide PMC ( 2 mm) is not uncommon in children the anteroinferior cerebellar artery (AICA), which, in turn under 5 years of age (Fig. 5.6) and contains invaginated arises from the basilar artery at the junction between the dura, which is a potential surgical hazard, particularly in proximal one third and distal two thirds of this vessel. cochlear implant (CI) candidates and those with chronic On occasion, the AICA arises from the posteroinferior otitis media (COM).15 ch05.qxd 9/23/08 11:54 AM Page 305

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A B

C D

Fig. 5.3 Coronal computed tomography images. (A) AT, apical semicircular canal; SSC, superior semicircular canal; OW, oval win- cochlear turn; MT, middle cochlear turn; PROX BT, proximal basilar dow; IAC, internal auditory canal; RW, round window; IAC, internal turn; PTS(F), proximal tympanic segment, facial nerve canal; DLS(F), auditory canal; CF, crista falciformis; J, jugular foramen; V, vestibule. distal labyrinthine segment, facial nerve canal; CF, cochleariform (D) LSC, lateral semicircular canal; SSC, superior semicircular canal; process (insertion of tensor tympani tendon); c, carotid canal. PSC, posterior semicircular canal; PMC, petromastoid canal; GS, glos- (B) LSC, lateral semicircular canal; SSC, superior semicircular canal; sopharyngeal sulcus; SMF, stylomastoid foramen; J, jugular foramen; OW, oval window; BT, distal basilar turn of the cochlea; IAC, internal H, hypoglossal canal. auditory canal; CF, crista falciformis; J, jugular foramen. (C) LSC, lateral

Innervation posterior semicircular canal/duct, also referred to as the Impulses from the utricular macula and the ampullae of singular nerve, often travels separately from the inferior the superior and lateral semicircular ducts travel via the vestibular nerve, either within this quadrant or within an superior vestibular nerve in the posterosuperior quadrant entire separate semicanal. This singular canal is clearly of the internal auditory canal (IAC). Impulses from the visualized on both coronal and axial computed tomogra- saccular macula and the ampulla of the posterior semicir- phy (CT) images. The aforementioned anatomic arrange- cular ducts travel primarily via the inferior vestibular ment allows for surgical denervation of the posterior nerve within the posteroinferior quadrant of the IAC. The semicircular canal/duct (singular neurectomy), a proce- saccule is actually innervated to some extent by all three dure that has been used to treat patients with chronic segments of the vestibulocochlear nerve. The nerve of the benign positional vertigo (cupulolithiasis).3 ch05.qxd 9/23/08 11:54 AM Page 306

306 Imaging of the Temporal Bone

Fig. 5.4 Sagittal computed tomography images. (A) AT, anterior turn of the cochlea; BT, basilar turn of cochlea; MT, middle turn of the cochlea; CNA, cochlear nerve aperture; IAC(F), fundus of internal auditory canal. Modiolus (outlined arrow). (B) Apical (AT), middle (MT), and basilar (BT) turns of the cochlea; VAQ, vestibular aqueduct; IAC(F), fundus of internal auditory canal; OSL, osseous spiral lamina; ISS, interscalar septum; C, carotid canal; J, jugular foramen. (C) RW, round window (leading to scala tympani of basilar turn of the cochlea); LSC, lateral semicircular canal; SSC, superior semicircular canal; BT, basilar turn of the cochlea; CC, common crus (posterior and superior semicircular canals); V, vestibule. Vestibular aqueduct (arising from common crus) (outlined arrow). (D) Promontory (bony covering of basilar turn of the cochlea) (outlined arrow). OW, oval win- D dow; RW, round window. ch05.qxd 9/23/08 11:54 AM Page 307

Chapter 5 The Inner Ear and Otodystrophies 307

E F Fig. 5.4 (Continued) (E) LSC, lateral semicircular canal; PSC, posterior semicircular canal; SSC, superior semicircular canal. (F) Lateral semicircular canal (outlined arrow), mastoid segment, facial nerve canal (straight white arrow).

The vestibular (Scarpa’s) ganglion is situated within systemic disorders. Peripheral vertigo refers to disease the IAC and is responsible for mediation of afferent and of the labyrinth, vestibular nerve, or cerebellopontine efferent impulses of the saccule, utricle, and all three angle. Central vertigo implies disease of the brainstem, semicircular ducts. As such, the vestibular nerve has five including the vestibular nuclei and vestibular terminal branches. Four vestibular nuclei are located in pathways.16 the brainstem at the pontomedullary junction medial to the cochlear nuclei at the level of the floor of the fourth ventricle. Fibers of the vestibular nerve synapse in these The Cochlea nuclei. Activity within the brainstem is quite complex and beyond the realm of this discussion. Suffice it to Hearing arises from the capability to transform mechani- say that fibers travel via the vestibulospinal tract (reg- cal energy to electrical energy.17 The external ear collects ulation of muscle tone), vestibulocerebellar tract and directs sound waves to the tympanic membrane. The (coordination), reticular formation (regulation of con- middle ear converts mechanical motion arising from sciousness), and medial longitudinal fasciculus (eye the tympanic membrane pulsations and transmits it to movement).9–11 the fluid in the vestibule via the lever effect of the ossicu- When the vestibular apparatus is rendered dysfunc- lar chain. The inner ear, specifically the cochlea, trans- tional such as by inflammation or neoplasm, a patient forms fluid motion into electrical energy. 1 may complain of vertigo, a symptom specific to disease The cochlea is a coiled structure consisting of 2 /2 to 3 of the vestibular system. Vertigo is described as a hallu- 2 /4 turns (Fig. 5.1C, Fig. 5.1D, Fig. 5.3A, Fig. 5.4A, cination of movement resulting in a sensation of turn- Fig. 5.4B). If it were elongated, the cochlea would be 30 ing, spinning, falling, or rocking. Patients may complain to 32 mm in length. The modiolus (Latin for “hub of a that the “world is spinning around me.” This is often wheel”), the central bony axis of the cochlea, is composed associated with other visceral disturbances, such as of spongy bone. A central bony defect within the core of nausea, vomiting, sweating, and tachycardia. Vertigo is the modiolus contains the cochlear nerve (Fig. 5.2D, to be distinguished from dizziness, a sensation of light- Fig. 5.2E, and Fig. 5.2F).The modiolus is normally a robust headedness, giddiness, faintness, or unsteadiness, which three-dimensional (3D) structure and should never appear is a nonspecific complaint and can be due to a variety of flattened or asymmetric at CT or magnetic resonance ch05.qxd 9/23/08 11:54 AM Page 308

A B

Fig. 5.5 Poschl computed tomography images. (A) Plane of section for Poschl projection. (B) SSC, superior semicircular canal; PMC, petromastoid canal; PSC, posterior semicircular canal (proximal); IB, incus body in attic; LSC, lateral semicircular canal; FNC, facial nerve canal (tympanic segment). (C) PSC, posterior semicircular canal; PMC, petromastoid canal; LSC, lateral semicircular canal; SS, sigmoid sinus. Vestibular aqueduct (outlined arrow). C

A B Fig. 5.6 Large petromastoid canal, child. (A) Axial and (B) coronal computed tomography images reveal that the petromastoid canal is very large (arrows). This is a normal variant in infancy and early childhood. ch05.qxd 9/23/08 11:54 AM Page 309

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imaging (MRI). The normal modiolar area is 4 mm2. On as fluid waves. These fluid waves are transmitted through axial MRIs, the modiolus appears as a trapezoidal, bowtie, the Reissner’s membrane into the endolymph of the or crown-shaped low-signal core at the cochlear apex, cochlear duct. This causes displacement of the basilar with thin fingerlike projections, which contains the spiral membrane, which stimulates the hair cell receptors of the ganglion (cell bodies of the cochlear nerve).18,19 Projecting organ of Corti. The movement of these hair cells generates outward from the modiolus throughout its length, similar the electronic potentials that are eventually converted to the head of a screw, is a thin bony plate referred to as into action potentials in the cochlear nerve fibers. It is the osseous spiral lamina (OSL) (Fig. 5.2E). The fibers interesting that the entire fluid volume of the perilym- of the vestibulocochlear nerve fan out in spiral fashion phatic spaces of the inner ear is only 0.2 cc, yet without from the modiolus to pass into a channel near the root of it hearing would not be possible.1 The perilymphatic the osseous spiral lamina, the canal of Rosenthal waves are transmitted to the apex of the cochlea (heli- (Fig. 5.2F). The OSL encircles the modiolus and projects cotrema) via the scala vestibuli to the scala tympani and outward to the outer cochlear wall, where it attaches to eventually dissipated at the round window, which has a the spiral ligament. The OSL encloses the cochlear duct flexible diaphragm. The round window is located 2 mm (scala media), which contains the organ of Corti, and sepa- posterior and 2 mm inferior to the oval window rates the scala vestibuli from the scala tympani.3 The (Fig. 5.3C, Fig. 5.4C, Fig. 5.7A, and Fig. 5.7B). interscalar septum (ISS) also projects outward from the The basilar membrane varies in width and tension modiolus. The ISS is distinguished from the OSL as it is from base to apex. Hence, different portions of the mem- much thicker (more easily appreciated at CT and MRI), brane respond to different auditory frequencies: higher does not contain neurovascular elements, and separates frequencies closer to the base, lower frequencies closer the apical from the middle (and middle from basilar) turn to the apex. Sensorineural hearing loss may be catego- of the cochlea. Defects in the ISS between the middle rized as sensory (cochlear) loss and neural (retrocochlear) and apical turns are not uncommon (scala communis) loss. Retrocochlear hearing loss implies involvement of (Fig. 5.2G).3 either the cochlear nerve or the cochlear nuclei. Defective The fluid-filled spaces of the cochlea (endolymphatic function of the cochlea results in sensory (cochlear) and perilymphatic labyrinth) are composed of three par- loss.11 allel spiral chambers contained within the bony shell of the cochlea: an outer anterior scala vestibuli (ascending spiral) and inner posterior scala tympani (descending spiral) surround the central cochlear duct (scala media) Vestibular Aqueduct and Endolymphatic (Fig. 5.1D). The scala vestibuli and scala tympani contain Duct System perilymph, and the scala media contains endolymph. The Vestibular Aqueduct cochlear duct is separated from the scala vestibuli by the vestibular (Reissner’s) membrane and from the scala The vestibular aqueduct (VA) is a bony channel originat- tympani by the basilar membrane.6,13 The organ of Corti ing from the posterosuperior portion of the vestibule resides within the cochlear duct on the basilar mem- near the common crus. It courses posteriorly, laterally, brane. The tectorial membrane is adherent to the roof of and inferiorly along the posterior petrous surface.3 The the organ of Corti, interposed between this structure vestibular aqueduct widens as it approaches its external and the endolymph. As indicated in the previous paragraph, aperture at the posterior margin of the petrous apex.20 In the OSL encompasses the cochlear duct (scala media) and the first 20 weeks of fetal life, the course of the VA is thereby separates the cochlea into an anterior scalar straight and parallel to the common crus. chamber (scala vestibuli and scala media) and posterior As the posterior fossa begins accelerated growth in the scalar chamber (scala tympani). The OSL is tethered to final 20 weeks of gestation, the VA and the contents the outer cochlear wall by means of the spiral ligament, assume its adult J-shaped configuration.3 The length of which is the periosteal covering of the cochlear duct. The the VA is determined by the degree of adjacent pneumati- stria vascularis is the inner lining of this ligament con- zation but is generally 6 to 12 mm (Fig. 5.4C and taining numerous capillary loops and small blood vessels. Fig. 5.5C).21 The vestibular aqueduct is considered large Episodic movement of the stapes results in direct when it measures 1.5 mm in width at the midpoint be- transmission of fluid waves via the oval window tween the common crus and the external aperture.22–24 (Fig. 5.4D) through the vestibule and subsequently to the Due to its oblique nature, only segments of the normal VA cochlear recess, which lies on the medial wall of the are consistently seen with axial CT imaging; however, this vestibule (Fig. 5.1). The cochlear recess communicates is usually sufficient to gain an impression of the overall directly with the scala vestibuli. Hence, the sound waves caliber (Fig. 5.2F). Multiplanar reformations using volume are transmitted directly to the perilymph of the cochlea acquisition CT particularly in the sagittal or parasagittal ch05.qxd 9/23/08 11:54 AM Page 310

310 Imaging of the Temporal Bone

A B Fig. 5.7 Stenver computed tomography image. (A) Plane of section for the cochlea (BT). This image plane is useful in evaluating the postopera- Stenver’s projection. (B) Stenver’s view reveals oval window niche (**) tive appearance of the cochlear implant, which is inserted into the scala leading to the scala vestibule (SV) of the basilar turn of the cochlea. tympani via either the round window or the adjacent cochleostomy. Round window niche (*) leads to the scala tympani (ST) of basilar turn of LSC, lateral semicircular canal; SSC, superior semicircular canal.

plane may be more helpful in ascertaining the complete The ELD terminates as the ELS, which is relatively large course of the VA. (10 to 15 mm) and often extends inferiorly along the posterior petrous surface for a significant distance.14 The ELS has a larger intradural portion and a smaller intraosseous Endolymphatic Duct System portion. The ELS is also described as having proximal The VA houses the ELD. The term endolymphatic duct sys- (rugose) and distal (smooth) segments. The rugose portion tem (EDS) has been advanced. The EDS is divided into an of the ELS is continuous with the distal ELD and consists endolymphatic duct (ELD) and an endolymphatic sac of a complex network of interdigitating canaliculi and (ELS) (Fig. 5.1B). crypts lined by highly differentiated epithelium consist- The ELD arises from the union of the utricular and sac- ing of irregularly dispersed tall, cylindrical cells. This seg- cular ducts and, after a right-angle turn, courses within ment of the ELS lies within a dural sleeve in the foveate the VA and emerges from an aperture along the posterior impression, which is situated along the posterior aspect surface of the petrous pyramid.14,25 Identical to other of the petrous bone, partially covered by a scale of bone, portions of the membranous labyrinth, the ELD contains the operculum.3 The distal (smooth) segment of the ELS is endolymph and is bathed in perilymph. The ELD is also lined by cuboidal epithelium and situated between the surrounded by loose connective tissue, which is continu- periosteal portion of the dura and the dura proper. The ous with the adjacent periosteum. The ELD can be further rugose portion is important for normal endolymph divided into two distinct sections, the sinus and the isth- resorption and for the digestion of foreign bodies. The mus. The sinus (horizontal) portion of the ELD (also smooth portion is thought by many to be involved in referred to as the endolymphatic sinus) is proximal to the pressure equalization between the cerebrospinal fluid origin of the VA and communicates directly with the sac- (CSF) and the endolymph, similar in function to the con- cular and utricular ducts. The isthmic (vertical) portion is tents of the CA. The ELD/ELS quite possibly plays a role in the continuation of the sinus portion and represents the autoregulation of the inner ear ion and fluid balance.26,27 intraosseous segment of the ELD housed by the VA. Histo- The presence of cellular debris, macrophages, and a vari- logically, the lining epithelium of the ELD is similar to the ety of blood cells (predominantly leukocytes) in the utricular and saccular ducts and is composed of simple lumen of the EDS suggests an active role in the immune squamous or low cuboidal cells. system of the inner ear as well. ch05.qxd 9/23/08 11:54 AM Page 311

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The arterial supply of the ELS and ELD originates from much smaller than the CA. As we will see below, an a dural branch of the stylomastoid artery, which, in turn, anomalously patent Hyrtl’s fissure is a potential site of may arise from either the occipital or posterior auricular congenital CSF fistulization. arteries.25 The supplying vessels are divided into a super- The function and potential dysfunction of the CA have ficial component, which directly enter the canaliculi of long been a subject of debate. The CA certainly provides at the vestibular aqueduct and supplies the ELS and ELD, least a potential conduit between the posterior fossa and and a deep component, which supplies the periductal inner ear. The narrow diameter of the CA is thought to connective tissue. buffer the inner ear from the wide pressure variations present within the posterior fossa subarachnoid spaces.28 A patent CA has been shown to permit transmission of Cochlear Aqueduct and Contents bacterial infection between the subarachnoid space and the inner ear, which is a cause of labyrinthitis superim- There is much confusion in the literature regarding the posed on meningitis. In theory, meningitis could be a anatomy, function, and dysfunction of the cochlear aque- complication of labyrinthitis via the same pathway. Hear- duct (CA) (Fig. 5.1).28 The CA is the narrow bony canal ing loss has been noted in several patients following sub- containing perilymph and loose connective tissue, which arachnoid hemorrhage and aneurysm surgery. It has been connects the scala tympani with the subarachnoid space. postulated that loss of CSF during operation results in There is no membranous perilymphatic “duct” per se. The diminished CSF pressure, which is transmitted to the per- CA runs a downward oblique course and is at least par- ilymph via the CA, resulting in the release of perilymph tially visualized in 90% of subjects upon evaluation of into the subarachnoid space. Hemolabyrinth caused by an axial and coronal CT images roughly parallel and immedi- inflow of subarachnoid blood through the CA could be an ately inferior to the internal auditory canal.29 The round additional factor in the development of hearing loss.33 window is an excellent landmark in this regard. Enhance- Massive perilymphatic leak as a complication of stapedec- ment with gadolinium in this region often occurs but is tomy (stapes gusher) has historically been linked to in- likely of no significance clinically.30 creased inner ear pressures caused by an enlarged and The CA has been divided into four segments.3,13,28 overly patent CA. This has been discounted in recent From lateral to medial the CA consists of the lateral ori- years.28 fice, labyrinthine segment, otic capsule segment, and medial orifice (Fig. 5.2H and Fig. 5.2I). The lateral orifice is the opening into the basal turn of the cochlea, located Pathology along the anteroinferior edge of the scala tympani immediately anterior to the crest of the attachment of Congenital Disorders the round window. The otic capsule segment courses Overview through the labyrinthine bone and never exceeds 2 mm at maximal diameter. The petrous apex segment courses Congenital hearing deficits may be genetic or nongenetic. through extralabyrinthine bone, which may or may Genetic causes may occur alone or in association with a not be pneumatized, and is more variable in size (aver- systemic syndrome and are the culprit in perhaps one half age diameter of 4.5 mm). This segment widens as it of the cases of profound childhood deafness.34–36 Genetic approaches the funnel-shaped medial orifice, which opens disorders may be autosomal dominant (one parent carries into the subarachnoid space adjacent to the jugular fora- the trait), autosomal recessive (both parents carry the men. The medial orifice of the CA is in close proximity to trait), or X-linked recessive (mother carries the trait).37 and should not be confused with the glossopharyngeal Each may have variable expressivity. In the X-linked vari- meatus, another funnel-shaped orifice transmitting the ety of transmission, only male offspring are affected. Sev- glossopharyngeal nerve into the anteromedial jugular eral autosomal recessive syndromes cause membranous foramen (pars nervosa).31 deformities currently beyond imaging resolution. Some of There are at least two additional closely related chan- these have associated retinal manifestations as well as nels. An accessory CA transmits the inferior cochlear vein sensorineural hearing loss (SNHL).37–39 These include and is referred to as Cotugno’s canal. This vein terminates Usher’s syndrome (retinitis pigmentosa, mental retarda- within either the inferior petrosal sinus or the jugular tion), Refsum’s syndrome (retinitis pigmentosa, increased bulb.3 The tympanomeningeal fissure (Hyrtl’s fissure), serum phytanic acid), and Cockayne’s syndrome (retinal also known as the second accessory canal, develops as a degeneration, dwarfism). X-linked hypophosphatemic patent communication between the round window and osteomalacia is also associated with SNHL.40 In these posterior fossa, normally closing at 26 weeks gestation.32 patients, there are audiometric findings suggesting This structure contains perilymph and, when patent, is endolymphatic hydrops similar to Meniere’s disease. ch05.qxd 9/23/08 11:54 AM Page 312

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Nongenetic etiologies include maternal transplacental as thin as 0.3 mm. As the technology develops, it may be viral infections (rubella, toxoplasmosis, cytomegalovirus), possible to visualize the components of the cochlear duct radiation exposure, metabolic disorders, and ototoxic poi- and identify structures such as Reissner’s membrane and soning (aminoglycoside antibiotics). This group of disor- the basilar membrane. ders generally results in maldevelopment/destruction of Bing–Siebenmann deformity is complete membranous sensory epithelium, although a teratogenic insult occur- labyrinthine dysplasia. This entity is extremely rare and ring between the fourth and eighth weeks of gestation may occur either as an isolated event or associated with could also cause maldevelopment of the otic capsule. the Jervell and Lange–Nielsen syndromes (concomitant As described earlier in this chapter and in Chapter 3, cardiac dysfunction).42 the inner ear and middle/external ear have mutually inde- As discussed earlier, the utricle, SCC, and ELD originate pendent embryological origins. As such, one would expect from the embryologically older pars superior, and the that these segments of the ear would rarely be affected cochlea and saccule originate from the pars inferior. together. In actuality, for reasons unknown, such anom- Scheibe syndrome (membranous cochleosaccular dyspla- alies do coexist on occasion. Inner ear deformities occur in sia) results from maldevelopment of the pars inferior and perhaps 10% of patients with external auditory canal (EAC) is believed to be the most frequent cause of congenital atresia, and middle/external ear anomalies are not rare in deafness.42–44 Pathologically, the organ of Corti is either association with inner ear dysplasias (Table 5.3).41 partially or completely missing. The cochlear changes tend to be more severe in the basilar turn and gradually lessen toward the apical turn. The cochlear duct is typi- Malformations Isolated to the Membranous cally collapsed, and Reissner’s membrane is deformed. Labyrinth The saccule is collapsed and contains degenerated sen- A variety of developmental malformations is limited sory epithelium. The utricle is normal. The hearing loss to the membranous labyrinth and result in congenital may be unilateral or bilateral. hearing deficit. The bony labyrinth is spared because the Alexander syndrome is a membranous dysplasia local- insult occurs later in development after formation of ized to the basilar turn of the cochlea. This results in 45–47 the bony labyrinth and prior to full maturation of the sen- familial high-frequency SNHL. sory epithelium, particularly the organ of Corti, which occurs between weeks 26 and 28 of gestation. These dysplasias are, as of this writing, beyond the limits of current Malformations of the Membranous Labyrinth imaging methods, but several of the more common vari- and the Bony Labyrinth eties are included here for completeness, specifically Bing–Siebenmann deformity, Scheibe syndrome, and Congenital malformations that affect the development of Alexander syndrome. The ability to detect membranous the otic capsule result in malformations of both the mem- defects may improve as technical imaging advances con- branous and bony labyrinth. These malformations can be tinue. Recent advances now permit slice thicknesses to be detected with current imaging methods, and the radiologist should be familiar with these disorders. The majority of congenital malformations asymmetrically affect both ears. In cases where only one ear has a radiologic abnor- Table 5.3 Congenital Sensorineural Hearing Loss mality, there is an 50% likelihood that the uninvolved Nongenetic ear will have normal hearing. The clinical findings are Viral highly variable. Some individuals maintain normal or Metabolic slightly diminished hearing, some patients experience progressive deafness, and some are deaf at birth. About Traumatic 20% of patients will have vestibular symptoms. Genetic There is a wide variety of inner ear malformations. Be- Associated with named syndrome (e.g., Pendred, Waardenburg) cause the spherical otic vesicle forms three “buds,” which Unassociated with named syndrome give rise to the cochlea, vestibule, and semicircular canals/endolymphatic apparatus, congenital inner ear Bony Labyrinth malformations may affect one or more of these structures. See Table 5.2 In previous editions, we have emphasized the overuse of Membranous labyrinth only the term Mondini malformation, which has in the past been Scheibe syndrome used in the literature to describe virtually any malformation short of complete aplasia. Since the last edition, there have Alexander syndrome been several additional advances in classification. Perhaps ch05.qxd 9/23/08 11:54 AM Page 313

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most important is the use of the term incomplete partition particularly that subtended by the lateral semicircular (IP), which refers to the configuration of the cochlear turns canal (Fig. 5.9 and Fig. 5.10).53,54 and loss of internal architecture. In this section, inner ear deformities are classified in Cochlear Aplasia order of descending severity (and later embryological insult): Michel deformity, cochleovestibular aplasia, com- This is a very rare deformity ( 3% of cochlear malforma- mon cavity, IP-1 (cystic cochleovestibular malformation), tions) characterized by complete absence of the cochlea cochleovestibular hypoplasia, and IP-2 (Mondini). (Fig. 5.11). The vestibule and semicircular canals are Developmental anteromedial migration of the facial somewhat developed but typically deformed. This malfor- nerve canal is consistently found when the rostral growth mation can be explained by an arrest in the development of the cochlea is either absent or stunted.48 This occurs in of the otic placode during the end of the third week, but most of the anomalies described in this section. The continued, albeit abnormal, development of the buds of notable exception is IP-2, the classic Mondini deformity. the vestibule and semicircular canal.55 This malformation In this circumstance, the cochlear volume is sufficient to may also be confused with labyrinthitis ossificans. Ears preclude this migration (Table 5.4 and Fig. 5.8). with cochlear aplasia are devoid of auditory function.

Michel Aplasia Common Cavity Deformity This entity is likely due to a developmental arrest of This malformation is characterized by confluence of the otic placode development at the third gestational week cochlea, vestibule, and semicircular canals, resulting in a before the formation of the otic vesicle, resulting in com- single common cavity. This entity is relatively common, plete labyrinthine aplasia.42,49–51 This may manifest as constituting 26% of cochlear malformations. The malfor- complete absence of the inner ear or a nondescript dense mation can be explained by an arrest in the development bony remnant. In either case, the middle and external ear of the otic vesicle during the fourth week of gestation af- is typically entirely intact. It is extremely rare, constituting ter differentiation of the auditory (otic) placode into the less than 1% of all congenital inner ear malformations. otocyst, but before differentiation of the otocyst into the Michel’s aplasia has been associated with anencephaly, primordia of the cochlea, vestibule, and semicircular thalidomide exposure, and external ear malformations. The ducts.42,55 The result is an ovoid cystic inner ear lesion diagnosis is relatively easy when inner ear structures are without internal architecture (Fig. 5.12). The size of this entirely absent.52 When dense bone is present, differentia- cyst varies significantly. Smaller cavities probably repre- tion from diffuse labyrinthine ossification (most commonly sent earlier developmental arrests. Cavity size averages due to childhood meningitis) may be a problem. In 7 mm vertically and 10 mm horizontally.51 The internal Michel’s deformity, the lateral wall of the inner ear rem- auditory canal may be large or small depending upon the nant is flat in contradistinction to labyrinthine ossification, size of the cyst (Fig. 5.13, Fig. 5.14, and Fig. 5.15). There is in which there is preservation of the normal convexities, a risk of gusher if the middle ear/oval window is surgically

Table 5.4 Malformations of the Membranous Labyrinth and the Bony Labyrinth Disorder Cochlea Vestibule Vestibular Aqueduct Timing Frequency Michel aplasia Absent Absent Absent 3rd week, early Rare Cochlear aplasia Absent Deformed Not enlarged 3rd week, late Rare Common cavity Cystic Cystic Normal 4th week Relatively common (same chamber) (same chamber) (not enlarged) Incomplete partition Cystic Cystic Normal 5th week Rare type 1 (entirely absent modiolus) (separate from cochlea) (not enlarged) Cochleovestibular Hypoplastic Hypoplastic Normal 6th week Rare hypoplasia (not enlarged) Incomplete partition Cystic apex Often normal Large 7th week Relatively common type 2 (normal basilar turn) Large vestibular Modiolar deficiency Variable Large 7th week Relatively common aqueduct syndrome ch05.qxd 9/23/08 11:54 AM Page 314

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Fig. 5.8 Line drawings of various inner ear deformities. (Modified from Sennaroglu L, Saatci I. A new classification for cochleovestibular malformations. Laryngoscope 2002; 112(12): 2230–2241.)

explored because the lateral aspect of the IAC is defective, and differentiated than the common cavity deformity resulting in increased perilymphatic pressure. Histologi- described above. The cochlea and vestibule have been cal examination has revealed some differentiation of the described as having a “snowman” or “figure 8” shape organ of Corti scattered along the cyst wall. However, the (Fig. 5.16).57 overall neural population is usually sparse or absent. Importantly, the overall dimensions of the cochlea Sagittal high-resolution T2-weighted MRIs (T2WIs) in and vestibule are normal in IP-1. This has been con- true common cavity malformations have demonstrated firmed with numerous measurements. The diagnosis is an absence of the cochlear nerve, precluding cochlear based on the absence of normal internal architecture. implantation. Specifically, the modiolus is absent, which gives the cochlea a cystic appearance. The vestibular aqueduct is normal in these cases, another important differentiating Incomplete Partition Type 1 point. The facial nerve is normally positioned as the IP-1 (cystic cochleovestibular malformation) consists of a inner ear volume is preserved.48 The cribriform area completely unpartitioned, empty, and cystic-appearing between the cochlea and the internal auditory canal is cochlea most likely resulting from an arrest in otic pla- often defective, and all patients have a large IAC (Fig. 5.17, code development in the fifth week of gestation.51,56 The Fig. 5.18, and Fig. 5.19). This predisposes to an increased vestibule is always grossly dilated but distinguishable risk of meningitis and to perilymphatic gusher in the from the cochlea and as such is one step more organized event of middle ear exploration. ch05.qxd 9/23/08 11:54 AM Page 315

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A B

C D Fig. 5.9 Total labyrinthine aplasia (Michel). (A) Magnified coronal axial CT image, left ear. Note that the middle ear and ossicular chains computed tomography (CT) image, right ear. (B) Magnified coronal CT are developed, but that the entire labyrinth is absent. (Courtesy of image, left ear. (C) Magnified axial CT image, right ear. (D) Magnified Robert A. Kaufman, MD.)

Cochleovestibular Hypoplasia may be explained by a developmental arrest occurring Cochleovestibular hypoplasia (CVH) represents 15% of during the sixth week of gestation. The cochlea and all cochlear anomalies42,56 and is more differentiated vestibule are differentiated from each other (Fig. 5.20). than IP-1, but less so than IP-2. CVH is characterized by The accompanying vestibule is hypoplastic or possibly reduced cochlear length, often a single turn or less, and even absent. The IAC dimension is usually normal or ch05.qxd 9/23/08 11:54 AM Page 316

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A B Fig. 5.10 Total labyrinth aplasia, Michel. (A) Coronal and (B) axial com- labyrinth by an inexperienced observer. The key is the flat lateral margin puted tomography images reveal complete lack of development of inner of the bone (arrows). There would be a convexity in this location if this ear structures. The dense bone could be misconstrued as an ossified were labyrinthitis ossificans.

perhaps slightly smaller than normal (Fig. 5.21). The subtle cochlear hypoplasia is sometimes overlooked on vestibular aqueduct is normal. The internal architecture initial inspection.22 A cochlear height of less than 4.35 mm of the cochlea is variable. Hearing deficit is also variable is beyond two standard deviations of normal and has and reflects the degree of membranous labyrinthine a high predictive value for sensorineural deficit. High- development. Some observers have advocated measure- resolution T2WIs reveal variable appearance of the ment of cochlear height on a routine basis, as relatively cochlear nerve, which may be normal or hypoplastic. As

A B Fig. 5.11 Bilateral cochlear aplasia, vestibule, and semicircular canal dysplasia. (A,B) Coronal computed tomography (CT) images, right ear. ch05.qxd 9/23/08 11:54 AM Page 317

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C D

Fig. 5.11 (Continued) (C) Coronal CT image, left ear. (D) Axial CT image, right ear. (E) Axial CT image, left ear. There is no evidence of any cochlear development on either side. Note the flat lateral labyrinthine wall on the coronal image of the right ear at this level (arrow, A). On the right, the vestibule is extremely large (*), and the superior and lateral semicircular canals are somewhat developed (small white arrows). The IAC is small (outlined arrow). On the left the vestibule is extremely large (*), the semicircular canals are better developed (small white arrows), and the IAC (outlined arrow) is large, a further indicator that there is is very slightly more E advanced development on this side. (Courtesy of Paul Caruso, MD.)

indicated elsewhere in this volume, a thorough evalua- cochlea and vestibule are normal, but the cochlea is limited tion of the cochlear nerve should be performed in to 1.5 turns. Importantly, the basilar turn of the cochlea is patients who are potential CI candidates. normal.58 The development of the organ of Corti and auditory neural population is variable, and as a result, the hearing loss ranges widely in these patients from normal Incomplete Partition-2 to profound. Hearing loss is often fluctuating in these IP-2 (classic Mondini malformation) can be attributed to patients similar to that which occurs in isolated large an arrest in inner ear development during the seventh vestibular aqueduct syndrome (LVAS). Successful cochlear week of gestation.42,55,56 The internal architecture is more implantation has been performed in several of these cases. developed than IP-1. Specifically, the defect is limited to Vestibular prominence is variable and often minimal the apical and middle turns of the cochlea, where there is (Fig. 5.23). The semicircular canals are normal. As the dean absent modiolus and deficient interscalar septum velopment of the vestibular aqueduct begins just before (Fig. 5.22). This confluence results in a cystic appearance the seventh week of gestation, the VA is always large in at the cochlear apex only. The overall dimensions of the these patients, an extremely important differentiating ch05.qxd 9/23/08 11:54 AM Page 318

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A B Fig. 5.12 Common cavity deformity. (A,B) The cochlea, vestibule, and semicircular canals appear as one common cavity without partition. The process is bilateral and symmetric. (Courtesy of Joel Curé, MD.)

A B Fig. 5.13 Common cavity deformity. (A) Magnified coronal computed cystic cavity without any evidence of partition. The middle ear and mas- tomography (CT) image, right ear. (B) Magnified axial CT image, right toid, including the ossicular chain (arrow), have developed normally. ear. The cochlea, vestibule, and semicircular canals conform to a single ch05.qxd 9/23/08 11:54 AM Page 319

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Fig. 5.13 (Continued)

point (Fig. 5.23, Fig. 5.24, and Fig. 5.25). Roughly, half Large Vestibular Aqueduct Syndrome /Large Endolymphatic Duct have a large IAC. and Sac Syndrome The triad of (1) normal basilar turn/cystic cochlear Historical Significance and Pathophysiology The most apex, (2) large vestibule with normal SCCs, and (3) large common imaging finding in individuals with sensorineural VA/ELD and ELS is the precise list of conditions of a deficit dating to infancy or childhood is the LVA associated patient that were first described by Carlo Mondini in with the large endolymphatic duct and sac (LED/LES). 1791 in a scientific report written in Latin, entitled “The There is a high incidence of bilaterality, perhaps 90%, but Anatomic Section of a Boy Born Deaf.”59–61 All subsequent findings are commonly asymmetric. This is important discussions of Mondini deformity should be limited to when cochlear implantation is contemplated, as the patients with this triad (IP-2). surgeon will want to know which ear is the most As the large vestibular aqueduct is a hallmark of this normal.62,63 As with IP-2, the developmental insult is likely disorder, there is considerable overlap between IP-2 and in the seventh week of gestation; however, recent data the large vestibular aqueduct syndrome. Quite possibly suggest that the vestibular aqueduct grows throughout these disorders are a developmental continuum. embryonic life and perhaps postnatally as well. This indicates that LVAS may be, to some extent, an acquired deformity rather than a stable congenital malformation.64 There is a slight female predominance. The pattern of inheritance is most likely autosomal recessive although a smaller component of autosomal dominant or multifactorial inheritance may exist (Fig. 5.26).65 The association between an LVA and SNHL was initially described by Valvassori and Clemis in 1978.24 They identified 50 patients with enlarged VAs using polytomography, coining the term large vestibular aqueduct syndrome (LVAS). Despite imaging limitations, they also astutely noted that 60% of patients with enlarged VAs had other inner ear malformations. In 1989, Levenson and colleagues identified LVAS as a distinct clinical entity.66 They determined that LVAS is a congenital anomaly of the temporal bone that predisposes patients to acquired, progressive, Fig. 5.14 Common cavity, small caliber. Axial computed tomography reveals that the inner ear consists of a small cystic cavity (large arrow). fluctuating, high frequency SNHL. The hearing loss may be The internal auditory canal is extremely narrow (small arrows). See triggered by head trauma and activity that causes sudden text. (Courtesy of Jan Casselman, MD.) fluctuation in CSF pressure. Based on their own similar ch05.qxd 9/23/08 11:55 AM Page 320

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A B Fig. 5.15 Common cavity deformity. (A) Axial and (B) coronal com- canals, although a tiny SSC remnant (short arrow, B) is noted. Oval win- puted tomography images. There is a small common cavity deformity dow (long arrow, B); note the presence of the ossicular chain. First genu (*) without differentiation into the cochlea or vestibule/semicircular of FNC (arrow, A). (Courtesy of Bernadette Koch, MD.)

A B Fig. 5.16 Incomplete partition type 1 (IP-1) anomaly. (A,B) Axial computed tomography images. ch05.qxd 9/23/08 11:55 AM Page 321

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C D

E F Fig. 5.16 (Continued) (C,D) Axial T2-weighted magnetic resonance im- vestibules are also cystic and undifferentiated (black arrows). Note the ages (T2WIs). (E) Magnified sagittal T2-weighted fast spin echo presence of a membranous partition between the cochlea and image, right ear. (F) Magnified sagittal T2-weighted fast spin echo im- vestibule (outlined arrow), indicating greater differentiation than a age, left ear. The cochleas have a cystic appearance (white arrows) due “common cavity” deformity. to the absence of the modiolus and osseous spiral laminae. The ch05.qxd 9/23/08 11:55 AM Page 322

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investigation, Jackler and De La Cruz advised patients with LVAS to avoid contact sports and activities that entail extreme barometric pressure changes.67 Harnsberger and Davidson, as well as Okamoto, noted that the bony changes of the enlarged VA are probably caused by the enlarged ELD and ELS and suggested that the name of the entity be changed to large endolymphatic duct and sac syndrome (LEDS) or, alternatively, large endolymphatic sac anomaly (LESA).18,57,68 The terminology used probably reflects which modality (CT or MRI) is used in diagnosis. The precise cause of the hearing deficit in these patients is unknown; however, numerous interesting theories have Fig. 5.17 Incomplete partition type I (IP-I) anomaly. Axial computed been advanced. Foremost among these theories are (1) tomography image reveals a bilaterally symmetric dysplasia character- hyperosmolar proteins in the enlarged ELS reflux into the ized by a cystic cochlea (absent modiolus) (white arrows) and cystic vestibule (black arrows). Note the well-defined partition (outlined cochlear duct (scala media) through a widely patent ELD, arrows) between them, indicating that this is a step advanced from which causes osmotic damage to the neuroepithelium; and the common cavity deformity. Note that examination of the posterior (2) associated modiolar deficiency allows CSF pressure petrous surface reveals no enlargement of the vestibular aqueduct, a waves into the labyrinth, damaging hair cells in the organ hallmark of this deformity. (Courtesy of C. Douglas Phillips, MD.) of Corti.19,66–70 The latter theory was advanced more

Fig. 5.18 Incomplete partition type I (IP-1) anomaly with modiolar deficiency, semicircular canal dysplasia. (A) Coronal computed tomography (CT) image at the level of the cochlear apex. (B) Axial and (C) coronal CT images at the level of the vestibule. There is a cystic cochlear apex (black arrows, A,B) resulting from modiolar deficiency, although the basilar turn of the cochlea is unremarkable (black arrow, C). There is no evidence of a large vestibular aqueduct that would indicate the classic Mondini deformity. This malformation is instead associated with hypoplasia of the semicircular canals (white arrows, B,C).

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A B

C D Fig. 5.19 Hybrid incomplete partition-1 deformity, left ear. (A,B) Coro- (long white arrow, C,E,F) between the cochlea and the vestibule. The nal computed tomography (CT) images (C) Stenvers and (D–F) axial cochlear neural aperture (short white arrow, B,E) is abnormally wide, images. There is a cystic cochlear apex (*) with modiolar absence; how- raising concern about a possible perilymphatic gusher if oval window ever, the basilar turn of the cochlea (double thin white arrows) has devel- exploration were entertained. The vestibular aqueduct is not enlarged. oped. The vestibule (V) is large, and the semicircular canals (short, thick (Courtesy of Paul Caruso, MD.) white arrows) are short and stubby. There is an incomplete partition (Continued on page 324) ch05.qxd 9/23/08 11:55 AM Page 324

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E F Fig. 5.19 (Continued)

recently by the observers who recognized the high inci- extreme barometric pressure changes. Patients may also dence of cochlear anomalies in LVAS/LEDS/LESA. Relative benefit from a no-salt-added diet.72,73 Others have sug- T2-weighted hyposignal is very commonly present in the gested that a buildup of toxic metabolic by-products in the large endolymphatic sac, likely reflecting the extremely endolymph or interference with the immune response high protein concentration known to occur in this region. could result from a dysfunctional endolymphatic sac. This fact is more supportive of the former theory (reflux Endolymphatic hydrops is an unlikely culprit, as the home- into cochlear duct).71 Internal fistulization (mixing of peri- ostatic disruption would be expected to involve the apex lymph and endolymph) likely also plays a role in the of the cochlea and result in a low-frequency (audiometri- pathogenesis of the episodes of hearing deterioration simi- cally up-sloping) sensorineural hearing deficit. As such, lar to that which occurs in other malformations. This endolymphatic sac shunting has fallen into disrepute; explains why patients are usually instructed to avoid contact however, surgical ELS obliteration has been determined to sports and activities, such as scuba diving, which result in be useful in stabilization of the progressive hearing loss

A B Fig. 5.20 Cochlear hypoplasia. (A) Axial computed tomography image (arrow). Note the normal semicircular canals. (Courtesy of Jan Casselman, reveals a small-caliber cochlear apex (arrow) and a normal vestibule. MD.) (See Color Plate Fig. 5.20B.) (B) Maximal intensity projection image confirms the hypoplastic cochlea ch05.qxd 9/23/08 11:55 AM Page 325

A B Fig. 5.21 Cochleovestibular hypoplasia. Axial computed tomography separately developed but of very small caliber. There is modiolar deficiency images through (A) the cochlear apex and (B) the basilar turn reveal (black arrow, A). (Courtesy of Tim Larson, MD.) that both the cochlea (black arrows) and the vestibule (white arrow) are

A B

C D Fig. 5.22 Incomplete partition type 2 (classic Mondini deformity), bilat- The intact basilar turn is a critical differentiating point. The vestibular eral. Coronal CT (A,B) left ear and (C,D) right ear reveal a cystic cochlear aqueduct was large on each side (not illustrated). Note that there is no apex (outlined arrows); however, the basilar turn (solid arrows) is normal. evidence of semicircular canal development. ch05.qxd 9/23/08 11:55 AM Page 326

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A B Fig. 5.23 Incomplete partition-2 (classic Mondini deformity). (A) Axial computed tomography image and (B) axial T2-weighted magnetic resonance image. There is a large vestibular aqueduct (black arrow, A) and a deficient modiolus (white arrows).

associated with this disorder.67,74,75 The reader should be Imaging Features of LVAS/LEDS The characteristic imaging aware that the overall size of the VA, ELD, and ELS and the features are the LVA on CT and the enlarged ELD and ELS degree of modiolar deficiency (see below) do not correlate on MRI.18,23,24,77 The VA/ELD is considered large when it with the degree of hearing loss.76 measures 1.5 mm in width at the midpoint between the

A B Fig. 5.24 Incomplete partition-2 (classic Mondini deformity). There is a cystic cochlear apex (black arrows), a dilated vestibule (V), and a large vestibular aqueduct (white arrows). (Courtesy of Barb Zeifer, M.D.) ch05.qxd 9/23/08 11:55 AM Page 327

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C D Fig. 5.24 (Continued)

common crus and the external aperture.21,23,24 The size of vestibulocochlear abnormalities are much more common the ELS is highly variable and not necessarily proportional in this disorder than originally thought.18,19,80 In particular, to the size of the VA. On occasion, the ELS may be cochlear anomalies are quite commonly appreciated with massive, with impingement upon the anterolateral both CT and MRI, but especially with high-resolution cerebellum, and could conceivably be confused with T2WI techniques. These range from simple modiolar defi- other pathological conditions18,78,79 ciency or scalar asymmetry to full-blown cochlear dys- There have been major advances in the evaluation of morphism.18 In another recent series, all patients had, at this disorder in recent years. These have revealed that minimum, anomalies in the modiolus of the cochlea.19

A B Fig. 5.25 Classic Mondini deformity. (A) Magnified axial T2-weighted fast vestibular aqueduct is quite large bilaterally, and the endolymphatic duct spin echo image, right ear. (B) Magnified axial T2-weighted fast spin echo and sac are extremely large, especially on the right (double large outlined image, left ear. There is a cystic cochlear apex bilaterally with modiolar arrows). The basilar cochlear turn was intact bilaterally (not illustrated). deficiency (c, arrow). The vestibule is moderately dilated (v, arrow). The ch05.qxd 9/23/08 11:55 AM Page 328

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Fig. 5.26 Large vestibular aqueduct; large endolymphatic sac anomaly. (A) Axial, (B) sagittal (right), and (C) sagittal (left) T2-weighted magnetic resonance images reveal large vestibular aqueducts with dilated endolymphatic ducts and sacs (thick arrows). The vestibule (V) is enlarged as well. The modiolus appears to be of normal caliber (outlined arrows). There is absence of a segment of the osseous spiral lamina, scala communis, a normal variant (thin arrows). If the cochlear apex were cystic without modiolar development, the diagnosis would be incomplete partition-2, the classic Mondini deformity. This case well exemplifies the potential overlap between these diagnoses. (Courtesy of Mauricio Castillo, MD.) A

B C

Other observers have noted that although modiolar defi- unusually large VA. Conversely, measurably large VA/ELD ciency is extremely common in this disorder, occasionally may be associated with a relatively unremarkable ELS.81 these patients do have a normal modiolus; in one series, As noted above, the severity of the hearing loss does not 14% of patients had a normal modiolus.18,71,76 As indicated correlate linearly with the size of the VA/ELD/ELS. A above in the anatomy section, the normal modiolus recent study revealed that a deformed LSCC was closely appears as a 3D structure on axial T2WI (and at CT) through associated with the presence of vertigo in patients with the cochlear apex. It often has the shape of a crown, a LVAS.82 bowtie, or a trapezoid; it should never appear flattened or The LVA (and dilated ELD/ELS) may also occur in asso- decidedly asymmetric (Fig. 5.27 and Fig. 5.28). ciation with several of the cochlear malformations As one would expect, T1WI and T2WI relaxation times described above and is a hallmark of the classic Mondini within the ELD are usually long, approaching those of deformity (IP-2). LVA does not occur with IP-1. It is inter- CSF, reflecting fluid content.73 Reflux of hyperosmolar esting to speculate on how many patients diagnosed in proteins may alter the MRI characteristics of the ELS, as the past with LVAS may actually have had classic Mon- high protein may shorten T1WI and T2WI relaxation dini deformity (IP-2). times (high signal intensity on T1, low signal intensity on As indicated elsewhere in this volume, LVAS is associated T2).68 Importantly, occasional patients with congenital with several named syndromes. Pendred syndrome (see SNHL are identified with a large ELS in the absence of an below) is the most notable of these. Recently, several patients

Fig. 5.27 Vestibular aqueduct syndrome; large endolymphatic sac Note the large endolymphatic duct/sac bilaterally (arrows). The anomaly; bilateral fluctuating severe sensorineural hearing loss. (A) vestibule (V) as well as the ampullae of the proximal lateral and poste- Magnified axial computed tomography (CT) image, right ear. (B) Magni- rior semicircular canals are also moderately prominent. (E) Magnified fied axial CT image, left ear. There is a very large vestibular aqueduct bi- axial T2-weighted magnetic resonance image (T2WI), right ear. The laterally (arrows). (C) Magnified axial T2-weighted fast spin echo image, modiolus is deficient (arrow). (F) Magnified axial T2WI image, left ear. right ear. (D) Magnified axial T2-weighted fast spin echo image, left ear. The modiolus is deficient (arrow). (See Color Plate Fig. 5.27E,F.) ch05.qxd 9/23/08 11:55 AM Page 329

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C D Fig. 5.28 Vestibular aqueduct syndrome; large endolymphatic sac image. The enlarged endolymphatic duct and sac (arrow) within the anomaly. (A) Magnified axial computed tomography (CT) image of nor- large vestibular aqueduct. (D) Axial CT image through the cochlear mal right ear. Normal configuration of posterior petrous surface. (B) apex. The modiolus is deficient (arrow). Note the asymmetry with lack Magnified axial CT image, left ear. Dramatic widening of the vestibular of normal “bowtie” appearance. (See Color Plate Fig. 5.28D.) aqueduct (arrow). (C) Sagittal T2-weighted thin-section fast spin echo

with mutations in the GJB2 gene have been described with sectional imaging. To understand the spectrum of malfor- findings indistinguishable from this disorder.83 mations, we must first review the embryogenesis. As previously discussed, the membranous labyrinth has three subdivisions, the endolymphatic duct and sac, the Semicircular Canal Anomalies pars inferior (cochlea and saccule), and the pars superior (utricle and semicircular ducts). The superior, posterior, Overview and lateral semicircular ducts reach their adult configura- Our understanding of congenital malformations of the tion by the eighth week of gestation. Ossification of the SCC has rapidly increased over the past few years. This is semicircular canals occurs at approximately midgestation. based on a greater knowledge of molecular genetics and The SSCC is completed first (19th week), and the LSCC is advances in our ability to visualize the SCC on cross- the last to completely develop (22nd week). There is ch05.qxd 9/23/08 11:55 AM Page 331

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consensus that because the horizontal canal is the last to 10 years of age. Patients often present with profound develop, it is more susceptible to anomaly. hearing loss that is difficult to explain. Affected children had some delay in supporting their head and sitting up in infancy and also had delayed milestones for walking. Semicircular Canal Dysplasia and Aplasia These deformities are not explained by a single classifica- As discussed in the above sections, the type of inner ear tion system based on embryonic arrest. Instead, altered malformation can often be attributed to the timing of the molecular genetics is a concept gaining greater acceptance, developmental arrest. Because the cochlea and SCCs have a implying that the isolated SCC aplasia may be due to specific common progenitor, the otic vesicle, dysplastic semicircu- gene mutations. Recent investigations in mice have corrobo- lar canals should be associated with cochlear malforma- rated this theory. This deformity may be an important marker tion. Similarly, patients with semicircular canal dysplasia identifying patients who may benefit from genetic testing. should have vestibular dysplasia due to their contiguity. SCC dysplasia may be sporadic or syndromic. In gen- However, in 1990, Parnes and Chernoff reported two eral, the dysplasia is more severe when syndromic. cases of bilateral complete SCC aplasia associated with a Importantly, absent semicircular canals are a hallmark of normal or near-normal cochlear development.84 This is the CHARGE syndrome.86–88 Several other ear anomalies difficult to explain embryologically; however, subse- are associated with this syndrome.88 Greater than 70% quently, several other reports of isolated SSC aplasia have will have oval/round window atresia, cochlear nerve surfaced.5,85 This anomaly appears to be more common in aperture atresia, facial nerve canal anomalies, and middle males, with the average of presentation between 5 and ear deformity (Fig. 5.29).

A B

Fig. 5.29 Semicircular canal dysplasia; modiolar deficiency. (A) Coronal computed tomography (CT) image at the level of the cochlear apex. (B) Axial and (C) coronal CT at the level of the vestibule. There is a cystic cochlear apex (black arrows, A,B) resulting from modiolar deficiency, although the basilar turn of the cochlea is unremarkable (black arrow, C). There is no evidence of a large vestibular aqueduct, which would indicate the classic Mondini deformity. This malformation is instead associated C with hypoplasia of the semicircular canals (white arrow, C). ch05.qxd 9/23/08 11:55 AM Page 332

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cephalosyndactyly type I (Apert) and Crouzon’s craniofacial dysostosis. Unilateral SCC aplasia has been diagnosed in a patient with Goldenhar’s syndrome (oculoauriculovertebral dysplasia).92 This is unusual because ear findings in this disorder typically involve structures subtended by the first and second branchial arches (middle and external ear).

Superior Semicircular Canal Dehiscence The syndrome of superior semicircular canal dehiscence (SSCD) has been described in the literature since our last edition.93–98 This results in dizziness and vertigo, which may be triggered by straining, heavy lifting, or loud (typically low frequency) sounds. Another common complaint is autophony (reverberation when speaking, chewing, or swal- lowing). Hearing loss is also associated, which is typically sensorineural, but can be conductive. Men are affected more commonly than women, and presentation is often between 30 and 50 years of age. This disorder is usually unilateral; however, a case of bilateral SSCD was recently reported.99 Fig. 5.30 Alagille syndrome. Axial computed tomography of the right The oval and round windows are normally the only ear. The posterior semicircular canal is absent (arrow). (Courtesy of two openings in the hydraulic system of the inner ear, and Bernadette Koch, MD.) as a result, movement of inner ear fluid with stapes motion is anatomically limited although physiologically crucial to normal hearing and balance.93 The inward bulging Selective aplasia of a specific SCC may also occur. of the oval window caused by sound-induced stapes Isolated lack of development of the posterior SCC has movement is compensated by outward bulging of the been described in Alagille’s syndrome (Fig. 5.30) (arte- round window, resulting in a precise equilibrium. Dehis- riohepatic dysplasia) and Waardenburg’s syndrome.89–91 cence of the bone overlying the SSSC creates a “third mobile Selective absence of the SSCC has been also been window,” which results in aberrant movement of inner reported. Isolated dysplasia of the LSCC (with dilated ear fluids. Loud sounds push the stapes inward, and the vestibule) may be sporadic, but it also occurs in acro- third window moves outward (Fig. 5.31A). This creates a

Fig. 5.31 Superior semicircular canal dehiscence syndrome. (A) Drawing illustrates the distention of the membranous labyrinth of the SSC, which occurs as a A result of a loud noise. (See Color Plate Fig. 5.31.) ch05.qxd 9/23/08 11:55 AM Page 333

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Fig. 5.31 (Continued) (B) Coronal CT reveals an absent cortex of the superior semicircular canal (arrow). (C) Coronal CT, opposite ear, reveals a normal cortex (arrow). (Case courtesy of C. Douglas Phillips, MD. Drawing courtesy of H. D. Curtin, MD.) C

wave in the perilymphatic compartment, which com- surface of the remainder of the petrous pyramid (arcu- presses the endolymphatic compartment, resulting in ate eminence). The CT diagnosis of SSCD is challenging, as dizziness. Sound-induced vertigo, nystagmus, or both are even a sliver of intact bone excludes the diagnosis (“pa- referred to as the Tullio phenomenon. This phenomenon pyraceous osseous margin”). The well-known partial vol- has been described in several other entities, including ume effect results when a structure is smaller and thinner erosive cholesteatomas, otosyphilis, and in patients who than the individual voxel used to generate the CT image. have undergone artificial lateral semicircular canal fenes- As the superior surface of the canal may be extremely tration, which was used in the past to treat otosclerosis thin, images obtained with 1.5 mm collimation may prior to the development of prosthetic stapedectomy (see create the illusion of a dehiscence in the normal patient. Chapter 3). Other types of surgery may also be causitive For this reason, 1.0 mm or 0.5 mm collimation is recom- (Fig. 5.32). Patients may also have Hennebert’s sign, mended. Oblique reformations further increase the posi- which refers to nystagmus caused by applied pressure tive predictive value of the examination, as the SSC plane within the external auditory canal.94 An interesting corol- is 45 degrees divergent from both the coronal and sagittal lary in these patients is the similar symptomatology cre- planes.19 As such, reformations in the planes of Stenver ated by the Valsalva maneuver, which results in a tran- and Poschl may be of value in many cases (Fig. 5.5A, Fig. sient increase in intracranial pressure and pushes the 5.6A, and Fig. 5.33).93,98 Both of these planes of section third window inward rather than outward. The only clini- are 45 degrees oblique to the coronal and sagittal planes, cal difference is that although the plane of nystagmus re- but perpendicular to each other (Fig. 5.5). The entire arc mains oriented with the plane of the SSC, the nystagmus of the superior semicircular canal is seen on one slice in produced with the Valsalva maneuver is in the opposite the plane of Poschl. Detailed diagnosis is crucial, as treat- direction. ment is craniotomy with middle cranial fossa repair by SSCD can be identified with high-resolution CT.94–97 plugging or resurfacing the bony defect. Surgery is often The imaging findings are absence of bone forming the highly successful in treating the vertigo; however, hearing roof of the superior surface of the canal (Fig. 5.31B,C). may improve or worsen.10 0 The roof of the SSC is composed of up to three layers: (1) Symptomatology identical to SSCD has been diag- otic capsule, (2) trabecular bone (may be pneumatized), nosed anecdotally in patients with a number of differ- and (3) cortical bone continuous with the superior ent pathologic and imaging findings.101–103 CT performed ch05.qxd 9/23/08 11:55 AM Page 334

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A B

Fig. 5.32 Surgical disruption of posterior semicircular canal; acquired posterior semicircular canal (white arrows). Labyrinthine ossification Tullio phenomenon. (A,B) Axial computed tomography (CT) images (white outlined arrow, B). (C) Coronal CT image, left ear, reveals hyperos- reveal a retrosigmoid surgical defect (black arrow). Operative dissection tosis within the apical cochlear turn (black arrow), consistent with resulted in disruption of the posterior petrous surface and breach of the chronic labyrinthitis.

in one patient revealed posterior SSCD caused by cular canal. The pathophysiology (third mobile window) petrous apex cholesteatoma. Another had a subarcuate in all three of these examples was identical to classic vascular malformation resulting in widening of the SSCD. petromastoid canal, which caused SSCD adjacent to the The thickness of bone between the carotid canal and common crus. As discussed in Chapter 6, the petromas- the basilar cochlear turn (cochlear-carotid interval) is toid canal is a curvilinear normal structure containing widely variable, and a case with completely absent bone the subarcuate artery and vein, which courses between was recently reported.104 It has been postulated that the limbs of the SCC. A third patient had classic auditory energy transmitted from artery pulsations may result in and vestibular symptoms that were proven to be caused alterations of intracochlear fluid dynamics and aberrant by developmental dehiscence of the posterior semicir- hair cell stimulation. Tinnitus and SNHL may result. In ch05.qxd 9/23/08 11:55 AM Page 335

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Fig. 5.33 Superior semicircular canal dehiscence syndrome, Poschl projection. (A) Drawing in axial plane with the line indicating the plane of section perpendicular to the long axis of the petrous pyramid. (B) Poschl projection computed tomography (CT) image reveals the absence of the bony cortex of the superior semicircular canal (arrow). (C) Poschl projection CT image reveals a normal bony cortex on the opposite side with C pneumatization (arrow). (Courtesy of C. Douglas Phillips, MD.)

many respects, this is analogous to SSCD as well.105 This with a positive predictive value for associated hearing loss, entity is discussed further in the section on cochlear a normative measurement has been devised through implantation. examination of the LSCC “bony island.” This measurement is from the apex of the canal turn to the junction of the canal with the vestibule. Measurements of 2.6 mm or Isolated Deformity of the Lateral Semicircular Canal 4.8 mm are beyond two standard deviations and indica- As indicated in previous paragraphs, the SSCC is the first to tive of hypoplasia and hyperplasia, respectively.22,107 develop, followed by the posterior and, finally, the lateral. As the LSCC is the last to develop, malformations isolated Syndromic Hearing Loss to the lateral semicircular canal are relatively common (Fig. 5.34). This deformity may be unilateral or bilateral Congenital sensorineural hearing deficit is associated and can be associated with sensorineural deficit, conduc- with a large number of systemic eponymically designated tive deficit, or normal hearing.106 Although not associated syndromes. A complete review is beyond the scope of this ch05.qxd 9/23/08 11:55 AM Page 336

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Fig. 5.34 Congenital deformity of the vestibule and lateral semicircular canal (LSCC). (A) Magnified coronal computed tomography (CT) section, right ear. (B) Magnified axial CT sections, right ear. The LSCC (arrows) is A usually wide and short and contiguous with the vestibule.

text. Rather, we focus on entities for which there are linked to chromosome 7, which is characterized by euthy- established inner ear deformities detectable with current roid (although hypothyroidism may occur in some) goiter, imaging methods. and a positive perchlorate discharge test.108 The thyroid The most common syndromic cause of profound hear- glands of affected individuals cannot organify iodide effi- ing loss is Pendred’s syndrome, accounting for perhaps ciently, and a variable amount of iodine taken up by the 10% of cases. This is an autosomal recessive disorder gland is discharged after administration of perchlorate. ch05.qxd 9/23/08 11:55 AM Page 337

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fluctuation and sudden worsening following episodes of trauma or infection (similar to LVAS/LEDS/LESA). The apical turn of the cochlea is commonly absent. Modiolar deficiency is a constant finding, 100% in one series.108 Rarely, Pendred syndrome is diagnosed in the absence of goiter. Anecdotal reports of the “Mondini type” of inner ear deformity have been reported with the syndromes of Klip- pel-Feil, Wildervanck, Alagille, Waardenburg, Pendred, and DiGeorge.35,44 Klippel–Feil syndrome (fused vertebrae, pectoral deformity) is associated with numerous other inner ear anomalies, including internal auditory canal duplication.109–112 Conductive hearing deficit (CHD) is more common in these patients and is secondary to anomalies of the distal incus and stapes. Wildervanck syndrome Fig. 5.35 Pendred syndrome. A 7-year-old boy with thyroid dysfunction (Fig. 5.36) (cervico-oculo-acoustic) consists of the Klip- and hearing deficit. Axial T2-weighted magnetic resonance image pel–Feil anomaly, abducens nerve dysfunction, and con- (T2WI) of the right ear reveals modiolar deficiency (black arrow), dilated genital deafness. The abducens dysfunction is believed to vestibule (*) and massively dilated endolymphatic duct and sac (multiple white arrows). T2-weighted hyposignal is noted in the large endolym- be supranuclear in origin and results in a distinctive eye phatic sac, likely reflecting high protein concentration. (Courtesy of Jan movement disorder known as Duane retraction syndrome. Casselman, MD.) The female to male inheritance ratio is 10:1. Severe anomalies including aplasia of the semicircular canals, cochlear hypoplasia, and incomplete partition type 1 have been de- This constitutes the basis of the perchlorate discharge test. scribed.50 Goldenhar’s syndrome is associated with Hearing deficit ranges from dramatic and prelingual to branchial arch deformity as well as findings consistent slowly progressive and fluctuating and may worsen follow- with the Klippel–Feil anomaly. As such, they may be part ing a traumatic event or infection. The vast majority of of the same spectrum. Alagille syndrome (arteriohepatic patients have a large vestibular aqueduct (with large dysplasia) is associated with chronic cholestasis, cardiovas- endolymphatic duct and sac) and a large vestibule (Fig. 5.35). cular abnormality, vertebral arch defect, growth and men- Therefore, it is not surprising that patients often suffer tal retardation, and hypogonadism. Severe hypoplasia

A B Fig. 5.36 Wildervanck syndrome (cervico-oculo-acoustic). Patient has ampullated end of the posterior SCC bilaterally (black arrows). There is Klippel–Feil deformity and long-standing hearing deficit. (A) Axial modiolar deficiency appreciated on the left (white outlined arrow). computed tomography (CT) image, right ear. (B) Axial CT image, left Similar findings would be expected with the CHARGE association. ear. The vestibule is large bilaterally (*) and there is almost complete (Courtesy of Paul Caruso, MD.) semicircular canal (SCC) aplasia. There is minimal development of the ch05.qxd 9/23/08 11:55 AM Page 338

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involving the posterior semicircular canal has been consis- Individuals with Down syndrome (trisomy 21) are well tently identified. Middle ear anomalies also occur. known to have middle and external ear anomalies. Inner Waardenburg syndrome (hypertelorism, iris het- ear anomalies are also not uncommon and usually involve erochromia, white forelock) has a strong association with the vestibule and lateral semicircular canal, which are congenital sensorineural hearing deficit. The most common often hypoplastic and partially fused.120 imaging finding is the large vestibular aqueduct with modi- Crouzon’s syndrome (craniofacial dysostosis) and olar deficiency.113 Pathological evaluation has also revealed Apert’s syndrome (acrocephalosyndactylism type I) are membranous labyrinth deformities, although a hypoplastic associated with large vestibules and short, deformed cochlea and posterior semicircular canal dysplasia have LSCC. Deformity of the middle cranial fossa secondary to been reported in several of these patients as well.114 the severe craniofacial asymmetry with upward angula- Branchio-oto-renal syndrome is well documented and tion of the petrous apex relative to the external auditory features auricular deformity, hearing loss, and renal canal is commonly associated. In point of fact, most ear anomalies (Fig. 5.37 and Fig. 5.38). Various reports have symptoms in these patients are referable to the middle linked cochlear hypoplasia (hypoplastic apical cochlear ear and mastoid due to the subsequent dysfunction of the turn), characteristic medial facial nerve deviation flared eustachian tube.39,121 Individuals with Crouzon’s syn- IAC, SCC deformities, and large VA with this autosomal drome have a high incidence of jugular bulb dehis- dominant disorder.115–118 A patulous eustachian tube is cence.122 The surgeon should be cautioned if this is diag- also consistently appreciated. nosed prior to myringotomy. A large number of inner ear anomalies are described in Cornelia de Lange syndrome is associated with cochlear CHARGE syndrome.87,88 SCC aplasia is virtually universal hypoplasia (two turns) and ossicular deformity123 in these patients. Oval window and cochlear nerve aperture atresia is also extremely common (Fig. 5.39). Various Internal Auditory Canal Anomaly cochlear deformities may occur, and numerous middle ear deformities are reported as well. Occasionally, IAC This is discussed more thoroughly in Chapter 8, but suf- hypoplasia and LVAS/ELD/ELS enlargement are also seen fice it to say that on occasion, the imaging specialist may in these patients.119 encounter IACs that are unusually wide, narrow, or perhaps

A B Fig. 5.37 Branchio-oto-renal syndrome. (A) Axial computed tomogra- semicircular canal (arrow). (Courtesy of Jan Casselman, MD.) (See Color phy (CT) of the left ear demonstrated modiolar deficiency (arrow). Plate Fig. 5.37A.) (B) Axial CT of the left ear reveals narrowing of the ampulla of the lateral ch05.qxd 9/23/08 11:55 AM Page 339

Fig. 5.38 Branchio-oto-renal syndrome, cochleovestibular hypoplasia. (A) Axial computed tomography (CT) image reveals bilaterally symmetric hypoplasia of the cochlea (C, arrow) with modiolar deficiency. There is bilateral and symmetric hypoplasia of the vestibule (V, arrow) as well. There is slight development of the ampullated end of the left posterior semicircular canal (outline black arrow). The cochlear neural apertures (*) are abnormally wide, creating concern about possible perilymph gusher if oval window exploration were attempted. The IACs are characteristically flared. (B,C) Coronal CT images reveal hypoplastic superior (S) and lateral (L) semicircular canals. Note the small caliber basilar turns (outlined C arrows). (Courtesy of Paul Caruso, MD.)

Fig. 5.39 CHARGE, semicircular canal (SCC) aplasia. (A) Axial and (B) coronal computed tomography (CT) images reveal complete absence of development of the SCCs, the classic finding in individuals with the A CHARGE association. This patient also has some degree of modiolar deficiency (outlined arrow) and a small vestibule (thin white arrows). ch05.qxd 9/23/08 11:55 AM Page 340

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even duplicated. Asymmetric canal widening is obviously (see Chapter 8).125 The embryological nature of congenital associated with schwannoma. Dural ectasia (neurofibro- IAC stenosis has not been completely elucidated, but most matosis) may result in bilaterally large canals even in the likely a developmental arrest of the vestibulocochlear nerve absence of acoustic tumor (Fig. 5.40).124 results in subsequent underdevelopment of the canal. This There is a wide variation of the normal diameter of the may be an isolated occurrence, or may it be associated with IAC. Canals less than 2 mm in diameter are clearly abnormal. widespread labyrinthine deformity. A severely hypoplastic IAC is classically associated with aplasia of the vestibulocochlear nerve (Fig. 5.41). In this Reduced IAC Caliber circumstance, the canal transmits only the facial nerve, Nonsyndromic congenitally narrow IAC is rare, especially as although dysfunction of each nerve in the canal can occur an isolated finding without additional inner ear anomalies, independently.125 Several reports have revealed that the whereas acquired stenoses are more frequently reported, size of the internal auditory canal in isolated cochlear resulting from osteomas, exostoses, and fibrous dysplasia nerve aplasia is variable and may be normal or only modestly

A B

Fig. 5.40 Deformity of internal auditory canals (IACs). (A,B) Axial computed tomography (CT) sections. The IACs are strikingly wide bilaterally (arrowheads). (C) Coronal CT section, soft tissue window. There is no evidence of abnormal enhancement within either IAC (arrowheads). The profound sensorineural hearing loss in this elderly patient began very early in life. There was a vague history of inflammatory process. The reason for this striking developmental variation is not known. The nerves appeared to be somewhat small on an air cisternographic study. C ch05.qxd 9/23/08 11:55 AM Page 341

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A B

C D Fig. 5.41 Hypoplastic internal auditory canal (IAC), occluded cochlear (black arrow). (C) Sagittal T2-weighted magnetic resonance image neural foramen. (A,B) Axial computed tomography (CT) images of the (T2WI) of the left ear reveals a vacant anteroinferior fundal IAC quadrant left ear reveal an extremely narrow internal auditory canal (white (arrow), indicating that the cochlear nerve is absent. (D) Sagittal T2WI arrows) contiguous with the anterior genu of the facial nerve canal of the right ear reveals a normal cochlear nerve (arrow). (Courtesy of C. (small arrow), with a bony plate occluding the cochlear neural foramen Douglas Phillips, M.D.)

decreased.126,127 There is better correlation with small size and type IIb—absent or hypoplastic cochlear nerve, mor- of the cochlear neural foramen (CNF) through which the phologically normal labyrinth.128 cochlear nerve courses at the lateral end of the IAC. A The integrity of the cochlear nerve is best seen on sagit- stenotic CNF is virtually always accompanied by cochlear tal thin-section T2WI, which may reveal a small caliber nerve deficiency (Fig. 5.42). cochlear nerve or even an entirely vacant anteroinferior Cochlear nerve deficiency is not an uncommon cause of quadrant at the fundus of the IAC. The caliber of the congenital hearing loss and can be reliably identified on cochlear nerve is crucial information in patients who are thin-section T2WI sequences. There are three categories of candidates for cochlear implantation, as severe hypoplasia cochlear nerve deficiency: type I—total absence; type IIa— or absence is a contraindication to this procedure. As such, absent or hypoplastic cochlear nerve, labyrinthine dysplasia; this entity is discussed further later in this chapter. ch05.qxd 9/23/08 11:55 AM Page 342

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C D Fig. 5.42 Congenitally occluded cochlear neural aperture, cochlear There is aplasia of the cochlear nerve, as indicated by the vacant nerve aplasia. (A) Axial computed tomography (CT), right ear. (B) Axial anteroinferior quadrant of the internal auditory canal on sagittal T2WI T2-weighted magnetic resonance image (T2WI), right ear. (C) Sagittal through the fundus. This is a contraindication to cochlear implantation. T2WI, right ear. (D) Axial T2WI, left ear. There is occlusion of the aper- Note the normal left ear for comparison. ture through which the cochlear nerve normally travels (arrows, A,B).

X-Linked Progressive Mixed Deafness munication, increased inner ear pressure, and the propen- In the patient with a wide IAC, careful study of the fundus sity to develop a perilymphatic gusher upon stapes and documentation of an intact bony partition between manipulation. A defective bony partition is often seen in the IAC and the base of the cochlea and vestibule are cru- association with other inner ear malformations or may be cial.129 Absence of the partition is associated with a strong identified as an isolated finding. This latter circumstance potential for fistulous subarachnoid space–inner ear com- has been documented to occur with an X-linked mode of ch05.qxd 9/23/08 11:56 AM Page 343

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A B Fig. 5.43 X-linked progressive mixed hearing loss. (A) Magnified axial and the adjacent cochlear turns. Findings are bilateral and symmetric. Peri- computed tomography (CT) image, right ear. (B) Magnified axial CT lymphatic gushers are usually encountered in this condition. (Courtesy of image, left ear. Note that the fundus of the internal auditory canal is large and Alan Tang, MD, and Lorne S. Parnes, MD, University of Western Ontario, that there is absence of the bony partition (arrows) between the fundus London Ontario, Canada. Reprinted with permission.)

inheritance (Fig. 5.22).130–134 These patients have a mixed specifically the perilymphatic spaces (scala vestibuli and hearing deficit, X-linked progressive mixed deafness scala tympani) with subsequent impingement on the (XLPMD) (Fig. 5.43 and Fig. 5.44). endolymphatic compartment (cochlear duct). The con- As indicated by the name of the disorder, hearing loss ductive component of the hearing loss is due to immobi- is mixed. The sensorineural component is due to in- lization of the stapes. This immobilization is due to a creased pressure within the cochlear duct. Wide commu- higher than normal pressure of the perilymphatic com- nication between the fundus of the internal auditory partment, specifically within the vestibule. This pressure canal and the cochlear apex allows pressure from the interferes with movement of the stapes footplate and the subarachnoid space to be generated into the labyrinth, transmission of sound waves.

A B Fig. 5.44 X-linked progressive mixed deafness. (A) Axial computed cochlear apex (arrow). (B) Axial T2-weighted magnetic resonance image tomography (CT) reveals a patulous internal auditory canal (IAC) (*) and reveals normal caliber neural structures and confirms wide communica- a large defect at IAC fundus, resulting in direct communication with the tion (arrow). (Courtesy of Jan Casselman, MD.) ch05.qxd 9/23/08 11:56 AM Page 344

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A B Fig. 5.45 X-linked progressive mixed hearing deficit. (A) Axial and wide cochlear neural aperture (white arrows). The pericochlear lucency (B) coronal computed tomography (CT) images reveal a patulous internal is probably not a significant finding. auditory canal (better appreciated on other images) with an abnormally

Despite the conductive deficit, stapes surgery is con- are classically present: from the subarachnoid space (SAS) traindicated due to the high incidence of associated profuse to the inner ear and from the inner ear to the middle ear. anomalous flow of perilymph (gusher). If the diagnosis of Direct SAS–middle ear communications are less common XLPMD is made before surgical intervention, this serious (Fig. 5.46). complication can be avoided (Fig. 5.45). Aberrant SAS–inner ear communication is usually Perilymphatic gushers have been historically linked to translabyrinthine, most commonly at the fundus of a bul- developmental prominence of the CA. This explanation bous IAC (Fig. 5.47 and Fig. 5.48).42,132,137,140 The offending has fallen into disrepute. A large caliber CA is not a cause defect is usually visible with CT as absence of the normal for perilymphatic gusher, as it does not result in increased bony partition between the IAC and the cochlea/vestibule. intralabyrinthine pressure.28 Perilabyrinthine leakage may occur around the first genu of the facial nerve as well. SAS–inner ear communication Fistulous Communications has been historically associated with abnormal patency of the CA. Although the potential for CSF transmission via Individuals with congenital inner ear malformations are at this pathway cannot be disputed, there is no proof that high risk for the development of recurrent meningitis due the CA has ever been the culprit in these patients. to CSF leakage into the middle ear space (CSF fistulas). The The associated inner ear–middle ear communications causative organism for meningitis in this context is usually occurring in this context are most commonly at the level either Streptococcus pneumoniae or Haemophilus influenzae. of the oval window and less frequently in the vicinity of Not without coincidence, these are also the most common the round window. Oval window defects may be located organisms causing otitis media in children. CT of the centrally or anteriorly, and congenital stapes deformity is temporal bone is recommended for all children with unex- associated.141 Isolated inner ear–middle ear communica- plained bouts of meningitis, as the diagnostic yield is tions (perilymphatic fistulas) will be considered below. relatively high.135,136 Much has been written about the so-called stapes Although many varieties of inner ear malformations gusher, whereby high-pressure perilymph/CSF flows into are associated, CSF fistulas appear to be particularly well the middle ear following stapes manipulation. This can be documented with the common cavity deformity.130,131 CSF quite difficult to manage and is often complicated by fistulas are much less likely to occur in individuals with meningitis.142 All individuals with aberrant SAS–inner ear the classic Mondini deformity (IP-2) due to the presence communications are at risk for this potentially dangerous of the normally developed basilar turn.136,137 In general, circumstance, and the imaging specialist must caution the fistulas are less common in patients with significant audi- surgeon when these defects exist (see above section on tory function, as this implies the presence of the spiral XLPMD). Abnormal CA patency has also been historically ganglion, another effective barrier.137 associated with these gushers. However, this concept has For a CSF fistula to occur in an individual with congeni- fallen into disrepute in recent years. Jackler and Hwang cite tal inner ear malformation, two aberrant communications the small size of the otic capsule portion of the CA as the ch05.qxd 9/23/08 11:56 AM Page 345

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Fig. 5.46 Otogenic fistulous communications chart. CSF, cerebrospinal fluid; CT, computed tomography; XLPMD, X-linked progressive mixed deafness. (See Color Plate Fig. 5.46.)

reason why pressure sufficient to cause a gusher is un- rior petrous surface (Fig. 5.50). As with AGs elsewhere, likely to develop via this pathway. Some authors suggest they appear as irregularly marginated defects at CT, which that this pathway may be the site of “oozers” rather than follow CSF on MRI, although some T2-weighted hyposignal gushers.132 An oval window convexity appreciated on may result from internal fibrous septation.14 9 When large, coronal CT may indicate the presence of elevated inner they may masquerade as neoplasm. In particular, when ear pressure.143 AGs are fortuitously located in the vicinity of the VA, confu- Direct SAS–middle ear communications (extra- sion with endolymphatic sac tumor may result. AGs may labyrinthine or perilabyrinthine) are also an important manifest as CSF fistula later in life as arachnoid villi enlarge cause of CSF otorhinorrhea but are associated with a much with age and physical activity due to intermittent changes less significant degree of hearing loss (Fig. 5.49). Defects in in subarachnoid pressure. This pulsatile pressure and the this context may occur via the tegmen tympani, aberrant weight of the temporal lobe result in bony erosion over arachnoid granulation, a giant apical air cell, or through time. Patients typically present with an apparent persistent defects in the facial nerve canal, petromastoid canal, unilateral serous otitis media. As such, the posterior or Hyrtl’s fissure.32,144–146 The latter is a congenital cleft petrous surface must be carefully studied when CSF fistula between the posterior fossa and the hypotympanum lying is diagnosed.145 in proximity to the CA and jugular fossa.32,145 Tegmen defects Acquired defects must also be considered in patients may be subtle or may be associated with variable-sized with clinical evidence of fistula. Trauma is by far the most meningoencephalocele (see Chapter 3).147 CHD is commonly common cause (see Chapter 6). Other causes in this con- associated.14 8 Arachnoid granulations (AGs) are most com- text are neoplasm, infection, and previous irradiation. monly located along the superior sagittal sinus but have Aggressive petrous apex/inner ear neoplasms could result been reported in numerous locations, including the poste- in CSF fistulas. A case of primary lymphangiomatosis has ch05.qxd 9/23/08 11:56 AM Page 346

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A B

C D Fig. 5.47 Perilymphatic fistula, pneumolabyrinth. (A–D) Axial computed tomography images. Congenital dilation of the cochlea and vestibule. There is air within both structures (arrows). Note the intact stapes (B, small arrows). (Courtesy of William W.M. Lo, MD.)

been reported with permeative bony changes and a direct Perilymphatic fistulas (PLF) require only one abnormal SAS–middle ear (petrous apex) communication.150 path of communication: inner ear to middle ear.152 They CSF otorrhea requires an SAS–middle ear fistula (or an may be congenital (with or without various associated in- SAS-inner ear and inner ear-middle ear communication) ner ear malformations), spontaneous, posttraumatic, or and a defective tympanic membrane (TM). Paradoxically, secondary to barotrauma or sudden physical exertion. The CSF rhinorrhea may occur when the TM is intact due to oval window is a more common site of origin than the egress anteriorly via the eustachian tube. round window. Perilymphatic fistulas occurring as a com- CSF leakage can be proven convincingly with CT per- plication of prosthetic stapedectomy are considered in formed following subarachnoid administration of con- Chapter 3. The posttraumatic variety is discussed in Chap- trast (usually done via lumbar puncture) (Fig. 5.51). Only ter 6. Other acquired perilymphatic fistulas may result a small volume (3 to 4 cc) of dilute contrast (180 to 200 from neoplasm or infection. Individuals with PLF have mg per cc) is needed to make this determination, pro- fluctuating sensorineural deficit presumably resulting vided the contrast is effectively manipulated into the from intermittent leakage.140,153 Sudden hearing loss is intracranial compartment. This migration is difficult to also associated with this disorder. demonstrate fluoroscopically due to the progressive fur- Imaging diagnosis is elusive in all varieties of PLF, ther dilution that occurs during ascent. Diffuse weighted regardless of etiology. CT demonstration of pneumolabyrinth MRI has been reported by some authors to be an extremely is the most convincing finding; however, the observer should sensitive technique for identification of localization of also be alert to unexplained middle ear effusion occurring CSF leaks. Flow rates as slow as 0.5 cc per second may be in the appropriate context.154,155 High-resolution CT is rec- detected.151 ommended by many authors (Fig. 5.52). Careful attention ch05.qxd 9/23/08 11:56 AM Page 347

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A B

C D Fig. 5.48 Encephalocele—cerebrospinal fluid (CSF) fistula. (A,B) Axial window. Note that the temporal lobe appears to be contiguous with this computed tomography (CT) sections, left ear. There is a striking defor- defect (arrowheads). This child had undergone spontaneous episodes of mity of the internal auditory canal contiguous with the first genu of the CSF otorrhea complicated by meningitis. Surgical exploration revealed facial nerve canal (arrowheads). (C,D) Coronal CT sections (reversed). (C) brain tissue protruding into the middle ear cavity at the vicinity of the Bone window. The deformity is again identified (arrows). (D) Soft tissue first genu (perilabyrinthine). (Courtesy of Eric N. Faerber, MD.)

to the stapes superstructure is required. Any variants from and careful study of the cochlea, vestibule, and vestibular normal in this regard must be viewed with suspicion.156–158 aqueduct is needed as well. PLF at the level of the round The stapes footplate has a dual embryological origin: the window has been described in large vestibular aqueduct outer lamina from Reichert’s cartilage (second branchial syndrome (LVAS).160 arch) and the inner vestibular layer from the otic capsule. In most cases, imaging evaluation in patients sus- Defects in this latter layer are believed to result in the con- pected of harboring PLF is performed to exclude other genital variety of these fistulas when they occur at the level demonstrable causes of associated symptoms. Diagnosis of the oval window.159 CT is often positive in these of PLF is important, as many otologic surgeons recommend cases.156,157 Diagnosis requires overlapping thin axial CT middle ear exploration when the diagnosis is suspected. sections through the oval window and a sound knowledge Surgical confirmation of these lesions is also difficult even of normal oval window/stapes superstructure anatomy. when the patients are subject to provocation, such as the Round window lesions essentially never have an imaging Valsalva maneuver, jugular vein compression, and the correlate.158 Inner ear anomalies are also not uncommon, Trendelenburg position. B2-transferrin is a protein that is ch05.qxd 9/23/08 11:56 AM Page 348

C D

Fig. 5.49 CSF leak in a 27-year-old woman with recurrent meningitis. Axial computed tomography (CT) image of the left ear. (A) 1 mm superior to first genu of the facial nerve canal reveals a focal defect (arrow) contiguous with epitympanum. Axial CT image (B) reveals a normal first genu (small black arrow). (C) Sagittal CT image (reconstructed) confirms the fistulous communication (arrow). Sagittal T2-weighted magnetic resonance images (T2WIs) at (D) and immediately adjacent to (E) plane of section of sagittal CT reveals the defect (arrows). Coronal T2WI (F) reveals the asymmetric E fluid signal in close approximation to the anterior genu (arrow). ch05.qxd 9/23/08 11:56 AM Page 349

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Fig. 5.52 Adult spontaneous perilymphatic fistula, indirect findings. Axial computed tomography image. Fluid level in the sinus tympani is seen on the right (arrow) in a patient with a fluctuating sensorineural hearing loss and vertigo on this side with a recent decrement in hearing. This is a nonspecific finding, but it essentially represents an unexplained middle ear effusion. Fig. 5.50 Presumed arachnoid granulation. Axial computed tomography image in an asymptomatic patient reveals an irregularly marginated defect along the posterior petrous surface (arrow) compatible with arachnoid granulation. These developmental defects have a found in CSF and in perilymph. Identification of this sub- propensity for causing cerebrospinal fluid (CSF) fistulas and must be stance within middle ear fluid increases the level of sus- sought in any patient with clinical evidence of CSF leak. picion that PLF is indeed present.157

Acquired Disorders of the Labyrinth Labyrinthitis Labyrinthitis refers to inflammatory disease of the perilymphatic spaces of the inner ear that results in secondary changes within the endolymphatic spaces (membranous labyrinth).161,162 There are a variety of causes for labyrinthitis. The most common symptoms are SNHL and vertigo, which may be recurrent or debilitating. Labyrinthitis has been classified in several ways. We will emphasize classification by route of spread and by agent (Table 5.5).

Classification by Route of Spread When classifying by the route of spread, labyrinthitis may be described as tympanogenic, meningogenic, hematogenic, or posttraumatic.163,164

Fig. 5.51 Congenital perilymphatic fistula, inner ear dysplasia. Magni- Table 5.5 Labyrinthitis Classification fied axial computed tomography (CT) image, left ear. Obtained after Route of Spread Agent Other intrathecal injection of contrast. Opacification of the internal auditory canal (i, arrow), as well as the cystic cochlea (c, arrow) and the dilated Tympanogenic Viral Serous Toxic vestibule (v, arrow), is seen. This provides definitive proof of SAS–inner Meningogenic Autoimmune Suppurative Epidemic ear communication. Opacified cerebrospinal fluid is also identified in the middle ear (inner ear–middle ear communication). (Courtesy of D. Hematogenic Bacterial Williams, E. Burton, LeBonheur Children’s Medical Center, Memphis, Posttraumatic Luetic Tennessee. Reprinted with permission.) ch05.qxd 9/23/08 11:56 AM Page 350

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Tympanogenic labyrinthitis is secondary to middle ear made with a positive lymphocyte transformation test and disease and as such is typically unilateral. Aggressive clinical improvement in response to steroid treat- middle ear infections may result in propagation of debris ment.165,168 Please see the discussion of Cogan’s syndrome into the fluid-filled spaces of the labyrinth, usually via the in the paragraphs below. round window or oval window. Labyrinthitis may also oc- Bacterial labyrinthitis results when pyogenic bacteria cur as the result of labyrinthine fistulas, which are most enter the inner ear. Streptococcus pneumonia and common at the level of the lateral semicircular canal due Haemophilis influenzae are the most common pathogens. to its middle ear exposure. These usually occur coexistent Bacterial invasion of the labyrinth can occur via three with erosive cholesteatoma. Iatrogenic causes of tym- routes, as indicated above: (1) hematogenic spread panogenic labyrinthitis must also be considered. In this through the cochlear vasculature, (2) as sequela to otitis context, prosthetic stapedectomy is typically the culprit. media that passes through the round window membrane, Meningogenic labyrinthitis results from meningitis, or (3) meningogenic spread from the subarachnoid space most commonly bacterial. This probably results from in meningitis. Facial nerve involvement is associated with spread of the inflammatory debris via the fundus of the bacterial labyrinthitis much more commonly than with internal auditory canal through the lamina cribrosa into viral disease. the vestibule or via the cochlear nerve foramen into the Luetic labyrinthitis is a manifestation of otosyphilis di- cochlear apex with internal dissemination via the modio- agnosed in patients with progressive otologic symptoms lus.165 Propagation of suppurative debris from the and a positive fluorescent treponemal antibody-absorption meninges via the CA into the basilar turn of the cochlea (FTA-ABS) test result. The Venereal Disease Research Lab- has also been demonstrated but is probably less common. oratory test (VDRL) is used to distinguish active from Meningogenic labyrinthitis typically occurs in children inactive disease.169 Penicillin/ampicillin and steroids are and is the most common cause of acquired childhood the primary treatment options.170 These individuals virtu- deafness.16 6 The involvement is usually bilateral. This di- ally always have systemic disease. There are numerous agnosis is straightforward if there is a history of child- possible manifestations of syphilis within the central hood meningitis with a resulting hearing loss. However, if nervous system (CNS). These include acute syphilitic no such history is available, the referring physician must meningitis, meningovascular syphilis, and parenchymal consider the possibility of a congenital malformation. neurosyphilis.171 Syphilitic meningitis may involve the Both processes may, of course, coexist. In the chronic cranial nerves, resulting in pathologic enhancement within stage of this disease, labyrinthine ossification may ensue. the internal auditory canal, and cause vestibulocochlear Carcinomatous meningitis can theoretically cause identi- and possibly facial nerve dysfunction. Luetic labyrinthitis cal findings, as the disease process is spread in a similar (Fig. 5.53) may result from hematogenous dissemination fashion. or result from syphilitic meningitis due to spread of infec- Hematogenic labyrinthitis and posttraumatic labyrinthi- tion via the intracanalicular portion of the eighth cranial tis are much less common. Measles and mumps are regarded in the literature as the classic causes of hematogenic labyrinthitis. Posttraumatic labyrinthitis is usually the result of fracture or perilymphatic fistula with superinfection.

Classification by Agent When classifying labyrinthitis by agent, one must consider viral, bacterial, autoimmune, and luetic (syphilitic) etiologies. Viral labyrinthitis is the most common and often occurs subsequent to upper respiratory infection. The spread to the inner ear is probably hematogenous and results in atrophy of the tectorial membrane, organ of Corti, and stria vascularis.167 Such disease is self-limited, and Fig. 5.53 Luetic labyrinthitis and meningitis. Axial T1-weighted mag- symptoms usually abate prior to the need for imaging. netic resonance image after gadolinium reveals intense enhancement Autoimmune labyrinthitis is a rare but well-recognized within the cochlear apex bilaterally (white arrows). In addition, there is intense enhancement within both internal auditory canals (outlined cause of SNHL and vertigo. Inflammation associated with arrows) as well as a manifestation of acute syphilitic meningitis. Note immune responses can damage the delicate cellular struc- pathologic enhancement of the leptomeninges elsewhere. (Courtesy tures that mediate hearing and balance. Diagnosis is of Michelle Michel, MD. Used with permission.) ch05.qxd 9/23/08 11:56 AM Page 351

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nerve to the cochlea.171 Otosyphilis may be complicated by to our knowledge. An internal auditory canal gumma has facial palsy; seventh nerve involvement appears as thicken- been reported.174 Rapid progression of otosyphilis is well ing/enhancement of the facial nerve on contrast- documented in human immunodeficiency virus (HIV-) pos- enhanced T1WI similar to that identified in individuals itive patients.17 5 with Bell’s palsy. Otosyphilis may also result in an osteitis in addition to or in lieu of labyrinthitis. The osteitis that Additional Considerations occurs in this disorder is characterized by a permeative or moth-eaten demineralization of the otic capsule easily Further pathological subclassification includes a division visualized at CT (Fig. 5.54 and Fig. 5.55). This has a clas- of labyrinthitis into serous and suppurative categories. In sic appearance, usually easily distinguishable from the this context, serous labyrinthitis is primarily an irritative diffuse homogeneous demineralization characteristic of disease in which vestibular symptomatology predomi- Paget’s disease and the plaque-like involvement typical of nates, although hearing loss may also occur. The clinical otosclerosis or osteogenesis imperfecta (OI).172 This is fur- symptoms are usually not permanent. Suppurative dis- ther discussed below in the section on otodystrophies. ease, on the other hand, is a far more severe disorder, Luetic endolymphatic hydrops is also a well-known clini- often characterized by total permanent loss of the inner cal condition.173 Imaging findings have never been reported ear function.176 ,177

A B

Fig. 5.54 Otosyphilis. (A) Coronal computed tomography (CT) image, left ear. (B) Axial CT image, left ear. (C) Axial CT image, left ear. There is diffuse heterogeneous demineralization of the otic capsule (C, arrows) in C this patient with positive serology. (Courtesy of B. Ziefer, MD.) ch05.qxd 9/23/08 11:56 AM Page 352

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A B

C D

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Toxic and epidemic varieties of labyrinthitis have also contrast-enhanced T1WIs as long as 6 months after been described. Ototoxic drugs must also be considered in symptoms have abated.180 The enhancement is believed to individuals with unexplained SNHL. Cryptococcal and cy- occur due to accumulation of gadolinium within inflamed tomegalovirus involvement of the inner ear has been labyrinthine membranes resulting from breakdown of demonstrated in HIV-positive patients.17 8 A meningogenic labyrinthine vasculature.162,181 The reader should be propagation is likely. Neurotologic manifestations of HIV- aware that the majority of patients diagnosed with viral AIDS (acquired immune deficiency syndrome) may also labyrinthitis will not have labyrinthine enhancement (or be caused by direct viral involvement of inner ear struc- any other imaging finding).182 tures.17 9 Aggressive bacterial labyrinthitis (and luetic labyrinthitis) on occasion may be complicated by facial palsy manifest by pathologic enhancement of the intratem- Imaging Findings poral seventh nerve (see Chapter 7). The combination of Acute/Subacute Stage The acute stage of labyrinthitis pathologic labyrinthine enhancement and thickening/ results when bacteria or other noxious agents fill the enhancement of the seventh nerve should also prompt perilymphatic spaces and incite an acute inflammatory inspection of the EAC. EAC vesicles in this context response. At this stage, the endolymphatic space is strongly indicate the diagnosis of herpes zoster oticus spared. CT scanning is normal. Regardless of etiology/ (Ramsay Hunt syndrome) (see Chapter 7).183,184 Human agent, the sole imaging finding in individuals with acute/ herpesvirus 1 (HHV-1) is a documented cause of sudden subacute labyrinthitis is enhancement of the normally SNHL and has been diagnosed in a patient with enhance- nonenhancing fluid-filled spaces of the labyrinth as seen ment of the membranous labyrinth and intracanalicular on contrast-enhanced T1WIs (Fig. 5.56, Fig. 5.57, and eighth nerve.185 Fig. 5.58). This enhancement is typically faint and Despite the faint diffuse nature of the contrast en- usually clearly differs from the intense and localized hancement, segmental involvement of the labyrinth is not contrast enhancement that occurs in individuals with uncommon (Fig. 5.59). Hearing loss may reflect cochlear intralabyrinthine schwannoma. The enhancement that disease to the extent that involvement of the basilar turn occurs in labyrinthitis may be prolonged and identifiable on of the cochlea correlates with high-frequency SNHL and disease of the apical turn with lower frequency hearing impairment.161,162 Such structural correlation has also been described in individuals with otosclerosis (otospongiosis) as well.

Chronic Stage If acute labyrinthitis does not resolve, a progression to chronic disease initially results in fibrous changes followed by ossification. This entire process likely transpires over several months to years.164,176,177,186 It has been postulated that these changes result from abnormal proliferation of the undifferentiated mesenchymal cell in the endosteum, modiolus, and basilar membrane. These cells differentiate into fibroblasts and finally into Fig. 5.56 Viral Labyrinthitis, cochlear involvement. Axial contrast- osteoblasts. Osteoblasts typically form abnormal bony enhanced T1-weighted magnetic resonance image. Enhancement 187 within the cochlea on the right (arrow). Compare with normal left trabeculae within the membranous labyrinthine spaces. side. Note that the internal auditory canals, vestibule, and semicircular The fibrous stage of this disorder consists of fibroblas- canals are essentially unremarkable. (Reprinted with permission.) tic proliferation within the perilymphatic spaces and

Fig. 5.55 Otosyphilis. (A,B) Patient 1. Associated facial palsy. (A) Mag- petrous temporal bone (arrow). This is quite different than the plaque- nified axial contrast-enhanced T1-weighted magnetic resonance image like demineralization seen in otosclerosis and the diffuse homogeneous (T1WI). There is contrast enhancement of the intracanalicular, intra- pattern seen with Paget’s disease. (D) Contrast-enhanced axial T1WI. labyrinthine, and proximal tympanic segments of the facial nerve There is bilateral pathological enhancement of this debris more notice- (arrows). (B) Magnified axial contrast-enhanced T1WI, left ear (more infe- able on the right (arrows). (E,F) Patient 3. Moderate sensorineural hear- rior). Intense enhancement of the cochlea, vestibule, and semicircular ing deficit. (E) Magnified axial CT image, right ear. (F) Magnified coronal canals is noted (arrowheads). (C,D) Patient 2. Severe sensorineural hear- axial CT image, right ear. Moth-eaten demineralization of the otic cap- ing deficit. (C) Magnified axial computed tomography (CT) image, right sule (arrows). ([C,D] Courtesy of Marlin Sandlin, MD, Houston, Texas. ear. Pronounced diffuse moth-eaten demineralization involving the [A–D] used with permission.) ch05.qxd 9/23/08 11:56 AM Page 354

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A B Fig. 5.57 Viral labyrinthitis. Recent onset of hearing loss and vertigo in The normally fluid-filled spaces of the anterior cochlear turns enhance a 47-year-old-man. (A) Precontrast coronal T1-weighted magnetic reso- intensely with contrast (arrows). nance image (T1WI), left ear. (B) Postcontrast coronal T1WI, left ear.

begins 2 weeks after the onset of infection. CT findings The ossific stage is characterized by the formation of remain sparse (Fig. 5.60, Fig. 5.61, Fig. 5.62, and Fig. 5.63). osteoid. Subsequent ossification and remodeling obliterate T2WIs will demonstrate replacement of the normally the perilymphatic and endolymphatic spaces and have fluid-filled spaces of the labyrinth. This is often most eas- been noted to occur within a few weeks to a year after ily detected at the cochlear apex. Quite often gadolinium meningitis, although the hearing loss occurs within a few days enhancement persists at this stage, as angiogenesis is also of the onset of infection. Progression to labyrinthine ossifica- present.188,189 tion results in the CT appearance of diffuse or localized, often

A B Fig. 5.58 Subacute labyrinthitis; labyrinthine enhancement. (A) Coronal cochlear apex (outlined arrows). The vestibule (solid arrow) is spared image, postcontrast. (B) Axial computed tomography (CT) image, post- (“cochleitis”). (Courtesy of Paul Caruso, MD.) contrast. There is diffuse pathologic contrast enhancement of the ch05.qxd 9/23/08 11:56 AM Page 355

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Intermediate stages also exist with varying degrees of fibrous changes and ossification, resulting in segmental areas of enhancement and T2-weighted hyposignal at MRI and subtotal ossification at CT. Ossification may be localized or diffuse. When localized, ossification is most common within the basilar turn of the cochlea (Fig. 5.68 and Fig. 5.69). Because the CA drains into the scala tympani of the basilar turn of the cochlea adjacent to the round window, the highest concentration of inflammatory debris is localized in this region, perhaps explaining the commonality of involvement of this segment of the labyrinth in meningogenic disease.190 Tympanogenic labyrinthine ossification is also most commonly localized to this region at least, in part, based on proximity to the middle ear via the round window.191 Poor blood supply also explains the propensity to develop ossification in this area, regardless of the underlying etiology.192 Disease within the basilar turn results in a cochlear stenosis when the obliterative changes are peripheral. In this circumstance, the appearance may be confusing, and comparison with the opposite ear may Fig. 5.59 Subacute labyrinthitis; segmental enhancement. Axial post- be needed. contrast T1-weighted magnetic resonance image reveals faint en- When labyrinthine ossification is severe and general- hancement at the cochlear apex perhaps at the junction between the apical and middle turns (arrow). ized, findings may be confusing to the inexperienced observer, particularly when a history of meningitis is not given. A total “white out” of the labyrinth at CT profound, ossification of the normally fluid-filled spaces of results in a homogeneous appearance that may be con- the inner ear, unilateral if tympanogenic and commonly fused with congenital dysplasias such as the Michel bilateral if meningogenic or hematogenic (Fig. 5.64, deformity or cochlear hypoplasia/aplasia (Fig. 5.66). The Fig. 5.65, Fig. 5.66, and Fig. 5.67). MRI is, of course, also differentiating point is the caliber of the otic capsule, abnormal at this stage of the disease. The characteristic MRI which is reduced with congenital deformity and normal findings are T2-weighted hyposignal replacement of the in individuals with labyrinthine ossification. In the normally high signal fluid residing within the otic capsule. Michel deformity, the lateral wall of the inner ear is flat

B A Fig. 5.60 Fibroosseous labyrinthitis. (A) Axial computed tomography to better advantage as it better depicts the fibrous nature of the (CT) image reveals some hyperattenuation (arrow) in the vicinity of the process. Indications are that the scala tympani is the most extensively modiolus, confirming modest osseous replacement. (B) Axial T2- involved. (Courtesy of Jan Casselman, MD.) weighted magnetic resonance image reveals the degree of involvement ch05.qxd 9/23/08 11:56 AM Page 356

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Fig. 5.61 Bilateral labyrinthine ossification (meningogenic). (A) Axial computed tomography (CT) image. There is obvious ossification in the vestibule bilaterally (thicker arrows). There are only minimal ossific changes appreciated at the cochlear apex bilaterally (somewhat more on the right) (thinner arrows). (B) Magnified axial T2-weighted fast spin echo magnetic resonance image, right ear. More evidence of membranous labyrinthine replacement (primarily fibrous) in the vicinity of the modiolus/osseous spiral lamina. (C) Magnified axial T2-weighted fast spin echo magnetic resonance image, left ear. Less impressive changes are seen in A the left cochlea (arrow).

B C

or concave. With labyrinthine ossification, the convexity developing inner ear fibrous changes or ossification subtending the LSCC will be preserved.187,193 Individuals (Fig. 5.70 and Fig. 5.71).194 Normal cochlear T2-weighted with advanced labyrinthine ossification typically have signal is associated with hearing preservation in this profound deafness and loss of vestibular function circumstance. (“dead ear”). The reader should be aware that diminished signal in- Other causes of labyrinthine ossification are obstruc- tensity in the vestibule on T2WI has been demonstrated tion of the labyrinthine artery, trauma, autoimmune inner in patients with CPA/IAC schwannoma (acoustic neuri- ear disease, otosclerosis, leukemia, and perhaps neoplasia. noma) but not in patients with CPA meningioma. This These imaging manifestations may have profound im- decreased signal intensity may result from increased pro- plications if cochlear implantation is contemplated. High- tein concentration in the perilymph associated with resolution CT and T2WI are often used for presurgical acoustic tumors.195 planning, particularly with asymmetric disease. The sur- Labyrinthine ossification is also an expected conse- geon will, of course, usually elect to implant the less quence in individuals who have undergone previous affected ear. labyrinthectomy. As some forms of labyrinthectomy do not involve alteration of the otic capsule, diagnosis is Additional Imaging Considerations Loss of inner ear signal difficult unless this history is available to the imaging on T2WI correlates with loss of hearing in patients who specialist. Many of our cases of diffuse labyrinthine ossi- have undergone surgery for cerebellopontine angle (CPA) fication have been in individuals who have undergone and IAC vestibular schwannoma, perhaps reflecting this procedure.16 4 ch05.qxd 9/23/08 11:56 AM Page 357

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A B

Fig. 5.62 Labyrinthine obliteration, ossific/fibrous. (A) Magnified axial computed tomography (CT) image, right ear. (B) Magnified axial CT image, left ear. Faint ossific changes are seen within the cochlea on the right (single arrow, A), with more striking ossific changes in the cochlea on the left (double arrows, B). (C) Magnified axial T2-weighted fast spin echo magnetic resonance image, right ear. Abnormal obliterative changes are seen within the cochlea at this level (arrow). As only a small amount of ossification is appreciated at CT, this presumably reflects predominantly C fibrous changes.

Table 5.6 Intralabyrinthine Schwannoma Neoplasia Localized to labyrinth Intralabyrinthine schwannomas (ILSs) arise from distal Intracochlear branches of the cochlear, superior vestibular, or inferior vestibular nerves. They may originate from vestibular Intravestibular nerve fibers of any of the cristae or maculae within the Intravestibulocochlear vestibule or nerve fibers of the cochlear nerve within the IAC involvement cochlea.196,197 Origination within the utricle, complicated Transmodiolar (cochlea and IAC) by endolymphatic hydrops due to obstruction of the ductus reuniens, has also been documented (Table 5.6).198 Transmacular (vestibule and IAC) ILSs are rare. They are somewhat more common in Middle ear involvement patients with NF-2, but the vast majority of cases are Transotic (ME, labyrinth, and IAC) sporadic.199 Lesions that are limited to the labyrinth are Tympanolabyrinthine (ME and labyrinth) classified as intracochlear, intravestibular, or intravestibulocochlear (Fig. 5.72). Lesions that also involve the IAC are Abbreviations: IAC, internal auditory canal; ME, middle ear. Source: Kennedy RJ, Shelton C, Salzman KL, Davidson HC, Harns- described as transmodiolar (cochlea and IAC) (Fig. 5.73) or berger HR. Intralabyrinthine schwannomas: diagnosis, transmacular (vestibule and IAC). Lesions that also involve management, and a new classification system. Otol Neurotol the middle ear (ME) are described as transotic (ME, 2004;25(2):160–167. ch05.qxd 9/23/08 11:56 AM Page 358

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A B Fig. 5.63 Labyrinthitis; intermediate stage. (A) Contrast-enhanced T1- resonance image shows replacement of the fluid signal in the cochlea weighted magnetic resonance image shows intense enhancement of the (large arrow) and vestibule (small arrow). cochlea (C, arrow) and vestibule (V, arrow) (B) Axial T2-weighted magnetic

labyrinth, and IAC) or tympanolabyrinthine (ME and data indicate that presentation is typically indistinguish- labyrinth).199 All patients report SNHL, which is of sudden able from that which occurs with acoustic tumors. A loss onset in perhaps one third of patients. ILSs are histologi- of conductive hearing is not uncommon and results from cally identical to their IAC counterparts and occasionally blockage of the conduction of sound waves through inner present with Meniere-type symptoms, although recent ear fluid.

A B Fig. 5.64 Labyrinthitis ossificans, basilar turn. (A) Coronal and (B) axial within the mastoid bowl. The patient has a “dead ear.” There is ossifica- computed tomography (CT) images reveal that patient has undergone tion of the basilar turn of the cochlea (arrows), reflecting the tym- canal wall down mastoidectomy, and there is significant residual debris panogenic etiology. ch05.qxd 9/23/08 11:56 AM Page 359

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A B

Fig. 5.65 Tympanogenic labyrinthitis ossificans, basilar turn. (A) Magni- fied coronal CT image, left ear. Complete ossification of the fluid-filled spaces of the basilar turn of the cochlea (arrow). (B) Magnified coronal T2-weighted fast spin echo image, left ear. Ossific encroachment confirmed (arrowhead). (C) Magnified coronal T2-weighted fast spin echo C image of a normal right ear for comparison.

Prior to the development of modern imaging methods, enhancement seen with labyrinthitis. The majority of diagnosis was usually made during surgical labyrinthine cases will be discovered during routine evaluation of the ablation. Currently, the mainstays of diagnosis are thin- “rule out acoustic” patient. The observer is encouraged to section gadolinium-enhanced T1WIs, which demonstrate avoid IAC “tunnel vision” and meticulously examine the a focal area of intense localized enhancement within the fluid-filled spaces of the labyrinth as well. ILS is rare a labyrinth (Fig. 5.74 and Fig. 5.75).161,189,196,200–202 This ap- lesion, but it is being detected more commonly as aware- pearance is usually quite different from the faint, diffuse ness of this entity increases. ILSs can also be visualized ch05.qxd 9/23/08 11:56 AM Page 360

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arise from either the jugular foramen or the tegmen tympani and invade the middle ear. The less common IAC meningiomas likely arises from arachnoid granulations located along the dural lining of the neural foramina.205 They may spread to the labyrinth, resulting in intense enhancement, often with ossification and demineralization reminiscent of otospongiosis. Fundal lesions may result in IAC block, described in the previous paragraph. The presence of associated ossification may be the key to diagnosis, although an atypically positioned ossified hemangioma must also be considered as a differential diagnostic possibility under this circumstance (see Chapters 7 and 8). Fibroinflammatory pseudotumor of the inner ear is a rare, locally aggressive, and destructive but histologically Fig. 5.66 Bilateral labyrinthine ossification secondary to childhood benign lesion, which may involve the inner ear and meningitis. Axial computed tomography (CT) image. There is ossifica- middle ear.206 Ossification would not be expected. tion of the vestibule (posterior arrows) and cochlea (anterior arrows) Hematogenous metastatic disease can result in destruc- bilaterally in a relatively symmetric fashion. tive changes involving the otic capsule. Perhaps somewhat more common is labyrinthine involvement secondary to with carefully preformed thin-section fast spin echo (FSE) carcinomatous meningitis with seeding along the IAC or T2WI as regions of hyposignal within the normally fluid CA in a manner similar to that seen with meningogenic intensity (bright) labyrinth (Fig. 5.76). labyrinthitis. Lymphoma and melanoma have been docu- The reader should be aware that nontumorous mented to spread in this manner.196 Langerhans’ cell labyrinthine enhancement may occur secondary to a fun- histiocytosis (LCH) is discussed in Chapter 3. Labyrinthine dal IAC lesion likely caused by venous engorgement and involvement in LCH is usually secondary but may be inflammation. This is referred to as IAC block. primary, and there seems to be a predisposition for the Neoplasms other than schwannomas are even more rare. vestibular aqueduct/endolymphatic sac.207 Squamous cell Intralabyrinthine meningiomas are also intensely enhancing carcinoma of the nasopharynx, EAC, or middle ear may lesions.203,204 Temporal bone meningiomas most commonly invade and destroy the otic capsule as well.

A B Fig. 5.67 Labyrinthitis ossificans, cochlear apex. (A,C) Right ear. (B,D) Left ear. There is ossification of the normally fluid-filled spaces of the cochlear apex on the right (arrows) when compared with the normal left side. (Courtesy of C. Douglas Phillips, MD.) ch05.qxd 9/23/08 11:56 AM Page 361

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C D Fig. 5.67 (Continued)

A B Fig. 5.68 Tympanogenic labyrinthitis ossificans. Axial computed spaces of the basilar turn (outlined black arrow). Incidental note is tomography (CT) image, right ear, reveals patchy middle ear debris made of abnormal soft tissue density in the oval window niche (small (outlined white arrow) in a deaf patient with a history of otitis media. white arrow); differential diagnosis includes a dehiscent facial nerve (B) Coronal CT image reveals ossification of the normally fluid-filled (see Chapter 7). ch05.qxd 9/23/08 11:56 AM Page 362

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Fig. 5.69 Tympanogenic labyrithitis ossificans. (A) Coronal computed tomography (CT) image, left ear, and (B) axial CT image reveal a stapes prosthesis with an anterior oval window plaque (short white arrow, B). (C) More inferior axial CT image and (A) coronal image reveal ossification of A the normally fluid-filled spaces of the basilar turn (outlined black arrows).

B C

Erosive changes of the labyrinth are much more likely to with fat suppression techniques. Neural transport of the be inflammatory rather than neoplastic, reflecting the rela- meninx primitiva along the developing eighth nerve has tive commonality of aggressive middle ear infection. been proposed as an etiology.210 This is one of the myriad Cholesteatomatous involvement of the labyrinth is well doc- of reasons we recommend a precontrast T1WI on every umented, and although this lesion does not enhance with rule-out acoustic patient. gadolinium, adjacent inflammatory granulation may result in pathological inner ear enhancement.196,208 Invasive middle Cogan’s Syndrome ear cholesterol granuloma may rarely involve the cochlea.209 Intravestibular lipomas have been reported manifest Cogan’s syndrome is the prototypical autoimmune inner by precontrast T1-weighted hypersignal, which disappears ear disorder and is diagnosed in patients who present ch05.qxd 9/23/08 11:56 AM Page 363

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Fig. 5.70 Abnormal membranous labyrinth. Postoperative vestibular schwannoma. (A,B) Axial pre- and postcontrast T1-weighted magnetic resonance images. The fluid-filled spaces of the cochlear apex enhance intensely in this patient who has undergone translabyrinthine resection for vestibular schwannoma (solid white arrows). Compare with the normal right side (outlined white arrow). (C) Axial T2-weighted fast spin echo A magnetic resonance image shows a diminished signal cochlear apex (solid white arrow). Compare with the normal right side (outlined white arrow). (Courtesy of Scott Marlowe, MD.)

B C

Miscellaneous Causes of Labyrinthine Enhancement with episodic nonsyphilitic interstitial keratitis and audiovestibular dysfunction.167,211,212 There is often a pre- Enhancement of membranous labyrinth has been described ceding upper respiratory infection. Aortitis with aortic in a variety of disorders and is not specific to labyrinthitis or insufficiency is also associated. Treatment with systemic neoplasm. We have identified enhancement within the steroids results in a variable clinical response. Pathologi- membranous labyrinth in individuals who have undergone cally, there is thickening of the lining of the membranous surgery and irradiation regimens for posterior fossa lesions. labyrinth with hypertrophy of the stria vascularis. Cellular Enhancement has also been identified in association with debris and new bone formation have been noted within Vogt–Koyanagi–Harada syndrome, in which simultaneous the membranous labyrinth (Fig. 5.77). involvement of the uvea and cochlea (stria vascularis) as Imaging findings are reminiscent of labyrinthitis. In well as vitiligo perhaps reflects a pigment sensitivity.196 the early stages of the disease, there is contrast enhance- These patients usually present with symptoms suggesting ment of the fluid-filled spaces of the inner ear, especially meningitis. The etiology is unknown. There are anecdotal the cochlea, which is usually faint and diffuse. Cogan’s reports of intralabyrinthine enhancement in individuals syndrome has been reported as a possible cause of intra- with labyrinthine concussion, labyrinthine ischemia, and labyrinthine hemorrhage as well. As fibrous replacement vasculitis.196 These are presumably secondary to vasculopathy. and neo-osteogenesis ensue, replacement of the fluid- Vasculitic changes within the cochlea are believed to be filled spaces of the labyrinth are identified initially at MRI responsible for the SNHL that occurs in association with and later at CT, similar to findings observed with other Behçet’s disease; however, to date there are no reported otic varieties of labyrinthitis. capsule imaging manifestations.213 ch05.qxd 9/23/08 11:56 AM Page 364

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A B Fig. 5.71 Labyrinthine enhancement; patient has undergone retromas- rather than a manifestation of residual/recurrent tumor. There is faint toid craniectomy for 8th nerve schwannoma and suffered persistent hypersignal within the fluid-filled spaces of the cochlea and vestibule on vertigo. (A) Axial T1-weighted magnetic resonance image (T1WI), pre- precontrast T1WI, perhaps reflecting some hemorrhage. Note the in- contrast. (B) Axial T1WI, postcontrast. The posterior wall of the IAC has tense contrast enhancement of the cochlea (small arrows) and vestibule been surgically removed. Plaque-like enhancement within the internal (large arrows). (Courtesy of C. Douglas Phillips, MD.) auditory canal is believed to be an expected consequence of the surgery

Intralabyrinthine Hemorrhage with or without fracture. Tumor fistulization into the labyrinth is a well-documented cause of ILH. ELSTs, Imaging documentation of intralabyrinthine hemorrhage hemangioma, and cholesterol granuloma have been di- (ILH) is rare, but fortunately relatively easy, as the re- agnosed in this context.161,202,222 Elevated intral- quest to perform the study generally occurs in the suba- abyrinthine pressure is another possible cause.223 ILH cute stage (methemoglobin).158,214 Noncontrast thin-sec- has also been described after gamma knife radiosurgery tion T1WIs easily demonstrate the bright signal from the for vestibular schwannoma.224 Venous obliteration re- methemoglobin in distinct contrast to the low signal/- sulting from intravascular outflow resistance due to signal void of surrounding bone. Despite the fact that sudden tumor swelling or direct thermal effect on en- this entity is rare, the ability to make this diagnosis again dothelial cells may be the cause. mandates the need for precontrast thin-section T1WIs Hyperintensity on noncontrast T1WIs could also be (Fig. 5.78 and Fig. 5.79). explained by the presence of fat or high protein content in There are several potential causes of ILH, and there the appropriate clinical circumstance (Table 5.7).223 have been numerous individual case reports docu- menting this process in various disease states. ILH can be secondary to coagulopathy, tumor, trauma, or Endolymphatic Hydrops and Meniere’s Disease sickle cell disease, or, rarely, in poststapedectomy patients.215–217 ILH has been documented in large vestibu- Endolymphatic hydrops (ELH) is defined as increased hy- lar aqueduct syndrome (LVAS) after sudden hearing draulic pressure within the endolymphatic system. This loss, viral labyrinthitis, chronic myelogenous causes fluctuating hearing loss, episodic vertigo, tinnitus, leukemia, systemic lupus erythematosus, and post- and aural fullness. ELH has very few imaging manifesta- stapedectomy serofibrinoid labyrinthitis.218–221 Post- tions. Nonetheless, we should have a working knowledge traumatic intralabyrinthine hemorrhage may occur of this entity due to its commonality. Quite likely with ch05.qxd 9/23/08 11:56 AM Page 365

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A B Fig. 5.72 Intervestibulocochlear schwannoma. (A) Axial T2-weighted vestibule (small arrow). (B) Axial T2WI reveals abnormal enhancement magnetic resonance image (T2WI) reveals abnormal hyposignal throughout the cochlear apex (outlined arrow) and a portion of the throughout the cochlear apex (outlined arrow) and a portion of the vestibule (small arrow). (Courtesy of Jan Casselman, MD.)

Fig. 5.73 Intralabyrinthine schwannoma, transmodiolar. (A) Axial postcontrast T1-weighted magnetic resonance image (T1WI). (B) Coronal postcontrast T1WI, vestibular level. (C) Coronal postcontrast T1WI, cochlear level. There is a mass in the cerebellopontine angle (thin white arrow, A,B). The lesion extends through the cochlear neural foramen into the cochlear apex (outlined white arrows, B,C). (Courtesy of C. Douglas Phillips, MD.)

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Table 5.7 Labyrinthine Hypersignal on T1WI and FLAIR Enhancement Inflammatory Labyrinthitis, subacute Cogan’s syndrome Otosyphilis Neoplastic Schwannoma IAC fundal tumor (“IAC block”) Meningioma Precontrast Hemorrhage (various causes) Lipoma Postoperative acoustic tumor in patients with elevated protein Fig. 5.74 Intralabyrinthine schwannoma. Axial contrast-enhanced T1-weighted magnetic resonance image shows an intensely enhanc- LVAS/LEDS elevated protein219 ing lesion in the vicinity of the vestibule on the right (double outlined Abbreviations: T1WI, T1-weighted magnetic resonance image; arrows). The well-marginated nature of this process and the intense FLAIR, fluid attenuated inversion recovery; IAC, internal auditory pathological contrast enhancement are typical for this rare neoplasm canal; LVAS, large vestibular aqueduct syndrome; LEDS, large and would be quite atypical for labyrinthitis. endolymphatic duct and sac.

A B Fig. 5.75 Interlabyrinthine schwannoma. (A) Axial T2-weighted magnetic resonance image reveals hyposignal at the cochlear apex (arrow). (B) Axial enhanced T1-weighted magnetic resonance image reveals intense enhancement. (Courtesy of Jan Casselman, MD.)

Fig. 5.76 Intralabyrinthine schwannoma. Magnified axial T2-weighted fast spin echo magnetic resonance image, left ear, shows a localized area of hypointensity within the fluid-filled spaces at the cochlear apex (arrow). Lesion enhanced intensely with contrast (not illustrated). ch05.qxd 9/23/08 11:56 AM Page 367

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A B

Fig. 5.77 Cogan’s syndrome. Child with orbital pseudotumor, uveitis, and sensorineural hearing loss. (A) Postcontrast axial T1-weighted magnetic resonance image (T1WI) reveals enhancement of the membranous labyrinth on the left (arrow). (B) Postcontrast axial T1WI reveals enhancemen of the membranous labyrinth on the right (arrow). (C) Axial T2-weighted fast spin echo magnetic resonance image reveals debris within the left mastoid (arrow). Image suggests perhaps some degree of fibrous replacement in the region of the modiolus (smaller C arrows) bilaterally. (Courtesy of Bernadette Koch, MD.)

advances in imaging techniques, we will be able to pro- Similarly, if the cause of vertigo is known, the diagnosis vide more insight into this often debilitating symptom cannot be Meniere’s disease. complex. Attacks are caused by an episodic increase in endolym- ELH often is used synonymously with Meniere’s dis- phatic pressure, which dilates the endolymphatic spaces ease and Meniere syndrome.225 Meniere’s disease is idio- (at the expense of the perilymphatic spaces) and ruptures pathic ELH, whereas Meniere syndrome is ELH occurring the membranes that separate the perilymph and the en- secondary to another disease process such as otosyphilis, dolymph. The resultant chemical admixture bathes the trauma, electrolyte imbalance, autoimmune dysfunction, vestibular nerve receptors, resulting in vertigo, and causes medications, infections, and hyperlipidemia. This distinc- a mechanical disturbance of the organ of Corti, resulting tion is analogous to that in Bell’s palsy. If the source of in hearing loss. Because the apex of the cochlea is wound facial paralysis is known, the diagnosis is not Bell’s palsy. much tighter than the base, the apex is more sensitive to ch05.qxd 9/23/08 11:56 AM Page 368

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For several years, researchers have been attempting to find an imaging correlate for ELH. Early reports using conventional multidirectional tomographic techniques indicated that the VA was visualized distinctly less often in patients with this disorder, whereas other reports disputed this.226,230–233 In the 1970s, studies from Sweden using large numbers of patients and control subjects indicated that the temporal bone morphology in patients with Meniere’s disease differs markedly from unaffected patients.231,232 These investigators concluded that the characteristic polytomo- graphic features of the VA area in Meniere’s patients include (1) lack of periaqueductal pneumatization, (2) lack Fig. 5.78 Intralabyrinthine hemmorhage. Noncontrast T1-weighted of pneumatization medial to the arcuate eminence, (3) magnetic resonance image reveals pathologic hypersignal throughout short vestibular aqueducts with narrow external aper- the cochlea and vestibule (arrows) in a patient on warfarin for cardiac tures, and (4) reduction of the size of the mastoid air cell disease. (Courtesy of Jan Casselman, MD.) system. With advances in CT, there was a focus on hypoplasia of the retrolabyrinthine region, which had been determined to be a predisposing factor for ELH. A statistically pressure change. This explains why hearing loss preferen- significant reduction in bone development between the tially affects low frequencies. posterior petrous surface and both the vestibule and the Idiopathic endolymphatic hydrops (Meniere’s disease) is posterior SCC was discovered.234 Others have demon- more common in Caucasians and there is a slight female strated that the VA is narrower in patients with Meniere’s predilection. A higher incidence is reported in England. The disease than in the normal population. However, later re- average age of presentation is between 40 and 60 years of ports indicated that there is no relationship between VA age. The disease is often bilateral. In the United States, as many dimensions and inner ear pressure obtained by static as 50% of patients have a positive family history, suggesting acoustic compliance measurements.235 Dilatation of the a genetic predisposition. Some studies have documented an endolymphatic system must occur at the expense of autosomal dominant mode of inheritance. The estimated the perilymphatic system. Nevertheless, these same ob- prevalence is 150 cases per 100,000 population. Overpro- servers have also determined that there is no significant duction of endolymph has been discarded as an etiology difference in the width of the perilymph containing CA because the stria vascularis of the membranous labyrinth between Meniere’s patients and normal subjects.236 Using has been proven histologically to be normal in these 3D-surface reconstruction, still other authors have patients. Decreased resorption, presumably at the ELS, is a found that the length of the external aperture of the VA in far more likely cause.226 ELH is most commonly found in the patients with Meniere’s disease is significantly shorter pars inferior (cochlea and saccule) and is manifest histologi- than in those without Meniere’s disease.237 The IAC and cally by bowing of the basilar membrane into the scala the VA develop synchronously and in parallel with the vestibuli and distention of the saccule.227–229 development of the periaqueductal air cells.238 Investigators

A B Fig. 5.79 Intralabyrinthine hemorrhage. (A,B) Axial noncontrast T1-weighted magnetic resonance image. There is faint pathologic hypersignal identified within the cochlear apex (white arrow, A) and basilar turn (arrow, B) in a patient with sickle cell disease. (Courtesy of Paul Caruso, MD.) ch05.qxd 9/23/08 11:56 AM Page 369

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believe that an understanding of this relationship may labyrinthitis, neoplasms of the brainstem or cerebellar shed some light on the morphological features of Meniere’s hemisphere, craniocervical malformations (including disease. Chiari I), multiple sclerosis, and vertebrobasilar insuffi- There have been sporadic reports of decreased MRI vi- ciency. MRI has also been used to diagnose neoplasms sualization of the ELD/ELS in Meniere’s patients. Some that are located in intimate relationship to the external have demonstrated localized pathological enhancement aperture of the vestibular aqueduct, which may result in along the posterior petrous surface in the vicinity of the Meniere’s disease symptomatology. CT is also of value to external aperture of the VA in the approximate location of exclude superior semicircular canal dehiscence (SSCD). the ELS, perhaps implying a superimposed inflammatory Benign paroxysmal positional vertigo is a common process.239,240 A case of unilateral duplication of the disorder in which basophilic deposits have been found vestibular aqueduct has been reported in an individual attached to the cupula of the posterior SCC (cupulolithia- with Meniere’s disease symptomatology.241 sis). In most cases, this disorder may be idiopathic in na- At present, the focus of research into the imaging ture and has been effectively treated with direct poste- diagnosis of endolymphatic hydrops lies in the potential rior SCC obliteration or via indirect elimination of ability to differentiate the perilymphatic labyrinth from function via singular neurectomy. The former has been the endolymphatic labyrinth as the pathophysiologic judged easier and safer.248 basis is engorgement of the endolymph containing spaces Finally, Meniere’s symptomatology and progressive of the inner ear at the expense of the perilymphatic hearing loss have been associated with retrosigmoid spaces. In 2001, Niyazov et al performed a study of dissection for acoustic tumors even when the labyrinth guinea pigs with surgically induced unilateral endolym- is preserved.249 This has been linked to inadvertent phatic hydrops utilizing contrast-enhanced T1WI. The damage to the ELD. Some observers have advocated a perilymph preferentially enhanced relative to the en- middle fossa approach to these tumors for this reason dolymph, resulting in a clear distinction between the (Fig. 5.32).250 scalae of the inner ear. Images at the midmodiolar level of the hydropic cochlea demonstrated a significantly enlarged scala media.242 In 2007, Nakashima et al studied Labyrinthectomy patients following intratympanic injection of gadolinium. Using 3D fluid attenuated inversion recovery (FLAIR) Intractable vertigo may become an intolerable condition. imaging in patients with endolymphatic hydrops, the Surgical labyrinthine destruction has been offered to perilymphatic space surrounding the endolymph was those patients with unilateral symptoms and no service- found to be small or had disappeared.243 able hearing in that ear. Labyrinthectomy may be per- Surgical treatments include endolymphatic sac decom- formed via several surgical routes. In most varieties, the pression/shunt, vestibular nerve section, and labyrinthec- membranous labyrinth is removed via picks and suctions. tomy.225,229,244–246 ELS shunt can drain into either the The CT appearance will initially depend on the amount of subarachnoid space or the mastoid. Success rates with this bony labyrinth that is sacrificed (Fig. 5.80, Fig. 5.81, and 251 procedure are reported at 60 to 80%, but the procedure re- Fig. 5.82). Labyrinthine ossification, likely due to inter- mains controversial. Postoperative visualization of the ruption of vascular supply, often develops subsequent to shunt is possible when a radiopaque barium-impregnated these procedures (Fig. 5.83). catheter is used.247 Vestibular nerve section is designed to Recurrent vertigo following labyrinthine ablation may preserve hearing as the IAC approach used (retrosigmoid occur secondary to incomplete destruction of vestibular or middle fossa) spares the cochlear nerve. This procedure sense organs, contralateral labyrinthine pathology, or has a 95% success rate. Labyrinthectomy is of value if hear- postlabyrinthectomy neuroma. The latter can be diag- 252 ing has already been destroyed on the affected side, as a nosed with gadolinium-enhanced T1WIs. This entity is craniotomy is avoided. Recently, transtympanic perfusion believed to represent a regeneration neuroma occurring of gentamycin, salicylates, or steroids has been used with secondary to amputation of vestibular dendrites. some success. The imaging specialist is commonly asked to evaluate patients with progressive/fluctuating SNHL and vertigo. Otodystrophies In many of these cases, the referring physician will sus- Paget’s Disease pect that the diagnosis is ELH. Nonetheless, the physician recommends imaging the patient to exclude a multitude Paget’s disease (osteitis deformans) is a progressive dis- of other possible etiologies for these symptoms. Fore- ease of unknown etiology that affects 3% of the popula- most among these are CPA tumors, especially schwan- tion over 40 years of age and up to 10% of patients over noma of the eighth cranial nerve. MRI is used to rule out 80. There are monostotic and more common disseminated ch05.qxd 9/23/08 11:56 AM Page 370

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A Fig. 5.80 Postlabyrinthectomy appearance. (A) Coronal and (B) axial computed tomography images. The promontory has been surgically removed (outlined white arrows) in this patient with intractable vertigo. Note that the patient is developing ossification within the proximal basilar and apical turns (small arrows). Incidentally noted is the ossicular chain, which is dislocated (thin white arrows). B

polyostotic forms. Men are affected more often than women Increased vascularity and cellularity affect the marrow- at a ratio of 4:1. The pathogenesis involves dismantling of containing periosteal bone initially. Therefore, the petrous the original bone by osteoclastic activity followed by apex, peritubal region, and peripheral mastoid are typi- waves of resorption and regeneration that severely alter cally the sites involved first (Fig. 5.84). Temporal bone the architecture. involvement usually extends inferiorly and laterally from Paget’s disease is classically divided into four phases: the petrous apex. Eventually, the petrous pyramid, EAC, osteolytic, mixed, osteoblastic, and remodeled. Mixed os- and ME are involved. Involvement of endochondral bone teolytic and osteoblastic phases result in the “cotton wool” appearance. Malignant degeneration occurs in 1 to 2%.253,254 The skull is commonly affected, and this is always associated with squamous temporal bone involvement.

Fig. 5.82 Labyrinthectomy, stapedectomy. Axial computed tomography section. The cochlea (c) appears normal. There is air in the vestibule (arrow). This patient underwent labyrinthectomy 10 years Fig. 5.81 Previous labyrinthectomy, transcanal approach. Coronal com- prior to this scan. Procedure used stapedectomy with removal of the puted tomography image section at the level of the vestibule. Note that oval window membrane. The vestibule is in obvious contiguity with a large portion of the promontory has been sacrificed (arrow). There the middle ear (fistula). Note that the incus has been sacrificed for do- was marked cochlear sclerosis (ossification) on this side (not illustrated). nation to a homograft bank. ch05.qxd 9/23/08 11:56 AM Page 371

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Fig. 5.83 Labyrinthine ossification, previous labyrinthectomy. Axial computed tomography section, left ear. There is diffuse cochlear sclerosis (c, thick outlined arrow). The promontory has been sacrificed Fig. 5.84 Paget’s disease. Axial computed tomography image reveals (outlined arrow) for the purposes of better exposure for labyrinthec- demineralization at the petrous apex (thick white arrows), peritubal re- tomy. This patient had undergone stapedectomy with prosthesis gion (outlined white arrow), and peripheral mastoid (thin white arrows). insertion. The patient had severe vertigo and hearing loss postopera- The labyrinth is spared (black arrow). tively. Labyrinthectomy via a transcanal approach was eventually necessary.

with demineralization of the labyrinth is a later manifes- and conductive). Theories explaining the cause of the tation (Table 5.8). hearing loss in this disorder are widely varied and have Disorders of hearing (30 to 50%), vestibular function been a subject of debate for several years (Table 5.8). (20 to 25%), and tinnitus (20%) are associated.255 Hearing They include encroachment on neural structures by bony loss is the most common symptom in patients with tempo- overgrowth and subsequent narrowing of the IAC.255 In- ral bone involvement and is usually mixed (sensorineural deed, when basilar invagination is associated, there is a derangement of the architecture in the vicinity of the IAC resulting in cochlear nerve torsion. Subsequent reports, Table 5.8 Hearing Loss in Paget’s Disease using more sophisticated diagnostic tests, including audi- Possible Causes of Sensorineural Hearing Loss in Paget’s Disease tory brainstem evoked responses, indicate that the hear- Encroachment by bony overgrowth – narrowing of the IAC ing loss is likely due to a toxic effect on the membranous labyrinth, which is similar to that hypothesized in oto- Derangement of IAC architecture – cochlear nerve torsion sclerosis, rather than derangement in cochlear nerve Toxic effect on the membranous labyrinth function.256,257 Other authors suggest that hearing loss re- Dampening of the mechanics of the inner ear sults from changes in bone density, mass, and form, Cystic degeneration of the spiral ligament which dampen the finely tuned mechanics of the middle and inner ears.258 Most recently, cystic degeneration of Possible causes of CHL in Paget’s disease the spiral ligament has been reported, which may be Encroachment of pagetoid bone on the ossicular chain unique to Paget’s disease.259 Primary pagetoid involvement of the ossicles Conductive hearing loss (CHL) can be due to several fac- Thickening of the footplate of the stapes tors, including encroachment of pagetoid bone on the ossicular chain. Primary pagetoid involvement of the ossicles is Encroachment in the epitympanum or oval window rare, although thickening of the footplate of the stapes has Tilt of the inferior oval window margin into the vestibule been reported. Bony encroachment can occur in the epi- Dampening of the mechanics of the inner ear tympanum or at the oval window, where an osseous bridge Abbreviations: IAC, internal auditory canal; CHL, conductive hearing may replace the annular ligament. Remodeling of the bony loss. margins of the middle ear is associated with the development ch05.qxd 9/23/08 11:56 AM Page 372

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A B Fig. 5.85 Paget’s disease, late stage. (A) Lateral skull series demon- (B) Axial computed tomography image reveals diffuse “cotton wool” strates diffuse thickening of the calvarium (arrow) with additional find- thickening of the cranial base with characteristic generalized demineral- ings indicating some degree of basilar invagination as well as platybasia. ization of the otic capsule (arrows). (Courtesy of C. Douglas Phillips, MD.)

of new bone near the promontory, with subsequent upward circumscripta results from increased vascularity and dem- tilt and protrusion of the inferior oval window margin into ineralization of the outer table of the skull. Demineraliza- the vestibule. Seventh cranial nerve dehiscence may occur tion of the squamous temporal bone and petrous apex is in its tympanic segment due to pagetoid involvement of generalized, diffuse, homogeneous, and quite striking. In- this segment of the canal.255,256,260 volvement of the bony labyrinth is a smooth resorption, Diffuse demineralization of the cranial base is identi- often asymmetric (Fig. 5.86 and Fig. 5.87). This appear- fied at CT in the acute phase of this disorder, correlating ance is very dissimilar to the plaque-like demineralization well with plain film evidence of calvarial osteoporosis cir- of otosclerosis and the moth-eaten permeative appearance cumscripta seen in the lytic phase (Fig. 5.85). Osteoporosis of otosyphilis.261 In our experience, sensorineural deficit

A B Fig. 5.86 Paget’s disease. (A,B) Axial CT images. ch05.qxd 9/23/08 11:56 AM Page 373

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C D

Fig. 5.86 (Continued) (C,D) Coronal computed tomography images reveal diffuse cranial base demineralization with obvious thinning/demineralization of the otic capsule (arrows). The process is quite symmetric. Note involvement of the first genu of the facial nerve canal (outlined arrows, A,B) and cortex over the posterior semicircular canal (outlined arrows, C,D). Enhanced coronal magnetic resonance image (E) reveals gadolinium E enhancement throughout.

correlates well with the degree of otic capsule demineral- The MRI findings in Paget’s disease are variable.57,263 ization, leading us to suspect that damage to the spiral lig- The T1- and T2-weighted signal intensities are heteroge- ament is a particularly important cause of the hearing loss neous due to a combination of fibrosis and vascular tissue as it is in retrofenestral otosclerosis. that results in deposition of blood products. The involved The CT appearance of advanced pagetoid involvement of bone enhances with contrast due to the vascular nature of the squamous and petrous portions of the temporal bone is the tissue. similar to that occurring in the calvarium, that is, a fluffy Early imaging diagnosis of temporal bone involvement cotton wool appearance (Fig. 5.88).262 Differential diagno- may lead to treatment with bisphosphonates such as sodium sis does include blastic metastatic disease (Fig. 5.89). etidronate, which is important to limit the development

A B Fig. 5.87 Paget’s disease, localized. (A) Axial computed tomography, right ear, reveals a localized area of demineralization in the otic capsule (black arrow). (B) Axial T2-weighted magnetic resonance image, right ear, demonstrates the correlating area of hypersignal (white arrow). ch05.qxd 9/23/08 11:56 AM Page 374

374 Imaging of the Temporal Bone

A B Fig. 5.88 Paget’s disease, late phase. (A) Axial computed tomography (CT), right ear. (B) Axial CT, left ear. Diffuse cotton wool appearance at the cranial base. There is clearly identifiable involvement of the petrous apex bilaterally. The otic capsule appears to be spared.

A B Fig. 5.89 Metastatic prostate carcinoma. (A–D) Multiple axial com- note the normal bone volume. There is also none of the “cotton wool” puted tomography images reveal a diffuse abnormal bony sclerosis changes that would be expected at this stage of Paget’s disease. (Courtesy perhaps more impressive on the left, where there is some associated of Deborah Reede, MD.) middle ear debris. Findings are remniscent of fibrous dysplasia, but ch05.qxd 9/23/08 11:56 AM Page 375

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C D Fig. 5.89 (Continued)

and progression of hearing loss.264 Mithramycin and calci- Pagetoid, sclerotic, and cystic forms of FD have been tonin may also be of value. described, directly reflecting the relative ratios of fibrous and osseous elements (Table 5.9).57,261,271,272 Pagetoid (56%) involvement is most common and results in a ground- Fibrous Dysplasia glass pattern due to a mixture of fibrous tissue and Fibrous dysplasia (FD) is a chronic, indolent, gradually pro- osseous elements, resulting in CT evidence of alternating gressive inherited disorder characterized by replacement areas of lucency and sclerosis (Fig. 5.90).271 The sclerotic of normal bone by an abnormal proliferation of isomorphic (23%) and cystic (21%) forms result from a predominance fibrous tissue elements intermixed with a haphazard of osseous and fibrous elements, respectively (Fig. 5.91, arrangement of the trabeculae of woven bone.254,265 The Fig. 5.92, and Fig. 5.93). The entirety of the temporal bone ability to form mature lamellar bone is defective due to may be affected, including the external canal, middle ear, disordered osteoblastic activity. This results in expansion, jugular foramen, or, rarely, the otic capsule. Labyrinthine distortion, and structural weakness. Women are affected involvement has been recently documented with CT, con- perhaps two or three times as often as men.260,266 Lesions tradicting early reports, which indicated that this region characteristically become quiescent after puberty, but this was immune.265,269,271 is variable.267 As with Paget’s disease, there are monostotic Some patients present with a postauricular mass or (70%) and polyostotic (30%) forms.260,268 The skull and facial tinnitus, but hearing loss is the most common presenting bones are involved in 10 to 25% of cases of monostotic symptom and may be conductive or sensorineural.267 fibrous dysplasia and in 50% of patients with polyostotic SNHL is increasingly recognized as a sequela of fibrous fibrous dysplasia. dysplasia and may be secondary to IAC encroachment or The etiology is unknown. Some authors suggest a cochlear replacement.265,271 CHD is far more common and perverted activity of bone-forming mesenchyme, and others postulate an extraskeletal disorder of calcium Table 5.9 Fibrous Dysplasia Subtypes and phosphate metabolism.269,270 Involvement of the temporal bone is typically monostotic, characterized Subtype % of Patients Characteristics most commonly by slow expansion with increased vol- Pagetoid 56 Fibrous tissue and osseous elements 270 ume of the mastoid. FD results in widening of the Sclerotic 23 Predominance of osseous elements bone due to replacement of the normal medullary Cystic 21 Predominance of fibrous tissue space. The cortical bone is rarely involved. ch05.qxd 9/23/08 11:56 AM Page 376

376 Imaging of the Temporal Bone

A B Fig. 5.90 Fibrous dysplasia, pagetoid. (A) Magnified axial computed of the temporal bone on the right side with petrous and occipital tomography (CT), right ear. (B) Magnified axial CT, left ear. Note the involvement on the left side. There is sparing of the otic capsule on both diffuse heterogeneous thickening of the squamous and petrous portion sides.

Fig. 5.92 Fibrous dysplasia, cystic. Magnified axial computed tomog- Fig. 5.91 Fibrous dysplasia, sclerotic. There is diffuse sclerosis of the raphy image, right ear. Diffuse thickening of the squamous and petrous mastoid characterized by increased bone volume (*). Note occlusive portions of the temporal bone within internal low density (arrows) changes in the external auditory canal, which commonly occur with compatible with the diagnosis of fibrous dysplasia of the temporal this disorder (arrows). bone, cystic variety. ch05.qxd 9/23/08 11:56 AM Page 377

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A B

C D Fig. 5.93 (A) Axial computed tomography image reveals low-density intensity. (C) Axial nonenhanced T1-weighted magnetic resonance im- mastoid characterized by bony expansion (arrow). (B) Axial T2-weighted age (T1WI). (D) Axial postcontrast T1WI reveals intense enhancement. magnetic resonance image (T2WI) is characterized by diminished signal (Courtesy of C. Douglas Phillips, MD.)

is typically the result of EAC obstruction or direct middle than in Paget’s disease and, to our knowledge, has never ear encroachment. EAC stenosis is particularly common been reported in the temporal bone. (Fig. 5.94 and Fig. 5.95). Superimposed chronic otitis Regardless of the variety (pagetoid, sclerotic, cystic), and its complications also play a role. Facial nerve the overriding imaging finding in temporal bone fibrous involvement is another sequela once thought rare, but dysplasia is increased bone volume.57,272 CT allows exqui- recently it has been appreciated more frequently (10%).265 site demonstration of the enlarged dense mastoid charac- Cholesteatoma is a well-known sequela of fibrous dyspla- teristic of the sclerotic form of this disease (Fig. 5.91, sia and may occur in as many as 40% of patients, often Fig. 5.96, and Fig. 5.97). Ossifying fibroma is easy to confuse arising within the EAC.273–275 These cholesteatomas may radiographically with this variety of fibrous dysplasia.265 extend widely throughout the temporal bone. Such dis- Microscopic evaluation is required to differentiate the lamel- ease may progress in an asymptomatic fashion when the lar pattern typical of ossifying fibroma from the woven otic capsule and facial nerve are spared, and, as such, regu- pattern of fibrous dysplasia. Pagetoid fibrous dysplasia is lar imaging follow-up is mandated. A case of parapharyn- characterized by a mixture of lucent and dense areas, and geal space extension from the petrous apex has been re- cystic fibrous dysplasia by predominant lucency (Fig. 5.91, ported.275 Malignant degeneration has also been reported Fig. 5.92, and Fig. 5.93). Purely cystic fibrous dysplasia in fibrous dysplasia; however, it is much less common may present a diagnostic dilemma, as it may masquerade ch05.qxd 9/23/08 11:56 AM Page 378

378 Imaging of the Temporal Bone

A B Fig. 5.94 Fibrous dysplasia, postoperative. (A) Axial and (B) coronal computed tomography images reveal sclerotic fibrous dysplasia and extensive postoperative changes. Of interest is oval window niche ossification (white arrow, A) and semicircular canal involvement (black arrows, B).

as several well-known aggressive disorders, such as rhabdo- presenting with the characteristic ground-glass appearance myosarcoma, aneurysmal bone cyst, giant cell tumor, and (Fig. 5.98, Fig. 5.99, and Fig. 5.100). MRI appearance metastatic disease. The sclerotic form is seen in 23% of temporal bone fibrous dysplasia is nonspecific and of cases and is the most easily recognizable form on CT, is typically diffusely hypointense on all spin echo pulse

A B Fig. 5.95 Fibrous dysplasia, sclerotic. (A) Magnified coronal computed identified. Note the highly stenotic right external auditory canal (oppos- tomography (CT) image, right ear. (B) Magnified axial CT image, right ing arrows) and dramatic encroachment upon the ossicular mass in the ear. Typical exuberant bony overgrowth diagnostic of fibrous dysplasia is attic (small arrows). ch05.qxd 9/23/08 11:57 AM Page 379

Chapter 5 The Inner Ear and Otodystrophies 379

A B Fig. 5.96 Fibrous dysplasia. (A,B) Axial computed tomography images reveal a well hyperattenuation (*) within the mastoid and evidence of increased bony volume. (Courtesy of H. Ric Harnsberger, MD.)

Osteopetrosis sequences. Occasional focal areas of T1-weighted hyperintensity are seen, and enhancement is variable.276 In- Osteopetrosis (Albers–Schönberg disease) is a rare meta- creased clinical activity of the lesion appears to correlate bolic disease characterized by a generalized increase in with regions of high signal on both T1WIs and T2WIs and skeletal mass caused by an abnormality of bone remodel- with strong enhancement.276 ing, resulting in overproduction of immature bone.254,277–280

A B Fig. 5.97 Fibrous dysplasia. (A) Axial and (B) coronal CT images reveal a well-marginated area of hyperattenuation within the mastoid. There is increased bony volume diagnostic of fibrous dysplasia. (Courtesy of H. Ric Harnsberger, MD.) ch05.qxd 9/23/08 11:57 AM Page 380

380 Imaging of the Temporal Bone

At least five types of this disorder have been described, and very likely more than one genetic or biochemical defect are causative. The two most commonly diagnosed varieties are the autosomal recessive (malignant) and autosomal dominant (benign) osteopetrosis, respectively, referred to as AROP and ADOP.281,282 AROP is diagnosed in infancy, results from deficient resorption of the primary spongiosa, and is associated with cranial nerve palsies, poor osseous growth, petrous ICA stenosis, and stenosis of the dural venous sinuses. Enhancement of the extracerebral spaces on T1WI is often the result of extramedullary hematopoiesis. Renal tubular acidosis secondary to car- bonic anhydrase II deficiency is also associated with recessive disease. This results in calcifications within the basal ganglia, thalami, dentate nuclei, and white matter.283 An intermediate variety (IOP) is diagnosed in older children and has a somewhat milder clinical course. ADOP is diagnosed in adulthood and is of variable severity. Type I ADOP is characterized by calvarial sclerosis and spine involvement. Fractures are rare, as the bone is quite strong. In type II ADOP, the skull base is thickened. This is the variety that is associated with “rugby jersey spine” and “endobones” (unresorbed primary ossification centers). Temporal bone involvement would therefore be most common with AROP and ADOP, type II. Fig. 5.98 Fibrous dysplasia. There is a sclerotic mastoid. Note the subtle changes of increased bone volume, which were characterized clinically CT may demonstrate diffuse bony sclerosis without by a cosmetic deformity (arrows). the increased volume of bone seen in fibrous dysplasia (Fig. 5.101). Sensorineural hearing deficit and facial palsy may occur, and most investigators believe that encroachment on the IAC and facial nerve canal are the cause.284 CHL is somewhat more common and is secondary to bony encroachment and COM. The IACs may be shortened

Fig. 5.99 Fibrous dysplasia. (A) Axial and (B) coronal computed tomography images. There is bony thickening/increased volume along the superior, medial, and posterior petrous surfaces (outlined white arrows) extending to (and beyond) the occipitomastoid suture (larger black arrow, A). The posterior semicircular canal (small black arrows) is surrounded by abnormal bone but maintains its integrity. There is involvement of the occipital condyle, A especially to the left (*). (Courtesy of Paul Caruso, MD.) ch05.qxd 9/23/08 11:57 AM Page 381

Chapter 5 The Inner Ear and Otodystrophies 381

The mastoid is dense and nonpneumatized, and the middle ear and attic are small but well formed. The IACs are rotated with short posterior walls and a flared porus. Deformity of the petromastoid canal and subarcuate fossa is presumably due to persistence of vascular channels.279 Investigators report sclerosis of the otic capsule with sparing of the oval window.

Progressive Diaphyseal Dysplasia (Camurati–Engelmann Dysplasia) This is a rare autosomal dominant disorder typically diagnosed in childhood and characterized by a disturbance in intramembranous ossification. Patients typically present with headache, muscle weakness, difficulty walking, bone pain, poor appetite, fatigue, and exoph- thalmus. The upper extremities are more commonly Fig. 5.100 Fibrous dysplasia. Axial computed tomography image reveals localized expansion of the mastoid with homogeneous interme- affected that the lower extremities. There is diffuse diate high density (ground glass) appearance characteristic of fibrous hyperostosis of the cranial base, which often results in dysplasia. (Courtesy of H. Ric Harnsberger, MD.) stenosis of the IAC and EAC. Findings are often progressive.287 Cholesteatomas may develop in a fashion similar to FD arising in the ME or EAC. Progressive retrocochlear and trumpet-shaped. Otitis media generally improves SNHL is associated with worsening stenosis of the IAC. 285 after tympanostomy. Pericochlear demineralization similar to cochlear oto- Similar diffuse bone sclerosis can be predicted in cra- sclerosis has been rarely described in this disorder.288 niometaphyseal dysplasia (Pyle’s disease), pyknodysostosis, On MRI, there is signal loss on T1WI and T2WI involving and Camurati–Engelmann disease (progressive diaphyseal the skull base and calvarium. Vestibular nerve symp- dysplasia) (Fig. 5.59). CHL is the predominant symptom toms secondary to the compressive IAC stenosis has also related to temporal bone involvement in osteopathia stri- been reported (Fig. 5.102).289,290 ata (Voorhoeve disease) when associated with cranial sclerosis.286 Individuals with ADOP who are treated early in life may have relatively few imaging manifestations.277

Fig. 5.102 Camurati–Engelmann disease (progressive diaphyseal dys- Fig. 5.101 Osteopetrosis. Axial computed tomography image reveals plasia). Axial computed tomography image. There is profound bony diffuse sclerosis of the entire cranial base. The homogeneity differen- sclerosis and overgrowth at the cranial base. The temporal bone is in- tiates this from Paget’s disease, and the symmetry and normal volved bilaterally. Findings of this type would also occur with bone volume differentiate from fibrous dysplasia. (Case courtesy of osteopetrosis or craniometaphyseal dysplasia (Pyle’s disease). (Courtesy C. Douglas Phillips, MD.) of Hugh D. Curtin, MD.) ch05.qxd 9/23/08 11:57 AM Page 382

382 Imaging of the Temporal Bone

Otosclerosis Fenestral Otosclerosis Otosclerosis is a unique disease of the otic capsule charac- These patients present with CHL due to restricted stapes terized by autosomal dominant inheritance with variable movement and subsequent audiometric air–bone gap. penetrance and expression.291 The term otospongiosis was The most common area of stapes fixation is the anterior used by Siebenmann in 1912 to describe spongiform crus in the region of the embryonic fissula antefenes- changes within the bone identified on microscopic exam- tram.292,295–297,303 This slit-like passage is an area of embry- ination. Histologically, this is disorganized bone rich in onic cartilage and connective tissue that extends within osteocytes with enlarged marrow space containing sub- the otic capsule from the anterior oval window region to stantial connective tissue and blood vessels. Patients typi- the vicinity of the cochleariform process between the cally present between the third and fourth decades of life. tympanic periosteum and vestibular endosteum. Sur- The disease is more common in women (2:1), may be ex- rounding bone often contains fibrous tissue and imma- acerbated by pregnancy, and is commonly bilateral (85%) ture cartilage. From this location, the disease may spread and often quite symmetrical. Despite this symmetry, pain finger-like extensions to involve the entire footplate tients are not always symptomatic in both ears simultane- and subsequently the cochlea as well (Table 5.10). When ously.292 Otosclerosis is far more common in Caucasians involvement of the annular ligament occurs, the most sig- and less common in blacks, Native Americans, and nificant early sequela of fenestral otosclerosis develops, Asians.291,293 In some patients there is increased incidence that is, CHD secondary to increased mechanical stiffness of dental caries, which infers a disorder of calcium and of the stapes arch and footplate, which may ultimately phosphate metabolism.292 Two thirds of patients may result in bony fixation of the stapediovestibular joint have tinnitus early in their course, which presents a con- (Fig. 5.103). There may also be bony fixation between the fusing clinical picture. stapes superstructure and the promontory or facial nerve The otic capsule has an outer endosteal (labyrinthine) canal. Malleoincudal fixation is uncommon but may layer, an inner periosteal (tympanic) layer, and an inter- occur as a secondary torsional sequel. Round window posed endochondral layer.291,292 The petrous temporal involvement is variable but usually does not interfere bone is thus unique in that its maturation is arrested in a with round window membrane function or subsequent state of primary ossification because endochondral bone sound transmission.81 The fossula postfenestram is an elsewhere is normally replaced by mature haversian additional small passage posterior to the oval window filled bone. One compelling theory suggests that otosclerosis with connective tissue, which is a much less common site occurs when foci of haversian bone develop in the endo- of predilection for these lesions. chondral layer of the labyrinthine capsule.291,294–297 A su- Complete replacement of the oval window may develop perimposed inflammatory response likely plays a role in (2%). This is referred to as obliterative otosclerosis, which pathogenesis.298 Investigators have found high levels of is significant in that surgical drilling is necessary prior to measles virus antibodies in the perilymph of several con- prosthesis insertion (Fig. 5.104).301,309 Obliterative changes secutive patients undergoing stapedectomy for otosclero- are occasionally associated with partial incus subluxation, sis.299 In patients with otosclerosis, the normal ivory-like also presumably as a secondary torsional sequel (Fig. 5.105). endochondral bone is replaced by foci of spongy vascular Short of obliteration, the oval window may be strikingly irregular new bone that is less solid than the bone it narrowed by the presence of both anterior and posterior replaces.300 These spongy decalcified foci, however, tend plaques.309 to recalcify and become less vascular and more solid. The term otosclerosis has therefore been well publi- cized as being a misnomer for a more appropriate term: otospongiosis.301–304 Table 5.10 Preoperative CT Evaluation of Otosclerosis Otosclerosis consists of two major categories, fenestral Status of oval window/location of plaques and retrofenestral (cochlear). The more common fenestral Facial nerve canal (tympanic segment) — r/o dehiscence variety involves the lateral wall of the labyrinth, including the promontory, facial nerve canal, and both the oval win- Jugular bulb dow and round window niche. Oval window involvement Round window is classic as conductive hearing becomes impaired. The Status of cochlea retrofenestral variety primarily involves the cochlea.305 Existence of concurrent middle ear disease or congenital Fenestral disease commonly occurs as an isolated phe- ossicular deformity nomenon. Retrofenestral (cochlear) disease rarely occurs Opposite ear without fenestral involvement, implying that these manifestations are a continuum rather than two separate Abbreviations: CT, computed tomography; r/o, rule out. entities.306–308 ch05.qxd 9/23/08 11:57 AM Page 383

Chapter 5 The Inner Ear and Otodystrophies 383

A B Fig. 5.103 Fenestral otosclerosis, right ear. (A) Diagrammatic representation on finding. (B) Diagrammatic representation of normal oval window.

In addition to preoperative evaluation of the presence an incidence of 1 to 2%, which may cause peculiar audio- and extent of oval window disease, the CT evaluation of metric findings and a less than successful surgical result these patients should be designed to include study of the (Fig. 5.106).310 On occasion, membranous labyrinthine os- round window, facial nerve canal, and jugular bulb. Con- sification limited to the basilar cochlear turn may occur. genital ossicular deformity must be excluded as an etiol- This manifestation and round window involvement have ogy of the hearing deficit. Concomitant study of the inner significant implications if cochlear implantation is con- ear for changes of retrofenestral disease should not be templated.311,312 The facial nerve canal should be evaluated for overlooked. Obliterative round window involvement is an dehiscence/protrusion in its tympanic segment (Fig. 5.107 uncommon complication of advanced otosclerosis with and Fig. 5.108).305,309 The otologic surgeon is grateful for

Fig. 5.105 Fenestral otosclerosis, incus subluxation. Axial computed Fig. 5.104 Fenestral otosclerosis, obliterative. Diagrammatic repre- tomography image of the left ear reveals a large anterior plaque (white sentation of coronal section, right ear. The entire oval window region arrow). There is secondary incus subluxation (black arrow) as a tor- is obliterated by bone. sional sequel. ch05.qxd 9/23/08 11:57 AM Page 384

384 Imaging of the Temporal Bone

A B Fig. 5.106 Fenestral otosclerosis—oval window/round window. (A) Magni- (arrow) in direct apposition to the anterior crus of the stapes. (B) Magnified fied axial computed tomography (CT) image, right ear. Moderate-sized coronal CT image, right ear. Occlusive otosclerotic changes are seen otosclerotic plaque is seen in the anterior oval window region on the right involving the round window (arrows).

preoperative knowledge of this anomaly, as the protruding nerve complicates oval window surgery. Historically, the wide CA was believed to play a role in the incidence of the perilymphatic (stapes) gusher, but this concept has fallen into disrepute in recent years. Deformity of the IAC fundus is much more commonly associated with this aberration. This is discussed elsewhere in this chapter. The dehiscent high-riding internal jugular vein is an obvious surgical hazard. Malleus and incus fixation (lateral ossicular fixation) is not rare and can also be ruled out with CT. Malleus head fixation within the epitympanum in this context is well known.313 When lateral fixation is caused by exuberant otosclerotic plaques along the lateral labyrinthine surface, this is referred to as the House syndrome.314 Preoperative diagnosis is important because removal of the otosclerotic incudomallear fixation is necessary prior to the prosthesis insertion. Fenestral foci are usually best diagnosed on axial CT sections due to the anteroposterior orientation of both the oval window and stapes crura (Fig. 5.109, Fig. 5.110, Fig. 5.111, Fig. 5.112, Fig. 5.113, Fig. 5.114, Fig. 5.115, and Fig. 5.116). These foci are of variable size and density and are most often seen in the anterior oval window region.57,305,309 Fig. 5.107 Dehiscent facial nerve, tympanic segment. Coronal computed tomography (CT) image reveals soft tissue prominence (white Posterior plaques can also be identified in the posterior arrow) in the oval window, representing a dehiscent facial nerve 305–307 portion of the oval window (fossula postfenestram). protruding inferiorly from its expected site along the undersurface Smooth, diffuse thickening of the stapes footplate/annular of the lateral semicircular canal. ch05.qxd 9/23/08 11:57 AM Page 385

Chapter 5 The Inner Ear and Otodystrophies 385

A B Fig. 5.108 Facial nerve dehiscence/protrusion. (A) Coronal computed ear. The facial nerve (arrow) is identified on this side as well, but note tomography (CT) image, right ear. There is a soft tissue prominence that there is no impingement upon the stapes. Note also subtle (but along the undersurface of the lateral semicircular canal (arrow), which significant) evidence of cortication along the undersurface of the nerve. impinges upon the stapes within the oval window. (B) Coronal CT, left

ligament complex may occur on occasion, but this is un- diameter of the oval window may appear to be paradoxi- common. Coronal CT sections are very useful for delineation cally increased in those individuals with active adjacent of this particular manifestation.145 The key to diagnosis in otospongiotic changes.315,316 this projection is the assessment of comparative oval The CT findings compatible with fenestral otoscle- window thickness. The vertical height or anteroposterior rosis have a limited differential diagnosis; however,

A B Fig. 5.109 Fenestral otosclerosis, left ear. (A) Axial computed tomography (CT) image, right ear, shows essentially normal findings, perhaps a minimal anterior plaque oval window (arrow). (B) Axial CT, left ear, depicts large anterior plaque, oval window (arrow). ch05.qxd 9/23/08 11:57 AM Page 386

386 Imaging of the Temporal Bone

Fig. 5.110 Fenestral otosclerosis, bilateral and asymmetric. (A) Right ear. (B) Left ear. Anterior oval window plaque is much larger on the left (arrows). B

postinflammatory fixation should be considered in the disease, including an underpneumatized mastoid, mak- appropriate clinical circumstance.305 Our experience in- ing differentiation from otosclerosis relatively easy. By dicates that such tympanosclerotic foci within the oval contrast, most patients with otosclerosis have normal or window niche are often much more irregular, although greater than normal mastoid pneumatization, as there is smooth thickening of the stapes footplate/annular liga- no obligatory history of eustachian tube dysfunction.317 ment complex may also occur and be indistinguishable Clinical differentiation from otosclerosis is often diffi- from otosclerosis (see Chapter 3). Patients with tym- cult, particularly when the tympanic membrane is healed, panosclerosis almost invariably have obvious middle ear as the degree of conductive deficit may be identical.

A B Fig. 5.111 Fenestral otosclerosis, subtle. (A) Right ear. (B) Left ear. There are bilateral and symmetric anterior oval window plaques, which are distinctive because they are in the classic location of the embryonic fissula antefenestram. ch05.qxd 9/23/08 11:57 AM Page 387

Chapter 5 The Inner Ear and Otodystrophies 387

A B Fig. 5.112 Fenestral otosclerosis, bilateral and symmetric. (A) Right ear. (B) Left ear. There are anterior oval window plaques identified (arrows).

Postinflammatory ossicular resorption must also be considered in this clinical context (see Chapter 3). The treatment of fenestral otosclerosis is primarily surgical, although some benefits from treatment with sodium fluoride have been reported, with diminished plaque size confirmed with CT.318,319 Stapedectomy is commonly performed, followed by insertion of a prosthesis. These

Fig. 5.113 Fenestral otosclerosis, moderate size plaque. Axial com- Fig. 5.114 Fenestral otosclerosis, minimal change. Axial computed puted tomography image, left ear, reveals anterior oval window plaque tomography image reveal a subtle plaque in the anterior oval window (arrow). region (arrows). ch05.qxd 9/23/08 11:57 AM Page 386

386 Imaging of the Temporal Bone

Fig. 5.110 Fenestral otosclerosis, bilateral and asymmetric. (A) Right ear. (B) Left ear. Anterior oval window plaque is much larger on the left (arrows). B

Chapter 5 The Inner Ear and Otodystrophies 387

A B Fig. 5.112 Fenestral otosclerosis, bilateral and symmetric. (A) Right ear. (B) Left ear. There are anterior oval window plaques identified (arrows).

388 Imaging of the Temporal Bone

A B Fig. 5.115 Fenestral otosclerosis, bilateral symmetric and subtle. (A) Right ear. (B) Left ear. Symmetric anterior oval window plaques (arrows).

devices have a characteristic CT appearance, and compli- There are differences of opinion regarding the pathogen- cations related to their insertion can be evaluated (see esis of the associated SNHL. There is a consensus that this Chapter 3) (Table 5.11). symptom results from hyalinization of the spiral ligament. The spiral ligament is the periosteal covering of the cochlear duct located at the surface of the membranous Retrofenestral (Cochlear) Otosclerosis labyrinth in direct contiguity with the bony labyrinth. Some The pathogenesis of the retrofenestral type of disease is observers believe that this hyalinization results from diffu- identical. The process of demineralization of the otic cap- sion of cytotoxic enzymes into the cochlear fluid.302,323,324 sule itself is poorly understood; however, osteoclasts have Changes in the spiral ligament have been demonstrated to been identified at the site and have been presumed to be be most severe when it is in contact with otosclerotic associated by many observers, although recent evidence bone.260 Others suggest that the sensorineural complaint re- suggests that osteoclast activated bony resorption occurs sults directly from the proximity to the otosclerotic focus, only in conditions that affect membranous bone, such as which affects the otic capsule in such a way that it inter- chronic otitis.302,320–322 The pathognomonic Schwartze feres with the functioning of the organ of Corti.325 sign (otoscopically demonstrable vascular hue) may be Foci of demineralization within the otic capsule identi- identified if this vascular demineralizing process reaches fied at CT examination are the diagnostic hallmark of this the outer periosteal surface of the promontory. disorder (Fig. 5.117 and Fig. 5.118). They are most common

A B Fig. 5.116 Fenestral otosclerosis, moderate to large, bilateral and sym- (B) Coronal CT reveals bilateral round window plaques (arrows) substan- metric with round window involvement. (A) Axial computed tomogra- tially larger on the right. phy (CT) image reveals large symmetric anterior plaques (arrows). ch05.qxd 9/23/08 11:57 AM Page 389

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Table 5.11 Classification of Otosclerosis Type Characteristics Type 1A Irregular thickened stapes footplate Type 1B 1 mm focus anterior oval window region Type 2 1 mm focus anterior oval window region Type 3 1 mm focus anterior oval window region in contact with cochlear endosteum Type 4A Extensive hypodense foci throughout middle layer of otic capsule Type 4B Otic capsule involvement includes semicircular canals Source: Adapted from Veillon F, Riehm S, Emachescu B, et al. Imaging of the windows of the temporal bone. Semin Ultrasound CT MR 2001;22(3):271–280.

in individuals with audiometrically progressive SNHL.307,326 Symmetry is quite common (Fig. 5.119 and Fig. 5.120). Fig. 5.117 Fenestral and cochlear otosclerosis. Obliterative oval win- Involvement has been demonstrated histopathologically to dow plaque (white arrow) appears continuous with extensive circum- be the most common between the 16th and 20th millimeters ferential demineralization of the otic capsule (black arrows). of the cochlear duct (upper half of the basal turn) (Fig. 5.121 and Fig. 5.122).327 Usually, the disease is obvious; however, these foci may be subtle and should be carefully sought As indicated above, retrofenestral foci are rare in the (Fig. 5.123).306,307,316 Many observers believe that recalcifi- absence of fenestral disease, implying a continuum rather cation of these foci of demineralization may be promoted than two separate entities (Fig. 5.124 and Fig. 5.125). The with the use of sodium fluoride because the level of cyto- reader should be aware that pericochlear hypoattenuating toxic enzymes within the cochlear fluid has been lowered areas are consistently visualized in normal children, experimentally.304,324 which appear to correspond to the embryonic fissula

A B Fig. 5.118 Asymmetric bilateral cochlear otosclerosis. (A,B) Diffuse bilateral disease (arrows). More extensive demineralization is noted on the right (A) involving the basilar turn. ch05.qxd 9/23/08 11:57 AM Page 390

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A B Fig. 5.119 Symmetric cochlear otosclerosis. Axial computed tomography images of (A) right and (B) left ears reveal symmetric demineralizing plaques in the otic capsules (black arrows). There is a round window plaque (white arrow) on the right.

antefenestram referred to earlier in this discussion (Fig. Retrofenestral disease may be also identified on MRI 5.126). This appearance should not be confused with oto- by a ring of intermediate signal in the pericochlear and sclerosis.328,329 perilabyrinthine regions on T1WIs (Fig. 5.128).330 There New bone formation (membranous labyrinth ossifica- is also mild to moderate enhancement after gadolinium tion) is very unusual with otosclerosis (hence the mis- administration (Fig. 5.129).330,331 Such enhancement may nomer) and almost invariably limited to the round window be due to pooling of gadolinium directly within these and basilar turn of the cochlea (Fig. 5.127). Labyrinthine vascular foci or, alternatively, may occur secondary to an ossification is vastly more common as a complication of associated inflammatory response, perhaps signaling an labyrinthitis (see earlier text).312 “active” plaque.319 The presence of abnormal T1-weighted

A B Fig. 5.120 Cochlear otosclerosis. Coronal computed tomography images at the level of the anterior turns of the cochlea reveal symmetric demineralization of the otic capsule (arrows). ch05.qxd 9/23/08 11:57 AM Page 391

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A B Fig. 5.121 Cochlear otosclerosis, promontory. (A) Coronal computed tomography image, right ear. (B) Coronal CT, left ear. There is demineralization of the basilar turn of the cochlea bilaterally and symmetrically (arrows). Stapes prosthesis is noted on the left.

signal and pericochlear enhancement should be specifi- from this procedure, although with particularly advanced cally sought in all patients undergoing MRI for hearing disease there is an increased risk of CSF leak.332,333 loss, as otosclerosis may not be initially considered as a cause of deficit, particularly by primary care physicians. Osteogenesis Imperfecta CT would be recommended for confirmation if the MRI is abnormal. OI is an inherited connective tissue disorder associated For years, cochlear otospongiotic changes were a rela- with involvement of chromosomes 7 and 17, resulting in tive contraindication for cochlear implantation; however, an abnormality of type I collagen characterized by varying with recent advances, many patients benefit significantly degrees of fragile bones, osteoporosis, blue sclerae, defective

A B Fig. 5.122 Cochlear otosclerosis, basilar turn. (A) Coronal computed to- may be appreciated otoscopically as a Schwartze sign. (B) Axial CT mography (CT) image–extensive region of demineralization involving shows circumferential involvement of the cochlear apex (arrows). basilar cochlear turn. The vascular nature of a plaque in this location ch05.qxd 9/23/08 11:57 AM Page 392

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Both SNHL and CHL occur. Pure SNHL is much more common than with otosclerosis, and hearing loss develops at a younger age.336 There is a remarkable proliferation of unmineralized bone involving all or part of the otic capsule (Fig. 5.130). Although almost uniformly more severe in degree, this plaque-like otic capsule demineralization is similar in appearance to that which occurs in cochlear otosclerosis (otospongiosis) (Fig. 5.131).291 This has led to speculation and subsequent controversy regarding the relationship of otosclerosis to OI. A few authors have suggested a common genetic abnormality, implying that otosclerosis is merely a localized form of OI. Biochemical data indicate that the two diseases are indeed enzymati- cally different because there is no similarity in the enzyme and protein concentrations. In addition, the SNHL occurring with OI is believed by some investigators to result from encroachment of reparative vascular and fibrous tissue in and about the cochlea or from hemorrhages and microfractures.337 The severity of demineralization of the otic capsule demonstrated with CT may reflect the fact that all three layers of the otic capsule are involved in OI in contradistinction to otosclerosis, in which disease is limited to the endochondral layer.335,338 There are indications that OI Fig. 5.123 Fenestral and cochlear otosclerosis. Large anterior oval 334 window plaque (white arrow). Subtle demineralizing otospongiotic may result in progressive demineralization over time. plaque (small black arrow). Changes in the otic capsule identical to those described with otosclerosis on nonenhanced T1WIs have also been described.339 Enhancement of these demineralized areas dentition, hyperextensible joints, wormian bones, and with gadolinium on T1WIs also occurs. Facial nerve canal hearing impairment. The currently accepted classification enhancement has been appeciated in these patients likely divides the disorder into four types based on the type of due to changes in the margins of the canal rather than the defect in type I collagen synthesis.334 Type I (tarda) is the nerve itself, as there is typically no evidence of facial most common and mildest form. There is autosomal dom- palsy.305,334 Decreased pericochlear bone density has been inant inheritance. Autosomal recessive type II (congenital) described to occur as a CT manifestation in lieu of the is the most severe form and is characterized by multiple typical plaque-like demineralization. This was associated fractures of the chest wall, skull, and vertebrae invariably with scintigraphic evidence of increased bone metabo- resulting in death of the fetus or newborn. Type III OI re- lism. These authors also report OI patients with hearing loss sults in skeletal deformity and early fractures of the long but no temporal bone CT findings.340 bones. Patients have abnormal production of dentin and CHL results from proliferation of abnormal bone with may have blue sclera that turn white as the patient grows. obliteration of the oval and round windows in a manner Type IV is a defect in a subunit of collagen and has vari- similar to fenestral otosclerosis. Stapes fractures make a able severity. This categorization has effectively replaced substantial contribution to the CHD as well.341 Prosthetic the congenital–tarda division, which merely refers to the stapedectomy is less effective for OI than otosclerosis but age at diagnosis. Hearing involvement is not commonly remains in use (Table 5.12).342 associated with types III and IV; therefore, the imaging findings described in this disorder are virtually always Differential Diagnosis of Otic Capsule type I (osteogenesis imperfecta tarda). In 1918 van der Demineralization Hoeve and his colleague, de Kleyn of Utrecht, emphasized the syndromic relationship of brittle bones, blue sclerae, As indicated in the above paragraphs and elsewhere in this and deafness in OI. The association of OI and hearing loss volume, several pathologic entities can result in demineral- is thus often referred to as van der Hoeve–de Kleyn syn- ization of the otic capsule (Table 5.12). This demineralization drome.335 Ekman–Lobstein syndrome is an infrequently can be described as plaque-like, moth-eaten, diffuse thin- used eponym, which denotes the association of brittle ning, permeative, or localized.261 Otosclerosis (cochlear) bones and blue sclerae, in the absence of deafness. and OI are typically plaque-like. As indicated earlier in ch05.qxd 9/23/08 11:57 AM Page 393

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Fig. 5.124 Fenestral otosclerosis, bilateral, with subtle cochlear otospongiotic changes. (A,B) Axial computed tomography images through the oval windows reveal well-defined anterior oval window plaques (white arrows), classic for otosclerosis. (C,D) More inferior axial images reveal subtle foci of demineralization (black arrows). D

this chapter, otosyphilis may present as an osteitis or a Paget’s disease is typically a diffuse thinning of the otic labyrinthitis. The osteitis has a classically moth-eaten capsule occurring in the context of skull base changes typi- appearance in contrast to the plaque-like appearance of cal for this disorder. Very rarely, pagetoid demineralization otosclerosis. Demineralization of the ossicular chain is a com- may be more localized. Camurati–Engelmann disease (promon finding in this disorder and may also help in the differ- gressive diaphyseal dysplasia) may also rarely result in otic ential diagnosis.172 The demineralization that occurs with capsule hypoattenuation. The end stage of postirradiation ch05.qxd 9/23/08 11:57 AM Page 394

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Table 5.12 Diseases Characterized by Otic Capsule Demineralization Otosclerosis, retrofenestral (cochlear) Osteogenesis imperfecta Paget’s disease Neoplasia (including schwannoma, meningioma) Otosyphilis Osteoradionecrosis Acquired cholesteatoma (usually recurrent) Cholesterol granuloma Camurati–Englemann (rare)

permeation typically involves much of the central and posterior skull base. Intralabyrinthine neoplasms such as schwannoma and meningioma may result in localized otic capsule demineralization, which can be confused with otosclerosis at CT. MRI will reveals intense enhancement diagnostic of neoplasia.343 Inflammatory conditions, specifically cholesterol granuloma and cholesteatoma, may also result Fig. 5.125 Fenestral and cochlear otosclerosis. Axial computed to- in otic capsule demineralization. Cholesteatoma invasion of mography image, left ear. Otospongiotic demineralizing plaque (black the otic capsule may occur as a primary manifestation, but arrow). Fenestral plaque, anterior oval window (white arrow) displaces it is more common in recurrent disease postmastoidectomy. anterior stapes crus (small white arrow). Unusually wide occipitomastoid suture is seen as a normal variant (large outlined arrow). Cochlear Implant Surgery change is referred to as osteoradionecrosis (see Chapter 3; Overview Fig. 3.282). A dose-dependent permeative demineralization of the bone labyrinth occurs and is associated with severe The conventional hearing aid is merely an amplifier of SNHL. This can usually be differentiated from other entities sound; hence many profoundly deaf individuals find by the clinical history. An additional clinical clue is that the these devices of limited or no use.

A B Fig. 5.126 Pericochlear lucency. This 5-year-old patient has pericochlear regions of low computed tomography density. This is a normal variant and should not be considered as evidence of cochlear otosclerosis. This is probably related to the fissula antefenestram. ch05.qxd 9/23/08 11:57 AM Page 395

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In the 1950s, investigators first recognized that auditory nerve fibers respond to electrical stimulation. This discovery paved the way for the first CIs in the 1970s, which were single channel devices. Multichannel devices became commercially available in the 1980s and are being improved continually. These multichannel implants have the advantage of stimulating many different nerve fibers individually, thereby transmitting more detailed information. State-of-the art CI devices now have up to 24 electrodes that stimulate the cochlear nerve. Cochlear implantation has become a routine procedure worldwide for the management of severe-to-profound SNHD (Fig. 5.132).344–350 A CI differs from a hearing aid in that the sound received by the device is processed (not just amplified) and converted into an electrical impulse. Sound is captured by a microphone and sent to a speech processor. The speech processor digitally encodes the speech and then sends the encoded signal to a transmitter, which is located behind the ear. The transmitter then sends the signal to the implanted stimulator, which, in Fig. 5.127 Otosclerosis, new bone formation. Magnified coronal com- turn, directly stimulates the spiral ganglion cells by puted tomography image, right ear. There is new bone formation (labyrinthine ossification) of the basilar turn (arrows). This is difficult to means of an electrode array implanted in the basal turn. differentiate from tympanogenic labyrinthitis ossificans. This process bypasses the severely degenerated hair cells

B Fig. 5.128 Cochlear otosclerosis. (A) Magnified coronal computed tomography (CT) image, right ear. There is diffuse demineralization involving the basilar turn of the cochlea (large arrow) with clearly definable involvement of the oval window as well (small arrow). (B) Magnified axial contrast-enhanced T1-weighted magnetic resonance image (T1WI), right ear. (C) Magnified axial contrast-enhanced T1WI, left ear. Patholog- ical enhancement is consistent with the diagnosis of cochlear otosclerosis (otospongiosis). Although, magnetic resonance imaging may eventually C prove to be more sensitive, CT remains the study of choice. ch05.qxd 9/23/08 11:57 AM Page 396

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degeneration. These hair cells, which reside within the organ of Corti, transduce mechanical energy to electrical energy carried by the cochlear nerve. In many of these patients, the organ of Corti is collapsed, and there is atrophy of the stria vascularis. The electrode array of the CI allows for direct stimulation of the spiral ganglion cells of the cochlear nerve, thus bypassing the damaged hair cells. Auditory brainstem implants (ABI) are used at some institutions. They are placed in the lateral recess of the fourth ventricle and allow for direct stimulation of the cochlear nuclei in the medulla in individuals with nonfunctioning or absent cochlear nerves.351 The flat rectangular shape of the stimulating array facilitates placement in the foramen of Luschka. An ABI is similar to a CI in the way it receives and processes sound. ABIs are currently indicated for neurofibromatosis type II patients with deafness following removal of bilateral vestibular schwannomas. Components of the CI include a speech processor, a headset and microphone, a receiver and stimulator, and Fig. 5.129 Retrofenestral otosclerosis, extensive. Coronal gadolinium- an intracochlear electrode array responsible for stimulat- diethylene triamine pentaacetic acid (DTPA)-enhanced magnetic reso- ing the cochlear nerve. The receiver/stimulator is placed nance image. Note abnormal pericochlear enhancement (arrows) in beneath the postauricular soft tissues within a well- this patient with computed tomographic evidence of retrofenestral drilled out area of the calvarium.352 The electrode array is (cochlear) otosclerosis. Compare with cases of enhancement of mem- inserted for a variable distance via the round window (or branous labyrinth. anteroinferior basilar turn fenestration–cochleostomy) into the scala tympani of the basilar turn. The interscalar septum and the basilar membrane provide protection for in the organ of Corti. The impulse then travels normally the scala media (cochlear duct). Scala vestibuli insertions along the remainder of the auditory pathway. are much more likely to cause damage to Reissner’s mem- Candidates for the procedure may have congenital brane and residual hair cells.353 An attempt is made to (prelingual) or acquired (postlingual) deafness. Substan- replicate the tonotopic organization of the cochlea by ori- tial success has been obtained in children with various enting the electrode to specific electrode contacts along congenital deformities if there is a functioning cochlear the electrode array. The electrical stimulation that corre- nerve. In most cases, profound SNHL results from hair cell sponds with the highest pitches is delivered within the

A B Fig. 5.130 Osteogenesis imperfecta. (A) Axial computed tomography in the right mastoid incidentally noted. (B) Coronal CT image. Demineral- (CT) image. The otic capsule is diffusely replaced by demineralized bone ized bone is again identified (arrows). The oval window obliteration is (arrows). The oval windows (small arrows) are obliterated. There is debris appreciated on the left (small arrow). (Courtesy of H. D. Curtin, MD.) ch05.qxd 9/23/08 11:57 AM Page 397

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A B Fig. 5.131 Osteogenesis imperfecta. (A) Coronal computed tomogra- reveals intense enhancement of these regions. (Courtesy of Doris D. Lin, phy image reveals profound demineralization of the otic capsule bilater- MD. Used with permission, Radiological Society of North America.) ally. (B) Coronal postcontrast T1-weighted magnetic resonance image

basilar region of the cochlea, and the lowest pitches are 3. Enlarged vestibular aqueduct delivered toward the apical region of the cochlea, consistent 4. Cochlear or vestibular malformation with normal physiology. The newest devices are carefully 5. The cochlear-carotid interval inserted in a perimodiolar orientation (“modiolus- hugging”) for a more direct stimulation of spiral ganglion Membranous labyrinthine replacement as described in cells rather than following the outer wall of the cochlea. detail earlier in the chapter usually results from chronic As such, great effort is made to avoid perforation of the long-standing labyrinthitis, typically a bilateral process basilar membrane. Indications for cochlear implantation when associated with meningitis. In the early stages, this are increasing to include those with loss of selective high- is fibrous in nature, subsequently becoming ossific. CT frequency hearing loss. is of limited value in the detection of fibrous changes but is ideally suited to detect ossific disease. Early fibrous replacement can be detected with high-resolution MR tech- Preoperative Evaluation niques prior to detection on CT (Fig. 5.133).355,356 The Preoperative CT without contrast is recommended for all presence of early fibrous disease may account for the re- CI candidates.354 As indicated below, MRI may be of signif- ported discrepancies between CT findings and surgically 349,350 icant value as well. Analysis of these images not only aids assessed cochlear patency. Ossification obliterates in determining the likelihood of success of the procedure, the membranous labyrinth and potentially limits cochlear but also influences the choice of implant and allows the patency. When extensive, such ossification may effec- 357 surgeon to choose the best side for implantation.355 The tively preclude implantation in many patients. Some studies should be specifically evaluated for authors recommend exploratory cochleostomy regardless of the degree of ossification because in many patients a 1. Presence of primary or secondary bony diseases in- surgical drillout may allow insertion of a short single- volving the cochlea channel device that may improve hearing to some 358 2. Appearance of the IAC degree. Patients with congenital cochlear deformity are increasingly benefiting significantly from the procedure.358–360 There are several reports of successful implantation in patients with severe inner ear malformations, including common cavity deformity and incomplete partition types I and II.361 Preoperative imaging in individuals with diffuse inner ear malformation must focus on the potential for communication between the CSF and the cochlea, which may result in a perilymph gusher following insertion of the electrode. Specifically, the images must evaluate the anatomy of the fundus of the IAC and the base of the cochlea. Preoperative study should also focus on anatomic variants such as the persistent stapedial artery.362 Fig. 5.132 The multichannel cochlear implant. Note the electrode The number of contraindications to CI is diminishing array within the cochlea. rapidly as the technology and surgical skill increase. The ch05.qxd 9/23/08 11:57 AM Page 398

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A B Fig. 5.133 Labyrinthitis ossificans: The role of MR prior to cochlear im- within the cochlea on the right than the left, which suggested that the plantation. Coronal CISS was obtained through the (A) right and (B) left left cochlea had more advanced disease. Based on this study, the right cochlea in a patient who was scheduled to undergo a cochlear implanta- ear was implanted, as it appeared to have less involvement and may per- tion for hearing loss due to fibroosseous obliteration resulting from form better after implantation. meningitis. The coronal images showed higher fluid signal (arrows)

lone complete contraindication is an absent cochlear depends upon the development of the vestibulocochlear nerve, which may be congenital or acquired (Fig. 5.134). nerve.355,358 As such, congenital vestibulocochlear nerve This is discussed in detail in Chapter 8. Suffice it to deficiency is consistently associated with a hypoplastic say that IAC hypoplasia raises the suspicion of congenital IAC containing only the facial nerve. Cochlear nerve absence of the cochlear nerve as the caliber of the IAC absence can be confirmed with oblique sagittal T2WI. The

A B Fig. 5.134 Cochlear hypoplasia with stenotic cochlear neural aperture. image reveals a stenotic cochlear neural aperture (black arrow). Note (A) Coronal computed tomography (CT) image reveals an asymmetrically the normal left side (black arrowhead). Note that the cochlea on this side narrow right internal auditory canal (outlined white arrow). (B) Axial CT is smaller than that on the left. ch05.qxd 9/23/08 11:57 AM Page 399

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Fig. 5.134 (Continued) (C) Sagittal T2-weighted magnetic resonance (T2WI) fast spin ech (FSE) image confirms a vacant anteroinferior internal auditory canal (IAC) quadrant (outlined white arrow), inferior image. F, facial nerve in anterosuperior quadrant. V, vestibular nerves (posterior quadrants); A, normal cochlear nerve in anteroinferior quadrant on opposite side. (D) Axial T2W FSE image confirms absent cochlear nerve within C IAC on right (white outlined arrow).

size of the IAC and development of the cochlear nerve are highly variable in congenital inner ear deformities. MRI is also quite valuable in the preoperative appraisal of these patients.363 Stenosis or complete occlusion of the cochlear nerve aperture at the fundus of the IAC is highly corre- lated with cochlear nerve deficiency, and this region must be carefully analyzed in all preoperative patients.364,365 Recent authors have suggested that under appropriate circumstances cochlear implantation may be successful in type IIb cochlear nerve dysplasia (morphologically normal labyrinth).366 The caliber of the IAC is variable in acquired cochlear nerve deficiency. Individuals with a small IAC may have normal cochlear nerves, and others with morphologically normal IAC may have hypoplastic or even an absent nerve. Again, MRI is quite useful in this regard. The cochlear–carotid interval refers to the thickness of bone between the petrous ICA and the basilar turn of the cochlea (Fig. 5.135). This thickness is widely variable and may be zero. In such cases, there is a genuine risk of damaging the ICA during the CI procedure.104 Bilateral acoustic neuromas and severe disruptive fractures of the cochlea are additional presumptive relative contraindications to implantation, as are active cochlear otosclerosis (otospongiosis) and uncontrolled middle ear Fig. 5.135 Absent cochlear-carotid interval. Coronal computed to- infection. Individuals with longstanding chronic otitis mography image reveals an absent cortex over the superior surface of media pose problems for the surgeon, and staged proce- the vertical portion of the carotid canal (arrow), resulting in direct apposition with the membranous labyrinth of the second cochlear turn. dures may be needed. Importantly, these patients should This resulted in sensorineural hearing deficit and represents a major be followed regularly with CT postimplantation due to the hazard of cochlear implant surgery. (Case courtesy of Deb Shatzkes, increased potential for infection.367,368 Many successful CI MD. Used with permission) ch05.qxd 9/23/08 11:57 AM Page 400

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procedures have been performed in individuals with se- been advanced to provide an assessment of the precise in- vere cochlear otospongiotic change.325 tracochlear position of the electrode array.371,372 This method allows for a 3D view of the device, which is not possible with conventional x-ray. The precise location of each elec- Postoperative Evaluation trode contact can be assessed in this manner (Fig. 5.136 and Plain film (x-ray) provides an excellent overview and as- Fig. 5.137). The osseous spiral lamina separating the scala sessment of insertion depth of the device.352 A modified vestibuli from the scala tympani is consistently visualized. Stenver’s view has been suggested for this purpose.352,369 As indicated above, successful CI requires that the elec- Intraoperative plain film monitoring has been reported to trodes be restricted to the scala tympani, and CT is useful be helpful as well.370 In difficult cases, postoperative CT has in this regard. CT was of significant value in a recent case in

A B

C D Fig. 5.136 Cochlear implantation for retrofenestral otosclerosis. (A,B) implantation. This was performed in a patient with hearing loss due to Axial and (C,D) coronal computed tomography images show the retrofenestral otosclerosis. expected appearance of the course of the electrode following cochlear ch05.qxd 9/23/08 11:57 AM Page 401

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Fig. 5.137 Cochlear implant, computed tomography (CT) appearance. (A) Axial CT image. (B) Stenver’s projection CT image. (C) Axial CT image through the cochlear apex. Examination reveals entry of an electrode array at the level of the round window (outlined arrow, A,B). The device extends to the level of the middle turn (white arrows, B,C) but not as far as the apical turn (black arrow, C). (Courtesy of C. Douglas Phillips, MD.)

B C

which the device (after successful introduction into the unexplained middle ear effusions may be helpful when scala tympani via cochlostomy at the round window) un- postoperative symptoms are consistent with this disorder. fortunately pierced the basilar membrane and entered the The presence of a functioning CI is a contraindication scala vestibuli, the vestibule, and, subsequently, the SSCC.373 to MRI examination. This is unfortunate, as many of these The patient was scanned because of unremitting dizziness patients may develop conditions for which MRI may be a and poor hearing response. Postoperative perilymphatic useful diagnostic procedure. Recently, investigators have fistula has also been reported.374 As indicated elsewhere in been experimenting with the use of nonferromagnetic this chapter, a search for intralabyrinthine air bubbles or circuitry.375

References 1. Bergeron RT. In: Bergeron RT, Som PM, eds. Temporal Head and Neck Imaging. Chicago: Mosby Yearbook; Bone Embryology and Anatomy. Head and Neck Imag- 1996: 1300–1318 ing. 2nd ed. St. Louis: Mosby-Yearbook; 1992:111–136 3. Schuknecht HF, Gulya AJ. Anatomy of the Temporal Bone 2. Curtin HD, Som PM, Bergeron RT. Temporal bone em- with Surgical Implications. Philadelphia: Lea and bryology and anatomy. In: Som PM, Curtin HD, eds. Febiger; 1986 ch05.qxd 9/23/08 11:57 AM Page 402

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Goh JP, Chan LL, Tan TY. MRI of cochlear otosclerosis. Br 312. Fayad J, Moloy P, Linthicum FH. Cochlear otosclerosis: J Radiol 2002;75(894):502–505 does bone formation affect cochlear implant surgery? 331. Stimmer H, Arnold W, Schwaiger M, Laubenbacher C. Am J Otol 1990;11:196–200 Magnetic resonance imaging and high-resolution com- 313. Xenellis JE, Linthicum FH Jr. Malleus head fixation with puted tomography in the otospongiotic phase of oto- stapedial otosclerosis. Otol Neurotol 2007;28:431–432 sclerosis. ORL J Otorhinolaryngol Relat Spec 2002;64(6): 314. Riehm SA, Veillon FV, Abu-Eid M, Enachescu B, Moser T, 451–453 Chassapi P. CT imaging in the House syndrome. Paper 332. Toung JS, Zwolan T, Spooner TR, Telian SA. Late failure of presented at: the 88th Scientific Assembly and Annual cochlear implantation resulting from advanced cochlear Meeting of the Radiological Society of North America; otosclerosis: surgical and programming challenges. Otol November 30–December 4, 2002; Chicago, IL Neurotol 2004;25(5):723–726 315. Mafee MF, Henrikson GC, Deitch RL, et al. Use of CT in 333. Ruckenstein MJ, Rafter KO, Montes M, Bigelow DC. Man- stapedial otosclerosis. Radiology 1985;156:709–714 agement of far advanced otosclerosis in the era of 316. Mafee MF, Valvassori GE, Deitch RL, et al. Use of CT in the cochlear implantation. Otol Neurotol 2001;22(4):471–474 evaluation of cochlear otosclerosis. Radiology 1985;156: 334. Alkadhi H, Rissmann D, Kollias SS. Osteogenesis imper- 703–714 fecta of the temporal bone: CT and MR imaging in Van 317. Sade J, Shatz A, Kremer S, Levit I. Mastoid pneumatiza- der Hoeve-de Kleyn syndrome. AJNR Am J Neuroradiol tion in otosclerosis. Ann Otol Rhinol Laryngol 1989;98: 2004;25(6):1106–1109 451–454 335. Marion MS, Hinojosa R. Osteogenesis imperfecta. Am J 318. Naumann IC, Porcellini B, Fisch U. Otosclerosis: inci- Otolaryngol 1993;14:137–138 dence of positive findings on high resolution computed 336. Tabor EK, Curtin HD, Hirsch BE, May M. Osteogenesis tomography and their correlation to audiological test imperfecta tarda: appearance of the temporal bones at data. Ann Otol Rhinol Laryngol 2005;114(9):709–716 CT. Radiology 1990;175:181–184 319. Veillon F, Riehm S, Emachescu B, et al. Imaging of the 337. Shapiro JR, Pikus A, Weiss G, Rowe DW. Hearing and windows of the temporal bone. Semin Ultrasound CT middle ear function in osteogenesis imperfecta. JAMA MR 2001;22(3):271–280 1982;247:2120–2126 320. Chole RA. Differential osteoclast activation in endo- 338. Heimert TL, Lin DD, Yousem DM. Case 48: osteogenesis chondral and intramembranous bone. Ann Otol Rhinol imperfecta of the temporal bone. Radiology 2002; Laryngol 1993;102:616–619 224(1):166–170 ch05.qxd 9/23/08 11:57 AM Page 411

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339. Ziyeh S, Berger R, Reisner K. MRI-visible pericochlear le- 358. Jackler RK, Luxford WM, Schindler RA, McKerrow WS. sions in osteogenesis imperfecta type I. Eur Radiol Cochlear pathway problems in cochlear implantation. 2000;10(10):1675–1677 Laryngoscope 1987;97:801–805 340. Ross UH, Laszig R, Bornemann H, Ulrich C. Clinical symp- 359. Tucci DL, Telian SA, Zimmerman-Philips S, et al. Cochlear toms and update findings in computed tomography and implantation in patients with cochlear malformation. tympano-cochlear scintigraphy. Acta Otolaryngol 1993; Arch Otolaryngol Head Neck Surg 1995;121:833–838 113:620–624 360. Sennaroglu L, Sarac S, Ergin T. Surgical results of cochlear 341. Armstrong BW. Stapes surgery in patients with osteoge- implantation in malformed cochlea. Otol Neurotol nesis imperfecta. Ann Otol Rhinol Laryngol 1984;93: 2006;27(5):615–623 634–636 361. Miyamoto RT, McConkey AJ, Myres WA, et al. Cochlear 342. Garretsen TJ, Cremers WR. Ear surgery in osteogenesis implantation in the Mondini inner ear malformation. imperfecta. Arch Otolaryngol Head Neck Surg 1990; Am J Otol 1986;7:258–261 116:317–320 362. Wardrop P, Kerr AI, Moussa SA. Persistent stapedial ar- 343. Hamed A, Linthicum FH. Intralabyrinthine schwan- tery preventing successful cochlear implantation: a case noma. Otol Neurotol 2005;26:1085–1086 report. Ann Otol Rhinol Laryngol Suppl 1995;166: 344. Balkany TJ, Dreisbach JN, Seibert CE. Radiographic imag- 443–445 ing of the cochlear implant candidate: preliminary re- 363. Fatterpekar GM, Mukherji SK, Alley J, Lin Y, Castillo M. sults. Otolaryngol Head Neck Surg 1986;95:592–597 Hypoplasia of the bony canal for the cochlear nerve in 345. Balkany T, Hodges AV, Goodman KW. Ethics of cochlear patients with congenital sensorineural hearing loss: ini- implantation in young children. Otolaryngol Head Neck tial observations. Radiology 2000;215(1):243–246 Surg 1996;114(6):748–755 364. Parry DA, Booth T, Roland PS. Advantages of magnetic 346. Facer GW, Peterson A, Brey RH, et al. The Mayo Clinic ex- resonance imaging over computed tomography in pre- perience with the cochlear implant. Ear Nose Throat J operative evaluation of pediatric cochlear implant can- 1994;73(3):149–155 didates. Otol Neurotol 2005;26(5):976–982 347. Facer GW, Peterson A, Brey RH, et al. The Mayo Clinic ex- 365. Glastonbury CM, Davidson HC, Harnsberger HR, Butler J, perience with the cochlear implant. Ear Nose Throat J Kertesz TR, Shelton C. Imaging findings of cochlear 1994;73(3):149–155 nerve deficiency. AJNR Am J Neuroradiol 2002;23(4): 348. Niparko J. Cochlear implants, auditory brainstem im- 635–643 plants, and surgically-implantable hearing aids. In:Cum- 366. Zanetti D, Guida M, Barezzani MG, et al. Favorable out- mings CW, Fredickson JM, Harker LA, Krause CJ, Schuller come of cochlear implant in VIIIth nerve deficiency. DE, eds. Otolaryngology Head and Neck Surgery, 3rd ed. Otol Neurotol 2006;27(6):815–823 St. Louis, MO: Mosby: 2934–2962 367. Gray RF, Irving RM. Cochlear implants in chronic suppu- 349. Seidman DA, Chute PM, Parisier S. Temporal bone imaging rative otitis media. Am J Otol 1995;16:682–686 for cochlear implantation. Laryngoscope 1994;104: 368. Ruckenstein MJ, Rafter KO, Montes M, Bigelow DC. Man- 562–565 agement of far advanced otosclerosis in the era of 350. Seldon HL, Kawano A, Clark GM. Is age at cochlear im- cochlear implantation. Otol Neurotol 2001;22(4):471–474 plantation in children important? A 2-deoxyglucose 369. Marsh MA, Xu J, Blamey PJ, et al. Radiologic evaluation study in cats. Adv Otorhinolaryngol 1997;52:30–32 of multichannel intracochlear implant insertion depth. 351. Lo WW. Imaging of cochlear and auditory brain stem im- Am J Otol 1993;14:386–391 plantation. AJNR Am J Neuroradiol 1998;19(6):1147–1154 370. Ito J. Considerations of cochlear implant surgery. Clin 352. Shpizner BA, Holliday RA, Roland JT, et al. Postoperative Otolaryngol 1993;18:108–111 imaging of the multichannel cochlear implant. AJNR Am 371. Aschendorff A, Kubalek R, Hochmuth A, et al. Imaging J Neuroradiol 1995;16:1517–1524 procedures in cochlear implant patients–evaluation of 353. Lane JI, Driscoll CL, Witte RJ, Primak A, Lindell EP. different radiological techniques. Acta Otolaryngol Scalar localization of the electrode array after cochlear Suppl 2004;552:46–49 implantation: a cadaveric validation study comparing 372. Verbist BM, Frijns JH, Geleijns J, van Buchem MA. Multi- 64-slice multidetector computed tomography with section CT as a valuable tool in the postoperative assess- microcomputed tomography. Otol Neurotol 2007;28(2): ment of cochlear implant patients. AJNR Am J Neurora- 191–194 diol 2005;26(2):424–429 354. Witte RJ, Lane JI, Driscoll CL, et al. Pediatric and adult cochlear 373. Mecca MA, Wagle W, Lupinetti A, Parnes S. Complica- implantation. Radiographics 2003;23(5):1185–1200 tion of cochlear implantation surgery. AJNR Am J Neuro- 355. Silberman B, Garabedian EN, Denogelle F, et al. Role of radiol 2003;24(10):2089–2091 modern imaging technology in the implementation of 374. Kusuma S, Liou S, Haynes DS. Disequilibrium after pediatric cochlear implants. Ann Otol Rhinol Laryngol cochlear implantation caused by a perilymph fistula. 1995; 104:42–46 Laryngoscope 2005;115(1):25–26 356. Arriaga MA, Carrier D. MRI and clinical decisions in 375. Heller JW, Brackmann DE, Tucci DL, et al. Evaluation of cochlear implantation. Am J Otol 1996;17:547–553 MRI compatibility of the modified nucleus multichannel 357. Phelps PD. Cochlear implants for congenital deformities. auditory brainstem and cochlea implants. Am J Otol J Laryngol Otol 1992;106:967–970 1996;17:724–729 ch06 9/19/08 2:00 PM Page 412

Temporal Bone Trauma 6 Edwin Y. Wang, Deborah Shatzkes, and Joel D. Swartz

The skull has been biomechanically adapted to resist fissure is best noted on axial imaging (Fig. 6.1B), originat- extreme amounts of force relative to the appendicular ing from the petrous apex anteriorly and medially and skeleton,1 and the temporal bone is not an exception, with bounded posterolaterally by the jugular foramen. It con- estimates of 1875 pounds of lateral impact required to tains cartilaginous material as well as the inferior petrosal generate a fracture within cadaveric temporal bone.2 sinus, along its course from the cavernous sinus to the Nonetheless, temporal bone injury, predominantly in the pars nervosa of the jugular foramen. More anteriorly are form of fractures, occurs with some frequency, estimated the shorter sphenopetrosal fissures, seen along the floor of at 10 to 22% of closed head injuries.3,4 In a recent review the middle cranial fossa between the posterior edge of the of 820 fractures,5 the most common cause of temporal greater wing of the sphenoid bone and the petrous apex; bone fractures was automobile accidents, followed by as- these are also called the angular or petrosphenoidal fis- sault, falls, and motorcycle accidents. Men were involved sures and are best visualized in patients with a nonpneu- in 76% of cases. In the pediatric population, motor vehicle matized sphenoid (Fig. 6.1C). The occipitomastoid sutures accidents and falls were the most common causes of tem- (Fig. 6.1B and Fig. 6.1G) can be seen at the posterior mar- poral bone fractures.6 Complications of temporal bone gin of the mastoid process, and can be quite asymmetric injury include hearing loss, facial nerve palsy, and vertigo. and irregular in appearance. Additional clefts can be seen Additional complications are related to the adjacent at this region due to mastoid emissary veins. intracranial compartment and include cerebrospinal fluid Recall that the temporal bone is made up of five por- (CSF) leak, meningitis, and contusion.7 This chapter is tions (see Chapter 3). Intrinsic fissures, formed at sites of organized into a discussion of normal anatomy and pseu- apposition of these various portions of the temporal bone, dofractures, temporal bone fractures, and complications include the petrosquamosal fissure, petrotympanic fis- of temporal bone injury. sure, tympanosquamous fissure, and tympanomastoid fissure. The petrosquamosal fissure varies in prominence but can sometimes be seen as a tiny defect within the Normal Anatomy and Temporal tegmen tympani on coronal images, or as a small oblique Bone Pseudofractures cleft extending anteromedially from the glenoid fossa toward the greater wing of sphenoid, seen on axial images The complex temporal bone anatomy and its relationship of the skull base (Fig. 6.1C). Körner’s septum represents a with adjacent bones of the skull create several normal lin- continuation of this fissure (Fig. 6.1D); this is seen along ear structures on cross-sectional imaging that can mimic lateral margins of the mastoid antrum, with a thicker temporal bone fractures, referred to as pseudofractures.8 The continuation of this septum variably seen extending infe- interpreting radiologist should have a good working knowl- riorly into the mastoid process (Fig. 6.1E). The petrotym- edge of the normal appearance of these structures, which panic (glaserian) fissure is poorly visualized on routine have previously been classified into extrinsic fissures and axial and coronal images due to its obliquity, but it can be sutures, intrinsic fissures, and intrinsic channels. seen on sagittal images (Fig. 3.9B), its contents including Extrinsic fissures and sutures separate the temporal bone the chorda tympani nerve and the anterior tympanic ar- from adjacent bones and can often be differentiated tery, a branch of the internal maxillary artery supplying from fractures by their irregular course and the presence of the middle ear. The tympanosquamosal and tympa- sclerotic, corticated margins; these structures include the nomastoid fissures are best seen within the anterosupe- temporoparietal suture, the petrooccipital fissure, the rior and posterosuperior walls of the external auditory sphenopetrosal fissure, and the occipitomastoid suture. canal, respectively, potentially mimicking EAC fracture The temporoparietal suture is best visualized on axial com- (Fig. 6.1B, Fig. 6.1F, and Fig. 6.1G). Medially, the tympa- puted tomography (CT) images as a cleft in anteroposterior nosquamosal fissure divides into the petrotympanic and (AP) orientation along the squamosal portions of the tem- petrosquamosal fissure. poral bone, with some overlap of the superior margin of Intrinsic channels, which can mimic temporal bone the squamosal portion of bone (Fig. 6.1A). The petrooccipital fractures, include the petromastoid canal, singular canal,

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B A

D C

E F Fig. 6.1 Pseudofractures. (A) Axial computed tomography (CT) image. men spinosum (arrowhead) and the carotid canal (cc). (D) Axial CT image. The temporoparietal suture is seen paralleling the outer table of the calvar- Körner’s septum (arrows) is seen along the lateral margins of the mastoid ium (arrows). (B) Axial CT image. The petrooccipital fissure (long arrows), antrum, representing a plane of fusion between the petrous and squa- occipitomastoid suture (dashed arrows), and tympanosquamous fissure mous portions of the temporal bone. (E) Axial CT image. A continuation of (arrowheads) are depicted. (C) Axial CT image. At the basal skull, anterior this septum (white arrows) along the plane of the petrosquamosal fissure is portions of the petrosquamosal fissure (white arrows) can be seen extend- seen extending inferiorly into the mastoid process, thicker than that seen ing anteromedially from the glenoid fossa. The sphenopetrosal fissure in Fig. 6.1D. (F) Coronal CT image. The tympanosquamous fissure is seen (thin black arrows) is seen between petrous bone and the posterior margin paralleling the external auditory canal at its superior aspect. of the greater wing of the sphenoid. Also noted on this image are the fora- (Continued on page 414) ch06 9/19/08 2:00 PM Page 414

414 Imaging of the Temporal Bone

G H

I J

K L Fig. 6.1 (Continued) (G) Axial CT image demonstrates the tympanomas- terior ampullary nerve to the posterior semicircular canal. (L) Mastoid toid fissure (arrowhead) and the occipitomastoid fissure (arrows). (H,I) canaliculus. Coronal CT images (different patients) demonstrate a chan- Petromastoid canal. Axial CT images demonstrate curvilinear course of nel extending inferolaterally from the jugular foramen to the mastoid the petromastoid canal (arrows) containing the subarcuate artery (J,K) segment of the facial nerve canal. This canaliculus (arrow) contains the Singular canal. (J) Axial and (K) coronal CT images. Narrow channel pos- nerve of Arnold (branch of vagus nerve). teroinferior (arrows) to the internal auditory canal transmitting the pos- ch06 9/19/08 2:00 PM Page 415

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M N

O P Fig. 6.1 (Continued) (M) Inferior tympanic canaliculus (Jacobson). Coro- internal auditory canal on axial images and which widens on its course nal CT image. Channel (arrows) through which the nerve of Jacobson to its medial external orifice. (P) Glossopharyngeal sulcus (*). Axial CT (branch of glossopharyngeal nerve) extends from the jugular foramen image reveals entry point for glossopharyngeal nerve and passage to to the hypotympanum. (N,O) Cochlear aqueduct. (N) Coronal and jugular foramen (pars nervosa). Site is too inferior for cochlear aque- (O) axial CT images demonstrate a channel (arrow) that parallels the duct, which should always be seen at level of basilar cochlear turn. ch06 9/19/08 2:00 PM Page 416

416 Imaging of the Temporal Bone

mastoid canaliculus, and inferior tympanic canaliculus, types.14–19 Given this orientation, axial images are helpful in as well as vestibular and cochlear aqueducts, the latter delineating the course of these fractures because of their described in Chapter 5 (Fig. 6.1N and Fig. 6.1O). excellent depiction of the long axis of petrous bone. The in- The petromastoid canal (PMC), averaging 1 mm in di- trinsic strength of the temporal bone is such that fractures ameter and 6 mm in length (Fig. 6.1H and Fig. 6.1I), is a traversing it will commonly extend between sites of least remnant of the subarcuate fossa, a large structure within resistance, typically intrinsic foramina and cavities. the fetus that extends from the vestigial mastoid to the Recently, with the adoption of high-resolution com- posterior fossa.9 Within the first 5 years of life, it narrows puted tomography (HRCT) as a routine imaging tool in to form its distinctive anteriorly convex curvilinear course temporal bone trauma, it has become apparent that many on axial images just beneath the superior semicircular fractures have features of both longitudinal and transcanal (SSCC).10 It is a useful surgical landmark, lined by verse types and may be classified as complex or mixed dura and containing the subarcuate artery and vein. The (Fig. 6.2).20–24 PMC is a potential source of dural tear, CSF leak, and subsequent meningitis, as it is a site of communication between the mastoid antrum and the intracranial cavity.1,11,12 Longitudinal Fractures The singular canal is visualized on axial and coronal CT images (Fig. 6.1J and Fig. 6.1K). It transmits the posterior Longitudinal fractures are those oriented parallel to the ampullary nerve to the posterior semicircular canal long axis of petrous bone. These are noted in multiple (PSCC), taking a posterolateral course from the internal series to represent the majority of temporal bone frac- auditory canal (IAC). It is a fairly narrow structure, 0.5 tures, constituting 70 to 90%. Fractures typically result mm in diameter and 2.5 to 4.0 mm in length.13 from a lateral blow to the temporoparietal region and are The inferior tympanic canaliculus (ITC) (Fig. 6.1M) is commonly associated with fractures of the squamosal best identified on coronal images obliquely coursing be- portion of the temporal bone (Fig. 6.3, Fig. 6.4, Fig. 6.5, tween the hypotympanum and jugular foramen contain- and Fig. 6.6).18,20,25 Subtypes of the longitudinal fracture ing the inferior tympanic branch of the glossopharyngeal include anterior and posterior varieties, in reference to nerve (nerve of Jacobson, CN IX). The aberrant internal the lateral origin of the fracture line.26 Posterior longitudi- carotid artery enters the tympanic cavity via the ITC (see nal fractures arise in the mastoid process or posterior Chapter 4). squamosa, extending anteromedially toward the foramen The mastoid canaliculus (Fig. 6.1L) courses mediolat- lacerum, and commonly involving the ossicular chain and erally between the jugular foramen and the descending first genu of the facial nerve. Anterior (oblique) longitudi- facial nerve canal, and as such can be seen on axial or nal fractures arise from the anterior squamosa and extend coronal CT imaging. Transmitted through this channel medially toward the petrous apex, spanning the tegmen is the nerve of Arnold, a vagus nerve branch providing tympani and facial nerve canal anterior genu, often in- sensation to a portion of the external auditory canal and volving the glenoid fossa of the temporomandibular joint middle ear. (Fig. 6.7).26,27 This subtype of fracture can be complicated The vestibular and cochlear aqueducts are considered by epidural hematoma resulting from middle meningeal in detail in Chapter 5 and will not be discussed in detail artery disruption. here. They could be confused with fractures by the novice Longitudinal fractures typically spare the otic capsule, observer. with the natural path of least resistance extending The glossopharyngeal sulcus is consistently seen anteromedially to the petrous apex.28 Fracture lines can inferior to the cochlear aqueduct on axial CT images extend to the carotid canal with subsequent vascular injury (Fig. 6.1P) and contains the glossopharyngeal nerve as it (Fig. 6.8; see subsection Brain and Vascular Injury below). passes from the medulla to the pars nervosa of the Longitudinal fractures can also extend to involve the con- jugular foramen. tralateral temporal bone across the sphenoid.17,29 Sudden momentary displacement of the petrous apex can result from disruption of the sphenopetrosal junction Temporal Bone Fractures (petrooccipital synchondrosis),28 an occurrence more common in children due to increased flexibility of the os- Traditional Classification seous structures and the unfused status of the synchondrosis. When this displacement is anterior, carotid artery The traditional classification of temporal bone fractures tears and traumatic arteriovenous fistulas are potential was organized with reference to the orientation of the frac- complications; brainstem and cerebellar contusions are ture line relative to the long axis of the petrous bone, with more common in the setting of posterior displacement.28 fractures divided into longitudinal and transverse Magnetic resonance venography (MRV) is recommended ch06 9/19/08 2:00 PM Page 417

Chapter 6 Temporal Bone Trauma 417

A B

Fig. 6.2 Mixed temporal bone fracture. (A) Axial computed tomography (CT) image demonstrates transverse fracture line extending to involve the basal turn of the cochlea (double arrows). Hemotympanum is present. Addi- tional longitudinal fracture component is noted (short arrow). (B) Axial CT image, more superior. The longitudinal fracture is better visualized. Note the singular canal, which mimics a fracture in this case (long arrow). (C) Axial CT image, more superior. Transverse fracture line (long arrows) crosses C the internal auditory canal.

in cases of associated sigmoid sinus plate violation, as this however, associated with immediate conductive hearing can herald direct venous injury. loss (CHL), due to ossicular disruption, as well as ab- A rare variant of the longitudinal fracture is known as ducens and facial nerve palsies. The sixth nerve palsy is the floating cochlea, separation of the petrous apex from due to rotation of the petrous apex with resultant com- its lateral and inferior attachments.30 In this setting, the pression of Dorello’s canal. Again, this type of fracture is middle ear is a plane of the cleavage, separating the most likely to result in the pediatric population due to in- petrous apex from mastoid portions of the temporal bone. creased flexibility of the skull. As the fracture lines run lateral to the otic capsule, the Longitudinal fractures extending through the tympanic labyrinth is preserved, and complete sensorineural hear- annulus are usually associated with tympanic membrane ing loss (SNHL) does not typically occur. This injury is, injury and hemotympanum, resulting in CHL.15,25 Ossicular ch06 9/19/08 2:00 PM Page 418

418 Imaging of the Temporal Bone

A B

C D Fig. 6.3 Longitudinal fracture and cerebrospinal fluid (CSF) otorrhea. ent patient, sagittal reconstruction. Longitudinal fracture line (arrows). (A) Axial computed tomography (CT) section. Anterior subtype fracture Ossicles appear spared, and there is complete opacification of the entire line is actually oblique rather than truly longitudinal. (B,C) Correspond- middle ear and mastoid and profuse CSF otorrhea. Note the fracture line ing coronal CT images. Fracture through the scutum (arrow). (D) Differ- extending to the tegmen (arrowhead).

injury is suspected if CHL does not improve following CT has become essential in diagnosing longitudinal healing of the tympanic membrane and resolution of fractures.20–22,35 Magentic resonance imaging (MRI) may hemotympanum (see subsection Hearing Loss below). demonstrate hemorrhagic products or fluid,7 but less com- Individuals with longitudinal fractures are also at in- monly identifies longitudinal fracture lines, with sensitiv- creased risk of developing acquired cholesteatoma in the ity 66% in one series.36 Dural enhancement at the rostral delayed setting (Fig. 6.9), resulting from ingress of squa- aspect of the injured temporal bone was identified in 68% mous epithelial debris into the middle ear through the of patients in the same series, regardless of whether or not fracture defect, as endochondral bone is limited in its a fracture line was visible; although histologic correlation ability to form callus.16,31–34 These cholesteatomas can be was not described, it was postulated that this may be due aggressive and difficult to manage surgically. to dural microtear or temporal bone microfracture.36 SNHL ch06 9/19/08 2:00 PM Page 419

Chapter 6 Temporal Bone Trauma 419

E F Fig. 6.3 (Continued) (E) Artist’s rendering of conventional longitudinal fracture line. (F) Additional patient, axial CT image, posterior subtype longitudinal fracture line (arrows).

resulting from longitudinal fracture is most often related from 2.5 to 5.6%.5,37 This may reflect both a decrease in the to labyrinthine concussion as direct labyrinthine involve- severity in the injuries currently reported and an increase in ment by longitudinal fractures is rare.14,15,18 the detection of less severe fractures, which tend to be longitudinal in nature. Transverse fractures run perpendicular to the long axis of petrous bone, typically resulting from Transverse Fractures frontal or occipital impact. These fractures extend from the Transverse fractures are significantly less common than jugular foramen and foramen magnum to the middle cra- their longitudinal counterpart. Historically, reported fre- nial fossa, commonly passing through the vestibular aque- 15,16,27,38–40 quency is 20%, but more recent studies suggest a range duct (Fig. 6.6, Fig. 6.10, Fig. 6.11, and Fig, 6.12).

A B Fig. 6.4 Longitudinal fracture, malleoincudal disruption, facial weak- orientation toward the fossa incudis. Medial to the malleus head there is ness. (A) Axial computed tomography (CT) image. Longitudinal fracture some abnormal soft tissue presumably representing hematoma in (small black arrows). There is a partial subluxation of the malleoincudal direct apposition to the first genu of the facial nerve canal. Some debris articulation (arrow) with counterclockwise rotation of the incus body. is inside mastoid air cells. (B) Axial CT, more inferior. Intact stapes super- The short process is rotated toward the fracture line rather than its normal structure (arrow). This is important in operative planning. ch06 9/19/08 2:00 PM Page 420

420 Imaging of the Temporal Bone

A B Fig. 6.5 Longitudinal fracture, carotid canal and eustachian canal in- within the external auditory canal, which appears mildly narrowed. volvement. (A) Axial computed tomography (CT) demonstrates longi- There is comminuted fracture involving the anterior tympanic cavity tudinal fracture line (short arrows) extending through mastoid air cells wall, bony eustachian tube, and carotid canal (triple arrows). It is uncer- into the tympanic cavity. Associated fracture of the squamous temporal tain to what extent the abnormal opacification is postobstructive in bone is noted (long arrow). Diffuse tympanomastoid air cell opacifica- nature. Fracture (arrowhead) also extends into the middle cranial fossa tion is present. (B) Axial CT, more inferior level. Fracture involves the from the lateral aspect. external auditory canal (long arrow) with linear fracture fragments

A B Fig. 6.6 Complex fracture, ossicular disruption, tegmen defect. (more inferior). Complete incus dislocation (black arrow). Oval win- (A) Axial computed tomography (CT) image, complete incus disloca- dow disruption (thin black arrow). Stapes malrotation (white arrow). tion (black arrow). Tegmen defect (white arrow). (B) Axial image ch06 9/19/08 2:00 PM Page 421

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C Fig. 6.6 (Continued) (C) Coronal CT image. Tegmen defect (white Fig. 6.7 Oblique fracture. Fracture line (arrows) is seen to extend arrow). Fractured scutum (black arrow). Due to tegmen defect, mag- through the glenoid fossa of the temporomandibular joint. Mastoid air netic resonance imaging was strongly recommended to evaluate for cell opacification is noted. encephalocele. Expansile nature of some of the middle ear debris is reminiscent of posttraumatic cholesteatoma. Patient refused surgery and further evaluation.

Medial and lateral subtypes have been described, with capsule result in greater risk for CSF fistula formation and lateral transverse fractures involving the otic capsule and facial nerve injury, as well as the development of SNHL. In often resulting in complete sensorineural hearing loss. the series of 820 patients reported by Brodie et al, only Lateral transverse fractures can also be associated with 2.5% of fractures violated the otic capsule.5 These patients stapes footplate injury, which may result in SNHL second- also have an increased incidence of intracranial complica- ary to perilymphatic fistula formation. Medial transverse tions, including intracranial hemorrhage.37 fractures typically cross the IAC at the fundus. In this Yanagihara et al45 analyzed 97 fractures and have group of fractures, SNHL is variable, but can be complete devised another system of classification in an attempt to with direct cochlear nerve injury or transection.26,41 A predict specific portions of the facial nerve at risk and case of fatal exsanguination from medial transverse frac- surgical intervention required. Type 1 fractures travel ture involving the carotid canal has been reported.42 across the mastoid process, mainly involving the mastoid segment of the facial nerve. Type 2 fractures extend Classifications across the mastoid process to the external auditory canal, typically involving the nerve at the tympanic or mastoid In 1992, Ghorayeb et al43 reviewed cases of HRCT with segment. In type 3 fractures, the fracture line extends three-dimensional reconstruction and described in detail across the mastoid cortex and external auditory canal to the oblique fracture classification. Typical longitudinal the tympanic portion of the facial nerve. These are often fractures travel vertically within the petrotympanic fissure; associated with ossicular injury. Type 4 fractures travel oblique fractures were seen to cross the petrotympanic fis- across the tegmen tympani and antrum, involving the sure in a more horizontal plane, extending superiorly to in- geniculate ganglion. This is subdivided into type 4A volve the middle cranial fossa. The clinical features of these (without involvement of the inner ear and IAC) and 4B oblique fractures are similar to those seen in longitudinal fractures. The latter fractures involve the labyrinthine fractures. and tympanic segments and can be complicated by loss of Some authors have argued for the adoption of an alter- lacrimation due to injury to the greater superficial pet- nate classification scheme into fractures involving the otic rosal nerve. These patients are also prone to CSF otorrhea. capsule and those sparing the otic capsule.44 Multiple It should be noted that these classification systems are studies have confirmed that fractures involving the otic not mutually exclusive, each addressing separate key ch06 9/19/08 2:00 PM Page 422

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Fig. 6.8 Fracture of the anterior portion of the tympanic cavity and carotid canal. (A) Axial computed tomography (CT) image at level of malleoincudal articulation. Disruption of the anterior wall of the epitympanum (open arrowhead). There is a pneumocephalus (double solid arrows). There is patchy debris presumably present and a hematotympanum through the attic and antrum. (B) Axial CT image, more inferior. There is bony disruption of the posterolateral wall of the horizontal segment of the canal (arrow). Note the tiny focus of air within the carotid canal, which is very abnormal. There is also a fracture of the external auditory canal with debris through this structure. (C) Three-dimensional phase contrast magnetic resonance angiography sequence. Pathological narrowing of the horizontal portion of the carotid canal (arrow) is evident. This could represent a dissection, but more likely it represents extrinsic narrowing secondary to C the presence of extramural edema and hemorrhage.

features of temporal bone fractures that need to be con- described in chin-dashboard trauma, typically in the setting sidered in radiologic interpretations of temporal bone im- of motor vehicle accidents. This results from impaction of aging studies, including morphology (longitudinal versus the mandibular condyle against the anterior tympanic transverse), labyrinthine involvement (otic capsule spar- spine, the inferior boundary of the petrotympanic fissure. ing versus otic capsule violating), and site of potential facial nerve injury (Yanahigara classification). An additional fracture involving the temporal bone is Pathologic Conditions Associated with the fracture of the styloid process (including fracture of Temporal Bone Trauma 46,47 ossified stylohyoid ligament). This typically presents Facial Nerve Injury with upper cervical pain, although temporal headache and temporomandibular joint complaints are also reported. Posttraumatic facial nerve injury is the second most Fractures of the tympanic ring and temporomandibular prevalent cause of facial nerve dysfunction following joint can result from direct impact to the mandible Bell’s palsy.15,16,48–54 In the setting of paresis or paralysis, ch06 9/19/08 2:00 PM Page 423

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A B Fig. 6.9 Complex fracture, ossicular dislocation, Oval window disrup- penetrated the oval window and resides in the vestibule (arrow). tion, posttraumatic cholesteatoma. (A) Axial CT image through the (B) Coronal CT image. Dislocated incus (arrow) has penetrated the tym- epitympanum. Ossicular chain is “exploded” (thick arrow). There is a panic membrane and resides in the external auditory canal. nondependent expansile soft tissue mass. A bony fragment (ossicle) has

lesions of the facial nerve can be localized by evaluation hematoma, complete transection (neurotmesis), exposure of adjunctive symptoms related to its branches, such as and compression (neuropraxia), and stretching and crush- taste, stapedius function, and lacrimation (see Chapter 7). ing injuries (axontomesis) (Fig. 6.6, Fig. 6.13, Fig. 6.14).55 Injury to the facial nerve can result from intraneuronal Transection of the nerve is associated with immediate

A B Fig. 6.10 Transverse fracture, medial subtype. (A) Axial computed to- nerve canal (f, arrow). There is air in the internal auditory canal and at mography (CT) section at the level of the right internal auditory canal. the petrous apex (outlined arrows). Fluid (*) is identified in the mastoid Fracture line is demonstrated extending from the level of the vestibular antrum. (B) Axial CT section, more inferior. Pneumovestibule (arrow). aqueduct (v, arrow) to the level of the labyrinthine segment of the facial ch06 9/19/08 2:00 PM Page 424

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A B

C D Fig. 6.11 Transverse fracture, medial subtype. (A,B) Axial and (C) coro- first genu of the facial nerve (anteriormost arrows A, B). The fracture also nal computed tomography (CT) images. Transverse fracture (arrows) is extends through the basilar turn of the cochlea (lower arrow, C). Note identified from the posterior surface of the petrous pyramid through that the middle ear and mastoid, including in the ossicular chain, is entirely the fundus of the internal auditory canal, extending to the level of the spared. (D) Artist rendering. ch06 9/19/08 2:00 PM Page 425

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A B Fig. 6.12 Complex fracture. (A) Axial computed tomography (CT) image tympanomastoid cavities is present. Fractures of the petrous apex (long demonstrates disruption of the mastoid portion of the right temporal arrow) is noted. Hemotympanum is present. (B) Axial CT image, same bone with significant lateral displacement of fracture fragment posteri- patient. Transverse fracture line (arrow) is seen to extend through the orly (arrow). Communication between the intracranial compartment and round window.

A B Fig. 6.13 Transverse fracture, mixed medial and lateral subtype. (A,B) the petrous pyramid through the fundus of the internal auditory canal Axial computed tomography (CT) images, more superior. Transverse to the level of the first genu of the facial nerve (anteriormost arrows). fracture (arrows) is indicated extending from the posterior surface of (Continued on page 426) ch06 9/19/08 2:00 PM Page 426

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C D Fig. 6.13 (Continued) (C,D) Axial CT images, more inferior. Fracture line lateral subtype component, axial CT image. There is air within the is clearly demonstrated extending through the vestibule. Fracture line vestibule, and there are countless fluid levels within the middle ear and also extends through the promontory (large solitary arrow). (D) Classic mastoid. This strongly suggests the presence of perilymphatic fistula.

and complete facial nerve paralysis. Facial nerve palsy palsy, resulting from increased utilization of seatbelts and was noted to occur in 20% of longitudinal fractures and airbag technologies, decreasing the severity of motor ve- 50% of transverse fractures.48,56 More recent data hicle trauma.57 Increased detection of less severe fractures demonstrate a lower rate of posttraumatic facial nerve by HRCT, which would have normally remained clinically

A B Fig. 6.14 Incus dislocation, facial palsy. (A) Axial computed tomography tympanic segment of the facial nerve (arrow). (B) Coronal CT image (CT) image. Subluxation and extreme clockwise rotation of the incus (image reversed). Incus compresses the proximal tympanic segment body with the short process lying in direct apposition to the proximal (arrow). ch06 9/19/08 2:00 PM Page 427

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occult, may also contribute to this apparent decrease. In In a review of 24 patients with posttraumatic facial Brodie’s series, 7% of fractures resulted in facial nerve nerve palsy,36 postcontrast MRI demonstrated that in the palsy, with approximately one quarter of these being majority of patients abnormal enhancement was seen at immediate in onset.5 In a pediatric series,6 the incidence the distal intracanalicular segment of the nerve, even of facial nerve paralysis was only 3%; this difference may when imaging was performed up to 2 years after the ini- relate to decreased ossification and increased flexibility in tial injury. This is likely secondary to disruption of the the pediatric skull.58,59 blood–nerve barrier. The majority of cases also demon- Multiplanar reconstruction along the course of the fa- strated enhancement involving the labyrinthine segment cial nerve canal may be helpful in more directly depicting and geniculate ganglion. However, no correlation was the relationship of temporal bone fractures and the facial noted between the degree of abnormal nerve enhance- nerve canal.60,61 ment and electroneuronography. Associated hematoma In longitudinal fractures, facial nerve lesions were can be seen on noncontrast T1-weighted MRIs in some seen most commonly at the geniculate ganglion (64%), patients. greater superficial petrosal nerve (25%), mastoid segment (7%), and labyrinthine segment (4%). In these Hearing Loss injuries, onset of symptoms tends to be delayed.15,18 In transverse fractures, locations of facial nerve lesions in- Sensorineural, conductive, or mixed hearing loss may all clude the IAC (10%), labyrinthine segment (80%), and occur in the setting of temporal bone trauma. Complaints geniculate ganglion (10%).50 Injury can also occur along of hearing loss were present in 24% of patients in Brodie’s the tympanic segment due to compressive forces from series,5 with 91 of 699 patients demonstrating hearing loss hemotympanum, with spontaneous resolution common documented by audiometry. In patients with documented in this setting. The labyrinthine segment is the narrow- hearing loss, 21% was conductive, 57% was sensorineural, and est and is the most vulnerable to injury50; at this site, 22% were of a mixed nature. movement within the immobile sheath can result in Sensorineural hearing loss may occur due to injury in- rupture of the vessels supplying the nerve, with result- volving the IAC, labyrinth, or brainstem at the level of the ant edema and hemorrhage.62 The edematous nerve can cochlear nuclei.16,18,38,65–68 Hearing loss may be permanent, then be compressed at the meatal foramen, the junction with multiple authors noting improvement over time.59 of the intracanalicular segment and the bony labyrinthine Imaging findings are often negative unless intra- segment. labyrinthine hemorrhage is present. One histopathologic Management of facial nerve palsy in the setting of review of a case of transverse temporal bone fracture temporal bone fractures is controversial, with many (over demonstrated destruction of the stria vascularis and 4000) articles on this topic published over the last 30 years.44 organ of Corti with inner ear hemorrhage, and subsequent Surgery is often performed in patients with immediate fa- labyrinthitis ossificans.69 Experimental studies demon- cial nerve paralysis and 90% degeneration by elec- strate the survival of only one third of the ganglion cells troneuronography within 6 days of the onset of palsy.53,63 following temporal bone fractures resulting in SNHL.70 Complete transection is often treated with reanastomosis Injury to the brainstem at the cochlear nuclei in the upper or sural autograft, with early grafting resulting in some medulla can also result in SNHL, as can shear injury at the improvement in outcome.64 Some investigators feel that nerve root entry zone. Traumatic injury to the inferior decompression is most effective in the 72-hour setting, colliculi can occur, related to impaction of the midbrain given the effects of wallerian degeneration in the distal against the tentorium.71 segment on the ability of the nerve to transmit impulses.15,49 SNHL that is delayed or fluctuating with persistent ver- In the setting of additional concomitant traumatic injury, tigo may relate to perilymphatic fistula (PLF) formation. this time frame may be difficult to achieve. In the experi- Perilymphatic fistulae are abnormal communications be- ence of Quaranta et al,63 decompression was beneficial tween the perilymphatic space of the inner ear and the air when performed within 14 days, although delayed de- space of the middle ear. Retrospective analyses demon- compression was still helpful in patients with 95% strate that 25 to 36% of cases of perilymphatic fistulae are degeneration on electroneurography, even up to 1 to 3 caused by trauma,72,73 often minor; in one series of 102 months after injury. Surgical approach is often transmas- patients, 33% of cases resulted from minor whiplash toid, with a supralabyrinthine approach allowing wide injury.74 Posttraumatic PLF occurs secondary to sudden surgical exposure of the geniculate ganglion region.45 increases in pressure, relating to tympanic membrane A middle cranial fossa approach may be needed in cases trauma (implosive) or transmission of CSF pressure to the of lesions in close proximity to the IAC, whereas a perilymph (explosive).73,75 The most common cause of translabyrinthine approach is typically used when pro- PLF is blunt trauma,76 though PLF may result from baro- found hearing loss is present.46 trauma or iatrogenic injury. Additional causes of PLF are ch06 9/19/08 2:00 PM Page 428

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displacement of a previously implanted stapedial pros- the malleus and the long process of the incus. The ossicles thesis and even “spontaneous” fistula between the middle are poorly adapted to resist fracture.1 Auditory mechani- and inner ear in the absence of trauma77,78 PLF can result cal advantage is increased by the ossicles being as stiff as in SNHL or CHL.79,80 In an experimental animal model, possible with minimal mass. This is achieved by a higher sensorineural hearing loss was induced with injection of degree of mineralization, which increases stiffness more air bubbles into the labyrinth, with disturbed propagation than density.91 As a result of this increased stiffness, the of the basilar membrane traveling wave, potentially con- ossicles are fairly weak and brittle.92 Although there are tributing to hearing loss in certain posttraumatic cases.81 many types of possible ossicular injuries, the incidence of In cases of posttraumatic PLF, the abnormal communi- ossicular injury is greatly decreased by the protection cation between the inner ear and middle ear allowing afforded by the overlying skull.80,93 perilymphatic leakage results from labyrinthine fracture, Meriot et al report an incidence of 32% of ossicular round window injury, or oval window injury.73 Imaging injury in the setting of 513 cases of temporal bone trauma, findings include pneumolabyrinth and unexplained mid- with fractures accounting for 96% of cases.93 In this group, dle ear effusion. Pneumolabyrinth is easily diagnosed on the most common injuries noted were incudostapedial CT,82–84 though it is uncommon even in fractures travers- joint (ISJ) separation, incudomallear joint separation, in- ing the otic capsule.77,82,83 When a fracture is not seen, cudal dislocation, and dislocation of the malleoincudal pneumolabyrinth implies disruption of the oval or round complex. Additional injuries, including stapedial, incudal, window and the presence of a PLF (Fig. 6.13 and Fig. 6.15). and mallear fractures, were noted less than 5% of the In the absence of fracture, middle ear or mastoid fluid may time, as was stapediovestibular dislocation. The incus is also be secondary to PLF, presumably reflecting exit of the ossicle most vulnerable to traumatic injury, given its perilymph into the middle ear78; this fluid may appear weaker ligamentous support in comparison to the the contained within a partly intact oval or round window malleus and stapes, and also due to its weight (25 g), pro- membrane. In general, though, these findings are uncom- viding it with relatively increased inertia.14,22,80,89,94 mon, and PLF remains difficult to diagnose on imaging Mallear ligaments (anterior, lateral, and superior), the studies. Treatment options consist of surgical exploration tympanic membrane, and tensor tympani tendon provide with closure of fistula (in patients with progressive or support to the malleus, whereas the stapes is supported fluctuating SNHL or persistent vertigo) and observation. by the annular ligament and stapedius tendon. Cochlear implantation has been successfully used ISJ subluxation is reported as the most common ossic- following bilateral injury with profound SNHL, or unilat- ular injury derangement (Fig. 6.16, Fig. 6.17, Fig. 6.18, and eral injury in the setting of prior contralateral hearing Fig. 6.19).80,94 This is at least in part due to the fact that loss. Six of seven patients with posttraumatic hearing loss the joint is a fragile enarthrosis and lies between two axes derived significant benefit from cochlear implantation in of rotation. It is suggested that dislocation results from one series.85 The authors of this study noted the useful- tetanic contraction of the tensor tympani and stapedius, ness of MRI in determining patency of the cochlea, given with sudden retraction of the incus medially and of the the frequency of labyrinthitis ossificans and the extent to stapes posteriorly.24 The ISJ is well seen on overlapping which it was often underestimated by CT imaging. axial imaging, with visualization improved in the aerated Posttraumatic conductive hearing loss is typically im- tympanic cavity.66,89,95 This injury is best noted as widen- mediate in onset and multifactorial in origin.14,16,19,24,68,86 ing and/or distraction of the joint on axial imaging. It can Causes of conductive hearing loss include tympanic ring also be detected as abnormal angulation of the incus injury, tympanic membrane injury, and hemotympa- lenticular process, a finding better noted in comparison to num.14,15,18,75 Hearing loss due to hemotympanum is typically a normal contralateral ossicular chain, if present. temporary, resolving following resolution of hemorrhage. In contrast, the malleoincudal articulation is somewhat The persistence of CHL following resolution of tympanic more stable, with relative protection in the epitympanic membrane injury and hemotympanum suggests ossicular recess, and firm ligamentous and muscular attachments to injury.22,38,39,41,87 Exploration is recommended following a the malleus. This injury is identified as derangement of the period of observation for spontaneous resolution (6 “ice cream cone” appearance on axial CT images, with rela- weeks). Exploration is not typically performed in the set- tive displacement well detailed on coronal imaging.93 ting of severe contralateral hearing loss,88 due to the risk Comparison with the contralateral ossicular chain is also of jeopardizing hearing in the only serviceable ear. helpful in making this diagnosis (Fig. 6.20 and Fig. 6.21). Ossicular injuries can be seen in the presence or ab- On sagittal imaging this joint, when intact, produces a sence of associated temporal bone fracture. Review of “molar tooth” appearance, with “roots” represented by the axial images allows for evaluation of the malleoincudal malleus handle and incus long process. This configuration and incudostapedial joints, as well as the stapedial super- was used in analysis to a greater degree prior to the advent structure.24,67,89,90 Coronal images aid in visualization of of CT, when tomography was more commonly used. ch06 9/19/08 2:00 PM Page 429

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C D Fig. 6.15 Pneumocephalus, pneumolabyrinth, hemorrhagic right tem- (C) Axial T2-weighted magnetic resonance imaging (MRI). There is an poral contusion. (A) Axial computed tomography (CT) section. There is edematous lesion in the right temporal lobe. Foci of deoxyhemoglobin a pneumocephalus and evidence of a hemorrhagic right temporal lobe are appreciated within (small arrows). (D) Coronal T1-weighted MRI. lesion. (B) Axial CT section (at level of internal auditory canal). There is a Bright signal within the right temporal lesion (arrows) represents extra- pneumolabyrinth (outlined arrow). Note debris in the mastoid. At sur- cellular methemoglobin in this subacute hemorrhage. There is a small gery, there was free communication between vestibule and the middle subdural collection (curved arrow). There is a hemorrhagic component ear via the ruptured oval window membrane (perilymphatic fistula). within the middle ear cavity proper as well (outlined arrows). ch06 9/19/08 2:00 PM Page 430

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Fig. 6.16 Incudostapedial joint disruption. (A) Axial computed tomography (CT) image. Pathologic orientation of the lenticular process of the incus (lateral arrow) relative to the capitulum (head) of the stapes (more medial arrow). (B,C) Different patient. (B) Axial image. The stapes is intact (white arrow). The incus is displaced laterally (larger arrow). The status of the lateralmost aspect of the carotid canal (CC) is unclear. (C) Coronal image confirms posttraumatic debris. A

B C

Complete incudal dislocation results from separation breach the tympanic membrane into the EAC and on of the incus from the malleoincudal and incu- occasion is completely absent.24,80,89 Knowledge of prior dostapedial attachments and is the second most ossiculoplasty with incus interposition graft is impor- common form of ossicular injury found on surgical ex- tant to avoid misdiagnosing a normal graft as incudal ploration (Fig. 6.22, Fig. 6.23, and Fig. 6.24).14,19,80,89,94,96 dislocation. Incudal dislocation has also been noted in As the displacement is often rotatory in nature, both patients with fenestral otosclerosis in the setting of axial and coronal images are helpful.93 Contraction of recurrent disease and prior prosthetic stapedectomy, the stapedius and tensor tympani musculature also due to torsional effects. In the setting of lateral subluxa- likely contributes to the mechanism of this injury. The tion, a Y configuration of the incus can be seen on coro- position of the dislocated incus is highly variable; it can nal images, with the short arm of the Y representing the be rotated, lodged in a fracture, or displaced into the subluxed incus and the longer arm representing the tympanic cavity proper. The dislocated incus may malleus (Fig. 6.22).97 ch06 9/19/08 2:00 PM Page 431

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A B Fig. 6.17 Incudostapedial joint disruption. (A) Axial computed tomography (CT) image reveals separation between the incus and stapes (arrows). (B) Coronal CT image (motion degraded) confirms findings (arrows). Identification of this type of deformity is most unusual in the coronal plane.

Dislocation of the malleoincudal complex can occur, These injuries are often difficult to identify on imaging, and with the complex inferiorly displaced from its position in stapediovestibular disarticulations can be present in the the epitympanum.93 Stapediovestibular dislocation is rare setting of a normal appearing CT examination. but can be caused by penetrating injury, tearing of the an- Although disarticulation and dislocation involving the nular ligament, or comminuted fracture of the oval window.93 incus are some of the most common posttraumatic ossicular

Fig. 6.18 Incudostapedial joint disruption. Axial computed tomogra- Fig. 6.19 Incudostapedial joint disruption. Axial computed tomography (CT) image, left ear. There is pathologic orientation of the more phy (CT) image reveals abnormal separation (arrows) between the lateral lenticular process of the incus with the more medial capitulum more lateral incus lenticular process and the more medial stapes of the stapes (arrows). superstructure. ch06 9/19/08 2:00 PM Page 432

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injuries, intrinsic incus fractures are in fact quite rare. In the series described by Meriot,96 these occurred in 6 of 166 cases of ossicular injury and most commonly involved the long process. Incus fractures can be seen in the setting of longitudinal fracture or isolated ossicular injury. Stapedial arch fractures typically result from torsional injury,68,80 with more frequent involvement of the posterior crus,29 possibly related to the attachment of the stapedius muscle (Fig. 6.25 and Fig. 6.26). Although footplate injuries may be seen in the setting of transverse fractures traversing the oval window,93 such injuries are often occult, even on HRCT. The stapedial footplate can be imploded into the vestibule, sometimes related to penetrating injury (e.g., “Q-Tip” injury).98 Footplate injury can be seen in the setting of barotrauma or acoustic trauma as well.1,80,99,100 As noted previously, stapedial footplate injury can result in PLF formation. CT imaging may not be definitive in the setting of stapedial arch fracture, but axial images should demonstrate the presence of the anterior and posterior crura in most patients.66,90,101 The absence of visualization of these structures is a highly Fig. 6.20 Malleoincudal joint disruption. Axial computed tomography (CT) image. Pathological widening (arrows) of the malleoincudal artic- suggestive finding of fracture or dislocation in the proper ulation reflecting a partial subluxation in this patient with a mild post- clinical context. traumatic conductive hearing loss. Malleus fractures/dislocations are uncommon, with fewer than 50 reported cases in the literature.102 Dislocation of the malleus is heralded by the missing ice cream from

A B Fig. 6.21 Remote fracture, labyrinthitis ossificans, malleoincudal disartic- patible with labyrinthitis ossificans. (B) Axial CT image, more superior. ulation. (A) Axial computed tomography (CT) image demonstrates a well- Previously noted fracture line (arrow) is seen to extend from the fundus visualized transversely oriented fracture line (double arrows) extending of the internal auditory canal, through the vestibule (*), and into the through the basal turn of the cochlea. Abnormal ill-defined high tympanic segment of the facial nerve canal. Abnormal widening of the attenuation present within more lateral aspects of the basal turn are com- malleoincudal joint space (white arrow) is seen at the epitympanum. ch06 9/19/08 2:00 PM Page 433

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Vertigo Vertigo is the illusion of linear or angular movement; in the setting of trauma, damage to the utricle, semicircular ducts, or vestibular nuclei in the brainstem is implied. Some potential etiologies for posttraumatic vertigo are shear injury to the vestibular nerves at the root entry zone, hemorrhage at the vestibular nuclei,73 and injury through the vestibular aqueduct and endolymphatic sac, the latter typically resulting from a transverse fracture. Other possible causes of vertigo in the absence of imaging findings are canalithiasis, cupulolithiasis, and labyrinthine concussion.18,79,105 Canalithiasis is defined as free-floating debris within the endolymph of SCCs, which causes inappropriate stimulation of nerve receptors during positional changes due to disruption of endolymph flow. Cupulolithiasis refers to debris from detached otoconia. The latter are biomineral particles embedded in a membrane overlying the sensory epithelium of the saccule and utricle, which help to activate sensory hair cells of the vestibule during motion. This debris attaches to the cupula of the PSCC, a gelatinous structure into which cilia C of the sensory hair cells project. This attachment makes it Fig. 6.21 (Continued) (C) Coronal CT image confirms separation of the malleus (arrowhead) and incus (white arrow) within the epitympanum. harder for the cupula to remain in a neutral position, resulting in inappropriate activation of hair cells and a sen- the “ice cream cone” on axial images. The dislocated ossicle sation of motion, with associated positional vertigo. This is usually visualized within the middle ear cavity (Fig. 6.27 entity is described earlier in this chapter. Labyrinthine and Fig. 6.28). Fractures of the malleus may also involve concussion is believed to result from biochemical changes, the neck or manubrium. Other malleus injuries are diffi- vasomotor alteration, or transmission of a traumatic pres- cult to categorize.93,103,104 sure wave from bone to the labyrinth, potentially resulting

A B Fig. 6.22 Incus subluxation (Y, deformity). (A) Axial computed tomography (CT) image. (B) Coronal CT image. (M, malleus; I, incus). The incus is dislocated anteriorly and laterally from its normal position. Note the Y shape on the coronal image. ch06 9/19/08 2:00 PM Page 434

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A B Fig. 6.23 Longitudinal fracture, incus dislocation. (A) Axial computed the interval between it and the stapes capitulum (white arrowhead). tomography (CT) image demonstrates longitudinally oriented fracture (B) Axial CT image, more superior. The body and short process of the line (black arrows). The lenticular process of the incus (white arrow) is lat- incus (white arrow) have been rotated counter clockwise, with the body erally deviated within the tympanic cavity, with abnormal widening of of the incus lodged within the fracture line defect.

in stimulation of the sensory epithelium and/or hemor- that displaced epithelial or cellular debris may decrease rhage.16,23,73 endolymph absorption.108 Shea described three mecha- Often, posttraumatic vertigo is self-limited, auditory nisms potentially causing posttraumatic hydrops: fis- and vestibular symptoms resolving over a period of days tulization of the bony labyrinth causing a disturbance in to weeks.15 Prolonged symptoms may result from damage pressure between the endolymphatic and perilymphatic to the sensory epithelium, development of endolymphatic compartments, injury to the membranous labyrinth, and hydrops, or hemorrhage with development of labyrinthitis injury to the endolymphatic drainage system (as in a frac- ossificans (see Chapter 5). MRI may be helpful in diagnos- ture involving the vestibular aqueduct).109 This represents ing intralabyrinthine hemorrhage, as methemoglobin in a distinct pathology from the perilymphatic fistula, al- the subacute setting will produce hyperintense signal on though the symptoms may be quite similar. Symptoms of noncontrast T1-weighted MRI silhouetted against the nor- posttraumatic endolymphatic hydrops are typically de- mal hypointensity of the temporal bone and associated air layed in onset (months to years), as opposed to PLF, in spaces. Patients with persistent vertiginous symptoms which symptoms develop soon after injury.110 Exploratory may require treatment in the form of deafferentation or surgery is recommended in posttraumatic patients with labyrinthine ablation.7, 73 ,10 6 persistent SNHL, persistent vestibular symptoms, or evi- PLF should be considered in the setting of vertigo asso- dence of oval window pathology on imaging.111 ciated with SNHL. Symptoms of PLF include fluctuating or stable SNHL, vertigo, tinnitus, and headache; this entity is Cerebrospinal Fluid Leak and Meningitis discussed in detail in the previous subsection Hearing Loss. Conditions with similar presentation include CSF fistula formation can occur following temporal bone Meniere’s disease (endolymphatic hydrops) and labyrinthine fractures, as seen in 122 of 820 patients in Brodie’s se- concussion. Healy107 noted endolymphatic hydrops as a ries. Nine of these patients developed meningitis.5 CSF cause of posttraumatic vestibular dysfunction, with hem- otorrhea can be delayed or immediate in onset and is orrhage in the membranous labyrinth leading to eventual typically due to tegmen tympani disruption,112 most distention of the endolymphatic system. Others suggest often in the setting of longitudinal fracture (Fig. 6.6). ch06 9/19/08 2:00 PM Page 435

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A B

Fig. 6.24 Incus dislocation. (A) Axial computed tomography (CT) image demonstrates the mastoid fracture line and abnormal appearance of the ossicles with dislocated and clockwise rotated incus (white arrow) and medially displaced malleus head. (B) Axial CT image, more inferior. There is evidence of rotatory displacement of the incus, with the short process (short white arrow) and the long process (long arrow) seen on the same axial image. This likely results in the medial displacement of the malleus. Note the normal cochlear aqueduct (pseudofracture) (black arrowhead). (C) Coronal CT image confirms rotational displacement of the incus into the axial plane (curved arrow), with additional high attenuation foci suggest- C ing fracture fragments. There is flattening of the normal “right angle.”

Another potential site of communication is between the fistula formation,24 with improved accuracy in the set- mastoid air cells and/or external canal and the intracra- ting of newer multidetector CT technology. In the setting nial compartment; individuals with highly pneumatized of an intact tympanic membrane, CSF rhinorrhea may re- mastoids are at increased risk. Infants and small chil- sult from CSF drainage via the eustachian tube.16 Other dren are at relatively decreased risk due to flexibility of modalities of evaluation for CSF leak are CT or radionu- the skull and immature mastoid air cell development.59 clide cisternography, and MRI with flow-sensitive tech- Fluid opacification of the tympanomastoid cavities on niques.113 In a review of the topic, it was found that CT imaging is generally nonspecific, with greater fluid HRCT was statistically most likely to identify a source of characterization possible with MRI. Multiplanar refor- a leak, although a multimodality approach was still rec- matted imaging may be helpful in identifying a site of ommended.114 In the majority of cases CSF fistulas close ch06 9/19/08 2:00 PM Page 436

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A B Fig. 6.25 Foreign body, stapes implosion. (A) Axial computed tomography (CT) image at the level of the oval window. Abnormal density (arrow) within the oval window niche represents foreign body. (B) Axial CT image, more superior. Fragments of the stapes (long arrows) are identified within the vestibule.

spontaneously with conservative management. Surgical closure of a leak is recommended when it persists for greater than 7 to 10 days, resulting in an increased risk of infection.5 Meningitis may be first detected months or even years following temporal bone fracture and is typically seen in the setting of persistent CSF leak.15 Pneumocephalus on imaging implies a direct communication between the intracranial compartment and the tympanomastoid cavity. Current imaging techniques are relatively insensitive for the evaluation of meningitis. MRI, including postcontrast sequences and fluid attenuated inversion recovery (FLAIR) imaging, provide the greatest sensitivity.115 Histopathologic study has demonstrated the potential of microbes to extend from the middle ear to the meninges through fibrous tissue in a clinically healed but unossified fracture.116 Endochondral bone of the otic capsule does not heal by callus formation in the setting of fracture; fractures persist as fibrous tissue, potentially reflecting the maturity of endochondral bone at birth and the absence of remodeling later in life.117 Risk factors for menin- Fig. 6.26 Stapes implosion. Axial computed tomography (CT) section, gitis in Brodie’s series included CSF fistulas persistent for left ear. A pristine stapes has dislocated into the vestibule, leaving over 7 days and the presence of concurrent infection. A patient at risk for perilymphatic fistula. (Courtesy of F. Veillon.) meningocele or meningoencephalocele can also result as ch06 9/19/08 2:00 PM Page 437

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A B Fig. 6.27 Malleus fracture. (A) Axial image reveals that the malleus is absent from its usual location in the attic (arrow). (B) More inferior axial image reveals a dislocated fragment (arrow).

A B Fig. 6.28 Malleus fracture. (A) Axial computed tomography (CT) image reveals that the malleus head is absent (arrow) (the “ice cream” has fallen off the “cone!”). (B) Axial CT image, more inferior. The malleus is visualized (arrow) (motion degradation). ch06 9/19/08 2:00 PM Page 438

438 Imaging of the Temporal Bone

A B

Fig. 6.29 Longitudinal fracture, meningoencephalocele. (A) Axial computed tomography (CT) image. Longitudinal fracture line (arrows) is seen extending through the anterior mastoid air cells and anterior tympanic cavity. (B) Coronal CT image demonstrates a large defect of tegmen tympani with soft tissue versus fluid attenuation material (thick white arrow) prolapsing through this defect with associated depression of the ossicular chain (long white arrow). (C) Coronal CT imaging with larger field of view demonstrates this prolapsed material (large white arrow) to be contiguous with the inferior right temporal lobe, compatible with meningoencephalocele. Hypodensity at the left inferior temporal lobe (*) is C compatible with gliosis and encephalomalacic change from prior contusion.

a delayed complication, which can be evaluated with CT or epidural) or brain contusion.7,10 6 Small amounts of or MRI, the latter preferred (Fig. 6.29).118 Surgery is rec- hemorrhage are better depicted on MRI; gradient-echo ommended for leaks that persist 2 weeks and for all imaging is particularly useful because the susceptibility delayed leaks.59 Recurrent meningitis, meningoen- artifact associated with blood products is enhanced on cephalocele formation, and large defects are additional T2-weighted sequences (Fig. 6.8, Fig. 6.29, Fig. 6.30, indications for intervention.3 and Fig. 6.31). The clinical utility of identifying patients with carotid canal fractures is uncertain. It is noted by several authors that those patients with carotid Brain and Vascular Injury canal fractures found to have carotid injury on subse- Temporal bone fractures are associated with intracra- quent vascular imaging on magnetic resonance angiog- nial injuries in 20% of cases.51 Associated brain injury raphy (MRA) had clinical findings of severe epistaxis, is typically well depicted on CT and MRI and may consist transient ischemic attack, or cavernous sinus syndrome. of extracerebral hemorrhage (subarachnoid, subdural, Asymptomatic patients with carotid canal fractures ch06 9/19/08 2:00 PM Page 439

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A B

Fig. 6.30 Hemorrhagic contusion, bilateral fractures. (A) Axial computed tomography (CT) image of the brain demonstrates rounded foci of high attenuation (arrow) at the right temporal lobe with surrounding low attenuation compatible with hemorrhagic contusion. (B) Axial CT image, right ear, demonstrates an oblique fracture line (arrow) extending to the tympanic cavity. Partial opacification compatible with hemotympanum is seen. (C) Axial CT image left ear. Fractures paralleling the external auditory canal are seen (arrows), with small locules of soft tissue gas and tympanomastoid cavity opacification noted. C

had no evidence of vessel injury on further vascular necessary in all cases of temporal bone trauma,121 others imaging.119 ,12 0 suggest it is only necessary in selected cases,5 with significant variation in the practice of level I trauma centers.119 It is reported that HRCT is routinely obtained in the setting Use of High Resolution Computed of temporal bone trauma by approximately two thirds of Tomography practitioners; another third obtains HRCT only in the setting of specified clinical situations.119 Kahn et al119 in a se- As with other aspects in the management of temporal ries of 105 patients with temporal bone trauma found bone trauma, the role of routine temporal bone HRCT is that the greatest utility of HRCT was in the setting of pro- controversial. Although some authors regard HRCT as longed CSF leak or CHL, with symptoms suggesting PLF, ch06 9/19/08 2:00 PM Page 440

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A B

Fig. 6.31 Subdural hematoma, hemorrhagic contusion, longitudinal fracture. (A,B) Axial computed tomography (CT) images of the brain. (A) Dif- fuse convexity, right subdural hematoma, is noted, with associated sulcal effacement and leftward midline shift. (B) Right temporal lobe parenchymal hematoma (double arrow) and subdural hematoma layering over the tentorium are noted (single arrow). (C) Axial CT image, left ear. Longitudi- C nal fracture line is noted (double arrows). Hemotympanum is present.

and in the localization of facial nerve paralysis prior to setting of trauma, 35% of patients with temporal bone planned surgical intervention. In other cases, manage- fractures as detected by CT imaging did not have clinical ment was not changed by HRCT findings. In a series of signs of injury. In this group, 12% of patients with temporal 350 patients undergoing temporal bone scanning in the bone fractures developed complications.4 ch06 9/19/08 2:00 PM Page 441

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References 1. Currey JD. How well are bones designed to resist frac- 23. Johnson DW, Hasso AN, Stewart CE III, Thompson JR, ture? J Bone Miner Res 2003;18:591–598 Hinshaw DB Jr. Temporal bone trauma: high-resolution 2. Travis LW, Stalnaker RL, Melvin JW. Impact trauma of computed tomographic evaluation. Radiology 1984;151: human temporal bone. J Trauma 1977;17:761–766 411–415 3. Nageris B, Hansen MC, Lavelle WG, Van Pelt FA. Tempo- 24. Swartz JD, Swartz NG, Korsvik H, et al. Computerized to- ral bone fractures. Am J Emerg Med 1995;13:211–214 mographic evaluation of the middle ear and mastoid for 4. Exadaktylos AK, Sclabas GM, Nuyens M, et al. The clinical posttraumatic hearing loss. Ann Otol Rhinol Laryngol correlation of temporal bone fractures and spiral computed 1985;94:263–266 tomographic scan: a prospective and consecutive study at a 25. Griffin JE, Altenau MM, Schaefer SD. Bilateral longitudi- level I trauma center. 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Pathology of the temporal computed-tomography (CT) diagnosis of longitudinal bone and mastoid. In: Newton TH, Hasso AN, Dillon WP, fractures of the petrous bone. Neuroradiology 1988; 30: eds. Computed Tomography of the Head and Neck, Neu- 166–168 roradiology. Vol. 3. New York: Raven Press;1988 21. Holland BA, Brant-Zawadzki M. High-resolution CT of 40. Schuknecht HF. Pathology of the Ear. Philadelphia, PA: temporal bone trauma. AJR Am J Roentgenol 1984;143: Lea and Febiger; 1993 391–395 41. Schubiger O, Valavanis A, Stuckmann G, Antonucci F. 22. Jazrawy H, Wortzman G, Kassel EE, Noyek AM. Com- Temporal bone fractures and their complications. Exam- puted tomography of the temporal bone. J Otolaryngol ination with high resolution CT. Neuroradiology 1986; 1983;12:37–44 28:93–99 ch06 9/19/08 2:00 PM Page 442

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42. Pollanen MS, Deck JH, Blenkinsop B, Farkas EM. Fracture 61. Marangos N, Berlis A. High resolution computerized to- of temporal bone with exsanguination: pathology and mography of the petrous bones in a bone algorithm 2D mechanism. Can J Neurol Sci 1992;19:196–200 reconstruction for evaluation of the facial nerve canal. 43. Ghorayeb B. Yeakley JW. Temporal bone fractures: longi- HNO 1995;43:732–736 tudinal or oblique? the case for oblique temporal bone 62. Sekiya T, Iwabuchi T, Okabe S. Occurrence of vestibular fractures. Laryngoscope 1992;102:129–134 and facial nerve injury following cerebellopontine angle 44. Kelly KE, Tami TA. Temporal bone and skull base trauma. operations. Acta Neurochir (Wien) 1990;102:108–113 In: Jackler RK, Brackmann DE, eds. Neurotology. St. Louis: 63. Quaranta A, Campobasso G, Piazza F, Quaranta N, Salonna Mosby;1994:1127–1147 I. Facial nerve paralysis in temporal bone fractures: out- 45. Yanagihara N, Murakami S, Nishihara S. 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Whinney DJD, Parisk AA, Brookes GB. Barotraumatic frac- 120. Resnick DK, Subach BR, Marion DW. The significance of ture of the stapes footplate. Am J Otol 1996;17:697–699 carotid canal involvement in basilar cranial fracture. 100. Patterson JH, Hamernik RP. Blast overpressure induced Neurosurgery 1997;40:1177–1181 structural and functional changes in the auditory sys- 121. Yamaki T, Yoshino E, Higuchi T, Horikawa Y, Hirakawa K. tem. Toxicology 1997;121:29–40 Value of high-resolution computed-tomography in diag- 101. Swartz JD, Lansman AK, Berger AS, et al. Stapes prosthesis: nosis of petrous bone-fracture. Surg Neurol 1986;26: evaluation with CT. Radiology 1986;158:179–182 551–556 ch07 9/19/08 11:54 AM Page 444

Anatomy and Development 7 of the Facial Nerve C. Douglas Phillips, George Hashisaki, and Francis Veillon

The facial nerve is worthy of considerable attention intratemporal, and extracranial. The intratemporal por- because of its very complex derivation, anatomy, and tion constitutes the anatomically most complex portion of pathology. It is composed of special visceral efferent, spe- this course and is the central focus of this chapter. How- cial visceral afferent, and general somatic afferent fibers ever, because the imaging issues of the facial nerve traveling a circuitous course from three central brainstem require familiarity with the entire course of the facial nuclei to terminations in the functional end plates of the nerve, we review the relevant anatomy and pathology of muscles of facial expression; taste buds of the anterior the facial nerve from its brainstem origins to its periph- tongue; lacrimal, nasal seromucus, and minor salivary eral insertions. glands; and ear canal skin (Fig. 7.1). The lengthy course of For background, we will begin with a discussion of the the facial nerve can be divided into three parts: intracranial, embryologic development of the facial nerve and proceed

Fig. 7.1 Main functions of the facial nerve. The solid black line corresponds to the somatic motor output to the facial musculature anteriorly and the occipital muscle posteriorly, exiting through the stylomastoid foramen. The upper hatched lines illustrate the course of the parasympathetic fibers that end in the lacrimal glands (L), as well as the nasal and palatal mucosa via the pterygopalatine ganglion. The inferior hatched lines correspond to the parasympathetic fibers that innervate the submandibular and sublingual glands (SL and SM) via the submandibular ganglion. Taste information is projected via the chorda tympani (CT), represented by the dashed line from the tongue to the facial nerve trunk. 444 ch07 9/19/08 11:54 AM Page 445

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to the normal anatomy of the entire facial nerve, using are distinct (Fig. 7.2). By day 33, the chorda tympani nerve computed tomography (CT) and magnetic resonance enters into the mesenchyme of the first branchial arch, and imaging (MRI) to illustrate. A practical imaging approach the facial motor trunk inclines caudally and ventrally in the to the facial nerve, including imaging techniques and second branchial arch mesenchyme. The greater superficial preimaging topographic localization, is presented. Next, petrosal nerve appears in the 8 to 11 mm fetus (day 37) pathological conditions affecting the facial nerve are and the nervus intermedius is present in the 16 to 18 mm briefly reviewed. Because many of the lesions that cause fetus (day 47.5). The horizontal or tympanic segment of the facial nerve injury are discussed in depth in other chapters facial nerve elongates from day 44 to 47.5, and the motor of this book, only the lesions not covered elsewhere (facial trunk in the vertical segment lengthens with the growing schwannoma, Bell’s palsy, hemifacial spasm, heman- second arch derivatives. With growth of the branchial arch gioma) are covered here. derivatives and the fetal head, the motor trunk elongates in a sinuous extratemporal course (Fig. 7.3). The intramedullary portion of the facial nerve can be Embryology recognized near the end of the fifth week of gestation as a collection of neuroblasts in the metencephalic portion of The embryological derivation of the facial nerve and fallop- the rhombencephalon. The motor nucleus of cranial nerve ian canal involves a complex interaction of the facial nerve, VI (CN VI) lies in close proximity. As the metencephalon otic capsule, and second branchial arch mesenchyme. elongates, the abducens motor nuclei ascend and move Development of the fallopian canal can be divided into dorsally, displacing the facial nerve fibers and creating the three phases—blastemal, cartilaginous, and osseous peri- internal genu of the facial nerve. ods. The intricate path of the facial nerve is largely deter- With development of the otic vesicle into the otic cap- mined during the blastemal phase, days 20 to 48, before sule and labyrinth during weeks 4 to 8, the facial nerve the surrounding otic capsule and mesenchyme embed the medial to the geniculate ganglion becomes distinct from, facial nerve in cartilage and, subsequently, bone.1 The neu- but in close proximity to, the acoustic nerve in the region ral crest cell progenitors of the facial nerve can be identi- of the future internal auditory canal and labyrinthine seg- fied as a facioacoustic primordium in a 3 mm fetus (day 20) ments. The semicircular canals (SCCs) and vestibule develop in the epipharyngeal placode of the second branchial caudal to the geniculate ganglion, placing the labyrinthine arch, adjacent to the otic vesicle and attached to the segment of the facial nerve between the cochlea and the rhombencephalon.2 By day 32, the geniculate ganglion has vestibular organs. During week 8, the rudimentary fallop- developed, and the motor trunk and chorda tympani nerve ian canal begins as a sulcus containing the facial nerve,

Fig. 7.2 Illustration of a 6-week embryo. The cells of the facioacoustic primordium lie in close proximity to the developing otic vesicle. This cell tract extends into the mesenchyme of the second branchial arch. (From Gasser RF, May M. Embryonic development. In: May M, Schaitkin BM, eds. The Facial Nerve. 2nd ed. New York, NY: Thieme Medical Publishing; 2000. Reprinted with permission.) ch07 9/19/08 11:54 AM Page 446

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Fig. 7.3 Illustration of an 8-week embryo. At this stage of development, the facial nerve is distinct from the cochleovestibular nerve. The chorda tympani nerve has exited from the future vertical segment of the facial nerve to enter the first branchial arch mesenchyme and develop connections at the otic ganglion. The greater superficial petrosal nerve extends from the geniculate ganglion to the pterygopalatine ganglion. The main motor trunk of the facial nerve branches within the growing second branchial arch mesenchyme, already demonstrating the turns in three-dimensional space that presage the completely developed facial nerve. (From Gasser RF, May M. Embryonic development. In: May M, Schaitkin BM, eds. The Facial Nerve. 2nd ed. New York, NY: Thieme Medical Publishing; 2000. Reprinted with permission.)

blood vessels, and stapedius muscle, on the posterior as- bulb are somewhat less common. Gaps more anteriorly in pect of the otic capsule.3 The portions of the facial nerve in the tympanic facial nerve canal, near the cochleariform close approximation to the otic capsule become enveloped process, and in the mastoid segment are rare.7 by cartilage and subsequently bone. With formation of the Dehiscent areas along the tympanic aspect of the facial periosteal portions of the temporal bone, the remaining nerve canal may result in inferior protrusion of the tym- intratemporal portions of the facial nerve become encased panic segment through these defects.11 Such a protrusion in bone. The vertical segment of the facial nerve and fallopian may vary from a slight bulge to a complete prolapse of the canal continue to elongate after birth as the mastoid tip nerve, allowing the nerve to abut the stapes superstruc- grows inferiorly. ture. A profound protrusion may result in conductive Because of this complicated derivation, localized areas hearing loss, although this is very uncommon.4 A proof bony dehiscences in the facial canal are common, in as lapsed nerve may conceal all or some of the oval window; many as 55% of temporal bones.4,5 More recent work, uti- preoperative knowledge of this anomaly is of consider- lizing light microscopy rather than visual inspection, able importance, particularly prior to stapes surgery.12 demonstrated focal dehiscence in 74% of specimens.6 The With CT, the appearance of the protruding nerve is that failure of periosteal bone to develop has been suggested of a smooth soft tissue density with inferior convexity to be responsible.4 Arterial and venous structures course emanating from the undersurface of the lateral SCC at the through the facial nerve canal along with the nerve itself; level of the oval window on coronal sections.11,12 The CT one theory is that unusually prominent vascular struc- diagnosis of this entity is only possible in the absence of tures may cause delay in development of the periosteal middle ear debris. If the inferior margin of the nerve is bone with subsequent dehiscences.4,6 An alternative the- not outlined by air because of middle ear inflammatory ory is based on the observation that most of the dehis- debris, it is difficult to distinguish the nerve with CT. cences are in areas where the canal is completed by When such an inferior protrusion is encountered, the sur- Reichert’s cartilage and that discontinuity of the cartilage geon should be cautious of the possibility of dehis- may result in canal wall defects.6 These normal defects cence.11,12 Because the tympanic segment most commonly are small, from 0.4 to 3.0 mm, generally less frequent produces a groove on the undersurface of the lateral SCC in well-pneumatized temporal bones, and often bilateral on coronal CT sections, absence of this groove should be and relatively symmetric.6,7 viewed with suspicion, particularly in those individuals in Gaps in the continuity of the osseous wall may be ob- whom middle ear opacity precludes identification of the served in any segment.4,8–10 Most commonly, dehiscences undersurface of the nerve itself. are located in the tympanic segment superior and posterior Numerous anomalies have been described in the to the oval window, especially along its medial wall. Focal course of the facial nerve canal. Commonly, they are asso- defects in the anterior epitympanic sinus and in the jugular ciated with congenital dysplasias of the temporal bone.13 ch07 9/19/08 11:54 AM Page 447

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Fig. 7.4 Diagrammatic representation of the facial nerve entering the temporal bone. The proximity of the labyrinthine segment of the facial nerve and the geniculate ganglion to the cochlea and semicircular canals may be appreciated. The cochlear nerve enters the cochlea from a position inferior to the intracanalicular portion of the facial nerve. The body of the incus is lateral to the tympanic segment of the facial nerve.

Normal Anatomy motor nucleus (Fig. 7.5 and Fig. 7.6), is a nuclear column in the ventrolateral pontine tegmentum.14–17 This motor The seventh cranial nerve supplies three principal func- nucleus is the origin for efferent motor fibers to the tions. In addition to its motor function, various branches muscles of facial expression and supplies motor fibers serve the sensory functions of transmitting taste from the to the stapedius, stylohyoid, and posterior belly of the anterior two thirds of the tongue and superficial sensa- digastric muscles. Cortical input to the facial nucleus is tion from the cutaneous regions around the auricle of the from the motor face area in the precentral and postcen- ear. Additional branches provide autonomic innervation tral gyri, with connections through the corticobulbar to the lacrimal, sublingual, submandibular, oral cavity tract to the internal capsule, midbrain, and pons. The minor salivary, and nasal seromucus glands (Fig. 7.1). The corticobulbar tract fibers serving the motor area of the facial nerve may be thought of (true enough) as a simple forehead/upper face are bilaterally innervated, whereas neural trunk exiting the pontomedullary junction to the tracts to the remainder of the face are crossed only, course through the temporal bone (Fig. 7.4), in proximity resulting in unilateral innervation. This is the anatomic to the organs of balance and hearing, but this disguises basis for the classical distinction between central facial the true complexity of its origin and destinations. nerve palsy, sparing the forehead, and peripheral facial The facial nerve, the nerve of the second branchial nerve palsy, involving both the upper and lower face. arch, arises from three brainstem nuclei. The largest, or This century-old interpretation of supranuclear innervation

Fig. 7.5 Diagram of the individual nuclei of the facial nerve and their relative positions in the pons. The motor nucleus of the facial nerve (CN VII Motor N) gives rise to fibers that course slightly medially and dorsally to loop around the abducens nucleus, then moves ventrally and laterally toward the root exit. Along the way, the nerve picks up fibers from the superior salivatory nucleus and nucleus solitarius. The fibers from the superior salivatory nucleus and the nucleus solitarius travel distinctly as the nervus intermedius. The facial nerve trunk moves through the cerebellopontine angle cistern to the porus. ch07 9/19/08 11:54 AM Page 448

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Fig. 7.6 Axial T2-weighted magnetic resonance image through the lower pons illustrates the positions of the nuclei and roots of the cisternal portions of the facial nerve. The somatic portion of the facial nerve originates in the motor nucleus in the pontine tegmentum (CN VII - Motor). This nucleus is ventral and slightly lateral to the abducens nucleus (CN VI). The bulges created by the looping motor fibers of CN VII in the floor of the fourth ventricle are the facial colliculi. Again, note the relative positions of the superior salivatory nucleus (CN VII - SSN) and nucleus solitarius (CN VII - NS). In the cerebellopontine angle cistern, and in the IAC, the facial nerve (*) is identified anterior to the vestibulocochlear nerve (**).

has been challenged by more recent data. One study of sensory fibers of proprioception and sensation from the macaque monkeys found scant bilateral direct cortical external auditory canal (Table 7.1).19–21 innervation to the upper facial motor subnucleus, but Within the lower pontine brainstem, the motor fibers robust bilateral cortical innervation to the lower facial of the facial nerve loop dorsally around the abducens motor subnucleus with a contralateral predominance. nerve nucleus (CN VI). The bulge in the floor of the fourth The upper facial motor subnucleus was presumed to ventricle formed by these looping fibers is referred to as receive additional indirect cortical inputs. A central or the facial colliculus (Fig. 7.5).22 These fibers then course supranuclear facial palsy would result in contralateral ventrolaterally to exit the anterolateral pons and enter lower facial muscle weakness because those lower facial motor neurons are much more dependent on direct cortical innervation. The ipsilateral lower facial motor neurons continue to receive their contralateral Table 7.1 Function of Facial Nerves dominant direct cortical innervation, and the upper Facial Nerve Nuclei Function facial motor neurons function from indirect cortical innervation.18 Motor Motor innervation to the muscles of facial expression, stylohyoid, stapedius, posterior The superior salivatory nucleus is located just dorsal to belly of digastric muscles the motor nucleus (Fig. 7.5) and contributes preganglionic parasympathetic secretomotor fibers. These fibers termi- Superior salivatory Preganglionic parasympathetic secretomotor stimulation to the lacrimal (via greater nate in and stimulate the lacrimal gland and nasal sero- superficial petrosal nerve), submandibular, mucus glands via the greater superficial petrosal nerve and sublingual glands (via chorda tympani and the submandibular, sublingual, and oral cavity minor nerve) salivary glands via the chorda tympani nerve. Solitary tract Receives afferent information (nucleus A third nuclear column found in the upper medulla, solitarius) of the special sensory fibers of the solitary tract nucleus (nucleus solitarius) (Fig. 7.5 and taste (via chorda tympani nerve), and Fig. 7.6), receives the afferent information of the special general sensory fibers of proprioception and sensation (external auditory canal) sensory fibers of taste via the chorda tympani, and general ch07 9/19/08 11:54 AM Page 449

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Fig. 7.8 Oblique coronal reconstruction of a three-dimensional T2- weighted sequence through the internal auditory canal (IAC) demon- Fig. 7.7 Axial reconstruction of a three-dimensional T2-weighted se- strates the cisternal segment of the facial nerve (CN VII – CS) directed quence demonstrates the lateral course of the facial nerve (CN VII) slightly superiorly and laterally to the IAC, and running horizontal to through the cerebellopontine angle cistern, and its anterior location the fundus (CN VII – IACS). The facial nerve is immediately superior to with respect to the normal vestibulocochlear nerve (CN VIII). the cochlear division of the vestibulocochlear nerve (CN VIII – Cochlear) in this section. The T2-weighted sequences are particularly useful in patients with capacious cerebrospinal fluid spaces in the IAC. the cerebellopontine angle (CPA) cistern (Fig. 7.7, Fig. 7.8, and Fig. 7.9). The parasympathetic secretomotor fibers from the superior salivatory nucleus (bound for the lacrimal, submandibular, and sublingual glands) combine with the special sensory fibers of the solitary tract nucleus (con- veying taste from the anterior two-thirds of the tongue) to form the nervus intermedius (of Wrisburg) or sensory root. The nervus intermedius fibers may join the motor root of the facial nerve just as they exit the brainstem, or may initially attach to the vestibulocochlear (VIII) nerve, joining the facial nerve near the meatus of the internal auditory canal (IAC).23,24 The two remain as a combined nerve trunk through the IAC to their diverging points within the temporal bone (Fig. 7.5 and Fig. 7.10).20 The facial nerve departs the brainstem at the lower border of the pons at the pontomedullary junction. (Fig. 7.5, Fig. 7.7, Fig. 7.8, and Fig. 7.9) Within the CPA cistern, the facial nerve is the most anterior, the vestibulocochlear nerve most posterior, with the nervus intermedius, as its name suggests, between the two. The facial nerve from the pontomedullary junction to parotid may be described as having six segments: cisternal, intracanalicular (inter- Fig. 7.9 Oblique coronal fast spin echo T1-weighted magnetic reso- nal auditory canal), labyrinthine, tympanic, mastoid, and nance image through the internal auditory canal (IAC) demonstrates extracranial (intraparotid) (Fig. 7.11 and Table 7.2).20,25,26 the cisternal segment of the facial nerve (CN VII – CS) directed laterally to the IAC, and running horizontal to the fundus (CN VII – IACS). The cisternal segment of the facial nerve, the portion of The facial nerve is immediately superior to the cochlear division of the the nerve that stretches across the CPA cistern from the vestibulocochlear nerve (CN VIII – Cochlear) in this section. This image brainstem to its entry into the porus acusticus of the IAC is the corollary of Fig. 7.8. ch07 9/19/08 11:54 AM Page 450

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subdivided into three segments: labyrinthine, tympanic, and mastoid. The anterior (first) genu (Fig. 7.13 and Fig. 7.14) where the geniculate ganglion can be found, separates the labyrinthine segment from the tympanic segment, and the posterior (second) genu separates the tympanic segment from the mastoid segment. The motor component of the facial nerve and its associated nervus intermedius both enter the labyrinthine segment through a narrow aperture at the IAC fundus, the narrowest portion of the fallopian canal.21,30–32 Throughout its course in the fallopian canal, the facial nerve is surrounded by a sheath consisting of periosteum, epineurium, and perineurium.33 The dura may extend as far peripherally as the geniculate ganglion. The labyrinthine segment of the facial nerve, so named because of its intimate relationship to the cochlea and SCCs, courses anterolaterally from the IAC fundus at an angle of 125 degrees relative to the long axis of the IAC.33 This segment of the facial nerve canal is the narrowest Fig. 7.10 Diagrammatic representation of the facial nerve functional dis- ( 0.7 mm) and shortest (3 to 5 mm). It follows a gentle tinction by segment. At the fallopian canal, the facial nerve is comprised and medially concave curve (Fig. 7.13 and Fig. 7.14A), lying of the motor trunk (MT), the parasympathetic secretomotor (PS) fibers, in a sulcus between the cochlear and vestibular labyrinth, and the special sensory (SS) fibers. The parasympathetic and special sen- the intervestibulocochlear groove. The facial nerve is par- sory fibers comprise the nervus intermedius. At the level of the genicu- ticularly vulnerable in this location and is subject to late ganglion (GG), the greater superficial petrosal nerve (GSPN) exits via the facial hiatus. A single motor branch to the stapedius muscle (S) exits compromise or complete transection by temporal bone just distal to the posterior genu. Along the course of the mastoid seg- fractures, particularly those in the transverse plane. Fur- ment, the special sensory fibers and remaining parasympathetic fibers ther, this segment is in close relationship to the vestibule exit as the chorda tympani (CT) to course through the middle ear. and ampulla of the superior SCC and may be compromised during translabyrinthine surgery. The bony margins of this short labyrinthine segment are complex. Medially, the labyrinthine segment is adjacent to the superior portions of the spiral turns of the (Fig. 7.7, Fig. 7.8, and Fig. 7.9), is 24 mm in length. With cochlea. Superiorly, the labyrinthine segment is bordered MRI, it is identified anterior to the vestibulocochlear nerve by the petrous cortex, which may or may not be pneuma- (CN VIII) within the CPA cistern (Fig. 7.6, Fig. 7.7, and tized by supralabyrinthine air cells. Laterally and posteri- Fig. 7.8).20,27,28 The nervus intermedius cannot be separately orly lie the ampullae of the horizontal and superior resolved from the main motor trunk of the facial nerve. SCCs.13,20,31,33 The facial nerve then enters the porus acusticus of the The labyrinthine segment of the facial canal terminates IAC to become the intracanalicular segment, 8 mm in in the geniculate fossa, a bulbous enlargement of the length, following a shallow gutter in the anterosuperior canal containing the geniculate ganglion (Fig. 7.13 and aspect of the IAC. In the lateral aspect of the IAC, a trans- Fig. 7.14A). The ganglion is usually enveloped by bone, but verse bony crest, the crista falciformis, separates the facial in up to 15% of patients it may be incomplete or absent, nerve above from the cochlear nerve below. This superior making it vulnerable during middle cranial fossa sur- compartment is further divided by a vertical crest of vari- gery.33 The geniculate ganglion contains the cell bodies of ably ossified arachnoid tissue (Bill’s bar), which separates the special sensory neurons subserving the taste function the facial nerve from the superior vestibular nerve.29 MR of the anterior two thirds of the tongue. These taste fibers sequences demonstrate the facial nerve and superior ascend to the geniculate ganglion by coursing centrally vestibular nerve in the IAC as discrete structures posi- with the lingual branch of the mandibular division of the tioned superior to the cochlear and inferior vestibular trigeminal nerve,34 then departing the lingual nerve to nerves (Fig. 7.8, Fig. 7.9, and Fig. 7.12). The mnemonic form the chorda tympani nerve as it enters the temporal “seven up, coke down” refers to the relative positions of bone via the canal of Huguier (chordae iter anterius) in these cranial nerves in the IAC. the petrotympanic fissure. At the geniculate fossa, the The facial nerve canal or fallopian canal begins as the facial canal turns posterior and lateral at an angle of facial nerve exits the anterosuperior portion of the IAC 75 degrees or less, referred to as the anterior genu, to fundus. Within the facial nerve canal, the facial nerve is become the tympanic segment (Fig. 7.13 and Fig. 7.14A).11 ch07 9/19/08 11:54 AM Page 451

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Fig. 7.11 Sagittal oblique diagram of the course of the seventh cranial lacrimation, (2) stapedius nerve/stapedial reflex, (3) chorda tympani/ nerve through the temporal bone displays six segments. From proximal anterior two thirds of tongue taste, and (4) terminal branches of the facial to distal: 1, cisternal; 2, intracanalicular; 3, labyrinthine; 4, tympanic; 5, nerve/muscles of facial expression. (From Harnsberger HR: Handbooks mastoid; and 6, extracranial (intraparotid). Four major facial nerve in Radiology, Head and Neck Imaging. St. Louis, MO: Mosby-YearBook branches or functions are numbered (circled) in order as they branch from Medical Publishers;1990: 456, Fig. 17-2B. Reprinted with permission.) the facial nerve. They include (1) greater superficial petrosal nerve/

The first major branch of the facial nerve exits the geniculate fossa anteromedially as the greater superficial petrosal nerve, courses through the facial hiatus, a small groove on the anterior surface of the petrous temporal bone, eventually to supply the lacrimal and nasal seromucus glands via the pterygopalatine ganglion.7 It additionally provides taste fibers to the palatal mucosa.24 The facial hiatus can occasionally be seen on axial high-resolution CT (HRCT) imaging as a small anteromedially oriented channel on the anterior surface of the superior temporal bone, arising in the region of the geniculate fossa (Fig. 7.13).35 Injury to this facial nerve branch may be manifested as an impairment of ipsilateral lacrimation. A large air cell referred to as the anterior epitympanic (geniculate) sinus is related to the geniculate fossa and

Table 7.2 Facial Nerve: Six Major Segments

I Cisternal (intracranial) segment Fig. 7.12 This sagittal reconstruction of a three-dimensional T2- II Intracanalicular (internal auditory canal) segment weighted sequence within the proximal internal auditory canal (IAC) demonstrates the vascular and neural structures of the normal cistern. III Labyrinthine segment (leads to anterior genu) The facial nerve is anterior and superior (F), the cochlear division of IV Tympanic (horizontal) segment (leads to anterior genu) the vestibulocochlear nerve is anterior and inferior (C), and the vestibular nerve is posterior, just at the division of the superior (S) and V Mastoid (descending) segment (leads to stylomastoid foramen) inferior (I) branches. There is also an inconstant loop of the anterior in- VI Extracranial (parotid) segment ferior cerebellar artery (AICA) inferior in the IAC on this image. Proxim- ity of the middle (MF) and posterior (PF) fossa are apparent. ch07 9/19/08 11:54 AM Page 452

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proximal tympanic facial nerve segment laterally. The lateral bony wall of the fallopian canal may be dehiscent in this location and must be surgically avoided. The relationships of the geniculate fossa are otherwise similar to those of the labyrinthine facial nerve segment, being separated from the vestibule and ampullae of the superior and lateral SCCs posteriorly by 3 mm of compact otic capsule bone. This location is a crossroad of four nerve canals: the labyrinthine segment of the facial nerve canal, the tympanic segment of the facial nerve canal, the facial hiatus containing the greater superficial petrosal nerve, and the accessory facial hiatus transmitting the lesser petrosal nerve.11,19,20,24,31 The tympanic segment of the facial nerve is usually straight and measures ~10 mm in length from its emergence from the geniculate fossa anteriorly to the posterior genu posteriorly.20 This segment of the facial canal courses along the superior portion of the medial wall of Fig. 7.13 Axial computed tomography image at the level of the superior quadrant of the internal auditory canal (IAC) demonstrates the fa- the mesotympanum. Anteriorly, the facial nerve lies lat- cial nerve entering the fallopian canal as the labyrinthine segment (CN eral to the ampulla of the horizontal SCC. As it courses VII – LS), and directed laterally and curving gently anterior, to arrive at posteriorly the nerve assumes a position that is inferior the geniculate ganglion (GG). The greater superficial petrosal nerve to the plane of the horizontal SCC. The tympanic segment exits anteriorly and medially from the geniculate ganglion, coursing in of the facial canal is readily visualized with either axial or the facial hiatus (FH). coronal CT (Fig. 7.13, Fig. 7.14, Fig. 7.15, Fig. 7.16, Fig. 7.17, and

A B Fig. 7.14 (A) This slight oblique axial computed tomography recon- (SVN) adjacent to the vestibule. (B) Red line illustrates the plane of orien- struction demonstrates continuity of the facial nerve from the fallopian tation to demonstrate the entire course of the labyrinthine and tym- canal to the posterior genu (PG). Continuity of the labyrinthine segment panic segment of the facial nerve. A coronal reconstruction at the level (CN VII – LS) and the tympanic segment (CN VII – TS) of the facial nerve of the cochlea shows the distal labyrinthine segment of cranial nerve VII is noted. The plane of section also depicts the superior vestibular nerve (DLS) and the proximal (PTS) in the “snake eyes” orientation. ch07 9/19/08 11:55 AM Page 453

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Fig. 7.15 Reconstructed coronal computed tomography image at the level of the external auditory canal. In the medial aspect of the temporal bone the fundus of the IAC is depicted (IAC – Fundus), and the labyrinthine segment of the facial nerve (CN VII- LS) exits superiorly and courses laterally. On this section, the normal tympanic segment (CN VII – TS) is seen medial to the ossicles in the middle ear cleft, surrounded by a perceptible bony encasement. Fig. 7.17 Reconstructed coronal computed tomography image at the level of the oval window, depicting the lateral semicircular canal (LSC) and the tympanic segment of the facial nerve (CN VII – TS) immedi- Fig. 7.18). The cochleariform process from which the ten- ately inferior to it. The tympanic segment is inconstantly encased in sor tympani tendon emanates lies immediately inferior bone, and in this case, appears to have a deficient bony inferior cover- to the proximal tympanic segment. In the coronal plane, ing. However, the depression of the nerve into the temporal bone is the cochleariform process, the proximal tympanic seg- quite obvious (TS – NOTE). ment, and the distal labyrinthine segment may be

Fig. 7.16 Reconstructed coronal computed tomography image in the plane of the cochlea demonstrates the distal labyrinthine segment of the Fig. 7.18 Axial computed tomography image in the plane of the facial nerve (CN VII - LS) and the proximal tympanic segment of the facial cochlea and vestibule demonstrates the continuous tympanic nerve (CN VII - TS) as the “snake eyes” above the turns of the cochlea. segment (CN VII – TS) of the facial nerve. ch07 9/19/08 11:55 AM Page 454

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visualized in close proximity on a single image. The nor- its second turn inferiorly into the posterior tympanic wall mal nonprotruding middle portion of the facial canal to become the mastoid segment. The facial recess is im- runs superior to the oval window and inferior to the mediately lateral to the facial canal in this location, and lateral SCC. Only 1 mm of bone separates the tympanic the stapedius muscle within the pyramidal eminence is segment of the facial nerve canal from the vestibule and immediately medial to it. The short process of the incus, lumen of the horizontal SCC medially. The impression sinus tympani, and pyramidal eminence all serve as use- that the superior aspect of the tympanic segment makes ful landmarks of the posterior genu in the axial CT plane. on the lateral SCC is variable. The posterior genu of the facial nerve canal between The tympanic segment of the facial nerve is densely the tympanic and mastoid segments forms an angle of be- concealed by bone only at its most anterior and posterior tween 95 and 125 degrees (Fig. 7.19).20 The concavity of ends. In the middle two thirds, the bony wall adjacent to this turn lies in the posterosuperior aspect of the tym- the middle ear is very thin and often cannot be resolved panic cavity in direct apposition to the ponticulus, a even with HRCT (Fig. 7.17).11 Focal areas of dehiscence may smooth bony ridge on the medial wall of the middle ear be present in up to 74% of temporal bones and are most that defines the superior boundary of the sinus tympani common in the region of the oval window.6 Cholesteatoma and separates the oval window niche from the round win- and other complications of chronic otitis media may cause dow niche. Medially, the sinus tympani separates the erosion of the canal in this location and thereby cause facial nerve canal from the bony labyrinth overlying the facial palsy. Also, the inferior surface of the tympanic posterior SCC. segment may partially conceal the oval window. The mastoid segment of the facial nerve extends 13 As it extends posteriorly, the facial nerve is inclined mm from the posterior genu to the stylomastoid foramen slightly inferiorly, generally in the plane of the petrous (Fig. 7.19 and Fig. 7.20). The jugular bulb lies medial to the pyramid, and courses obliquely from medial to lateral mastoid segment of the facial canal. The medial aspect of toward the posterior mesotympanum. The posterior tym- the mastoid facial canal may be dehiscent within the panic segment courses immediately beneath the short jugular fossa or may be separated from it by 7 mm of process of the incus at the fossa incudis, where it begins bone or more. The distance between the mastoid segment

A B Fig. 7.19 (A) The reconstructions performed from the projection in (B) continuity. (B) Line illustrates the plane of orientation to demonstrate demonstrate the posterior genu of the facial nerve (PG) to advantage. the entire course of the mastoid segment of the seventh cranial nerve On this oblique reconstruction, the facial nerve is depicted from the an- (Fig. 7.15). The axis closely approximates the Stenvers’ projection along terior genu (AG) to the stylomastoid foramen (SMF). The tympanic seg- the long axis of the petrous temporal bone. ment (CN VII – TS) and mastoid segment (CN VII – MS) are depicted in ch07 9/19/08 11:55 AM Page 455

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Fig. 7.21 Axial computed tomography image in the plane of the cochlea demonstrates the pyramidal eminence (PE) over the stapedius origin, with the sinus tympani (ST) anterior and the facial Fig. 7.20 Sagittal T1-weighted magnetic resonance image in the recess (FR) posterior in relation. The mastoid segment of the facial plane of the temporomandibular joint (TMJ) demonstrates the mas- nerve (CN VII – MS) is depicted just inferior to the posterior genu. toid segment of the facial nerve (CN VII – MS) from the posterior genu The cochlea and vestibule are evident in the otic capsule anterior (PG) to the stylomastoid foramen (SMF), where it becomes impercepti- and medial. ble in the parotid gland. The cerebellum is seen near the horizontal fissure in the posterior fossa (PF). course upward and anteriorly through the canaliculus chordae tympani (iter chordae posterius) into the middle and the jugular bulb is related not so much to the degree ear, where it crosses the middle ear cavity lateral to the of mastoid pneumatization as to the size of the jugular long process of the incus and medial to the malleus, bulb itself.12,20 It is in this location that the facial nerve finally exiting the temporal bone at the petrotympanic may be compromised by erosive jugulotympanic paragan- fissure in the canal of Huguier.24,33,36 The origin of the glioma involving the jugular fossa. Three millimeters or nerve is usually 5 mm or so proximal to the stylomastoid less may separate the proximal mastoid segment from the foramen, although it can rarely arise from an extratempo- posterior tympanic annulus. Distally, or more inferiorly, ral location.7, 2 0 It carries afferent fibers for taste sensation there is more separation from the tympanic annulus. The from the anterior two thirds of the tongue and efferent mastoid segment can be readily identified on axial CT or parasympathetic secretomotor fibers to the submandibu- MR section, again depending on the degree of mastoid lar, sublingual, and minor salivary glands in the floor of pneumatization (Fig. 7.19, Fig. 7.20, and Fig. 7.21).11 Excessive the mouth. Injury to this facial nerve branch causes loss of pneumatization can make CT evaluation more difficult; taste from the anterior two thirds of the tongue and however, following the course of the nerve on contiguous atrophy of the ipsilateral submandibular and sublingual sections will usually identify its location. Identification is salivary glands.16 usually straightforward in the sclerotic or diploic mastoid. The stylomastoid foramen opens inferiorly between Two major branches emerge from the facial nerve the mastoid process posterolaterally and the styloid along its mastoid segment, the stapedius nerve and the process anterolaterally. Often, the facial nerve exiting the chorda tympani nerve (Fig. 7.10, Fig. 7.11). The stapedius stylomastoid foramen into adjacent fat can be identified nerve diverges from the facial nerve in the proximal mason axial CT or MR sections obtained a few millimeters in- toid segment to provide motor innervation to the ferior to the stylomastoid foramen.11,37,38 The extracranial stapedius muscle. Injury to this branch may result in hy- facial nerve then delivers branches to the posterior belly peracusis. The chorda tympani nerve is the terminal of the digastric and the stylohyoid muscles as it courses branch of the nervus intermedius. It arises from the distal anteriorly, inferiorly, and laterally to pierce the substance third of the mastoid segment and follows a redundant of the parotid gland to form the parotid plexus. Terminal ch07 9/19/08 11:55 AM Page 456

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branches to the numerous muscles of facial expression advantage (Fig. 7.19). The mastoid segment of the facial diverge from the parotid.39,40 nerve canal and stylomastoid foramen may be seen on The arterial supply to the facial nerve is provided by axial CT, direct coronal CT sections, and oblique sagittal three vessels.33,41 The best known is the stylomastoid ar- reformatted CT images (Fig. 7.19 and Fig. 7.21). With axial tery, a branch of the occipital or posterior auricular artery, sections, one can identify this segment in cross section which enters the facial canal via the stylomastoid fora- and discern its relationship to the external auditory canal men. This vessel primarily supplies the mastoid segment. and the jugular foramen.11,37,45 A second vessel, the superficial petrosal artery, a branch The extracranial facial nerve is first seen outlined by of the middle meningeal artery coursing in the facial hia- surrounding fat on sections just inferior to the stylomas- tus with the greater superficial petrosal nerve, supplies toid foramen, unless this area is obliterated by inflamma- the tympanic segment. The internal auditory artery, a tory or neoplastic tissue.37,38,42 If perineural tumor from a branch of the anteroinferior cerebellar artery from the parotid malignancy along the facial nerve is suspected, basilar, supplies the intracanalicular and labyrinthine seg- identifying a normal nerve trunk in the fat of the stylo- ments of this nerve. Rich anastomoses exist at the sites of mastoid foramen clears the mastoid segment of involve- overlap of these territories, which may play a role in the ment. The extracranial facial nerve within the parotid tendency of certain lesions, hemangiomas as an example, gland has never been satisfactorily demonstrated by CT to occur at the junctions of these distributions. or MRI.41

Imaging of the Facial Nerve Magnetic Resonance Imaging Delineation of the Normal Facial Nerve All segments of the facial nerve canal within the temporal bone can be imaged with HRCT or MRI using proper tech- With MRI the normal facial nerve is readily visualized in nique.11,19,42–44 The intracranial segment of the facial nerve the CPA cistern and the IAC using T1- or T2-weighted se- within the CPA cistern and IAC is now routinely noninva- quences, and with proper sequences (see below), can be sively imaged with MRI.43 This evaluation has supplanted separated from the other nerves with which it traverses the use of intrathecally administered air or water-soluble these regions. The intratympanic segment can be visual- contrast as a contrast agent in CT cisternography, rendering ized in either the axial or coronal plane, but it is more them as historical interest alone, although cisternography apparent following gadolinium administration (Fig. 7.22). may rarely be used for the patient with MRI contraindica- The normal facial nerve, particularly the geniculate tions who requires imaging of the cisternal segment of the nerve.

Computed Tomography Delineation of the Normal Facial Nerve Within the temporal bone, CT displays the facial nerve bony canal, whereas MRI shows the facial nerve itself. With CT, the long axis of the labyrinthine segment, the proximal tympanic segment, and the intervening geniculate fossa are best seen with contiguous axial sections (Fig. 7.13, Fig. 7.18, and Fig. 7.21), although occasional utilization of slight off-axis axial images may depict longer contiguous segments of the nerve (Fig. 7.14 and Fig. 7.19). The “snake eyes” of the paired distal labyrinthine segment and proximal tympanic segment may be visualized in cross section on coronal sections obtained at the level of the cochleariform process (Fig. 7.16). Coronal CT sections are also required for visualization of the tympanic segment in cross section and in identifying its relationship to Fig. 7.22 Axial postgadolinium T1-weighted magnetic resonance the oval window. The posterior genu is equally well seen image with fat saturation at the level of the internal auditory canal on both routine axial and coronal sections; however, (IAC) and cochlea and vestibule illustrates normal subtle enhancement oblique sagittal CT reformations reveal this genu to best of the tympanic segment of the facial nerve (CN VII - TS). ch07 9/19/08 11:55 AM Page 457

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ganglion and the anterior tympanic segment, will often continue to view the dataset reconstructed with an algo- enhance to a mild to moderate degree due to the presence rithm that provides maximal bone detail, or with some of a rich perivenous plexus surrounding the nerve in the form of edge enhancement. A wide window and level set- fallopian canal and in the region of the geniculate gan- ting, which depicts the bone anatomy at a reasonable gray glion. The CPA cisternal and intracanalicular segments scale, can be also chosen at the workstation to maximize and the extracranial facial nerve do not normally en- the depiction of subtle pathology. In addition, confirma- hance.46 The posterior genu may be seen to best advan- tion of a finding on one plane with its identification in an- tage with oblique sagittal images angled along the course other plane keeps the neuroradiologist from mistaking of the tympanic segment of the facial nerve. The mastoid complex normal variations as pathology. In the axial segment and stylomastoid foramen may also be seen on plane, images should extend from the stylomastoid fora- direct sagittal or coronal imaging. Axial nonenhanced T1- men inferiorly to just above the tegmen tympani superi- weighted magnetic resonance images (T1WIs) at the level orly. In the coronal plane, the reconstructed images of the stylomastoid foramen may display the main trunk should extend from the carotid canal anteriorly through of the facial nerve as a black dot surrounded by high sig- the mastoid air cells posteriorly. Intravenous contrast is nal fat. This image is very useful in excluding perineural not routinely recommended because thin-section imag- tumor spread into the temporal bone along the mastoid ing, bone detail algorithms, and the presence of extensive segment of the facial nerve in cases where parotid malig- cortical bone adjacent to the facial nerve work in combi- nancy is found. Beyond the stylomastoid foramen the nation to limit the utility of contrast. Details of a sug- facial nerve has not been convincingly and reproducibly gested CT protocol are in Table 7.3. The application of CT visualized. Although MRI frequently demonstrates a low imaging to many various pathologies of the facial nerve, intensity linear structure on T1WIs on the axial plane as in much temporal bone imaging, has led to an appro- within the parotid gland, this has been shown to repre- priate concern of patient exposure. Current 64-slice sent the main intraglandular duct of the parotid gland MDCT imaging devices can obtain incredibly detailed rather than the intraparotid facial nerve.42,47 images of the temporal bones, but the neuroimager must be constantly aware of the radiation exposure from each exam and do whatever is possible to reduce the dose. Imaging Protocols Fortunately, the high inherent contrast between imaged structures (largely bone and air or soft tissue) means that CT and MRI often play complementary roles in the evalu- dosages may be often considerably reduced in compari- ation of peripheral facial nerve pathology, particularly son to other soft tissue imaging strategies. Reduction of when evaluating the intratympanic segment. Each modal- the dose can be performed in a variety of ways—increasing ity should be optimized, from an anatomic and a technical tube rotation speed, lowering tube mA, a greater perspective, to provide maximum information available pitch are some options. There is literature support for with current technologies. Although it is generally accepted diagnostic quality images at doses of less than 15% of that MRI holds distinct advantages over CT in visualizing standard brain CT imaging.48 Other benefits can accrue to the facial nerve itself, particularly in the cisternal, intra- the speed and volume scanning capability of MDCT units. canalicular, mastoid, and extracranial segments, CT plays Children may be successfully scanned without sedation an important role in specific settings. These include the when gently restrained by an adult, given the short scan assessment of the intratympanic facial nerve relative to times.49 nearby osseous structures, such as the stapes footplate Imaging may be obtained through both temporal and lateral SCC, and the relationship of the mastoid facial bones simultaneously by using a 20 to 25 cm field of view nerve canal to the jugular foramen. Bone destruction by with a targeted and magnified display field of view, and facial nerve lesions, “honeycomb” new bone formation by displayed in that format. This technique has the advan- facial nerve hemangiomas, and facial nerve injury related tage of allowing easy side-by-side comparison, but the to temporal bone fracture are also better defined by CT. disadvantage of relatively small image size may not always Current CT imaging of the facial nerve has undergone be perfectly symmetric. Imaging of both temporal bones considerable change with the advent of multidetector CT may be obtained as above, then targeted to reconstruct (MDCT) units, using 16 or 64 detector arrays. This tech- and display each side individually. We now routinely nology, with the acquisition of near-isotropic voxels of 0.6 archive both the large field of view images and as the mm or smaller, has nearly eliminated direct coronal imag- individually targeted and reconstructed axial and coronal ing. The helical acquisition technique allows reconstruc- images of each side. tion of the data at slightly overlapping intervals, which Alternatively, each temporal bone may be individually promotes the generation of excellent reconstructed im- magnified, at the expense of minor image distortion.50 ages in any chosen plane. Most neuroradiologists will We do not recommend this technique. Oblique sagittal ch07 9/19/08 11:55 AM Page 458

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Table 7.3 Computed Tomography Protocol for Imaging Patients with Peripheral Facial Nerve Palsy MDCT acquisition parameters: intratemporal facial nerve only Slice thickness: 0.625 mm, helical acquisition Algorithm: edge enhancing algorithm (bone algorithm, bone detail) Scan angle: parallel to hard palate Scan extent: inferior mastoid process/stylomastoid foramen below to tegmen tympani above 120 kV Scan field of view: 20 to 25 cm to include both temporal bones Intravenous contrast: None Window width and window level: 4000/300 to 500 Hu Reconstructions: intratemporal facial nerve only Individual temporal bone display Acquired scan data reconstructed with 10 to 20% overlap Reconstructed on 10 to 12 cm displayed field of view Individually targeted for right and left temporal bone Extracranial (intraparotid) facial nerve CT Reconstructed thickness: 2.5 to 4 mm axial sections, with 10 to 20% overlap Algorithm: soft tissue algorithm Intravenous contrast: yes CT scan extent: stylomastoid foramen above to hyoid bone below 140 kV 180 mA Window width and window level: 350 to 450/30 to 50 Hu If MRI is not an option for an individual patient and the decision is made to image the entire peripheral facial nerve with MDCT, it is possible to give iodinated contrast during the temporal bone CT scan described above, then acquire helical sub-mm contiguous slices from the top of the petrous temporal bone to the hyoid bone. Reconstruction of the axial temporal bone data into soft tissue algorithm can allow a reasonable evaluation of the brainstem, cerebellopontine angle cistern, and internal auditory canal for intraaxial cisternal lesions. Bone algorithm images of the intratemporal facial nerve canal will be of high quality. Soft tissue algorithm reconstructions below the stylomastoid foramen as above will demonstrate the intraparotid structures at a high quality. If MRI is accessible, MDCT of the intratemporal segment as determined necessary can be performed alone. Abbreviations: MDCT, multidetector computed tomography; HU, Hounsfield units; MRI, magnetic resonance imaging.

reconstructions through the course of the tympanic and examination continues into the parotid gland. We would mastoid segments including the stylomastoid foramen, again emphasize that MRI can provide improved imaging additional oblique coronal reconstructions through the over CT along the course of the extracranial facial nerve. If mastoid segment, and curvilinear reconstructions through imaging of the entire facial nerve from its origin in the several segments of the facial nerve are readily produced pontine nuclei to the extracranial segments is indicated, from any of the above datasets, and may be intermit- MRI should be the initial study of choice. tently helpful, although not part of our routine CT exami- Although a thorough facial nerve protocol for MRI may nation (Fig. 7.14 and Fig. 7.19). be useful, individual circumstances of the patient, the sus- If the clinical setting requires CT imaging of the expected pathology, and the capabilities of the MRI unit may tracranial facial nerve, sections should continue below all contribute to the chosen study. A complete MRI proto- the level of the stylomastoid foramen, through the col for facial nerve imaging should include T1WI and T2WI substance of the parotid. Generally, because soft tissue through the course of the nerve from brainstem to parotid. regions have less contrast conspicuity, increasing The MRI examination should routinely include gadolin- the thickness of the reconstructed images to 3 mm or ium-enhanced T1 fat-saturated sequences as well. A stan- increasing technique otherwise will provide better image dard head coil typically extends sufficiently inferior to quality. Intravenous contrast may prove useful if the include the parotid and is optimal for brain imaging. Some ch07 9/19/08 11:55 AM Page 459

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centers have utilized dedicated surface coils for temporal and should be positioned to extend from the midportion bone imaging. Suggested scan parameters are included in of the pons in the coronal plane posteriorly through the Table 7.4. Saturation bands and gradient moment nulling parotid anteriorly. Pregadolinium T1WI assists with dif- should be optimized to eliminate flow artifacts in the ferentiation of gadolinium-enhancing structures on sub- region of the internal carotid artery and jugular bulb. sequent imaging from substances with inherently short Coronal T1 localization provides anatomic data from T1, such as fat in marrow, or some pathologic processes, the cisternal segment of the seventh nerve to the parotid such as cholesterol granuloma. Axial fast spin echo T2WI

Table 7.4 Magnetic Resonance Imaging Protocol for Patients with Peripheral Facial Nerve Paralysis* Localization sequence: 3-plane sequence Fast spin echo axial whole brain T2-weighted sequence Slice thickness/increment: 4 to 5 mm, interslice gap of 1.0 to 2.5 mm TR/TE: 4000 to 6000/80 to 120 Scan extent: Whole brain, to include parotid if possible Purpose: Diagnosis of intraaxial (nuclear) lesions and may assist in characterizing brainstem pathology; also permits evaluation of upper parotid gland Pre- and postcontrast axial high-resolution T1-weighted sequence Slice thickness/increment: 3 mm, interslice gap optimal at 0 mm TR/TE: 400 to 500/17 to 20 Field of view: Minimum to incorporate the temporal bones (16 to 22 cm) Contrast-enhancement technique: 0.1 mmol/kg dose is administered by intravenous bolus Other notes: Use available techniques to reduce flow artifact (e.g., flow compensation); fat saturation applied on postcontrast acquisition Scan extent: Tegmen tympani superiorly, stylomastoid foramen inferiorly; entire facial nerve excluding intraparotid segment seen on this sequence from pontine nuclei to stylomastoid foramen Purpose: Diagnosis of lesions with blood–brain alteration in the brainstem, or evaluate normal and pathologic enhancement in the cisternal, IAC, and intratemporal segments of the facial nerve Postcontrast coronal high-resolution T1-weighted sequence Slice thickness/increment: 3 mm, interslice gap optimal at 0 mm TR/TE: 400 to 500/17 to 20 Field of view: Minimum to incorporate the temporal bones (16 to 22 cm) Other notes: Use available techniques to reduce flow artifact, fat saturation Extent: Posterior pons to anterior parotid gland Purpose: Provides additional plane through facial nerve, particularly intratympanic segment; confirms pathology Optional postcontrast oblique sagittal T1-weighted sequence Slice thickness/increment: 3 mm, interslice gap optimal at 0 mm TR/TE: 400 to 500/17 to 20 Extent: Fundus of IAC medially to descending facial nerve canal laterally; may use axial T1-weighted sequence to determine plane of tympanic segment of the facial nerve Purpose: Delineates the intratemporal facial nerve from the geniculate ganglion anteriorly to the stylomastoid foramen inferiorly, often on a single image; additional confirmation of pathology and review of proximal intraparotid facial nerve Optional postcontrast axial T1-weighted sequence through parotid gland Slice thickness/increment: 4 mm, interslice gap of 1 mm TR/TE: 400 to 500/17 to 20 Field of view: 22 to 25 cm Other notes: Unnecessary if previous sequences show normal parotid gland, fat saturation Extent: Lower mastoid segment of CN VII superiorly to the parotid tail inferiorly Purpose: Further delineation of lesion identified on previous sequences within the parotid gland (Continued on page 460) ch07 9/19/08 11:55 AM Page 460

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Table 7.4 (Continued) Magnetic Resonance Imaging Protocol for Patients with Peripheral Facial Nerve Paralysis* High-resolution 3D GRE sequence (vendor-specific naming) Slab thickness: 76 mm Slice thickness: 0.8 mm reconstructed from slab TR/TE/FA: 12.38/6.19/70° Matrix: 512 512 Field of view: 18 cm Scan extent: Tegmen tympani to mastoid process Purpose: High-resolution demonstration of nerve, vascular structures in IAC-CPA 3D time-of-flight MRA Slab thickness: 80 mm Slice thickness: 1 mm TR/TE/Flip angle: 40/7.2/25 Matrix: 512 512 Field of view: 18 to 24 cm Other notes: Superior presaturation band Scan extent: Foramen magnum to suprasellar cistern Purpose: Evaluation of posterior fossa vascular structures Abbreviations: CPA/IAC, cerebellopontine angle/internal auditory canal; 3D, three-dimensional; GRE, gradient echo; MRA, magnetic resonance angiography. *TR/TE/FA recommendations are approximate, vary between manufacturers, and can be altered within guidelines.

of the whole brain assesses the facial nerve nuclei and postcontrast T1 pulse sequence, extending from the re- supranuclear pathways and evaluates for other possible gion of the stylomastoid foramen through the parotid brain lesions. Multiple sclerosis, as an example, a known gland. We prefer to perform this imaging with fat satura- cause of facial neuropathy, may be suspected by finding tion, which reduces high signal intensity fat and also im- numerous periventricular lesions, which strongly suggest proves the dynamic gray-scale range of the image, making the diagnosis and thereby assist in characterizing a lesion the margins of an enhancing intratemporal lesion more involving the facial nerve nuclei or tracts. conspicuous. Postgadolinium T1WIs in the axial, coronal, and sagittal Nearly all MRI vendors now offer additional techniques planes allow identification of lesions that result in that can provide useful images of the facial nerve. High- blood–brain barrier breakdown, or that result in abnor- resolution T2-weighted gradient recalled echo (GRE) mal enhancement of the cisternal, intracanalicular, or in- techniques with three-dimensional (3D) acquisition can tratemporal facial nerve. Remember that enhancement of generate very thin axial slice profiles to depict the cister- the facial nerve within the geniculate ganglion, tympanic nal segment of the facial nerve and also improve the segment, and mastoid segment is a normal finding, owing evaluation of the pons. These high-quality images can be to the presence of vascularity within the epineurium and manipulated into multiple oblique reformations (Fig. 7.7, perineurium (Fig. 7.22).51 Some criteria for abnormal Fig. 7.8, and Fig. 7.12) and permit separation of the facial enhancement include enhancement of the nerve outside nerve, superior vestibular nerve, cochlear nerve, and infe- the facial canal, extension of enhancement to CN VIII, and rior vestibular nerve in the internal auditory canal. The intense enhancement of the labyrinthine and mastoid neural structures, as well as vascular structures, are well segments.52 At least two planes of imaging are recom- depicted as low signal intensity adjacent to the high sig- mended to avoid potential partial volume averaging nal of cerebrospinal fluid (CSF), which surrounds them. effects. Fortunately, with increasing gradient strength, This technique can be used to aid in distinguishing the minimum T1 slice thickness is decreasing, reducing the nerve of origin for neuromas. The depiction of the intratem- problem of partial volume averaging. Imaging of the ex- poral segments of the facial nerve are still best done by tracranial facial nerve should be performed using an axial T2-weighted or postcontrast T1-weighted techniques. ch07 9/19/08 11:55 AM Page 461

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Thin section FSE T2-weighted techniques can demon- may fail to demonstrate the facial nerve or pathological strate the normal facial nerve in the temporal bone and processes involving it in the tympanic segment, where also help characterize pathology in this region. The move- the nerve is no longer surrounded by CSF. Many GRE im- ment to higher field MRI (3T [tesla] and greater) have ages, due to local field inhomogeneities inducing mag- resulted in the ability to perform routine very thin section netic susceptibility artifact, are of limited utility within (1 to 2 mm) T2WI and also GRE T1WIs, but the increased the temporal bone. Contemporary fat saturation tech- artifact due to susceptibility of the adjacent bone and niques make it more difficult to achieve water saturation air also plays into the quality of imaging of the intratem- instead of fat saturation, but this can still occur. At least poral facial nerve. Details of these sequences are found in one standard T1 acquisition is useful, to avoid overlooking Table 7.4. a fatty lesion of the temporal bone. In some selected clinical settings, notably in the evalu- When and how to image a patient with a facial nerve ation of hemifacial spasm, magnetic resonance angiogra- palsy are influenced by the clinical presentation and the phy (MRA) can provide additional useful data (Fig. 7.23C). suspected location and etiology of the offending lesion. We have routinely used 3D time-of-flight MRA in this One method for dealing with peripheral facial nerve setting. The MRA should encompass from just below the paralysis is to consider seventh nerve palsy as to present- foramen magnum to above the temporal bone. The MRA ing nature and course. This results in delineation of the is typically acquired in the axial plane, with a superior palsy as acute and monophasic, gradually progressive, or saturation band to suppress signal from venous flow. These recurrent. Typically, acute palsies are related to trauma or data can be displayed as individual source images or as to Bell’s palsy. Temporal bone trauma is best imaged with multiplanar maximum intensity projection (MIP) images. CT and is discussed in depth in Chapter 6. Bell’s palsy, if The limitations and potential pitfalls of MRI can obvi- the clinical presentation is typical, need not be imaged. It ously limit the application of MRI in the evaluation of the should be stressed, however, that both benign and malig- facial nerve. Failure to consider adjacent structures can be nant tumors involving the facial nerve may present as an a problem in the review of a normal or diseased facial acute facial nerve palsy, and that the entirety of the clini- nerve. Techniques chosen for the study may also have sig- cal history is often needed to determine the necessity of nificant limitations. The 3D GRE techniques mentioned imaging.

A B Fig. 7.23 (A) Hemifacial spasm. The coronal postcontrast weighted demonstrates considerable elongation and tortuosity of the distal left magnetic resonance image with fat suppression demonstrates the de- vertebral artery, posteroinferior cerebellar artery origin, and proximal formity of the lateral pons (arrowheads) adjacent to the tortuous ver- basilar artery (arrowheads), with indentation of the pons near the tebral artery (VA). The facial nerve (CN VII) and cochlear nerve expected exit zone of CN VII (focal deformity), with good visualization (Cochlear N) are depicted in the internal auditory canal (IAC). (B) Axial of the anteroinferior cerebellar artery in the IAC in this elderly patient T2-weighted magnetic resonance image at the level of the IAC with left hemifacial spasm. (Continued on page 462) ch07 9/19/08 11:55 AM Page 462

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C D Fig. 7.23 (Continued) (C) Axial source image from magnetic resonance microvascular decompression of PICA and the vertebrobasilar junction. angiography demonstrates the tortuous vertebrobasilar junction (VBJ) The Teflon pledget is depicted as a high density ovoid density between and also the loop of the posteroinferior cerebellar artery (PICA) indent- the pons and the previously noted vascular loops. The proximal basilar ing the pons. The level is clearly demarcated by the appearance of the artery (arrowheads) is evident adjacent to the ventral pons. facial colliculi (FC). (D) Axial computed tomography image following

Gradually progressive paresis that ends in complete the lesion is superior to the pontine nuclei (supranuclear) paralysis is seen in only a small percentage of patients and causes loss of function of the muscles of facial expres- with seventh nerve palsy. This presentation suggests be- sion of the contralateral lower face with sparing of the nign or malignant neoplasm.53,54 Imaging evaluation forehead. Peripheral facial neuropathy, conversely, indi- should consist of MRI throughout the course of the facial cates injury to the facial nerve from its pontine nuclei to nerve, including gadolinium enhancement. Postcontrast its motor end plates in the face, and is manifested by loss T1-weighted sequences must cover the entire intracranial of function of the muscles of facial expression of the en- and extracranial facial nerve course. tire ipsilateral face. The special functions of the facial Recurrent facial nerve palsy may also herald benign or nerve, to include lacrimation via the greater superficial malignant neoplastic involvement, or it may represent nerve, stapedial reflex via the nerve to the stapedius, and vascular irritation of the nerve at its root exit zone in the taste via the chorda tympani, are variably involved. We cerebellopontine angle. MRI is again the recommended will focus on peripheral facial lesions. approach to this setting. MRA of the posterior fossa may The lesion is generally localized to one of three main additionally contribute, particularly in the setting of regions—intracranial (brainstem, CPA cistern, or IAC), hemifacial spasm. intratemporal, or extracranial—by employing clinical diagnostic clues (Table 7.5). Pontine lesions often cause other cranial neuropathies, particularly sixth nerve abnormali- Pathology ties, may result in long tract signs, and often involve all three special functions of the facial nerve.29,33,53 If these Preimaging Localization of Facial Nerve special functions are impaired in conjunction with ipsilat- Lesions eral vestibulocochlear neuropathy, the CPA cistern and IAC are implicated. If the three special functions are vari- Facial nerve palsy is clinically divided into central type, ably involved, an intratemporal lesion is suspect. If all involving upper motor neurons, and peripheral type, in- three special functions are spared, an extracranial seventh volving lower motor neurons. In central facial neuropathy, nerve abnormality should be sought. ch07 9/19/08 11:55 AM Page 463

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Table 7.5 Preradiological Topographical Localization of Lesions Causing Peripheral Facial Nerve Paralysis Facial Palsy Lacrimation (GSPN) Stapes Reflex Taste and Salivation (Nerve of the Stapedius) (Chorda Tympani Nerve) Intracranial Absent Absent Absent Brainstem Cranial Nerve VI may also be involved CPA/IAC Cranial Nerve VII also involved Intratemporal Functions variably affected, depending on precise location of offending lesions Functions drop out from proximal to distal (lacrimation stapedius reflex anterior two thirds of tongue taste) Extracranial Present Present Absent Intraparotid Abbreviations: GSPN, greater superficial petrosal nerve; CPA/IAC, cerebellopontine angle/internal auditory canal.

Facial nerve lesion localization allows for a more di- (Table 7.6) are generic: in most instances, they can cause rected imaging procedure, with a corresponding appro- any individual or complex cranial neuropathy, depending priate choice of imaging modality. However, this localiza- on which cranial nerve nucleus is affected.58 This differen- tion scheme is imprecise. Tumors may variably involve tial diagnosis list includes pontine malignancy (primary nerve fibers, sparing some special functions.29 If multiple glial neoplasms, metastatic tumor, lymphoma), multiple lesions involve the facial nerve, only the most proximal sclerosis, inflammation, abscess, and vascular lesions may be clinically evident. If the multiple involvement is such as arteriovenous malformations (AVMs), cavernous central and peripheral, the peripheral lesion will mask the hemangioma, and cerebral infarction. These brainstem central one.55 Finally, there are numerous and extensive lesions classically present with complete facial nerve dys- interconnections between the facial nerve and other cra- function (motor VII paralysis, all three special functions nial nerves, and special functions may be mediated by absent). Due to its anatomic contiguity, an abducens palsy these collateral neural routes.33,53,55 Fortunately, typical (CN VI) may also be associated. MRI coverage will allow for coverage of the entire course Lesions of the cisternal and intracanalicular segments of the facial nerve within a manageable time frame. Local- of the facial nerve (Table 7.6) are best thought of together ization prior to imaging may have its greatest significance because the differential diagnosis of diseases of these two in focusing attention on potential areas of abnormality segments is similar. It is interesting that even the largest during interpretation. of these CPA/IAC lesions rarely causes associated facial nerve palsy. The cisternal and intracanalicular segments of the facial nerve are evidently forgiving, stretching to Pathologic Conditions Affecting the Facial accommodate the adjacent tumors, with dysfunction seen Nerve by Segment only in the unusual case. Granulomatous meningitis from sarcoidosis or infectious causes can also cause facial nerve The facial nerve may be compromised in numerous loca- paralysis by affecting the nerve in the cisternal or intra- tions by various pathologic processes along its protracted canalicular segments. Vascular lesions (vertebrobasilar course from the pontine nuclei to the extracranial termi- dolichoectasia, AVM, unusual aneurysms, posteroinferior nal ramifications.19,26,32,37,56–63 Many of these diseases are cerebellar artery loop) can cause either facial nerve paral- unique to a specific anatomic segment of the nerve. As a ysis or hemifacial spasm (see below).34,58,64 The clinical result, a discussion of the lesions causing facial neuropa- clues indicating a cisternal or intracanalicular lesion usu- thy is most readily approached by facial nerve segment. ally include complete facial nerve dysfunction (motor VII Most of the diseases listed in the tables in this chapter are paralysis, three special functions absent) in combination thoroughly discussed in the chapters covering the area with vestibulocochlear neuropathy. When hemifacial where they are most frequently found. We focus in this spasm is the predominant symptom, the proximal portion section on those lesions with particular affinity for caus- of the cisternal segment of the facial nerve should be ing facial nerve paralysis. closely scrutinized. The brainstem lesions that affect the facial nerve nuclei The intratemporal causes of peripheral facial nerve and cause either central or peripheral facial nerve paralysis paralysis (Table 7.7) generally present with variable ch07 9/19/08 11:55 AM Page 464

464 Imaging of the Temporal Bone

Table 7.6 Brainstem and Cisternal Causes of Facial Nerve Paralysis Table 7.7 Intratemporal Causes of Facial Nerve Paralysis Brainstem causes Congenital Primary cholesteatoma Tumor Trauma – surgery Fracture through facial nerve canal Primary brainstem glioma Postmastoid surgery Metastatic tumor Tumor Hemangioma Non-Hodgkin’s lymphoma Facial nerve schwannoma Inflammatory Paraganglioma Multiple sclerosis Metastases Cerebritis Non-Hodgkin’s lymphoma Abscess Adenomatous tumor of the endolymphatic sac Vascular Inflammatory Acquired cholesteatoma Arteriovenous malformation with or without hemorrhage Severe otitis media Cavernous hemangioma with or without hemorrhage Bell’s palsy (herpes simplex neuritis) Infarction

Cisternal and intracanalicular causes cholesteatoma, paraganglioma, hemangioma, facial nerve Tumor schwannoma (discussed below), metastases, and peri- 67–70 Schwannoma neural tumor from parotid malignancy origin. Chronic otitis media or cholesteatoma can invade the facial nerve Neurofibroma canal, particularly at dehiscent locations within the tym- Meningioma panic segment. Bell’s palsy is included in the differential Epidermoid diagnosis of intratemporal causes of facial nerve paralysis Inflammatory because the facial nerve is presumed to be injured from vascular compromise from the swollen facial nerve in the Granulomatous meningitis facial nerve canal; this subject is discussed in detail in the Sarcoidosis next section. Tuberculosis, other mycobacterial infections The extracranial segment of the facial nerve (Table 7.8) Bacterial meningitis is injured by parotid malignancy and necrotizing otitis Facial neuritis Herpes simplex or other undefined neurotropic virus Table 7.8 Extracranial and Miscellaneous Causes of Facial Nerve Paralysis Ramsay Hunt syndrome (herpes zoster oticus) Forceps delivery Vascular Extracrania Trauma surgery Penetrating trauma Vertebrobasilar dolichoectasia* Parotid surgery Vertebral artery aneurysm* Tumor Primary parotid malignancy Posterior or anteroinferior cerebellar artery aneurysm* Metastatic tumor to Posterior or anteroinferior cerebellar artery loop* intraparotid nodes Miscellaneous Invasive malignant Subarachnoid hemorrhage tumor from adjacent deep facial space *May produce hemifacial spasm. Inflammation Malignant otitis externa Parotid infection (usually involvement of the three special functions of the facial secondary to calculus disease) nerve in conjunction with motor VII dysfunction. Trauma to the intratemporal facial nerve canal, either from tem- Möbius syndrome poral bone fracture (see Chapter 6) or related to tem- Miscellaneous Diabetes mellitus poral bone surgery, is a common cause of facial neuropa- Myasthenia gravis thy in this region.65,66 The more common intratemporal Hyperparathyroidism tumors that may affect the facial nerve include primary ch07 9/19/08 11:55 AM Page 465

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externa (skull base osteomyelitis).19 Erosive lesions in- parotid masses.78,80 Facial nerve dysfunction results from volving the mastoid cortex or the digastric groove, partic- gradual compression of the nerve rather than neoplastic ularly necrotizing external otitis, can compromise the invasion or destruction. Motor nerves have thicker myelin nerve in its mastoid segment or at the stylomastoid fora- sheaths than do sensory nerves (for example, the cochlear men.37 Parotid neoplasia may compromise the nerve in a nerve), are relatively resistant to mechanical compression, similar fashion.19,71 Infiltrating malignancy of the parotid and therefore facial palsy is not invariably present.57,81 In gland and deep lobe parotid lesions may be nonpalpa- some series, facial nerve paralysis is not the most common ble.19 Imaging of the extracranial facial nerve is critical in presenting symptom.75 Intratemporal schwannomas com- all cases of peripheral facial nerve paralysis where an iso- press the facial nerve within the rigid fallopian canal more lated motor facial neuropathy is present, particularly with readily than tumors not confined by bone, thus producing sparing of the three special functions of the facial nerve. facial nerve palsy earlier in the clinical course.19,82 Onset of Perineural parotid malignancy will access the temporal facial nerve palsy related to schwannoma is typically grad- bone along the mastoid segment of the facial nerve from ual, but can be acute and mimic Bell’s palsy, or may be re- the parotid gland.19,71 When an infiltrating malignancy of current.19,63,77 Also consider the association of schwanno- the parotid gland is identified, imaging of the intratemporal mas with the entity of neurofibromatosis type II in facial nerve is critical. evaluating these patients (Fig. 7.24). Hearing loss may be sensorineural or conductive, again depending on tumor location. Lesions of the CPA or IAC Special Imaging Issues of the Facial Nerve segments tend to result in sensorineural hearing loss due to compression of the eighth cranial nerve. Schwannomas Most of the lesions found in the differential diagnosis of within the middle ear space may directly erode or me- facial nerve paralysis are discussed in depth in other chanically impair the ossicles and produce conductive chapters. This section discusses facial nerve schwanno- hearing loss.79,80 Hearing loss may precede clinical evi- mas (neuromas), hemangiomas of the facial nerve, Bell’s dence of facial nerve dysfunction by some time.63 Less palsy, Ramsay Hunt syndrome, and hemifacial spasm. than 10% of facial nerve schwannomas are extracranial, usually presenting as asymptomatic parotid masses.83 These masses may reach considerable size, yet facial Facial Nerve Schwannomas nerve function remains normal.84 Schwannomas of the facial nerve are rare tumors, ac- A variety of other symptoms have been described in as- counting for no more than 5% of facial palsies and less sociation with facial nerve schwannoma. These include tin- than 1% of all intrapetrous tumors.61,72–74 Preoperative nitus, vertigo, hemifacial spasm, facial pain, and otalgia. identification of this lesion is of importance because Chorda tympani involvement may result in taste alterations awareness of risk of injury to the facial nerve has signifi- and greater superficial petrosal nerve involvement in cant impact on therapeutic decisions and presurgical lacrimation abnormalities.53,63,78,80,85 counseling.73,74 Schwannomas may involve the facial The imaging findings of intracranial facial schwanno- nerve at any location from its origin in the pons to its exit mas may mimic those of vestibular schwannoma, appear- at the stylomastoid foramen as well as the intraparotid ing as an enhancing mass involving the IAC-CPA region, portion, with a strong tendency to involvement of multi- with expansion of the canal, on either CT or MRI.61 The ple contiguous segments.75 There is general agreement pattern of enhancement is typically homogeneous with that they tend to occur in the vicinity of the geniculate smaller lesions, becoming more heterogeneous with in- ganglion.19,60,61,67,69,73–76 Extension both proximal and distal creasing tumor size (Fig. 7.24, Fig. 7.25, and Fig. 7.26).86 to the geniculate ganglion occurs, as does expansion into However, additional findings may suggest a facial nerve the middle cranial fossa.61,77 This lesion may also be re- origin. These include erosion of the superior margin of ferred to as a neuroma or neurilemmoma, depending on the IAC, expansion of the labyrinthine facial nerve canal the orientation of the surgical pathologist. Schwannomas (Fig. 7.25 and Fig. 7.26), erosion of the region of the genic- characteristically arise from the outer layer (nerve sheath) ulate fossa, and eccentricity of the CPA portion of the of the involved nerve, expanding eccentrically away from tumor relative to the porus of the IAC.61,79 This latter find- the nerve.61,75 ing is more reliable when the size of the CPA component Clinical features of facial nerve schwannomas are influ- is under 2 cm.86 An important finding suggesting that an enced by the intracranial, intratemporal, or extratemporal IAC/CPA mass is a facial nerve schwannoma is extension location of the tumor and the involvement of adjacent into the labyrinthine segment of the facial nerve (Fig. 7.26). structures.69,78–80 Intracranial schwannoma commonly re- This labyrinthine segment “tumor tail” may help to correctly sults in neurotologic symptoms, intratemporal masses in differentiate a facial nerve schwannoma from a vestibular facial nerve dysfunction, and extratemporal tumors in nerve schwannoma preoperatively. ch07 9/19/08 11:55 AM Page 466

466 Imaging of the Temporal Bone

A B Fig. 7.24 (A) Axial postcontrast T1-weighted magnetic resonance involved with schwannomas, including CN V in Meckel’s cave (MC) and image in a young adult with neurofibromatosis type II demonstrates along the V2 branch (V2). (B) Coronal postcontrast T1-weighted mag- numerous schwannomas. One of the bilateral vestibular schwannomas netic resonance image demonstrates the bilateral vestibular schwan- (VS) is present at the fundus of the internal auditory canal (IAC). nomas (VS), the facial nerve schwannoma in the tympanic segment A facial nerve schwannoma is evident in the tubular and modestly (CN VII – TS), and an additional schwannoma of CN XII (HS) in the enlarged tympanic segment (TS). Multiple other cranial nerves are hypoglossal canal.

A B

Fig. 7.25 (A) Axial computed tomography (CT) image demonstrates distinguished from this obstructive fluid. (B) Coronal CT image demon- enlargement of the labyrinthine segment (LS) and mild enlargement of strates the enlarge labyrinthine segment (LS) and the considerable mass the geniculate ganglion (GG) but considerable enlargement of the tympanic of the schwannoma in the tympanic segment (arrowheads), which ex- segment (TS) of the facial nerve canal. This is indicative of fusiform in- tends to the tegmen tympani, and also erodes and displaces the malleus volvement of the nerve characteristic of schwannoma. The mastoid is and incus (Ossicles), narrowing Prussak’s space. The tegmen is intact, obstructed, with fluid (effusion) within the air cells. The lesion cannot be but the lesion is in close proximity to the floor of the middle fossa. ch07 9/19/08 11:55 AM Page 467

Chapter 7 Anatomy and Development of the Facial Nerve 467

C D

Fig. 7.25 (Continued) (C) Axial postcontrast T1-weighted magnetic resonance image (T1WI) with fat suppression of the tympanic segment extension of this facial nerve schwannoma. The lesion has a smooth lobulated border (arrowheads) within the middle ear cleft. On this section, the lesion does not extend to the internal auditory canal (IAC). Note the proximity to the middle fossa (MF). The mass is clearly distinguished from obstructive fluid in the mastoid air cells. (D) Axial reconstruction of a three-dimensional T2-weighted sequence of the facial schwannoma. Again, note that the lesion has a smooth lobulated border (arrowheads) and is intermediate in signal intensity on this sequence. While the mass is lower in signal intensity than CSF in the internal auditory canal (IAC), or fluid in the labyrinth, as seen in the cochlea and semicircular canals (LSSC), it is nearly isointense with the mastoid effusion previously noted. (E) Coronal postcontrast T1WI with fat suppression demonstrates a lobulated border (arrowheads) and close proximity with the middle fossa (Temporal lobe). Large lesions may extend into the floor of the middle fossa, eroding the tegmen tympani, and result in considerable mass effect. E

In addition to focal erosions, facial nerve schwannomas cranial nerve within the temporal bone is highly sugges- involving the geniculate ganglion may produce focal re- tive of the diagnosis of facial schwannoma.79 modeling of the geniculate fossa, resulting in a thin cover Intratemporal facial schwannomas may be detected of bone surrounding the anterior surface of a soft tissue with either CT or MRI as focal mass or enlargement along mass on CT.87 Schwannomas involving the ganglion may the course of the nerve.61,72,85 However, CT may be limited also extend anteriorly and superiorly into the middle cra- in its ability to distinguish facial schwannoma from nial fossa, enlarging to considerable size prior to detec- cholesteatoma or other masses within the middle ear tion, and often resulting in erosion of the midportion of (Fig. 7.25).61 MRI with gadolinium demonstrates facial the petrous bone.77 Further, schwannomas with both IAC- nerve enlargement and enhancement and assesses the CPA and middle fossa components occur, connected remaining segments of the nerve for additional involve- through the labyrinthine segment. This pattern of tumor ment. CT remains extremely valuable, however, in defin- growth is readily demonstrated with either CT or MRI. Ev- ing the relationship of the tumor to adjacent osseous idence of involvement along the course of the seventh structures such as the ossicles (Fig. 7.25) and the lateral ch07 9/19/08 11:55 AM Page 468

468 Imaging of the Temporal Bone

A B Fig. 7.26 (A) Axial postcontrast T1-weighted magnetic resonance superior to (A) demonstrates enhancing tumor (*) extending into the image (T1WI) with fat suppression demonstrates a facial nerve labyrinthine segment of the facial nerve canal (arrow), representing schwannoma (*) filling the internal auditory canal and smoothly en- schwannoma extension along the facial nerve. Extension of a schwan- larging it (arrows). The mass is relatively uniform in enhancement. (B) noma into the fallopian canal is strongly suggestive of a facial nerve A second axial postcontrast T1WI with fat suppression immediately origin.

SCC, and may therefore play a role in surgical planning. nerve schwannomas; for example, a facial nerve schwan- Because these lesions have a tendency to erode the otic noma extending from the IAC to the geniculate ganglion capsule and produce asymptomatic perilymph fistulas, may assume a “dumbbell” shape as it extends through the preoperative assessment of the relationship of the mass labyrinthine segment of the fallopian canal, or a lesion pri- to the cochlea and the remainder of the labyrinth may as- mary to the greater superficial petrosal nerve may appear sist in preventing a postoperative symptomatic perilymph as a rounded, extradural mass of the middle fossa.74 fistula.75 Mastoid segment intratemporal facial schwanno- Facial nerve neuromas, developing following trauma or mas may be detected on CT as enlargement of the de- nerve section, and in rare instances secondary to chronic scending canal or on MRI as an enlarged, enhancing mas- inflammation, have also been described, and are not toid facial nerve segment. unique in their imaging appearance. A clinical history Extratemporal facial schwannomas may be imaged with may be most helpful in making this diagnosis.88 either CT or MRI. When a parotid mass is associated with facial palsy, or there is other reason to suspect that the Hemangiomas lesion is a facial schwannoma, MRI has the advantage of evaluating all segments of the facial nerve at the same time Hemangiomas of the facial nerve are benign, slow grow- that the parotid is studied and may show continuity of the ing, localized but nonencapsulated lesions, composed of intraparotid mass with the facial nerve. A tubular mass in vascular channels of varying size.89 The term benign vas- the parotid gland along the expected course of the facial cular tumor has also been applied to these lesions and is nerve branches is highly suggestive of the diagnosis of used interchangeably with hemangioma.90 The size of the intraparotid facial nerve schwannoma. However, the lack of vascular channels in this lesion varies, as does the thick- surrounding bony canal allows the tumor to grow in an ness of the vessel walls. Lesions with smaller channels are oval or round shape out into the parotid gland substance. It referred to as capillary type, and those with larger chan- is also important for the neuroimager to remember that nels are called cavernous type.15,63,64 Both histological pat- the anatomic confines of the facial nerve in the temporal terns may be seen in an individual tumor. Those facial bone, and the occasional absence of significant impedi- nerve vascular lesions with thick walls have been addi- ment to tumor growth that results from anatomy and vari- tionally described as vascular malformations, with the ants thereof may result in a variety of appearances of facial recognition that they are histologically unlike vascular ch07 9/19/08 11:55 AM Page 469

Chapter 7 Anatomy and Development of the Facial Nerve 469

A B Fig. 7.27 (A) Axial computed tomography image demonstrates exten- uninvolved. (B) Postcontrast axial T1-weighted magnetic resonance sive facial nerve hemangioma (FNH) within the otic capsule, involving image at a slightly inferior level as (A) demonstrates avid enhance- the region of the geniculate ganglion lateral and posterior to the tym- ment of the facial nerve hemangioma (FNH) and involvement of the panic segment of the facial nerve canal, which is enlarged. This lesion labyrinthine segment (LS) of the facial nerve. ([A] Courtesy of Richard demonstrates the typical “honeycomb” new bone of facial nerve H. Wiggins III, MD.) hemangioma. The adjacent cochlea and vestibule are normal and

malformations in any other part of the body.89 Some particularly if detected early.92 Once neural invasion has hemangiomas, occasionally referred to as ossifying heman- occurred, segmental facial nerve resection and repair giomas, produce spicules of lamellar bone, typically is required, with a variable outcome in facial motor beyond the margin of the adjacent temporal bone.90,91 function.92 Facial nerve hemangiomas are reported with increas- Hemangiomas may be detectable by CT despite their ing frequency and in some centers are as common as small size due to the tendency to produce bone spicules facial schwannomas.29,90–92 They occur most frequently at or amorphous “honeycomb” bone changes (Fig. 7.27 and the level of the geniculate ganglion (Fig. 7.27 and Fig. 7.28), Fig. 7.29). This honeycomb bone formation is seen in followed by the internal auditory canal (Fig. 7.29), and 50% of facial nerve hemangiomas.85 Enlargement of the least commonly at the posterior genu.29,90,92,93 The abun- labyrinthine segment of the facial nerve canal or genicu- dant vascular anastomoses supplying the facial nerve in late fossa associated with irregular, poorly defined these locations may contribute to this distribution pat- margins also suggests this diagnosis.29,90,92,93 These subtle tern. Hemangiomas are commonly small at presentation, findings require high-resolution bone algorithm CT tech- frequently under 1 cm. This highlights a distinguishing nique with careful attention to detail during interpreta- feature of these lesions; they often produce symptoms tion.92 Intravenous contrast does not add to the evalua- that belie the small tumor size. Facial nerve schwanno- tion; however, hemangiomas that do not produce bone mas, on the other hand, often reach considerably larger spicules or honeycombing of bone will appear as a mass size prior to the production of symptoms. The most fre- along the course of the facial nerve, with less sharp mar- quent clinical presentation of hemangioma is facial nerve gins than typically seen with facial nerve schwannoma palsy, which may be acute, slowly progressive, or inter- (Fig. 7.27 and Fig. 7.29). mittent. Pulsatile tinnitus has also been reported.89,94,95 Contrast-enhanced MRI has made even those lesions Lesions with an IAC component may produce sen- that were difficult for HRCT easier to diagnose.93 They ap- sorineural hearing loss, facial twitching, and/or facial pear as mildly hypointense or isointense to brain on T1WI paresis.92,96 These lesions are extraneural and may possi- hyperintense on T2WI,92 and demonstrate avid enhance- bly be resected with preservation of facial nerve function, ment following contrast administration, with irregular ch07 9/19/08 11:55 AM Page 470

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A B Fig. 7.28 (A) Axial T1-weighted magnetic resonance image (T1WI) facial nerve hemangioma (arrowheads). This lesion is relatively well de- demonstrates low signal intensity facial nerve hemangioma (FNH) of fined on MRI and could be mistaken on MRI alone for a facial nerve the geniculate ganglion extending anteriorly toward Meckel’s cave schwannoma. ([A] Courtesy of Richard H. Wiggins III, MD.) (MC). (B) Postcontrast T1WI demonstrates avid enhancement of the

margins (Fig. 7.27 and Fig. 7.28).95 Contrast-enhanced T1WIs produce only subtle widening of the facial nerve canal on are helpful in the region of the geniculate ganglion, where CT. Contrast-enhanced T1WIs demonstrate an intensely the lesion may be isointense to adjacent brain.92 Further, enhancing mass in this location. Those hemangiomas that lesions at the posterior genu of the facial nerve may do contain bone may appear as heterogeneous signal

A B Fig. 7.29 (A) Axial computed tomography (CT) image at the level of reconstruction from the CT depicted in (A) also at the level of the IAC the internal auditory canal (IAC) demonstrates characteristic calcifica- demonstrates the extensive calcification of the hemangioma (FNH) tions within an intracanalicular facial nerve hemangioma (FNH). There with scalloped expansion of the canal. The middle ear cleft is normal. is mild expansion of the bony IAC and no erosion into the cochlea or ([A] Courtesy of Richard H. Wiggins III, MD.) vestibule. The geniculate ganglion (GG) also appears normal. (B) Coronal ch07 9/19/08 11:55 AM Page 471

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intensity, with areas of low intensity representing the mature lamellar bone.95

Bell’s Palsy and Ramsay Hunt Syndrome The term Bell’s palsy or idiopathic facial paralysis is reserved for the acute onset of lower motor neuron facial paralysis for which there is no definable cause. Athough historically described as idiopathic, there is now evidence of a strong association between herpes simplex virus and Bell’s palsy, possible via reactivation of latent viral genome in the geniculate ganglion.97 The term herpetic facial paralysis has been suggested to replace current terminology, although Bell’s palsy remains in widespread use.98 The peripheral facial paralysis is believed to be secondary to neural entrapment due to interstitial edema with subsequent swelling within the tight confines of the bony facial nerve canal, leading to ischemia and eventual neural dysfunction.99,100 Over 80 causes of acute peripheral facial nerve palsy Fig. 7.30 Axial postcontrast T1-weighted magnetic resonance image have been described.10 0 The diagnosis of Bell’s palsy should with fat suppression in a patient with typical Bell’s palsy demonstrates be assigned only to patients with the typical acute onset enhancement of the facial nerve at the fundus of the internal auditory clinical presentation and in whom no concurrent evidence canal (IAC) extending into the labyrinthine segment (LS) and also along the tympanic segment (TS) of the nerve. of central nervous system, temporal bone, or parotid disease is present.101,102 In many cases, the onset of the facial paralysis is preceded by a viral prodrome. Seventy percent beyond clinical improvement and has been observed for as of patients complain of alterations in taste in the week long as 13 months following initial diagnosis.102,113,116 prior to the onset of the facial paralysis. Fifty percent of pa- The mechanism of enhancement of the facial nerve in tients report pain in or around the ipsilateral ear, and 20% Bell’s palsy is uncertain, but it may relate to either hyper- have numbness somewhere in the ipsilateral face.102–107 vascularity of the perineural structures of the nerve or Contrast-enhanced MRI as proposed in Table 7.4 typi- actual disruption of the blood–nerve barrier by acute in- cally demonstrates Bell’s palsy as a uniformly enhancing flammation. Hyperemia of the facial nerve and perineural facial nerve, either normal in size or mildly enlarged.102,108,109 structures may result in enhancement based on an The enhancement pattern is linear; no nodularity or focal increased vascular pool of the contrast material.102 A com- enlargement is present, an important feature that assists in bination of these two mechanisms is also possible. What- differentiating Bell’s palsy from neoplasm along the course ever the mechanism, not all patients with the clinical of the facial nerve.10 0 ,10 2 ,110 ,111 Enhancement commonly ex- diagnosis of Bell’s palsy demonstrate contrast enhance- tends from the distal internal auditory canal through the in- ment of the involved facial nerve; reported enhancement tratemporal segments, although the distal portion of the rates vary from 57 to 100%.110 ,111,113 ,114 ,116 In theory, severe nerve (distal intratympanic, mastoid segments) enhances edema in the facial nerve can impair the neural microcir- less frequently (Fig. 7.30, Fig. 7.31, and Fig. 7.32).10 2 ,111,112 Focal culation, reduce contrast delivery to the affected region, enhancement of the facial nerve in the fundal portion of the and result in a negative enhanced MRI study. IAC is a frequent, distinctive MRI finding (Fig. 7.30, Fig. 7.31, The typical patient with acute onset peripheral facial and Fig. 7.32).99,102,111,113–115 This segment of the facial nerve nerve paralysis (Bell’s palsy) need not undergo radiologi- does not normally enhance. Oblique sagittal images could cal evaluation in the initial phase of the illness. Even show the enhancing nerve from the geniculate ganglion to though MRI usually demonstrates characteristic findings, the stylomastoid foramen in one image, although standard imaging of this common malady is not cost-effective. coronal and axial images may segmentally demonstrate Only in the exceptional patient for whom decompressive enhancement and are adequate. Because the facial nerve surgery is anticipated in an attempt to assist facial nerve can normally enhance at its anterior and posterior genu, recovery should MRI be performed to help identify the af- contiguous enhancement must be present to diagnose fected facial nerve segment and to exclude another lesion Bell’s palsy. The pattern and location of enhancement are causing the facial nerve paralysis. not helpful in predicting outcome for an individual It is the patient with the atypical Bell’s palsy who patient.111,112 ,116 Abnormal enhancement may persist well should be examined with MRI to search for a clinically ch07 9/19/08 11:55 AM Page 472

472 Imaging of the Temporal Bone

A B Fig. 7.31 (A) In this patient with right Bell’s palsy, axial postcontrast T1- petrosal nerve (GSPN) in the facial hiatus. (B) The coronal postcontrast weighted magnetic resonance image (T1WI) demonstrates enhance- T1WI at the level of the geniculate ganglion (GG) demonstrates avid ment of the intracanalicular segment (CS) of the facial nerve, at the enhancement of the ganglion. The cochlea is normal. The geniculate level of the tympanic segment (TS), and along the greater superficial ganglion appears prominent but is not enlarged.

occult cause of the paralysis. Atypical Bell’s palsy is de- mass lesion.45,117,122,123 Abnormal enhancement of the facial fined as slowly progressive palsy, facial hyperfunction nerve may be absent in up to 50% of patients with Ramsay (spasm) preceding the palsy, recurrent palsies, unusual Hunt syndrome. This may be related to the timing of the degrees of pain, multiple cranial neuropathies, or periph- MRI examination during the course of the infection. eral facial nerve paralysis persisting beyond 2 months. Gadolinium enhancement may not occur until the infec- Virtually all patients with Bell’s palsy recover at least tion has produced sufficient inflammation and some facial nerve function.105 When no facial nerve recov- edema.120,124 Recently, abnormal T2-weighted signal in the ery occurs, the diagnosis of Bell’s palsy should be ques- cochlea and vestibule has also been described in Ramsay tioned, and the MRI protocol suggested in Table 7.4 Hunt syndrome patients.125 should be performed in a search for treatable causes of facial nerve paralysis. Hemifacial Spasm Ramsay Hunt syndrome, also known as herpes zoster oticus, is a facial neuritis of acute onset associated with Hemifacial spasm (HFS) is a condition of facial hyperfunc- painful, often hemorrhagic, vesicles in the external tion characterized by intermittent tonic and clonic auditory canal, tympanic membrane, and pinna.117–119 It contraction of muscles innervated by the facial nerve, may involve the eighth cranial nerve also, resulting in affecting one half of the face. The muscular contractions vertigo, hearing loss, and/or tinnitus. Symptoms are felt are involuntary and spasmodic. The condition is slowly to result, similarly to Bell’s palsy, from reactivation of progressive, beginning as a mild, infrequent spasm of the latent Varicella zoster virus infection of the geniculate orbicularis oculi and progressing to severe, repeated con- ganglion.120 tractions of all of the muscles of one side of the face, to MRI findings in Ramsay Hunt syndrome vary. Contrast- include the platysma. The frontalis muscle may be spared. enhancement of the geniculate, intratympanic, and mas- HFS commonly presents in middle age and affects women toid portions of the facial nerve, identical to Bell’s palsy, more frequently than men; familial hemifacial spasm has can be seen (Fig. 7.33).121 In some patients with both sev- been described.126,127 Although pain does not typically enth and eighth nerve symptoms, enhancement of the accompany HFS, patients may complain of dull, aching eighth nerve may be demonstrated, including the intra- pain related to long-standing muscular spasm, and the canalicular segment, with extension into the cochlea and coexistence of trigeminal neuralgia and HFS occurs in up vestibule. The intracanalicular abnormality may mimic a to 11% of trigeminal neuralgia patients, a condition known ch07 9/19/08 11:55 AM Page 473

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A B

Fig. 7.32 (A) Coronal postcontrast T1-weighted magnetic resonance image (T1WI) with fat suppression in a patient with typical left Bell’s palsy just posterior to the internal auditory canal demonstrates enhancement of the geniculate ganglion (GG), closely ap- proximating the floor of the left middle fossa and the left temporal lobe. (B) Coronal postcontrast T1WI adjacent to (A) demonstrates enhancement in the “snake eyes” of the distal labyrinthine segment (DLS) and proximal tympanic segment (PTS) of the facial nerve. The adjacent cochlea is normal. (C) Coronal T1WI section through the mastoid segment (MS) of the facial nerve demonstrates enhancement to the level of the extracranial segment below the stylomastoid foramen. C

as “tic convulsif.”128–130 In advanced stages, the spasms are disorders are separate and distinct from synkinesis, which so frequent and severe that the patient is no longer able is the mass movement of multiple muscle groups during to see clearly out of the affected eye.34,64,130 purposeful movement of the face. Synkinesis is usually HFS is to be distinguished clinically from myokymia, the result of aberrant regeneration following facial nerve which is a condition of fine, continuous and undulating palsy or surgical repair of a transected facial nerve.128,129 movements of the face, involving fascicles rather than en- The most common etiology of hemifacial spasm is tire muscle groups. The two may rarely coexist. compression of the cisternal segment of the facial nerve Myokymia is most commonly related to intramedullary by a redundant artery, reported in up to 92% of pontine lesions near the facial nucleus.34,128,129,131,132 Both cases.34,64,128–130,133 The most common arteries implicated ch07 9/19/08 11:55 AM Page 474

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A B

Fig. 7.33 (A) Axial T1-weighted magnetic resonance image (T1WI) of a patient with Ramsay Hunt syndrome, with typical zoster oticus on clinical presentation. Both internal auditory canals (IACs) and the cranial nerves within are normal on this unenhanced image. (B) Axial postcontrast T1WI (same level as in [A]) demonstrates enhancement of CN VII at the fundus of the IAC (IAC), extension into the labyrinthine segment (LS), and also avid enhancement of the geniculate ganglion (GG). (C) Coronal postcontrast T1WI at the level of the “snake eyes” of CN VII demonstrate asymmetric enhancement of the distal labyrinthine segment (DLS) and proximal tympanic segment (PTS). The contralateral DLS and PTS are indicated for comparison (Normal). C

are the anteroinferior cerebellar artery, the posterior by a redundant vessel.127 At the junction of the thin cen- inferior cerebellar artery (Fig. 7.23), and the vertebral tral myelin of the facial nerve and the thicker peripheral artery.133 The auditory artery, the cochlear artery, and the myelin, called the Obersteiner–Redlich zone, the redun- CPA cistern veins also have been implicated.127 The basilar dant vessel may gradually erode the insulating myelin artery is rarely the offending vessel. The vessel compress- sheath, thereby causing a “short-circuiting” phenomenon ing the nerve usually lies at right angles to the facial of ephaptic conduction and ectopic excitation, producing nerve in the root exit zone, close to the brainstem. At the intermittent, involuntary contractions of the facial mus- root exit zone, the motor fibers of the facial nerve lie culature on the affected side.128,130 It is important to medial to both the nervus intermedius and the vestibulo- remember, however, that a prominent vessel can be de- cochlear nerve, and are therefore preferentially impacted tected in the CPA cistern in up to 30% of asymptomatic ch07 9/19/08 11:55 AM Page 475

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individuals, and the significance of such a loop must be the normal neural anatomy is excluded from depiction on evaluated in clinical context.128 MIP images (Fig. 7.23).136–138 Some authors report in- Other etiologies of HFS have been documented, includ- stances in which only the source images define the abnor- ing cholesteatoma, schwannoma, meningioma, lipoma, mal vessel.136 However, the lack of identification of a re- aneurysms,134 and AVM of the ipsilateral CPA cistern. dundant vessel on MRI does not preclude surgical Intratemporal facial nerve schwannoma, intraparotid treatment of a patient with hemifacial spasm as long as tumor, bony abnormalities of the skull base, and con- other potential etiologies have been excluded. Smaller tralateral CPA neuroma resulting in kinking of the brain- vascular loops may escape detection with any MRI stem have also been reported to cause HFS. Very rarely, technique. intramedullary pontine lesions such as multiple sclerosis Management of HFS has included the use of medica- may be responsible. tions, botulinum toxin injections into the facial muscula- Radiological investigation of patients with hemifacial ture, and microsurgical decompression of the facial nerve. spasm is performed not specifically to identify the offend- Baclofen, clonazepam, carbamazepine, and phenytoin may ing vascular loop (although it may be identified), but to provide transient relief but are not effective for long-term identify a potential lesion other than a vascular loop. MRI treatment.139 Botulinum toxin injections have proven an is the study of choice in the evaluation of patients with effective management option for HFS, with repetitive in- hemifacial spasm because of its inherent ability to visual- jections necessary for long-term relief.139,140 ize the relationships of the structures of the CPA cistern Surgical treatment of patients with debilitating hemi- and to evaluate the facial nerve from pons to parotid.133,135 facial spasm unresponsive to conservative treatment in- As with other clinical settings involving the facial nerve, volves decompression of the facial nerve by mobilizing imaging should include the entire course of the nerve, the redundant vascular loop away from the cisternal seg- with T1-, T2-, and contrast-enhanced T1-weighted se- ment of the facial nerve with the use of microsurgical quences. MRA techniques that may improve the visualiza- techniques (microvascular decompression).64,130,141–149 Var- tion of redundant or aberrant vessels in the CPA cistern ious forms of surgical packing may be inserted between should also be used and are described in Table 7.4. It is the offending loops and the facial nerve. Surgical inter- important to review the source images of the MRA in ad- vention is 80% successful on the first attempt, with disap- dition to the maximum intensity projection images when pearance of the hemifacial spasm occurring immediately assessing for vascular compression of the facial nerve as after the surgery in most cases.142

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Mi- ogy 1991;179:795–796 crovascular decompression for hemifacial spasm: a ch07 9/19/08 11:55 AM Page 479

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long-term follow-up of 1,169 consecutive cases. Stereo- 146. Moller AR. Vascular compression of cranial nerves: II: tact Funct Neurosurg 2001;77(1–4):190–193 pathophysiology. Neurol Res 1999;21(5):439–443 143. Kalkanis SN, Eskandar EN, Carter BS, Barker FG II. Mi- 147. Samii M, Gunther T, Iaconetta G, Muehling M, Vorkapic crovascular decompression surgery in the United States, P, Samii A. Microvascular decompression to treat hemi- 1996 to 2000: mortality rates, morbidity rates, and the facial spasm: long-term results for a consecutive series effects of hospital and surgeon volumes. Neurosurgery of 143 patients. Neurosurgery 2002;50(4):712–718 2003;52(6):1251–1261 discussion 61–2 148. Wilkinson MF, Kaufmann AM. Monitoring of facial mus- 144. McLaughlin MR, Jannetta PJ, Clyde BL, Subach BR, cle motor evoked potentials during microvascular de- Comey CH, Resnick DK. Microvascular decompression of compression for hemifacial spasm: evidence of changes cranial nerves: lessons learned after 4400 operations. in motor neuron excitability. J Neurosurg 2005;103(1): [see comment] J Neurosurg 1999;90(1):1–8 64–69 145. Moffat DA, Durvasula VSP, Stevens King A, De R, Hardy 149. Yuan Y, Wang Y, Zhang S-x, Zhang L, Li R, Guo J. Mi- DG. Outcome following retrosigmoid microvascular de- crovascular decompression in patients with hemifacial compression of the facial nerve for hemifacial spasm. J spasm: report of 1200 cases. Chin Med J (Engl) 2005; Laryngol Otol 2005;119(10):779–783 118(10):833–836 ch08 9/19/08 11:57 AM Page 480

The Vestibulocochlear Nerve, 8 with an Emphasis on the Normal and Diseased Internal Auditory Canal and Cerebellopontine Angle Christine M. Glastonbury

The vestibulocochlear nerve is the eighth cranial nerve causes of hearing loss and as they may be unexpectedly (CN VIII) and is responsible for the transmission of electri- discovered at the time of temporal bone imaging for SNHL cal impulses from cochlear hair cells of the inner ear to or conductive hearing loss (CHL). the cochlear nuclear complex in the brainstem. The vestibulocochlear nerve passes through the internal auditory canal (IAC) and cerebellopontine angle (CPA), forming Normal Anatomy of the Auditory the extraaxial component of the central auditory path- Pathway way. Dysfunction in this pathway results in sensorineural hearing loss (SNHL). The most common abnormality The cell bodies of the cochlear nerve are located in the when imaging a child with SNHL is a congenital inner ear modiolus, the spongy bone at the center of the cochlea. malformation,1 whereas the most common cause of uni- These spiral ganglia are bipolar, with one axon arising lateral or asymmetric SNHL in an adult is a schwannoma from the cochlear organ of Corti that receives auditory of the vestibulocochlear nerve. information and one axon that transmits this information When presented with a request to image a patient to the brainstem. The cochlear nerve is formed from those with a history of SNHL, dedicated imaging is required of axonal fibers that exit the modiolus of the cochlea the cochlea, IAC, and the CPA. If additional cranial neu- through a small bony opening called the cochlear canal or ropathies are present in association with the SNHL, such cochlear aperture.2–4 This cochlear nerve enters the an- as trigeminal neuralgia or facial nerve palsy, then a large teroinferior quadrant of the fundus of the IAC and courses CPA mass, a leptomeningeal process, or a brainstem ab- medially toward the CPA and brainstem auditory nuclei normality such as multiple sclerosis must be considered. (Fig. 8.1). Because the cochlear nerve is a sensory nerve, SNHL in association with cerebellar-type neurological the centripetal pathway toward the brainstem is consid- findings such as ataxia and weakness suggests the pres- ered the anterograde direction. The bony contours of the ence of a posterior fossa and/or brainstem abnormality. cochlear aperture and the IAC are readily appreciable on Bilateral SNHL or complex auditory dysfunction, such as temporal bone CT imaging when acquired at 1 mm auditory agnosia, suggests a process that is more centrally thick slices using a bone algorithm (Fig. 8.2). The internal located along the auditory pathway. auditory canal with its lateral “dead-end” fundus and This chapter begins with a discussion of the anatomy medial internal auditory meatus, or porus acusticus, is of the retrocochlear auditory pathway from the cochlear roughly cylindrical in shape. There are variations between modiolus to the primary auditory cortex of the superior patients of the vertical height and transverse diameter, temporal gyrus. Magnetic resonance imaging (MRI) plays with the average height (from tomographic studies) an important role in the evaluation of patients with SNHL, measured at 4 mm (range 2 to 8 mm). More important, and a discussion of the currently available techniques for the IAC is essentially symmetric in patients with a differ- high-resolution imaging of the inner ear, IAC, and CPA fol- ence in dimensions of 1 mm in 99% of patients and 1 to lows. The congenital and acquired pathologic conditions 2 mm in 1% of patients.5 The IAC is directed at 45 degrees that may be found along the central acoustic pathway to the long axis of the petrous bone, which is at 45 degrees from the IAC to the auditory cortex are then discussed, to the true sagittal plane of the skull. with an emphasis on the most commonly found lesion At the fundus, or lateral aspect of the IAC, the three causing adult SNHL, the vestibular schwannoma. Finally, components of the vestibulocochlear nerve are distinct lesions of the petrous apex are discussed, both as potential separate nerves: the cochlear nerve lies in the anteroinferior

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A B Fig. 8.1 Internal auditory canal (IAC) anatomy. Heavily T2-weighted superiorly, the facial nerve is seen in the CPA and IAC (arrows). The FIESTA sequence through the IACs (A) shows the normal anatomy with fluid-filled vestibule and canals are also clearly seen bilaterally (curved the thick vestibulocochlear nerve (VCN) in the CPA and IAC (arrows), arrows). The flocculus of the cerebellum is a rounded “mass-like” structure reaching the modiolus of the fluid-filled cochlea (curved arrow). Branch- in the CPA (*). ing of the VCN can be seen in the axial plane (open arrows). (B) More

aspect of the IAC, the inferior vestibular nerve posterior to nerves at the fundus of the IAC shows the cochlear nerve to this, and the superior vestibular nerve in the superior be larger than the superior or inferior vestibular nerves, aspect of the fundus, posterior to the facial nerve (Fig. 8.3 and of similar size or larger than the facial nerve in nearly and Fig. 8.4). In 90% of normal cases, evaluation of the two thirds of normal cases.6 At the medial aspect of the

A B Fig. 8.2 Internal auditory canal (IAC) anatomy by computed tomogra- arrows). (B) Axial CT through the superior aspect shows the labyrinthine phy (CT). (A) Axial CT through the mid-IAC demonstrates the porus segment of the facial nerve (arrow) and the small canal for the nerve to acusticus (white arrow), the fundus (*), and the cochlear aperture (black the horizontal semicircular canal (*). ch08 9/19/08 11:57 AM Page 482

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Fig. 8.3 Drawing of membranous labyrinth and distal internal auditory quadrant of the IAC. It is separated from the facial nerve by the crista canal (IAC) shows the relationship of the cochlea to other labyrinth struc- falciformis in the fundus of the IAC. (SCC, semicircular canal; U, utricle; tures. Inset shows the position of the cochlear nerve in the anteroinferior S, saccule; G, vestibular ganglion; A, anterior; S, superior.)

IAC the superior and inferior vestibular nerves and the and inferior vestibular); however, the location is relatively cochlear nerve join to form the vestibulocochlear nerve. symmetric within individuals.6,7 At the level of the porus There is significant variability between individuals in the acusticus, CN VIII is usually found as one nerve bundle exact site of union of these three nerves (cochlear, superior, with an elongated, almost rectangular, cross-sectional shape (Fig. 8.5). Oblique sagittal T2-weighted magnetic resonance images (T2WIs) performed perpendicular to the course of the IAC allow appreciation of the anatomical arrangement of the facial and cochleovestibular nerves, as they are hypointense and are surrounded by the marked hyperintensity of the cerebrospinal fluid (CSF) that fills the IAC.6,7 On computed tomography (CT) evaluation of the IAC, the nerve elements cannot be identified, though their location can be inferred using bony landmarks. The superior half of the IAC fundus (containing the facial nerve with the nervus intermedius and the superior vestibular nerve) is separated from the inferior IAC (containing the cochlear and inferior vestibular nerves) by the crista falciformis (falciform crest). This is a horizontal bony bar that is evident on coronal CT imaging, and frequently also seen as an area of signal void on T2WIs , which lies at or above the midpoint of vertical canal height (Fig. 8.6).5 A vertical crest called Bill’s bar separates the superior fundus above the crista falciformis into anterior and posterior portions containing the facial nerve and superior vestibular nerve, respectively. Bill’s bar is described as consisting of a thin layer of arachnoid tissue that may Fig. 8.4 Normal nerves at the internal auditory canal (IAC) fundus. have an osseous medial component, but it itself is not Oblique sagittal T2-weighted magnetic resonance image demonstrates discernible at high-resolution CT (HRCT) or MRI.8–10 The the four nerves at the fundus of the IAC: the facial nerve superiorly and anteriorly, the cochlear nerve anteroinferiorly, and the superior and infe- superior vestibular nerve has several branches that sup- rior vestibular nerves posteriorly (curved arrow). ply the superior and horizontal semicircular canals and ch08 9/19/08 11:57 AM Page 483

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A B Fig. 8.5 Nerves in the Internal auditory canal (IAC). Sagittal T2-weighted more laterally in the mid-IAC, the VCN (curved arrow) starts to elongate magnetic resonance image through the IAC. (A) At the porus, the facial more, before becoming three nerves, as seen in Fig. 8.4 at the more nerve is anterior (arrow), with the vestibulocochlear nerve (VCN) poste- lateral aspect of the IAC. rior (curved arrow) as an elongated thick bundle. (B) As it is imaged

the saccule. The inferior vestibular nerve supplies the which can be identified on axial temporal bone CT aris- utricle and has a separate branch to the ampulla of the ing from the mid to distal portion of the IAC (Fig. 8.7). posterior semicircular canal. This posterior ampullary The singular canal is an important surgical landmark nerve (or “singular nerve”) traverses the singular canal, identified for a retrosigmoid approach for resection of a

Fig. 8.7 Singular canal. Axial computed tomography scan at the level Fig. 8.6 Crista falciformis. Coronal computed tomography image of the modiolus shows this tiny canal (arrow) from the posterosuperior shows the horizontal crista falciformis (arrow) that divides the internal aspect of the internal auditory canal to the ampulla of the posterior auditory canal into superior and inferior halves. semicircular canal (curved arrow). ch08 9/19/08 11:57 AM Page 484

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vestibular schwannoma. It should not be mistaken for a Four vestibular nuclei are also located in the brainstem fracture on CT. medial to the cochlear nuclei.15 As the vestibulocochlear nerve traverses the CPA, it is Some second-order neurons arising from the dorsal posterior to CN VII, and both of these nerves are inti- and ventral nuclei of the cochlear nuclear complex cross mately related to the anteroinferior cerebellar artery in the trapezoid body of the medulla, while some (AICA). This vessel is a branch of the basilar artery, which synapse in the superior olivary nucleus of the medulla. is ventral and inferior to CN VII and CN VIII. On axial These fibers then ascend to the contralateral inferior T2WIs, the AICA is seen as a flow void. In two thirds of colliculus of the midbrain. Other fibers do not cross, but normal cases this artery loops into the IAC or projects to ascend on the ipsilateral side to the inferior colliculus. the porus acusticus (Fig. 8.8).11 Up to four internal audi- These ascending crossed and uncrossed fibers form the tory arteries arise from the AICA to supply the inner ear.12 lateral lemniscus of the pons (Fig. 8.11). There is further The vestibulocochlear nerve enters the brainstem at crossing of fibers in the commissure of the inferior colli- the root entry zone of the upper lateral medulla immedi- culi. Third-order neurons from the inferior colliculus ately superficial to the inferior cerebellar peduncle.13,14 ascend to the medial geniculate body of the thalamus, The cochlear component of CN VIII synapses with two nu- where fibers from fourth-order cell bodies form the audi- clei known as the cochlear nuclear complex. The dorsal tory radiation to the transverse temporal gyrus of Heschl. nucleus receives high-frequency signals from the lower Heschl’s gyrus is usually identified as a single gyrus and turns of the cochlea, and the ventral cochlear nucleus less commonly as two gyri, at the posterior aspect of the receives lower frequencies from the upper cochlear superior temporal gyrus. It can be identified on sagittal, turns.13 The cochlear nuclear complex produces a bulge of axial, and coronal planes at MRI (Fig. 8.9).16 Heschl’s the medulla into the lateral recess of the fourth ventricle gyrus roughly corresponds to the primary auditory cor- and the foramen of Luschka (Fig. 8.9). Additional useful tex (A1) in Brodmann’s area 41 and 42, with both left and landmarks for identifying the site of the cochlear nuclear right hemispheres receiving information from each complex on imaging studies are the cerebellar flocculus, cochlea.16,17 Just as the motor cortex has the “homuncu- which lies posterolateral to the nerve complex, and the lus” arrangement of motor tasks, the auditory cortex has intervening choroid plexus, which may protrude through a tonotopic organization of frequencies also.18 The supe- the foramen of Luschka from the fourth ventricle (Fig. 8.10). rior surface of the temporal lobe behind Heschl’s gyrus is

A B Fig. 8.8 Anteroinferior cerebellar artery (AICA) loop. (A) Axial unen- VII and CN VIII (open arrow). (B) Axial heavily T2-weighted constructive hanced computed tomography image performed after craniotomy interference in steady-state (CISS) sequence in a different patient simi- shows air in the cerebellopontine angles and air outlining a right AICA larly demonstrates a vascular AICA loop (arrows) in the IAC. (arrow) as it loops into the internal auditory canal (IAC) adjacent to CN ch08 9/19/08 11:57 AM Page 485

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A B

C D Fig. 8.9 High-resolution axial fast spin echo (FSE) T2-weighted mag- (B, brachium pontis; V, vermis of cerebellum). (C) Midpons at the level netic resonance images through the central auditory pathway. (A) The of the facial colliculus (black arrow), which indents the fourth ventricle medulla with the dorsal and ventral nuclei of the cochlear nuclear com- (4); the lateral lemniscus is found within the body of the pons. The supe- plex (circles), lateral to the restiform body (*) (also known as the inferior rior vestibular nucleus (*) is also found at this level. Note also the mem- cerebellar peduncle). The medial and inferior vestibular nuclei are branous labyrinth (white arrow) and vestibulocochlear nerve (curved located medial to the restiform body. Note the close relationship of the arrow). (D) Superior pons shows the position of the lateral lemniscus. cochlear nuclear complex to the foramen of Luschka (arrow). (B) The The medial longitudinal fasciculus can be seen in cross section as a inferior pons with the centrally located trapezoid body (also known as slightly hypointense fiber tract (arrow). Much of the body of the pons is the inferior acoustic stria) and the medial lemniscus (*) lateral to this. formed by the pontocerebellar tracts (p) and anterior to these by pon- The superior olivary nucleus (S), adjacent to this receives fibers from the tine nuclei and the corticospinal, corticopontine, and corticobulbar trapezoid body and contributes to the formation of the lateral lemniscus tracts fibers (c).

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E F

Fig. 8.9 (Continued) (E,F) At the mesencephalon (midbrain), the inferior colliculus (arrow) receives input from the adjacent lateral lemniscus and projects to the medial geniculate nucleus. (F) The medial geniculate nucleus can be found on the same axial slice as the red nucleus (arrow). Note also the pulvinar of the thalamus (p) has connections with the medial and lateral geniculate bodies and supratentorial cortex. (G) Midbasal ganglia and superior temporal gyrus. The anterior transverse temporal gyrus (Heschl’s gyrus, H) and the adjacent gyrus form the primary auditory cortex. G

called planum temporale and is probably related to the Imaging the Internal Auditory Canal, cortical representation of language.18 Functional MRI (fMRI) studies, positron emission tomography (PET), and Cerebellopontine Angle, and amobarbital angiographic studies have shown laterality Vestibulocochlear Nerve for listening and speech. In most people, regardless of preferred handedness, the left temporal lobe appears to There are two imaging tools available to the radiologist be better for processing language information, and the when evaluating a patient for SNHL. Computed tomography right temporal lobe more important for processing non- is ideal for evaluation of the inner ear and otic capsule verbal natural sounds (Fig. 8.12).19–23 when bone pathology is suspected such as with traumatic ch08 9/19/08 11:57 AM Page 487

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Fig. 8.10 Drawing of the vestibulocochlear nerve, root entry zone, and M, medial vestibular nucleus; Md, medulla; 4V, fourth ventricle; Fl, nuclei within inferior cerebellar peduncle (restiform body). Facial nerve foramina of Luschka; F, flocculus; CP, choroid plexux. The cochlear nu- has not been included in drawing. The cochlear nerve is drawn with clei are normally found on the superficial edge of the inferior cerebellar hatch marks. Note the close relationship of the cochlear nuclei to the peduncle. Although the nuclei themselves are not visible, finding the lateral recess of the fourth ventricle and foramina of Luschka. V, ventral inferior cerebellar peduncle contour on high-resolution MR imaging cochlear nerve; D, dorsal cochlear nucleus; L, lateral vestibular nucleus; can localize their approximate location.

SNHL or with otodystrophies (otic capsule dysplasias such T1WIs, axial T2WIs, and fluid attenuated inversion recovery as osteogenesis imperfecta), or suspected acquired bone (FLAIR) images, and axial whole brain gadolinium-enhanced pathology such as Paget’s disease or cochlear otosclerosis. axial T1WIs. Axial and coronal postgadolinium thin-section In these cases, CT evaluation of the temporal bone should (3 mm) images should be obtained through the IACs. be performed with thin sections of the order of 1 mm in Gadolinium-enhanced MRI has a high sensitivity and thickness, preferably in two planes directly obtained, or specificity for the detection of vestibular schwannoma, with coronal reformations of axial slices. Images should which is the most common pathology found in cases of always be processed with a high spatial frequency (bone) acquired, unilateral sensorineural hearing loss. The use of algorithm and viewed with wide windows (window three-dimensional spoiled gradient recalled (3D SPGR) width of 4000, window level 500 to 600). sequences allows 1.5 mm section thickness and thus Most other causes of SNHL warrant MRI to best evaluate better depiction of the tumor and its relation to the brain- the nerves of the IAC and the CPA, as well as to review stem or the fundus of the IAC. the central auditory pathway from the inferior cerebellar peduncle to the auditory cortex at the superior temporal gyrus. The MRI study for evaluation of SNHL can be performed as a Screening Internal Auditory Canal Protocols “brain-IAC study” with the administration of gadolinium High-resolution, heavily T2WI of the IAC and CPA has to evaluate for IAC or CPA masses and for complete cover- been suggested as an alternative to whole brain gadolin- age of the central auditory pathway. In some practices, ium imaging as a significant reduction in scan time and high-resolution, thin-section T2WI “screening examination” cost.24 It should only be used alone as a screening study in is performed alone; however, this should only be per- selected cases of unilateral isolated SNHL, and is usually formed in cases of uncomplicated unilateral SNHL when a performed after complete clinical examination and audiom- vestibular schwannoma is strongly suspected by an otolo- etry. It should be recognized that this screening protocol gist. More frequently, the high-resolution T2WI is employed has the potential to miss small tumors, many of which in addition to a brain-IAC study. would be followed clinically at this size. The choice of a T2-weighted sequence is a heavily Brain–Internal Auditory Canal Protocols debated, discussed, and published topic. Essentially there are two types with many variations: fast spin-echo (FSE) A protocol to encompass the central auditory pathway and based sequences and gradient echo (GRE) based sequences. IAC typically consists of whole brain sagittal and axial Initially, GRE-based sequences offered thinner slices for ch08 9/19/08 11:57 AM Page 488

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Fig. 8.12 Primary auditory cortex. Functional magnetic resonance imaging study in a teenager with a large left frontoparietal pericentral arteriovenous malformation, performed for evaluation of risks associated with possible treatment. Auditory evoked potentials localize bilaterally to the posterior superior temporal gyri (arrows), with the right being more anterior than the left side.

and –90 degrees (x plane) pulses at the end of the echo train flips residual spins from the transverse plane to the longitudinal axis. It thus enhances the signal of slowly recovering tissues such as CSF, allowing increased contrast resolution or a shorter time- to-repetition (TR) and therefore significant time Fig. 8.11 Diagram of the entire course of the acoustic pathway from 25 its end organ, the cochlea, to its central processing area, the superior reduction. temporal gyrus. Notice the majority of centrally projecting fibers cross • 3D fast asymmetric spin echo (FASE). This is a half in the midpontine tegmentum in the trapezoid body. Fourier rapid acquisition with relaxation enhancement (RARE) type sequence, based on 3D FSE, but with a long echo train length (ETL).26 A modification improved spatial resolution; however, these were ham- of this, the zero-fill interpolated (ZIP) fast recovery 3D pered by local magnetic field susceptibility artifacts, which FASE sequence, can significantly reduce the scan time the FSE-based sequences are not. The recent advances in of the FASE sequence. both types of sequences have been in an attempt to mini- • 3D constructive interference in the steady state (CISS). mize scan time without loss of signal-to-noise (SNR) or This sequence allows better spatial resolution than the resolution to make the study as acceptable to patients as initially available FSE sequences with minimization of possible. Below is a short summary of some of the myriad CSF flow artifacts and a short scan time. The sequence of sequences available. For the best spatial resolution and is acquired by averaging two 3D Fourier transformed SNR, surface coils, such as the temporomandibular joint datasets, one with an alternating radiofrequency (RF) (TMJ) coil, can be used. pulse and the other with a nonalternating RF pulse. The signal acquired is partially from GRE mechanisms, • 3D T2 FSE. Very good quality thin-section images; how- resulting in some problems with susceptibility artifacts ever, scan time is considered excessively long. in the membranous labyrinth mimicking pathology, • 3D T2 FSE with fast recovery (FRFSE) (driven equilib- and significant image degradation with excessive den- rium pulse). The addition of 180 degrees (y plane) tal amalgam.27–29 ch08 9/19/08 11:57 AM Page 489

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• 3D segment interleaved motion compensated acquisition Pathology in the steady state (3D-SIMCAST). This sequence uses more than two-directional phase cycling and a shorter Lesions of the Internal Auditory Canal TE by fractional echo, resulting in reduced susceptibil- and Cerebellopontine Angle ity artifacts but increased scan time. Nearly isotropic voxels are created after interpolation.30 Among the lesions of the auditory pathway causing SNHL • 3D true-fast imaging with steady-state precession (FISP) and detected at imaging, the IAC–CPA complex is the and a variant of this, full balanced steady-state coherent most common location, and vestibular schwannoma is imaging (FBSSC). These have also been recommended. the single most common pathologic entity responsible for The FBSSC requires a high-performance gradient sys- SNHL.34,35 Meningioma and epidermoid are the next most tem but allows for very short TR and TE values, and frequently found CPA masses, with these three lesions therefore a shorter scan time. responsible for more than 90% of all CPA lesions. The remaining 10% are made up of more than 60 different Many of these 3D sequences can be postprocessed to CPA masses, reflecting a wide variety of pathologies.36 For produce maximum intensity projection or 3D volume- discussion it is perhaps best to divide these lesions into rendered or endoscopic-type images of the inner the diagnostic groups of congenital and acquired neoplas- ear.25,26,31,32 tic and nonneoplastic entities, with an emphasis on the “big three” masses of the CPA. 3T Magnetic Resonance Imaging The emergence of ultra-high field (3.0 Tesla) MRI has Congenital Internal Auditory Canal heralded the possibility of significant improvements in Malformations signal to noise and spatial resolution in IAC imaging. There are several technical and safety issues that must The IAC essentially forms by default early in gestation. be addressed. The presence of a vestibulocochlear nerve at the medial aspect of the otic capsule inhibits cartilage formation • A basic consideration in the modification of any neuro- leaving a canal connecting the inner ear to the CPA. radiology sequence for 3T imaging is that the T1 of CSF The facial nerve and its canal develop independently of will be prolonged (as T1 field strength x gyromag- the vestibulocochlear nerve but become enveloped in netic ratio). A longer TR is thus required which directly the developing otic vesicle. If the vestibulcochlear nerve is increases scan time (as scan time TR). absent due to otic capsule malformation, such as a Michel • Susceptibility artifacts are more pronounced at 3T as anomaly with absence of the cochlea, the IAC cannot compared with 1.5T, making the GRE-based sequences form and the canal becomes the caliber of the facial nerve (e.g., 3D-CISS, 3D-SIMCAST, 3D true FISP) potentially alone.37,38 In early tomographic and CT studies, an IAC more problematic. measuring less than 2 mm in diameter was defined as IAC • The specific absorption rate (SAR) is increased with a aplasia.39,40 High-resolution MRI obtained with oblique higher field strength, and this is particularly so with sagittal thin slices perpendicular to the course of the IAC GRE-based sequences, which have a higher SAR at 3T allows demonstration of this small canal, but also absence than 3D FSE-based sequences. The higher field SAR of the vestibulocochlear nerve (Fig. 8.13).4,41 A small or concerns will also limit the use of a longer echo train hypoplastic cochlear nerve may also be found, where the length (ETL) with FSE-based sequences. It has been nerve is similar in size or smaller than either of the suggested that the fast recovery FSE will help to offset vestibular nerves. A normal-sized IAC with an absent or this problem.33 small cochlear nerve suggests that the nerve abnormality • Although TMJ surface coils are advantageous with high- is acquired after formation of the internal auditory canal. resolution imaging to improve the signal-to-noise ratio, This has been observed in patients with acquired SNHL these are receive-only coils requiring the whole body such as labyrinthitis ossificans.4 Abnormality of vestibulo- coil for RF transmission. This is associated with an in- cochlear nerve caliber may have important implications crease in SAR, which is within acceptable limits at 1.5T, in patients with bilateral SNHL requiring cochlear implan- but becomes unacceptable at 3T. Kocharian et al have tation on one side, and it has been suggested that the suggested the use of a hybrid phased array coil (two cir- more robust-appearing nerve be selected. Absence of the cular surface receive-only coils combined with a transcochlear nerve is a contraindication to implantation.40 mit-receive birdcage head coil). Using this coil and the Acquired narrowing of the IAC secondary to bony over- 3D FR FSE high-resolution sequence, higher signal-to- growths, either exostoses or osteomas, has also been de- noise images can be obtained in less than 9 minutes.32 scribed.41 Although these bony lesions are particularly rare, ch08 9/19/08 11:57 AM Page 490

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they may clinically mimic vestibular schwannomas by com- Arachnoid Cysts pression of the vestibulocochlear nerve (Fig. 8.14). Hearing An arachnoid cyst is a round, smooth mass contained loss and vestibular symptoms, including dizziness and ver- within, but separated by a thin membrane from, the sub- tigo, may improve after surgical removal of the bony lesion. arachnoid CSF. These lesions probably develop through An enlarged IAC ( 9 mm) may be seen as an incidental failure of embryonic meninges to merge, resulting in a finding (Fig. 8.15), but has been described with the X-linked subarachnoid CSF-filled cyst.52 Pathologically, a thin stapes gusher. This syndrome is typically seen in male membrane of flattened, nonneoplastic arachnoid cells is patients with congenital mixed hearing loss and is charac- found and the cyst fluid is identical to CSF. Arachnoid terized by the presence of a fixed stapes footplate and cysts are most frequently found in the middle cranial “gushing” of perilymph at attempted stapedectomy.42 An fossa, with up to 5% located in the posterior fossa.53 Their enlarged or “bulbous” IAC has been described at CT imag- clinical presentation may be related to compression of ing, with incomplete separation of the basal turn of the neurovascular structures (such as CN V, VII, or VIII) of cochlear from the IAC fundus (deficient lamina cribrosa) and the posterior fossa, though arachnoid cysts are frequently widened labyrinthine and proximal tympanic facial nerve incidental findings at imaging. canals.43,44 At CT imaging, CPA arachnoid cysts are hypodense, nonenhancing rounded masses without calcifications. Congenital Internal Auditory Canal Scalloping of adjacent bone is more frequently reported in and Cerebellopontine Angle Masses middle cranial fossa lesions. At MRI, arachnoid cysts are homogeneous and isointense to CSF on all sequences, Epidermoids including FLAIR and DWI, which differentiates them from epidermoid tumors (Fig. 8.18).49 Epidermoids are benign extraaxial, intradural tumors that are most frequently located in the CPA. These masses Lipomas arise as ectopic inclusions of epithelial cells at the time of neural tube closure around 3 to 5 weeks of gestation.45 Intracranial lipomas are hamartomatous lesions com- Although they are congenital, they are also slow-growing posed of mature adipose tissue, which are thought to masses that enlarge by accumulation of keratin and cho- result from in utero aberrant differentiation of the lep- lesterol as the lining epithelium desquamates. Malignant tomeningeal component of the meninx primitiva.54 They transformation is extremely rare.46 are most commonly found as supratentorial midline Epidermoids typically present in the third to seventh lesions and are frequently associated with cerebral mal- decades as irregular lobulated masses with prolonged formations, though are rarely themselves symptomatic. symptoms due to involvement of nerves or displacement Lipomas are rarely found in the CPA, and in the posterior of the brainstem and cerebellum. These tumors tend to fossa they are usually isolated lesions not associated with surround and encase neurovascular structures such as CN other abnormalities; however, they can become sympto- V, VII, and VIII, and the basilar artery. A tendency for matic.55 CPA lipomas may present with symptoms related adherence to these structures may also make complete to cranial nerve irritation, such as trigeminal neuralgia surgical resection difficult.47 (CN V), hemifacial spasm (CN VII), or vertigo and hearing Focal calcifications are uncommonly found at CT. Epi- loss (CN VIII).55,56 Symptoms such as hearing loss, vertigo, dermoid tumors are usually similar to water attenuation and tinnitus related to involvement of CN VIII are the and do not typically enhance following contrast adminis- most frequent presentation. At imaging, neurovascular tration. At MRI, epidermoids appear similar to CSF in structures appear to pass through the lipoma; at surgery, intensity on T1-weighted and T2-weighted sequences, these structures are frequently found to be densely adher- which can make differentiation from arachnoid cysts dif- ent to these elements. Hence, conservative management ficult. However, on close inspection of these images and of lipomas is often preferred unless the symptoms are some manipulation of the windowing, one frequently disabling and uncontrollable. Cranial nerve decompression may find tiny internal septations within these tumors. In or vestibular transection may then be considered for addition, frequently on FLAIR imaging epidermoids are treatment.55,56 higher in signal intensity than CSF (Fig. 8.16).48 Another On CT imaging, lipomas are of fat attenuation (-50 to important sequence that may help in differentiating -100 Hounsfield units) and do not show contrast en- epidermoids from arachnoid cysts is diffusion weighted hancement (Fig. 8.19). Lipomas on MRI follow the signal imaging (DWI) where epidermoids tend to be markedly intensity of fat, with suppression of signal on chemical hyperintense compared with arachnoid cysts.49,50 This selective fat-saturation images (Fig. 8.20). CPA lipomas have also serves as a useful imaging feature for detection of been reported in association with intravestibular lipomas postoperative residual tumor (Fig. 8.17).51 in patients with SNHL. It is proposed that this occurs very ch08 9/19/08 11:57 AM Page 491

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Fig. 8.13 Absent CN VIII. (A,B) Child with unilateral congenital sensorineural hearing loss has malformation of the right cochlea (curved arrow) and a bony bar at the expected cochlear aperture (arrow). The internal auditory canal (IAC) also appears to be narrow on these axial images. (C) This is confirmed on the oblique sagittal T2 MR where a small IAC is evident containing one nerve bundle superiorly (arrow), C which represents the facial nerve.

early in gestation from either direct incorporation of the dency for adherence to neurovascular structures making meninx primitiva in the developing otocyst or from neu- resection technically difficult or not possible (Fig. 8.21). ral transport of meninx primitiva along the developing CN VIII.57 Other hamartomatous lesions of the brain are of Acquired Neoplastic Internal Auditory Canal glioneural origin. These are rare lesions with few CPA and Cerebellopontine Angle Pathology hamartomas reported in the literature.58 Some authors Vestibular Schwannoma describe only slight contrast enhancement, whereas others describe intense enhancement, mimicking a vestibular Vestibular schwannoma, also known as acoustic neuroma, schwannoma.58,59 Like lipomas, hamartomas have a ten- is the most common CPA tumor and the most common ch08 9/19/08 11:57 AM Page 492

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Fig. 8.14 Acquired stenosis of the internal auditory canal (IAC) porus. Adult with increasing bilateral but predominantly left sensorineural hearing loss and dizziness. (A) The postgadolinium fat saturated magnetic resonance image shows no evidence of an IAC or cerebellopontine angle mass, but an unusual contour of the porus on both sides (arrows). A computed tomography angiogram performed several months prior shows this similar bony overgrowth of the margins of the porus in (B) the axial and (C) reformatted left sagittal plane. The patient had bony exostoses elsewhere, and this was presumed to be a proliferative bone abnormality. C

lesion found in patients with unilateral acquired acusticus.62 Uncommonly, schwannomas arise in the CPA SNHL.24,60 This benign tumor is sometimes referred to as a and do not have an IAC component.63,64 neurinoma or neurilemmoma. Despite the moniker Adults with vestibular schwannomas typically pres- “acoustic neuroma,” these tumors do not arise from the ent with slowly progressive hearing loss with or without cochlear nerve. Vestibular schwannoma is considered the tinnitus, which on audiometric testing is a high fre- correct terminology as the tumor arises from Schwann quency SNHL.24 Schwannomas with a large CPA compo- cells covering the lateral aspect of either the superior or nent may also impinge on the facial or trigeminal nerves inferior vestibular.61 Most schwannomas arise lateral to the resulting in additional cranial neuropathies, or compress junction of Schwann cells and neuroglial cells (i.e., lateral the pons and produce fourth ventricular obstruction. The to the Obersteiner-Redlich zone) in the IAC or at the porus presence of bilateral vestibular schwannomas is diagnostic ch08 9/19/08 11:57 AM Page 493

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Fig. 8.15 Incidental large internal auditory canal (IAC). ”Patulous” internal auditory canals were noted on a computed tomography (CT) scan performed of the sinuses, which prompted a temporal bone CT (A,B) and MRI (C, constructive interference in steady state [CISS] sequence), where no abnormality other than the large canals was evident. The patient was C asymptomatic and the anomaly symmetric.

of neurofibromatosis type II (NF2). Identification of a sin- nent, which appears on CT as an area of low density, and gle vestibular schwannoma in a child ( 20 years) should on MRI as high T2 signal intensity (Fig. 8.24). These tu- raise suspicion for the possibility of NF2 (Fig. 8.22). mors have a much faster growth rate and a less favorable The classic large IAC–CPA schwannoma is described surgical outcome with a higher incidence of postoperative as an “ice cream and cone” shaped lesion with a larger, facial nerve dysfunction.65–67 This intratumoral cystic homogeneous, enhancing mass in the CPA, which has pro- component should be distinguished from an extrinsic lapsed from a smaller funneled IAC component, produc- arachnoid cyst, which may be found in association with ing widening of the porus (Fig. 8.23). Large IAC–CPA vestibular schwannomas in a small percentage of cases vestibular schwannomas may have a cystic CPA compo- (Fig. 8.25 and Fig. 8.26). The CPA component of the ch08 9/19/08 11:57 AM Page 494

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C D Fig. 8.16 Cerebellopontine angle (CPA) epidermoid in a 19-year-old (FLAIR) image shows the mass to be hyperintense relative to cere- with an 8-month history of headaches but no hearing loss or facial brospinal fluid. There is no hydrocephalus. (C) Contrast-enhanced nerve dysfunction. (A) Axial T2-weighted magnetic resonance image T1-weighted magnetic resonance image shows no enhancement. shows the extraaxial hyperintense right CPA mass with no adjacent (D) Diffusion weighted image shows restricted diffusion and confirms parenchymal edema. (B) Coronal fluid attenuated inversion recovery that there is no extension in the internal auditory canal. ch08 9/19/08 11:57 AM Page 495

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C D Fig. 8.17 Epidermoid. (A) Preoperative gadolinium-enhanced T1- following subtotal surgical resection shows heterogeneous signal, and weighted magnetic resonance image (T1WI). (B) Diffusion weighted residual tumor cannot be distinguished from postoperative changes. image shows a prepontine epidermoid tumor with characteristic (D) Diffusion weighted imaging confirms residual epidermoid, seen as restricted diffusion. (C) Gadolinium-enhanced T1WI performed focal high signal intensity. ch08 9/19/08 11:57 AM Page 496

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C D Fig. 8.18 Cerebellopontine angle (CPA) arachnoid cyst. (A) Sagittal T1- hemisphere. (D) Axial diffusion-weighted image shows low signal inten- weighted and (B) axial T2-weighted magnetic resonance images show a sity (no restricted diffusion), confirming the cerebrospinal fluid/fluid smoothly contoured fluid-intensity left CPA mass, which suppresses nature of this mass. Despite significant local mass effect, there is no completely on axial fluid attenuated inversion recovery (FLAIR) imaging obstructive hydrocephalus in this child who presented with macrocrania (C). No abnormal signal is seen in the adjacent medulla or left cerebellar and head tilt. (Courtesy of Gary Hedlund, MD.) ch08 9/19/08 11:57 AM Page 497

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A B Fig. 8.19 Incidental cerebellopontine angle (CPA) lipoma. Axial computed tomography scan with brain (A) and bone (B) windows shows a fat-density mass in the right CPA. This child’s scan had been performed for trauma, and there was no history of hearing loss. (Courtesy of Kenneth Martin, MD.)

A B Fig. 8.20 Internal auditory canal (IAC) lipoma on magnetic resonance inhomogeneous hypointensity in the left IAC, intimately related to imaging (MRI). (A) Axial constructive interference in steady state T2- the IAC nerves (arrow). (B) Axial and weighted MRI through the cerebellopontine angle shows abnormal (Continued on page 498) ch08 9/19/08 11:57 AM Page 498

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C D Fig. 8.20 (Continued) (C) coronal unenhanced T1-weighted MRIs show shows no abnormal enhancement and complete saturation of the focal hyperintense tissue in the inferior aspect of the IAC, below the crista falci- T1-hyperintensity, consistent with lipoma. No intralabyrinthine compo- formis. (D) Gadolinium-enhanced fat-saturated coronal T1-weighted MRI nent was identified. (Courtesy of Andy Whyte, MBChB, FRCR, FRANZCR.)

A B Fig. 8.21 Internal auditory canal (IAC) mesenchymal hamartoma. (A,B) Axial T2-weighted magnetic resonance images in an 11-year-old boy with congenital hearing loss show dysplastic cochlea, vestibule, and semicircular canals on the right. ch08 9/19/08 11:57 AM Page 499

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neoplasm may sometimes appear hemorrhagic with a heterogeneous predominantly hyperdense appearance on CT, and more mixed signal intensity on T1WIs and T2WIs. Rarely, patients with vestibular schwannoma may present acutely with vertigo and vomiting from acute hemorrhagic expansion (Fig. 8.27 and Fig. 8.28).6,68 The intracanalicular portion of a schwannoma may extend laterally from the fundus to the cochlea or vestibule, or both, producing what has been described as a dumbbell schwannoma.69,70 This can be demonstrated with either high-resolution T2WI or with T1-weighted gadolinium enhanced images (Fig. 8.29). As hearing is never salvageable, these lesions are managed conservatively unless disabling vestibular symptoms or a large CPA mass is present.69 Rarely, a schwannoma may be localized only to the cochlea (Fig. 8.30). These are also treated conservatively. In the era of high-resolution MRI of the IAC–CPA, it is most frequent to be searching for a small ( 10 mm) homogeneous, entirely intracanalicular schwannoma. On high-resolution T2WI, these vestibular schwannomas C appear as oval-shaped, low-signal-intensity masses in close Fig. 8.21 (Continued) (C) A lobulated, hypointense mass is present in the IAC (arrow), which enhances following gadolinium administra- association with the nerves in the IAC. Strong contrast tion. Linear enhancement is seen superiorly in the cerebellopontine enhancement is observed with T1WI and gadolinium angle on this coronal image (curved arrow). This diagnosis is sus- (Fig. 8.31). Early detection of schwannomas while they pected in the setting of an abnormally formed inner ear, but surgery are still small is an important step to improve the surgical (for pathological confirmation) has not been planned. (Courtesy of outcome, and specifically to preserve residual hearing and Nancy Fischbein, MD.) facial nerve function.63

A B Fig. 8.22 Neurofibromatosis type II. (A) Coronal and (B) axial the IAC bilaterally, and compressing the pons. Note also the presence gadolinium enhanced T1-weighted magnetic resonance images show of bilateral enhancing masses involving the fifth cranial nerves and bilateral lobulated, enhancing cerebellopontine angle–internal audi- Meckel’s cave (arrows) consistent with schwannomas. tory canal (IAC) vestibular schwannomas extending to the fundus of ch08 9/19/08 11:57 AM Page 500

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C D Fig. 8.23 Large vestibular schwannoma. Large left Internal auditory resonance image (MRI) (A) and enhances uniformly on the post- canal–cerebellopontine angle mass (*) displaces the medulla at the gadolinium images (B,C). (D) Axial high-resolution T2-weighted MRI level of the root entry zone of the eighth cranial nerve. This tumor (*) shows a rim of cerebrospinal fluid (arrow) between the apex of the is slightly hypointense to brain on the axial T1-weighted magnetic mass in the fundus and the cochlear aperture.

There are currently two options for treatment of beams are focused on the center of the schwannoma using vestibular schwannomas, both having merit and risks. Sur- cobalt sources (12 to 16 Gy). This method has largely been gical treatment has been the gold standard of management reserved for schwannomas where the CPA component is with three main microsurgical techniques, described 3 cm in size and without large cystic components, and for below. There has been increasing use of gamma knife radio- patients who for other health reasons might be considered surgery, for the treatment of small- to moderate-sized poor operative candidates.63,71,72 Hearing preservation and tumors. With gamma knife radiosurgery, multiple radiation facial nerve function posttreatment appear to be comparable ch08 9/19/08 11:57 AM Page 501

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Fig. 8.24 Vestibular schwannoma with cystic change. (A) High-resolution axial T2-weighted magnetic resonance image (T2WI) shows a complex left cerebellopontine angle–internal auditory canal (CPA-IAC) mass with a solid component (curved arrows) and a proteinaceous cystic component in the prepontine cistern that displaces the basilar artery (arrow) to the right. (B) The cystic component is almost isointense to brain on unenhanced axial T1-weighted images. (C) On gadolinium-enhanced MR, there is rim enhancement of the cystic component and intense enhancement of the solid CPA-IAC component. C

for the techniques, although the surgical and radiation with high surgical risk, advanced age, small tumors, or therapy literature are conflicting as to the better outcome minimal symptoms, conservative management (“wait and with each.73,74 The surgical literature cites the small risk scan”) with 6-month interval follow-up MRI evaluations of malignant degeneration of vestibular schwannomas may be acceptable as these tumors are usually slow- and the lack of long-term data thus far with gamma knife growing.64,71,74,75 Small intracanalicular lesions are often treatment, in addition to the greater complexity of surgical resected with the aim of conservation of current hearing resection if gamma knife fails to adequately treat a and the intent of preservation of facial nerve function. A schwannoma.72,75 subtemporal middle cranial fossa approach allows excel- The surgical management for vestibular schwannoma lent access to the entire length of the IAC, though it is is determined by several factors including tumor size and complicated by the increased vulnerability of the more location, the patient’s age, health, and hearing. In patients superficially situated facial nerve and limited access to ch08 9/19/08 11:57 AM Page 502

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A B Fig. 8.25 Vestibular schwannoma with intratumoral cystic change. (A) Axial intracanalicular component (white arrow). The mass has a surrounding T2-weighted and (B) corresponding axial enhanced T1-weighted magnetic cerebrospinal fluid cleft (black arrow), illustrating that it is extraaxial. The resonance image show a heterogeneous, predominantly hyperintense fourth ventricle (V) is displaced to the left. An adjacent associated arach- right cerebellopontine angle mass with a nodular, solidly enhancing noid cyst is also noted (curved arrow), without rim-enhancement.

the posterior fossa for a large CPA component. A retrosig- of tumor to the lateral third of the IAC prohibits complete moid approach allows wide access to the posterior fossa, resection via this approach. Thus, the most lateral extent which may be important for a large IAC-CPA tumor, but of the schwannoma is an important feature to describe only exposes the medial two thirds of the IAC. Extension at MRI evaluation.63,77 In addition, of the most significant

A B Fig. 8.26 Vestibular schwannoma and coexistent arachnoid cyst. (A) There is a cerebrospinal fluid intensity component (arrow) posterior to Axial T2-weighted and (B) corresponding enhanced axial T1-weighted the schwannoma consistent with an arachnoid cyst. (Courtesy of Andy magnetic resonance image show a large right cerebellopontine Whyte, MBChB, FRCR, FRANZCR.) angle–internal auditory canal mass distorting the right brachium pontis. ch08 9/19/08 11:58 AM Page 503

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A B Fig. 8.27 Hemorrhagic vestibular schwannoma. (A,B) Noncontrast adjacent low-density edema and hydrocephalus (dilated temporal axial computed tomography images show a heterogeneous, hyper- horns). The patient had a prior diagnosis of vestibular schwannoma and dense right cerebellopontine angle mass with significant mass effect presented with new headache and somnolence. upon the pons, right cerebellar hemisphere, and fourth ventricle, with

radiological features correlating with poor hearing out- has been observed with certain heavily T2-weighted se- come is the presence of tumor at the IAC fundus.63,78–80 quences, is a relative decrease in T2 signal intensity of the Evaluation of the extent of IAC and fundal involvement fundal CSF “cap” or of the membranous labyrinthine, as with 3D heavily T2WIs (characterized by loss of CSF compared with the unaffected side. It has been postulated bright signal) has been found to be more accurate than that this is due to impaired vascular supply from impaction gadolinium-enhanced MRI, and is recommended for com- of the tumor in the IAC. This finding has also been shown plete presurgical evaluation. An additional finding, which to correlate with a poorer hearing outcome (Fig. 8.32).80 It

A B Fig. 8.28 Hemorrhagic vestibular schwannoma. (A) Noncontrast axial computed tomography image shows hyperdensity in the left cerebellopontine angle (CPA) (arrow). (B) Axial T1-weighted (T1WI) and (Continued on page 504) ch08 9/19/08 11:58 AM Page 504

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Fig. 8.28 (Continued) (C) T2-weighted magnetic resonance images reveal a CPA-internal auditory canal mass with T1 and T2 shortening from blood products. (D) On enhanced coronal T1WI, the mass shows heterogeneous enhancement. (E) Coronal gradient echo (GRE) magnetic resonance image shows marked hypointensity. The patient presented with sudden onset of left headache and hyperacusis and was E found to be thrombocytopenic.

has not been observed with all 3D-FSE sequences (personal Early postoperative arterial or venous complications may be communication, Jan W. Casselman, April 2005). better evaluated with MRI due to the reduced sensitivity to The translabyrinthine approach for tumor resection posterior fossa abnormalities with CT. Stroke is an uncom- is reserved for those patients where hearing conservation is mon complication and is most often related to damage to no longer an option, as this route by definition interrupts the distal AICA with cerebellar peduncle infarction.83 Dural the otic capsule and results in profound SNHL. As an advan- sinus thrombosis and edema from occlusion of a dominant tage, however, this route allows complete exposure of the venous sinus have also been observed. IAC and facilitates facial nerve preservation, particularly in CSF leak can occur with any of the three surgical ap- those with a large schwannoma ( 20 to 25 mm) who are proaches, though this complication is more common with at greatest risk for poor postoperative facial nerve function the retrosigmoid approach and with larger tumors. and hearing loss.81,82 In large, complicated lesions exten- Translabyrinthine surgery can result in a middle ear CSF sively involving the CPA and IAC, combined surgical ap- fistula that drains through the nose through the eu- proaches may be used (retrosigmoid and translabyrinthine). stachian tube, resulting in rhinorrhea. These leaks fre- In the immediate postoperative period, CT scans are frequently occur to the temporal bone/mastoid air cells and quently obtained to evaluate for complications such as for this reason bone wax or tissue (fat/muscle/fascia) graft bleeding, cerebral or cerebellar swelling, and hydrocephalus. may be employed at the time of surgery to prevent leak. ch08 9/19/08 11:58 AM Page 505

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Fig. 8.29 Transmodiolar vestibular schwannoma. (A–C) Axial enhanced T1-weighted magnetic resonance images from superior to inferior show a large heterogeneously enhancing right CN V schwannoma (black arrow) and adjacent vestibular schwannoma (curved arrow). These masses expand the cerebellopontine angle and distort the pons. The vestibular schwannoma fills the internal auditory canal, extending to the fundus. In addition, there is enhancement extending into the cochlea (white arrow), representing transmodiolar spread (“dumbbell” schwannoma). Note also a meningioma along the posterior aspect of the petrous apex, left Meckel’s cave schwannoma, left facial nerve schwannoma, and previous left vestibular schwannoma resection. This patient has neurofibromatosis type II. C

This tissue can make postoperative evaluation of the IAC represent methemoglobin, and the presence of new for residual tumor, and later for recurrent tumor, difficult. labyrinthine enhancement, which may be due to labyrinthi- Although tumor recurrence is rare and surgical resec- tis or granulation tissue.84 The most difficult problems tions are most commonly complete unless tumor adherent arise with the presence of nodular or mass-like enhance- to the facial nerve is intentionally left behind, postopera- ment in the IAC, the presence of graft material, and in tive IAC MRI poses a challenge to the radiologist.84 It is determining the optimal time for evaluation of the post- normal to find peripheral linear contrast enhancement of operative IAC. the IAC and nerves after schwannoma resection, repre- It has been suggested that as schwannomas are so slow senting postoperative irritation and blood–brain barrier growing the most useful time for assessing for recurrent breakdown.84–87 Other features that may be seen include disease after a complete resection may be at 5 years, unless T1 shortening in the labyrinth, which is postulated to clinical symptoms warrant earlier evaluation.88 Others ch08 9/19/08 11:58 AM Page 506

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C D Fig. 8.30 Labyrinthine schwannoma. (A) Axial fast spin echo (FSE) T2- axial and (D) coronal T1-weighted MRIs better show an enhancing weighted magnetic resonance image (MRI) through the inner ear mass in the vestibule and semicircular canals. There is medial exten- shows subtle loss of the normal T2 high signal intensity of the en- sion into the superior aspect of the fundus of the internal auditory dolymph in the left vestibule (curved arrow). (B,C) Contrast-enhanced canal, along the superior vestibular nerve (arrow).

have suggested that an initial postoperative MRI study is no clear consensus in the literature, and individual in- performed within 3 days was most helpful for determin- stitutions tend to develop their own follow-up protocols. ing the presence of residual disease and serving as a base- Studies performed with imaging in the first 6 to 12 line study for subsequent evaluation for recurrence.87 months following surgery suggest that nodular enhance- Others suggest postoperative imaging at 6 months and 18 ment in the IAC or CPA may represent residual tumor and months, with either follow-up of questionable findings in warrants close imaging follow-up (Fig. 8.33).85,86 Some of 12 months or no further imaging for 3 to 5 years.89 There this nodularity may resolve over time consistent with ch08 9/19/08 11:58 AM Page 507

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Fig. 8.31 Small intracanalicular schwannoma. (A) Axial and (B) coronal contrast-enhanced T1-weighted magnetic resonance images (MRIs) show a small entirely intracanalicular enhancing mass on the right (white arrow). (C) Axial fast spin echo (FSE) T2-weighted MRI shows this lesion in the posterior aspect of the IAC with the cochlear nerve (black arrow) passing anterior to it. C

granulation tissue. Any progression of nodularity suggests requiring repeated imaging and close neurotological fol- residual tumor growth. The retrosigmoid approach has low-up.87,88 Fat packing used for the translabyrinthine ap- the greatest risk of unintentional residual tumor in the proach or fatty degeneration within muscular IAC grafts lateral aspect of the IAC, and this area should be carefully can also make evaluation of gadolinium enhancement dif- searched with postoperative scans (Fig. 8.34).89–91 ficult, and fat-saturation MRI techniques must be used to Postoperative evaluation can further be complicated avoid confusion and misinterpretation (Fig. 8.35, Fig. 8.36, by the presence of fat packing and synthetic or muscular and Fig. 8.37).91 graft materials. Graft material used for the prevention of It is important to be familiar with the changes and CSF leaks in the temporal bone and IAC will show enhance- radiological appearances of these changes after gamma ment from 6 weeks postsurgery that may persist long term, knife treatment. The bulk of the schwannoma remains in ch08 9/19/08 11:58 AM Page 508

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C Fig. 8.32 Schwannoma “blocking” the internal auditory canal (IAC). (A) ence in steady state [CISS] sequence; Siemens AG, Munich, Germany) Axial contrast-enhanced T1-weighted magnetic resonance image (MRI) shows reduced signal intensity distal to the tumor in the left schwannoma shows a large enhancing schwannoma blocking the left IAC and a small as compared with the right side. This predicts a poorer outcome with schwannoma on the right (arrow) in a patient with neurofibromatosis hearing preservation surgery. (Courtesy of Jan W. Casselman, MD.) type II. (B,C) Corresponding axial T2-weighted MRI (constructive interfer-

the IAC/CPA, although in the first 6 to 12 months there is difficult, rare malignant transformation in the schwan- more heterogeneous enhancement as the center of the noma, or a second primary neoplasm.96–98 For these rea- lesion undergoes cell death and fibrosis (Fig. 8.38, sons, radiation therapy has generally been reserved for Fig. 8.39).92–94 Temporary enlargement after radiation has elderly or surgically unfit patients with enlarging tumors, been reported in the 2 years following treatment, which postoperative residual enlarging tumors, or for those pa- is why lesions 3 cm and those with significant brain- tients refusing surgery.74 stem compression are excluded from radiosurgery.92 Tumor enlargement may require steroids or shunting, and Other Cerebellopontine Angle Schwannomas surgical intervention is warranted if there is a new cranial neuropathy.95 Complications from gamma knife therapy Although vestibular schwannoma is clearly the most com- include communicating and noncommunicating hydro- mon intracranial nerve sheath tumor, schwannomas may cephalus, fibrosis—making subsequent surgery more arise from any of the posterior fossa nerves from CN V to ch08 9/19/08 11:58 AM Page 509

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Fig. 8.33 Postoperative changes: residual schwannoma. (A) Axial T1- weighted magnetic resonance image (T1WI) shows fat packing (f) in the right temporal bone from prior translabyrinthine subtotal resection of a large cerebellopontine angle–internal auditory canal (CPA-IAC) schwannoma (arrow). (B) Contrast-enhanced T1WI with fat saturation shows enhancement of the right CPA mass (arrow) and suppression of the fat packing (f). The low signal intensity in the right cerebellar hemisphere (*) is malacia related to prior surgery. (C) Axial T2WI shows right cerebellar malacia (*) and residular schwannoma (arrow) which showed slow inter- C val growth over 3 years (not shown).

CN XII and result in a CPA mass (Fig. 8.40 and Fig. 8.41).99–101 may cause the most difficulty with differentiation from Imaging characteristics (CT density, MR signal intensity vestibular schwannoma. and enhancement) are similar to those of vestibular Although facial nerve tumors commonly present with schwannomas. The nerve of origin of most CPA schwanno- slowly progressive facial nerve palsy, IAC or CPA facial mas can be determined by the clinical symptomatology nerve schwannomas may present with SNHL, vertigo, and and the cisternal course of the lesion with respect to the tinnitus and rarely with facial nerve symptoms.10 0 The key pons and brainstem and the skull base foramina. It is the differentiating feature on MRI is the presence of an en- facial nerve schwannoma arising in the IAC or CPA that hancing tumor component along the labyrinthine segment ch08 9/19/08 11:58 AM Page 510

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Fig. 8.34 Postoperative changes: retrosigmoid resection. (A) Axial T2-weighted and (B) contrast enhanced T1-weighted magnetic resonance images show malacia in the left cerebellar hemisphere following retrosigmoid resection of a left cerebellopontine angle–internal auditory canal (CPA-IAC) schwannoma. The medial aspect of the posterior wall of the IAC has also been removed, widening the porus. (C) Linear enhancement (arrow) is still seen in the IAC several years after surgery. C

of the facial nerve to the geniculate ganglion (Fig. 8.42).102 Meningiomas Schwannoma may extend from here along the tympanic Meningiomas are extraaxial neoplastic lesions arising facial nerve through the middle ear, or anteriorly along the from “cap” cells lining the arachnoid villi of the dural greater superficial petrosal nerve. At CT, the enhancing venous sinuses of the brain or spine. Up to 10% of all intratemporal component may be difficult to identify; intracranial meningiomas arise in the posterior fossa and however, bone windows may reveal enlargement of the meningiomas are the second most frequent CPA tumor facial nerve canal.10 0 Because facial nerve function is difficult after vestibular schwannoma.104 These tumors tend to to preserve with surgery these tumors are often followed present in middle-aged to elderly patients and are rare in until there are disabling symptoms, though facial nerve young patients in the absence of NF2. cable grafting may be successful.10 0,103 ch08 9/19/08 11:58 AM Page 511

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Fig. 8.35 Postoperative changes: middle cranial fossa approach. (A) Preoper- ative contrast-enhanced axial T1-weighted magnetic resonance image (T1WI) (A) shows a right internal auditory canal (IAC) vestibular schwannoma. (B) Baseline postoperative contrast-enhanced axial T1WI shows linear enhancement within the IAC and postoperative enlargement of the porus acusticus. (C) Axial contrast-enhanced T1WI 3 years later shows less marked enhancement but residual linear enhancement at the posterior aspect of the IAC that presumably represents granulation tissue. Note susceptibility artifact E in the right temporal region from the middle fossa surgical approach (B,C). ch08 9/19/08 11:58 AM Page 512

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Fig. 8.36 Postoperative changes: early appearance posttranslabyrinthine resection. (A) Axial T1-weighted magnetic resonance image (MRI) (following translabyrinthine resection of an internal auditory canal–cerebellopontine angle [IAC-CPA] schwannoma) shows extensive high signal intensity fat filling the resected temporal bone site. (B) Axial T2-weighted MRI with fat saturation shows loss of signal/suppression of the fat packing, and even lower signal intensity in the left CPA (arrow) consistent with blood products from the recent surgery. (C) Axial contrast- enhanced T1-weighted MRI shows enhancement around the blood in the CPA and around the periphery of the fat packing, which presumably represents early granulation tissue. Curvilinear enhancement also in- C volves the IAC.

Cerebellopontine angle meningiomas usually arise from more challenging, though the presence of a dural tail, calci- the dura of the posterior surface of the petrous temporal fications, or hyperostosis of the temporal bone are differen- bone. Grossly, they have a broad base, frequently a dural tiating features consistent with meningioma (Fig. 8.44 and tail, and tend to cross the porus acusticus of the IAC rather Fig. 8.45). Importantly, in cases of meningiomas, enhance- than entering and filling it (Fig. 8.43).105 These menin- ment in the IAC is frequently peripheral as it is dural in eti- giomas may remain asymptomatic until large when pa- ology (compared with vestibular schwannomas where en- tients may present with impingement on any of the cranial hancement is typically central), and widening of the porus nerves of the CPA or compression on the brainstem. Up to acusticus is uncommon with meningiomas compared with 75% of CPA meningiomas present with hearing loss.106 A schwannomas. Differentiation is almost impossible with large tumor may secondarily involve the IAC (5%), making the rare meningioma that is entirely intracanalicular, aris- differentiation from a CPA/IAC vestibular schwannoma ing from arachnoid granulations within the canal.105,107–109 ch08 9/19/08 11:58 AM Page 513

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Fig. 8.37 Postoperative changes. (A) Axial T2-weighted magnetic resonance image (MRI) shows prior translabyrinthine resection on the left. (B) Contrast-enhanced axial and (C) coronal T1-weighted MRI show no evidence of a residual mass, but subtle persistent linear enhancement (arrow) that has remained stable for several years. C

As with meningiomas found elsewhere, they tend to be Metastatic Disease hyperdense to brain at noncontrast CT imaging and show homogeneous contrast enhancement. Focal areas of calci- Metastatic disease to the CPA can present in two gross fication are best appreciated prior to contrast and evident pathologic forms. Large extraaxial metastases can mimic in up to 25%. At MRI, the majority of meningiomas are large vestibular schwannomas or meningiomas of the isointense to gray matter, with avid contrast enhancement. CPA and may be difficult to differentiate clinically, par- Unlike schwannomas necrosis or cystic degeneration is ticularly when they also involve the IAC.110 Although uncommon with meningiomas. Although most menin- metastases may appear more heterogeneous than typical giomas are benign, a small proportion show atypical or large schwannomas, metastases represent less than 1% malignant features histologically. of all CPA masses, and so a heterogeneous schwannoma ch08 9/19/08 11:58 AM Page 514

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C D Fig. 8.38 Vestibular schwannoma: response to gamma knife radio- greater heterogeneity of the tumor with reduced T2, suggesting hem- surgery. (A,B) Pretreatment magnetic resonance image (MRI) shows a orrhagic change, and new T2 prolongation in the brachium pontis, con- heterogeneous, but homogeneously enhancing right cerebellopontine sistent with radiation effects. There is little change in size of the schwan- angle–internal auditory canal (CPA-IAC) schwannoma with local mass noma. (D) Coronal gadolinium enhanced T1-weighted MRI shows effect on the brachium pontis without associated edema. (C) Axial T2- central necrosis (arrow). weighted MRI performed 6 months after gamma knife surgery reveals

is statistically more likely than a metastasis (Fig. 8.25 most common presentation is SNHL, tinnitus, and vertigo, and Fig. 8.46).104 followed by palsies of CN VII then CN V, though up to 25% CPA metastases can also present as leptomeningeal may be asymptomatic.112 Although involvement of CN VIII carcinomatosis with diffuse seeding of the CSF. This is may mimic a small vestibular schwannoma, enhancement most frequently due to a solid somatic neoplasm, most of multiple cranial nerves and/or the leptomeninges, is commonly adenocarcinoma of the lung or breast, or seen in most patients (Fig. 8.47), making the diagnosis of melanoma.111 Such leptomeningeal seeding of tumor can carcinomatosis evident.112 ,113 A new diagnosis of NF2 in an also be seen with non-Hodgkin’s lymphoma. Although adult patient should be considered suspect with a thor- most patients have a prior diagnosis of malignancy, multiple ough search performed for other intracranial metastases cranial neuropathies can be the presenting feature. The and the CSF sampled for malignant cells. ch08 9/19/08 11:58 AM Page 515

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Fig. 8.39 Vestibular schwannoma: response to gamma knife radio- developing in the cystic medial portion of this large left cystic and surgery. (A) Axial heavily T2-weighted images (fast imaging employ- solid cerebellopontine angle–internal auditory canal vestibular ing steady-state acquisition [FIESTA]) through the IAC before, and schwannoma. There was overall minimal decrease in the size of the (B) 18 months following gamma knife radiosurgery show hemorrhage cystic component.

CNS lymphoma occurring in the infratentorial region is brainstem/cerebellum away resulting in widening of the most frequently cerebellar; however, both primary and ipsilateral CSF cistern). Parenchymal edema is frequently secondary CNS a lymphoma has been reported in the observed. CPA.114–118 The tumor may take one of three forms: an ex- Intraventricular masses such as choroid plexus papil- traaxial mass, a leptomeningeal seeding (Fig. 8.48), or an loma or ependymoma can extend to the CPA through the intraaxial exophytic mass extending into the CPA. These foramen of Luschka (Fig. 8.50). Ependymoma has also tumors have a tendency to present with hearing loss or been described as a rare, purely extraaxial posterior fossa cerebellar signs such as unsteady gait and ataxia. tumor (Fig. 8.51).121 Other rare extraaxial glial tumors such as astrocytoma, oligodendroglioma, glioblastoma, and mixed gliomas have also been described and are thought Intraaxial Masses Involving to arise from heterotopic rests of glial cells in the sub- the Cerebellopontine Angle arachnoid space and leptomeninges.121–123 These are rare Focal intraaxial lesions along the acoustic pathway may extraaxial posterior fossa and CPA masses, without specific be responsible for SNHL or complex auditory dysfunction, imaging features to indicate the pathologic diagnosis. and are discussed. Masses arising in the brainstem, cerebellum, or fourth ventricle may, however, extend into the CPA and cause confusion in the differential diagnosis of a Acquired Nonneoplastic Internal Auditory CPA mass. Several key imaging features help in the deter- Canal and Cerebellopontine Angle mination of the true site of origin of the mass. Pathology Intraparenchymal lesions such as brainstem gliomas, Inflammatory and Infectious cerebellar medulloblastoma, and pilocytic astrocytoma have been reported as presenting as CPA masses and Any inflammatory or infectious process that results in dural may show an exophytic component invading the CPA or leptomeningeal enhancement may affect the CPA and (Fig. 8.49).119 ,12 0 These intraaxial lesions will have no CSF IAC and result in a mass or abnormal enhancement at MRI interface between the tumor and brain, and even when (Fig. 8.52 and Fig. 8.53).124 This includes meningitis and post- pedunculated will narrow the ipsilateral cistern (com- meningitic or postoperative fibrosis. The imaging appear- pared with extraaxial lesions that push the adjacent ance of many of these lesions can be difficult or impossible ch08 9/19/08 11:58 AM Page 516

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Fig. 8.40 Trigeminal schwannoma. (A) Axial fluid attenuated inversion recovery (FLAIR) magnetic resonance image (MRI) shows a hyperintense, lobulated mass involving right Meckel’s cave (arrow) and in the right prepontine cistern, deforming the pons, but without pontine edema. Contrast enhanced axial T1 (B) and sagittal T1 (C) shows this to be partially cystic and coursing along the fifth cranial nerve. Note the normal appearance of the left fifth nerve (open arrow, B). C

to distinguish from several entities and from neoplastic lep- VII, can occur as part of this leptomeningeal process or tomeningeal or dural disease without clear clinical history in isolation with enhancement and enlargement of the or CSF sampling. nerves. CNS involvement occurs in up to 25% of patients with Superficial siderosis is the chronic deposition of he- systemic sarcoidosis.125 This idiopathic disorder is char- mosiderin on pia and subpial tissues from repeated sub- acterized by the presence of noncaseating granulomas arachnoid hemorrhage due to vascular lesions such as an and lymphadenopathy. Neurosarcoidosis is typically aneurysm, AVM, or superficial cavernoma, or neoplasms manifest as leptomeningeal disease (40%) with thicken- such as spinal ependymoma.126 Hemosiderin coats the ing and enhancement, particularly of the basal cisterns cisternal segment of cranial nerves including CN VIII, (Fig. 8.54). Cranial nerve involvement, particularly CN with its toxicity resulting in neuropathies such as hearing ch08 9/19/08 11:58 AM Page 517

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C D Fig. 8.41 Schwannomas of CN VIII and CN IX. (A,B) Contrast-enhanced The latter lesion is thought to be a glossopharyngeal nerve schwan- axial and coronal (C,D) T1-weighted images of the posterior fossa with a noma. Both masses were treated with gamma knife radiation with little small, right “typical” intracanalicular vestibular schwannoma (arrow) and change in their size, but more heterogeneous enhancement on follow- a larger mass in the right cerebellopontine angle abutting the pon- up imaging (not shown). tomedullary junction at the inferior cerebellar peduncle (curved arrow).

loss. On MRI, siderosis is manifest as thin linear low The multiple refocusing 180-degree pulses of fast spin signal intensity outlining the pons, brainstem, and cra- echo (FSE) imaging may make the hemosiderin less appar- nial nerves, best appreciated on a gradient echo suscep- ent as they reduce the T2* effect from a T2WI, and low field tibility sequence (Fig. 8.55). Gradient-echo imaging magnets are also less susceptible to the paramagnetic effects which exploits the T2* effect is the ideal sequence for of hemosiderin. Neurocysticercosis results from infestation identifying the presence and extent of hemosiderin with the tapeworm Taenia solium and may result in space- deposition. occupying cystic masses that involve the cisterns of the ch08 9/19/08 11:58 AM Page 518

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Fig. 8.42 Facial nerve schwannoma. A 46-year-old man with asymmetric sensorineural hearing loss. (A) Axial fast spin echo (FSE) T2-weighted magnetic resonance image (MRI) shows a large heterogeneous, complex right cerebellopontine angle (CPA) mass (arrows) extending into the internal auditory canal (IAC). (B,C) Contrast-enhanced axial and (D,E) coronal fat-saturated T1-weighted MRIs illustrate the heterogeneous nature of this mass that looks like a “typical” CPA-IAC vestibular schwannoma. Note, however, that there is anterior extension of the schwannoma to the geniculate ganglion along the labyrinthine segment of the facial nerve canal (open arrow), indicating this mass is of facial nerve origin. E ch08 9/19/08 11:58 AM Page 519

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Fig. 8.43 Cerebellopontine angle (CPA) meningioma. (A) High-resolution axial fast imaging employing steady-state acquisition (FIESTA) T2-weighted and (B) contrast-enhanced axial T1-weighted magnetic resonance images show a T2 hypointense, heterogeneously enhancing left CPA mass that is centered posterior to the left internal auditory canal and the cisternal segments of the vestibulocochlear and facial nerves. There is a small dural tail (curved arrow), and there is some hyperostosis of the posterior margin of the temporal bone/porus acusticus (arrow). (C) Coronal post- C contrast T1-weighted image shows the hypertosis (arrow) also.

posterior fossa.127 These subarachnoid space cysts are usually The neural changes are thought to reflect a primary neuri- multiple in nature, both supra- and infratentorial, and are as- tis with spread of inflammation along the nerve segments. sociated with communicating hydrocephalus from chronic At MRI, intense smooth contrast enhancement of the meningeal inflammation. CT or MRI will also show canalicular segments of CN VII and CN VIII and enhance- meningeal enhancement. The neurocysticercal lesion in the ment of parts of the membranous labyrinth and intratem- subarachnoid space usually lacks a scolex. poral CN V have been described (Fig. 8.56). Retrograde Ramsay Hunt syndrome is the combination of auricular spread of infection to the root entry zone with gadolinium pain, vesicles, and acute peripheral CN VII and CN VIII enhancement of the facial nerve nucleus in the pons has palsies secondary to varicella zoster herpetic infection. also been reported.128 ch08 9/19/08 11:58 AM Page 520

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Fig. 8.44 Cerebellopontine angle–internal auditory canal (CPA-IAC) meningioma. (A) Axial T1-weighted magnetic resonance image (MRI) shows an almost isointense mass in the right CPA (*) distorting the brachium pontis and displacing the fourth ventricle to the left. A thin rim of low signal intensity represents a cleft of cerebrospinal fluid (arrows) between the mass and the right cerebellum and pons. (B) Contrast-enhanced axial and (C) coronal T1-weighted MRIs show the mass avidly enhances and extends into the IAC that is not expanded. Although it might be mistaken for a vestibular schwannoma, this mass has a linear lateral contour, which subtends the posterior margin of the right petrous bone, suggesting it represents a dural-based lesion, in this case a meningioma. C

this does not constitute a vascular loop (Fig. 8.57). Vascular Aneurysms arising from the AICA are rare, representing Vascular loops can compress the vestibulocochlear nerve 0.1 to 0.5% of all intracranial aneurysms, and mostly in- to produce auditory or vestibular symptoms, though it is volving the distal artery near the CPA and IAC.129,130 This probably necessary that this compression occur near the location has resulted in misinterpretation of the glial-Schwann cell junction (the Obersteiner-Redlich aneurysm as an enhancing vestibular schwannoma.131 zone) to result in symptomatology. It is a normal Although they may present with headache from rupture anatomic variation for the anteroinferior cerebellar ar- and subarachnoid hemorrhage, symptoms related to CN tery (AICA) to enter the porus acousticus of the IAC, and VII and CN VIII dysfunction are also frequently present. ch08 9/19/08 11:58 AM Page 521

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Fig. 8.45 Porus meningioma. (A) Axial contrast-enhanced fat-saturated the margin of the porus acusticus and extending into the superior as- T1-weighted magnetic resonance image (MRI) shows an enhancing left pect of the IAC (curved arrows). (D) Axial computed tomography scan cerebellopontine angle–internal auditory canal (CPA-IAC) mass, mim- confirms the diagnosis of meningioma with focal hyperostosis of the icking a vestibular schwannoma. (B,C) Coronal contrast enhanced fat- posterior margin of the porus (arrow). (Courtesy of Andy Whyte, saturated T1-weighted MRIs suggest the tumor is dural based around MBChB, FRCR, FRANZCR.)

At CT, AICA aneurysms are usually slightly hyperdense a flow void is expected on T1WIs and T2WIs unless with strong uniform enhancement commensurate with thrombus is present which may result in variable signal that of normal cerebral arteries. Multidetector CT an- intensities. giography allows good demonstration of these lesions Other vascular lesions such as cavernomas or arteri- even when they are intracanalicular in nature.129 At MRI ovenous malformations (AVMs) are rare in the CPA.132 ch08 9/19/08 11:58 AM Page 522

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A B Fig. 8.46 Metastatic adenocarcinoma to cerebellopontine angle (CPA) contrast-enhanced T1-weighted magnetic resonance image shows (unknown primary). The patient presented with a headache and no per- marked enhancement and a superior dural attachment at the tentorium ceived neurological deficits. (A) Axial unenhanced computed tomogra- (white arrows). Despite the mass effect on the fourth ventricle, there is phy scan reveals a heterogeneous solid and cystic right CPA mass (arrows) no hydrocephalus. (Courtesy of Sundeep Nayak, MD.) with blood-fluid levels and mass effect upon the pons. (B) Coronal

A B Fig. 8.47 Leptomeningeal spread to the cerebellopontine angle. A of the left trigeminal nerve (CN V) (open arrow). (B–D) Axial contrast 20-year-old man with a history of Burkitt lymphoma presented with enhanced T1-weighted MRIs from inferior to superior show bilateral fatigue and new cranial neuropathies. (A) Coronal gadolinium-enhanced glossopharyngeal nerve (CN IX) enhancement (arrows), bilateral CN V T1-weighted magnetic resonance image (MRI) shows enhancement in enhancement (open arrows), and bilateral third nerve enhancement both internal auditory canals (arrows), and enlargement and enhancement (curved arrows). ch08 9/19/08 11:58 AM Page 523

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C D Fig. 8.47 (Continued)

A B Fig. 8.48 Cerebellopontine angle (CPA) (choroid plexus) lymphoma. foramen of Luschka (normal left choroid plexus; *. (B) Coronal contrast- (A) Axial fluid attenuated inversion recovery (FLAIR) magnetic resonance enhanced T1-weighted MRI reveals nodular enhancement of the right image (MRI) shows hyperintensity in the right CPA (arrow) that appears choroid plexus at the CPA (white arrow) and abnormal enhancing tissue to arise from the flocculus and/or choroid plexus as it emerges from the involving the choroid in the lateral ventricles (black arrows). ch08 9/19/08 11:58 AM Page 524

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C D Fig. 8.49 Brainstem tumor extending to the cerebellopontine angle (FLAIR) MRI, and there is no solid enhancement of the pontine or exo- (CPA). (A) Axial and (B) coronal T2-weighted magnetic resonance im- phytic CPA components on sagittal contrast-enhanced T1-weighted ages (MRIs) show a lobulated hyperintense mass centered in the pons MRI (D). This child presented with multiple cranial nerve palsies and (arrow) with an exophytic component extending into the left CPA (*). neck pain the mass represented a grade III astrocytoma. (Courtesy of (C) The mass is hyperintense on axial fluid attenuated inversion recovery Gary Hedlund, MD.)

AVMs are characterized by enlarged intensely enhancing Intracranial Lesions along the Auditory vessels (Fig. 8.58). As with other cerebral AVMs, angiogra- Pathway phy will best demonstrate the feeding and draining vessels to determine the best therapeutic management. An Intraaxial lesions responsible for SNHL are rare but can be important differential is the acquired dural arteriovenous broadly defined into five groups: ischemic, demyelinating, fistula with venous varix. traumatic, vascular malformations, and neoplastic lesions. ch08 9/19/08 11:58 AM Page 525

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Fig. 8.50 Cerebellopontine angle (CPA) choroid plexus papilloma. (A) Ax- ial T2-weighted and (B) axial fluid attenuated inversion recovery (FLAIR) magnetic resonance images (MRIs) show a hyperintense mass in the left CPA at the level of the internal auditory canal and the foramen of Luschka. The mass has a “cauliflower-like” contour, with cerebrospinal fluid in the interstices and at the periphery of the mass, suggesting an extraaxial nature. There is no edema in the adjacent medulla or left cerebellar hemisphere. (C) Axial gadolinium-enhanced T1-weighted MRI shows intense enhancement of the mass. Note normal enhancement of the right C choroid plexus (arrow) in the foramen of Luschka.

Although the etiologies may vary, the specific symptom side.133 A lesion involving the most central portions of the complex bringing the patient to imaging is largely depen- pathway and particularly the primary auditory cortex is dant on the precise location of the lesion along the retro- more likely to present with complex auditory dysfunction cochlear intracranial portion of the auditory pathway. such as auditory agnosia.134 This is defined as preservation Generally, lesions involving the cochlear nuclei of the up- of the sensation of hearing, but impaired recognition of per medulla result in unilateral SNHL. Involvement of the sound and words. Inferior colliculus lesions have been de- auditory pathway proximal to this—that is the trapezoid scribed as producing hearing loss and tinnitus, but in body, lateral lemniscus, inferior colliculus, or medial some cases producing complex auditory dysfunctions sim- geniculate body, if it produces hearing loss, tends to result ilar to those of cortical lesions.135 Clearly, any lesion in- in bilateral SNHL, which is worse on the contralateral volving the intracranial portion of the auditory pathway ch08 9/19/08 11:58 AM Page 526

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Fig. 8.51 Ependymoma of the fourth ventricle. (A) Axial fluid attenuated inversion recovery (FLAIR), (B) contrast-enhanced axial, and (C) coronal T1-weighted magnetic resonance images show a heterogeneous solid and cystic extraaxial mass in the right cerebellopontine angle (arrows). This enhancing tumor is contiguous with the fourth ventricle (*) through the right foramen of Luschka. C

will be more readily detectable and better evaluated with colliculi.138,139 In some patients with MS and SNHL, a de- MRI than with CT. finitive plaque may not be found along the course of the The most common intraaxial lesions resulting in auditory pathway, and in these patients it is proposed hearing loss are focal ischemic infarcts and focal plaques that the plaque is too small to be recognized by current of multiple sclerosis (MS).133,136,137 Multiple sclerosis is an imaging methods.136,138 The advantage of whole brain unusual cause of hearing loss, and hearing loss is a rare evaluation at MRI is that the classic periventricular le- presentation of MS. It has been suggested as the likely sions of MS may be evident in an undiagnosed patient cause of SNHL in 1.5 to 5% of patients.137,138 Demyelinat- presenting with SNHL. This will also help to distinguish ing plaques have been described at many locations along demyelinating plaques of the brainstem or pons from the auditory pathway from the cochlear nuclei of the up- ischemic foci, which are statistically more common per medulla and trapezoid body to the pons and inferior lesions (Fig. 8.59). ch08 9/19/08 11:58 AM Page 527

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Fig. 8.52 Postviral syndrome (Guillain-Barré). The patient presented with 1 week of progressive facial palsy, limb weakness, and gait instability. (A) Axial contrast-enhanced T1-weighted magnetic resonance image (MRI) of the right internal auditory canal shows intense enhancement in the fundus, extending into the geniculate ganglion, indicating CN VII enhancement (arrows). (B) Coronal contrast enhanced T1-weighted MRI shows this to be bilateral. (C) Sagittal contrast-enhanced T1-weighted MRI of the lumbar spine shows abnormal enhancement of lumbar nerve roots (arrows). Cerebrospinal fluid and serum studies were negative for Lyme disease and sarcoidosis, and his symptoms responded to intra- C venous immunoglobulin.

Most traumatic SNHL is caused by contusion or frac- resection of pineal tumors has also been described, with ture of the ipsilateral membranous labyrinth. For injury of resulting mild to moderate bilateral SNHL and loss of the more central auditory pathway to result in hearing speech perception and localization.142 These complex au- loss, there must be bilateral discrete lesions without in- ditory agnosia syndromes have been reported with non- volvement of the centrally located reticular activating sys- operated pineal region tumors and ascribed to distortion tem that would produce coma or death and mask the of the inferior colliculus. Hearing loss and/or tinnitus may hearing loss. Focal bilateral inferior collicular hemor- be found in up to 18% of patients with pineal tumors; rhagic contusions resulting in hearing loss are rare but however, these masses are more likely to present with vi- have been described.140,141 Postoperative injury of the infe- sual pathway dysfunction from superior colliculus com- rior colliculus and medial geniculate body following pression.136,143,144 ch08 9/19/08 11:58 AM Page 528

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complex auditory dysfunction. It is thus important when imaging patients with SNHL that whole brain imaging, preferably T2-weighted, is performed in at least one plane. This allows detection of these less common causes of SNHL, and also allows detection of supratentorial lesions that might indicate undiagnosed white matter disease (Fig. 8.62).

Petrous Apex Lesions The petrous apex is the portion of the petrous temporal bone anteromedial to the otic capsule and posterior to the carotid canal, separated from the sphenoid bone by the petroclival synchondrosis. As it cannot be examined clinically, imaging plays a significant role in the detection and characterization of lesions in this area. Although lesions of the apex are uncommon, there is a wide variety of pathology that may manifest in this region. As with most lesions of bone origin, both CT and MRI are frequently required in their characterization. Additionally, although Fig. 8.53 Bell’s palsy. Gadolinium-enhanced axial T1-weighted mag- both imaging modalities are effective tools for detection netic resonance image (MRI) shows abnormal enhancement in the of petrous apex abnormalities, normal variations in fundus of the internal auditory canal (open arrow) extending to the pneumatization and benign asymptomatic changes may geniculate ganglion of the facial nerve (curved arrow) and the greater superficial petrosal nerve (straight arrow). This patient presented with masquerade as masses at MRI. 147 facial weakness, and despite a history consistent with uncomplicated The petrous apex is pneumatized in 35% of patients. Bell’s palsy, an MRI was requested to rule out stroke. (Courtesy of These apical air cells develop as extensions of aerated Kenneth Martin, MD.) tracts from the middle ear and are lined by connective tissue and a flat epithelial layer.147,14 8 The degree of pneumatization correlates nearly linearly with that of mastoid air Primary auditory cortex lesions such as cavernous an- cells. That is, poor pneumatization of the apex is seen in giomas (cavernomas) may present with complex auditory patients with a poorly pneumatized mastoid.147 Asym- agnosia syndromes and have also been described as pro- metric petrous apex pneumatization is reported in 4 to 7% ducing auditory hallucinations preceding seizure activity of cases.147,14 9,150 Although this is not generally of clinical (“acoustic aura”).16,134 Cavernomas typically have com- significance, the nonpneumatized apex, which contains plete hemosiderin rings frequently identified on T2WI, normal fatty marrow, will appear asymmetrically bright bloom on gradient echo susceptibility imaging, and in the on T1WIs and FSE T2WIs (Fig. 8.63), and should not be absence of recent bleeding have no edema or T2 signal mistaken as a hemorrhagic mass. If there is uncertainty abnormality in the adjacent brain (Fig. 8.60). Contrast en- then noncontrast CT will confirm asymmetric pneumati- hancement is variable, but usually mild. Other vascular zation. lesions such as capillary telangiectasias and arteriovenous malformations have been found along the central auditory pathway, particularly the pons, and ascribed as the Petrous Apex Air Cell Disease cause of acute or gradual hearing loss.133,144,145 Capillary telangiectasias are characterized on MRI as ill-defined le- Pneumatized bone has the potential for acquired disease sions, which may be occult on routine T1WIs and T2WIs, due to fluid accumulation and then secondary hemor- but show contrast enhancement and hemosiderin deposi- rhage or infection. Obstruction of secretions from apical tion on gradient echo imaging (Fig. 8.61). Although the air cells occurs in the same manner as mastoid air cell onset of SNHL is generally thought to be due to hemor- opacification, with impaired communication with the rhage into vascular malformations, hearing loss may oc- middle ear due to otitis media. This trapped fluid or cur in association with capillary telangiectasia without petrous apex effusion will appear of increased signal MRI evidence of hemorrhage.145,146 intensity on T2WIs. If the fluid is uncomplicated It is clear that almost any disease process strategically then T1WIs reveal low signal intensity, similar to CSF located along the retrocochlear acoustic pathway may re- (Fig. 8.64). The fluid may however have variable protein sult in hearing loss, tinnitus or if more centrally located, a content and concentration, and thus be of intermediate or ch08 9/19/08 11:58 AM Page 529

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C D Fig. 8.54 Neurosarcoidosis. A 35-year-old man with a 5-year history of resonance images show extensive patchy areas of enhancement of the progressive neurological and systemic symptoms and myelopathy. leptomeninges along the folia of the cerebellum and the surface of the (A–C) Contrast-enhanced axial and (D) coronal T1-weighted magnetic brainstem and cerebrum (arrows).

bright signal intensity on T1WIs. To confirm a benign epithelium.151 The obstructed cells appear bright on T2WI. fluid nature in these cases, it is recommended that a CT Their signal intensity on T1WIs is dependent on the con- be obtained to assess for absence of an expansile mass centration of the mucocele contents and may be low to and the presence of intact trabeculations.150 intermediate to high signal intensity. Only the periphery A mucocele of the petrous apex is an uncommon of the lesion shows contrast enhancement. CT better expansile lesion resulting from complete obstruction of reveals the smooth expansile nature of this low-density the air cells with ongoing mucous secretion from the lesion (Fig. 8.65). ch08 9/19/08 11:58 AM Page 530

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Fig. 8.55 Superficial siderosis. A 56-year-old stuntman presented with hearing loss, tinnitus, ataxia, and recurrent headaches. (A,B) Axial T2-weighted magnetic resonance images (MRIs) show low signal intensity outlining the surface of the pons and along the folia of the cerebellum (arrows). The left internal auditory canal nerves are visible (open arrow, A), but alteration in their signal intensity would be difficult to detect due to their small size. Fast spin-echo T2-weighted MRI alone can make establishing this diagnosis more difficult due to reduced sensitivity of it to the magnetic field. (C) Coronal gradient echo susceptibility image emphasizes this magnetic susceptibility that is due to pial hemosiderin C deposition (arrows).

One lesion that can appear similar to a mucocele is the hemorrhage and cyst formation is from exposed petrous cholesterol granuloma. It is the most common surgical le- apex marrow. Initial hemorrhage during normal air cell sion of the petrous apex.152 Cholesterol granuloma is a development would probably be as a result of a traumatic, foreign body giant cell reaction to the deposition of cho- hypertensive, or barotraumatic event, with sustained lesterol crystals in apical air cells, with fibrosis and vascu- hemorrhages occurring from a cycle of exposure of more lar proliferation. The traditional theory of mechanism of marrow from the expanding cystic lesion.156 Regardless, development of these lesions is that cholesterol is pro- cholesterol granulomas are characteristically expansile in duced from hemosiderin degradation after epithelial nature and on with smoothly expanded bony margins and hemorrhage, which has resulted from reduced pressure in loss of internal trabeculae. As they enlarge, cholesterol obstructed cells.153–155 A more recent theory proposes that granulomas encroach on adjacent structures with erosion ch08 9/19/08 11:58 AM Page 531

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Fig. 8.56 Ramsay Hunt syndrome. (A,B) Contrast-enhanced axial T1-weighted magnetic resonance images show abnormal linear enhancement in the right internal auditory canal involving both the nerves and the dural lining (curved arrow), and enhancement of the right CN VII (arrow) in the temporal bone. This HIV-positive patient presented with facial palsy and new auricular vesicles suspected to be herpes zoster C reactivation.

of the clivus and otic capsule. Such lesions may present Infection occurring in a pneumatized petrous apex, or with temporal headaches from traction on the dura, or apical petrositis, has become increasingly uncommon in neuropathies such as hearing loss and/or tinnitus (CN the antibiotic era, but typically follows acute otitis media VIII), facial weakness (CN VII), diplopia (CN VI), or facial and less commonly chronic otitis media.159,160 The clinical paresthesias (CN V).153–155,157 On MRI, cholesterol granulo- triad of acute otitis media, CN VI palsy and severe unilat- mas are characteristically bright on both T1WIs and fre- eral retroorbital or ear pain (distribution of CN V) is called quently T2WIs due to their cystic nature with concen- Gradenigo syndrome, though apical petrositis may not trated cholesterol crystals (Fig. 8.66). Hemorrhage fluid present with all three.159,161,162 The diagnosis is often best levels may be present, and these can be multiloculated. made with thin-section temporal bone CT imaging, re- Treatment is surgical drainage of the lesion with connec- vealing destruction and expansion of the apex with tion of the apical air cells to ventilated spaces.158 breakdown of internal trabeculae, so-called confluent apical ch08 9/19/08 11:59 AM Page 532

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A B Fig. 8.57 Vertebrobasilar dolichoectasia. (A) Axial T1-weighted (three- left brachium pontis. (B) Axial T2-weighted MRI shows the vessel to be dimensional spoiled gradient recalled [3D SPGR]) magnetic resonance displacing the medial portion of the left vestibulocochlear nerve (arrow) image (MRI) at the level of the left internal auditory canal shows flow just above the root entry zone at the lateral medulla. The patient had left voids from a tortuous left vertebral artery (curved arrows) indenting the sensorineural hearing loss, and no other cause for hearing loss was found.

petrositis. The middle ear and mastoid are usually also enhancement with gadolinium (Fig. 8.69).157,167 Early DWI opacified from acute infection. MRI should be performed indicates that temporal bone cholesteatomas have high to evaluate for intracranial complications. The adjacent signal intensity (reduced diffusion), though the location meninges including those of Dorello’s canal (CN VI) fre- of these lesions frequently makes measurement of appar- quently enhance avidly with gadolinium, as may adjacent ent diffusion coefficient (ADC) values unreliable.16 8 These structures such as Meckel’s cave and the gasserian gan- slow-growing masses are usually resected due to the glion and branches of CN V (Fig. 8.67 and Fig. 8.68).163 Cav- potential for cranial neuropathy including SNHL, which is ernous and sigmoid sinus thrombophlebitis and epidural the most frequent presenting symptom, and neuropathies or intracranial abscess are potential complications, which of CN VI and CN VII.157,165 must also be excluded. Although aggressive surgical man- Petrous apex cephaloceles may be confused with other agement has been the standard, some pediatric reports cystic-appearing masses such as cholesteatoma, apical have shown success with myringotomy, and mastoidectomy, petrositis, or mucocele. These lobulated cystic masses intravenous antibiotic treatment and careful follow-up for have also been called arachnoid cysts or meningoceles of disease progression.159,161,16 4 the apex, but appear to result from herniation of the posterolateral dural wall of Meckel’s cave into the anterolateral aspect of the petrous bone.169,170 This herniation may Congenital Masses be congenital or acquired and results in smooth scalloping of the bone on CT. MRI demonstrates a homogeneous Cholesteatoma arising in the petrous apex is a rare con- cystic mass contiguous with and arising from Meckel’s genital lesion resulting from aberrant embryonic rests of cave.157,169,170 Rim enhancement may be seen with contrast epithelium. Uncommonly, apical cholesteatomas, or epi- administration, and DWI shows low signal intensity con- dermoids, result from anteromedial spread of an acquired sistent with CSF (Fig. 8.70). middle ear lesion.165,166 The stratified squamous epithelium produces keratin and the lesion may be surrounded by fibrosis and granulation tissue. Typically on CT imag- Inflammatory and Neoplastic Disease ing, there is smooth scalloping of the apical bony margins. On T2WI, an ovoid to round, expansile hyperintense mass There is a wide variety of inflammatory and neoplastic that is hypo or isointense on T1WI may show subtle rim lesions that may be found as destructive, solid masses of ch08 9/19/08 11:59 AM Page 533

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A B

C D Fig. 8.58 Cerebellopontine angle arteriovenous formation (AVM). of vessels in the left cerebellopontine angle extending into the internal (A) A 28-year-old pregnant woman presented with a large cerebellar auditory canal, representing an AVM (arrows). There was superficial ve- parenchymal hemorrhage with intraventricular extension (*) and mild nous drainage to the sigmoid sinus and arterial supply from left poste- hydrocephalus on unenhanced axial computed tomography (CT). rior cerebral artery branches. Multiple feeding artery aneurysms were (B–D) CT angiogram and coronal reformations show an abnormal tangle also found at angiography.

the petrous apex. Such lesions may be centered on the CT scan or MRI, or present with headache or cranial neu- petrous apex, from which they have arisen, or involve the ropathies. Hearing loss (CN VIII) may be present from apex having arisen from the sphenoid bone, the middle cra- involvement of the otic capsule or IAC, and CN V, VI, or VII nial fossa, or nerves and dura. These lesions may be may be involved depending on the degree of infiltration asymptomatic and incidentally discovered at whole brain of Meckel’s cave, Dorello’s canal, and the CPA. ch08 9/19/08 11:59 AM Page 534

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A B

Fig. 8.59 Multiple sclerosis presenting with hearing loss. (A) Routine gadolinium enhanced axial T1-weighted magnetic resonance image (MRI) screening study performed for investigation of asymmetric hearing loss showed no enhancing cerebellopontine angle–internal auditory canal mass. (B,C) Axial T2-weighted MRIs showed numerous periventricular areas of T2 and T1 prolongation (arrows), suggesting a demyelinating process. Multiple sclerosis had not been previously suspected. No plaques were identified along the ascending tracts of the auditory pathway. C

The petrous apex is the most frequent subsite of tem- retropharyngeal lymph nodes (Fig. 8.71, Fig. 8.72).172 poral bone involvement with metastatic disease, and Most metastases are osteolytic with loss of normal tra- bilateral involvement may be seen in up to 62%.171 The beculations and cortical contours of the apex on CT most frequently observed metastasis is from breast carci- (Fig. 8.73). Enhanced CT imaging or MRI will show en- noma, with lung and renal being the next most common hancement of a solid mass, with fat saturation on post- primary tumors. Most disease is from hematogenous gadolinium images enabling detection of such lesions spread in patients with metastatic disease elsewhere, but and allowing differentiation from enhancing normal fatty apical destruction can occur with direct superior exten- marrow (Fig. 8.74). Lymphoma or myeloma involving the sion of nasopharyngeal tumors or metastatic disease in petrous apex, or neuroblastoma in children, will have a ch08 9/19/08 11:59 AM Page 535

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Fig. 8.60 Cortical cavernoma. Large temporal cavernoma involving the superior, middle, and inferior temporal gyri presenting with new onset seizures in a teenage girl. (A) Typical findings are illustrated on sagittal T1-weighted, (B) axial T2-weighted, and (C) coronal fluid attenuated inversion recovery (FLAIR) magnetic resonance images. Cortical cavernomas have been reported to present with complex auditory hallucinations when confined to the superior temporal gyrus (Heschl’s gyrus). The C site of Heschl’s gyrus in the normal contralateral temporal lobe (*).

similar destructive appearance, and these patients fre- Aggressive lesions arising outside the petrous apex quently also have other systemic markers of disease.173 may also have a destructive appearance at imaging. Chor- Other tumors or tumor-like lesions arising primarily in domas usually arise in the midline from the basisphenoid the petrous bone are rare, but include Langerhans cell his- synchondrosis and have a characteristic homogeneous tiocytosis, sarcoidosis, rhabdomyosarcoma, myxoma, and bright T2 signal intensity, with bone destruction seen on bone neoplasms such as giant cell tumors and aneurys- CT (Fig. 8.75). Chondrosarcomas more frequently occur mal bone cysts.174–182 These lesions do not often have dis- off-midline, arising from the petro-occipital fissure, and tinguishing radiologic findings, but appear as enhancing extending laterally to the petrous apex. T2WIs show simi- solid, destructive masses of the petrous apex. Both CT and larly bright signal intensity, but CT imaging may reveal gadolinium-enhanced MRI are indicated to identify the stippled chondroid calcification (Fig. 8.76). Both chordo- full anatomic extent of the abnormality. mas and chondrosarcomas enhance with gadolinium. ch08 9/19/08 11:59 AM Page 536

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Fig. 8.61 Pontine cavernoma. (A) Axial T2-weighted magnetic resonance image (MRI) shows subtle focal signal loss (arrow) in the midpons without surrounding T2 prolongation. (B) Coronal T1-weighted MRI suggests two focal areas of T1 prolongation (arrows), with the inferior lesion corresponding to the axial T2-weighted MRI. (C) Coronal gradient echo susceptibility image clearly shows two separate areas of signal loss (arrows), consistent with midbrain and pontine cavernomas. C

Benign masses arising outside the petrous apex, but though rarely arising from the apex, may produce hyperos- extending to involve it include hemangioma of the genicu- tosis. Aneurysms of the petrous portion of the internal late ganglion and schwannoma of Meckel’s cave, which can carotid artery produce focal remodeling of the petrous produce erosion of the anterior or anterolateral aspect of carotid canal and may also reveal linear calcifications on the temporal bone, and as with petrous apex cephaloceles, CT. MRI with MR angiography best demonstrate the true it is important to recognize that these lesions arise from contour of the aneurysm, which can then be obliterated outside the petrous temporal bone. Similarly meningiomas, with endovascular therapy.182,183 ch08 9/19/08 11:59 AM Page 537

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A B Fig. 8.62 Pontine capillary telangiectasia. (A) Axial fluid attenuated in- (B) Contrast enhanced T1-weighted MRI shows feathery enhancement version recovery (FLAIR) magnetic resonance image (MRI) through the in the midpons. This was an incidental finding. pons shows a very subtle focus of high signal intensity in the left pons.

A B Fig. 8.63 Asymmetric petrous apex marrow. (A) Axial and (B) coronal side is pneumatized. Although this may appear readily apparent on un- unenhanced T1-weighted magnetic resonance images (MRIs) show hy- enhanced T1-weighted MRI, difficulties in interpretation can arise on perintensity of the right petrous apex due to fatty marrow (*). The left enhanced images in determining that this is not an apical mass.

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C D Fig. 8.63 (Continued) Axial T2-weighted MR (C) and coronal post-contrast T1-weighted MR (D) show a less prominent but persistent asymmetric appearance with some residual T2 signal and some enhancement despite fat saturation techniques with both exams (arrow).

A B Fig. 8.64 Petrous apex fluid. (A) Sagittal T2-weighted and (B) T1-weighted magnetic resonance images through the cervical spine found incidental signal abnormality in the right petrous apex (arrow) that is hyperintense to cerebrospinal fluid on both sequences. ch08 9/19/08 11:59 AM Page 539

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C D Fig. 8.64 (Continued) (C) Axial unenhanced thin-section computed apex. (D) Axial thin-section CT image shows the left petrous apex is tomography (CT) image shows this material represents fluid in the petrous pneumatized and clear (open arrow). apex with preservation of the bony trabeculae and no expansion of the

A B

Fig. 8.65 Petrous apex mucocele. (A) Axial T2-weighted magnetic resonance image (MRI) shows an expanded right petrous apex (arrow), with hyperintense T2 signal, which remains hyperintense relative to cerebrospinal fluid on fluid attenuated inversion recovery (FLAIR) MRI (B).

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C D

Fig. 8.65 (Continued) (C) Contrast-enhanced axial T1-weighted MRI shows no enhancement of this abnormality. The signal characteristics suggest complex fluid. (D) Expansion of the petrous apex is confirmed with axial computed tomography image. Note small, presumed vestibular schwannoma in the left E internal auditory canal (curved arrow, C).

A B Fig. 8.66 Petrous apex cholesterol granuloma. (A) Axial T2-weighted areas of T2 hypointensity and intrinsic T1 hyperintensity, suggesting the and (B) T1-weighted magnetic resonance images (MRIs) show an presence of blood products. expansile heterogeneous mass in the left petrous apex (arrows), with ch08 9/19/08 11:59 AM Page 541

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C D

Fig. 8.66 (Continued) (C) The coronal gadolinium enhanced T1-weighted MRI shows inferomedial extension to the occipital condyle (*) and no appreciable enhancement. (D) Coronal and (E) axial computed tomography images show the expansile nature of this petrous apex mass (arrows) as it E extends inferomedially. ch08 9/19/08 11:59 AM Page 542

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C D Fig. 8.67 Atypical apical petrositis, without bone destruction. (A) Axial shows abnormal enhancement, suggesting infection. (D) Although the T2-weighted magnetic resonance image (MRI) shows a fluid filled right axial computed tomography in bone algorithm showed no destruction, petrous apex (arrow), which on (B) axial T1-weighted MRI is of heteroge- the patient improved significantly on antibiotic treatment, suggesting in- neous signal intensity. (C) Contrast enhanced axial T1-weighted MRI fection of petrous apex fluid as a cause of her severe temporal headaches. ch08 9/19/08 11:59 AM Page 543

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A B

C D

E F Fig. 8.68 Apical petrositis in a young girl with headaches and multiple posteriorly to the left CPA and prepontine cistern. A “cleft” of absence cranial neuropathies. (A) Axial T1-weighted MR shows diffuse infiltra- of enhancement within the apex corresponds to a cystic or fluid filled tion of the left petrous apex (arrow) with soft tissue which is hyperin- space in the apex on T2 WI (*, images A–D). Axial (E) and coronal (F) CT tense but heterogeneous on (B) T2-weighted MRI. The post-contrast ax- images confirm extensive bone destruction. (Courtesy of Kevin R. ial (C) and coronal (D) T1-weighted MRI show this process spreading Moore, MD.) ch08 9/19/08 11:59 AM Page 544

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A B

C D

Fig. 8.69 Residual petrous apex cholesteatoma. Axial (A) and coronal (B) T1-weighted MR show a heterogeneous expansile mass in the right petrous apex (arrow). The mass is also heterogeneous in signal intensity on axial (C) and coronal (D) T2-weighted MRI. Restricted diffusion is seen on diffusion weighted imaing (E). (Courtesy of Andy Whyte, MBChB, FRCR, FRANZCR.) E ch08 9/19/08 11:59 AM Page 545

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Fig. 8.70 Petrous apex cephalocele. (A) Axial T2-weighted fat-saturated and (B) T1-weighted magnetic resonance images (MRIs) show abnormality (arrow) involving the anterolateral aspect of the left petrous apex with a smooth scalloped contour of the bone, which otherwise contains fatty marrow. (C) Contrast enhanced fat-saturated T1-weighted MRI shows rim C enhancement continuous with Meckel’s cave (curved arrow). ch08 9/19/08 11:59 AM Page 546

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Fig. 8.71 Nasopharyngeal carcinoma. The close proximity of the fossa of Rosenmüller allows early spread of nasopharyngeal carcinoma to the petrous apex. (A,B) Axial T1-weighted magnetic resonance images show a left nasopharyngeal carcinoma infiltrates the prevertebral muscles and extends into the left petrous apex with replacement of normal hyperintense fatty marrow (arrows). (C) The coronal enhanced T1-weighted MR demonstrates superior extension of tumor through foramen lacerum (black arrow), around the petrous and cavernous segments of the left C internal carotid artery. ch08 9/19/08 11:59 AM Page 547

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Fig. 8.72 Nasopharyngeal carcinoma. Gadolinium-enhanced axial T1-weighted magnetic resonance image in another patient with nasopharyngeal cancer with spread to the clivus and petrous apex (*) and posterior extension to the dura, with tumoral spread to the internal auditory canal (arrows).

A B Fig. 8.73 Petrous apex metastasis in an elderly woman with a history of lytic, permeative appearance extending to the anterior margin of the breast cancer and recent onset of dizziness. (A,B) Axial computed internal auditory canal (arrows). tomography scans show destruction of the right petrous apex with a

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C D Fig. 8.73 (Continued) (C) Axial FLAIR from the preoperative STEALTH heterogeneous enhancement which also involves the dorsal petrous demonstrates loss of the normally hyperintense fatty marrow from bone dura and extends into the IAC (arrows). A nasopharyngeal- the right apex and right side of the clivus (arrow), with soft tissue in- approach biopsy proved carcinoma. tensity extending to the IAC margin. (D) Post-contrast T1WI shows

A B Fig. 8.74 Tumor invading the petrous apex. (A,B) Axial and (C) coronal the right petrous apex. (D) Follow-up computed tomography scan gadolinium-enhanced T1-weighted magnetic resonance images show shows a smooth scalloped-type appearance of the right petrous apex an enhancing extraaxial mass in the right middle cranial fossa eroding (arrows). This proved to be a solitary fibrous tumor. ch08 9/19/08 11:59 AM Page 549

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C D Fig. 8.74 (Continued)

A B Fig. 8.75 Clival chordoma. A 62-year-old man with multiple cranial neu- arrows) eroding through its posterior margin (black arrow). (B) The axial ropathies. (A) Axial contrast-enhanced T1-weighted magnetic reso- T2-weighted MRI shows marked hyperintensity, typical of chordoma but nance image (MRI) shows a large enhancing midline clival mass (white also seen in chondroid tumors.

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Fig. 8.75 (Continued)

A B Fig. 8.76 Chondrosarcoma. (A) Axial T2-weighted magnetic resonance petrous apex. (B) The mass is minimally hypointense compared with image (MRI) shows an irregular mass (arrow) that is hyperintense but lo- brain on sagittal T1-weighted MRI, with a focal area of T1 hyperintensity cated laterally at the petroclival synchondrosis and invading the right (curved arrow) that may represent hemorrhage or calcification. ch08 9/19/08 11:59 AM Page 551

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Fig. 8.76 (Continued) (C) Axial gadolinium-enhanced T1-weighted image shows uniform intense contrast enhancement.

A B Fig. 8.77 Fibrous dysplasia. (A) Sagittal unenhanced T1-weighted magnetic resonance image (MRI) shows a heterogeneous appearance to the central skull base. (B) Contrast-enhanced coronal and

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C D Fig. 8.77 (Continued) (C) Axial MRIs show avid enhancement, suggesting a tumor extending into the greater wing of the sphenoid (arrows). This was an incidental finding. (D) Axial computed tomography scan confirms that the heterogeneous MR signal abnormality represents a benign bone process.

A B Fig. 8.78 Paget’s disease of the temporal bone. (A,B) Axial computed including the petrous apices and the calvarium. There is narrowing of tomography scans in a 75-year-old woman with diffuse abnormality, in- the internal auditory canals from bony expansion (arrow) and involve- cluding sclerosis, and regions of cortical thickening of the skull base, ment of the otic capsule (curved arrow). ch08 9/19/08 11:59 AM Page 553

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Intrinsic Bone Abnormalities involvement is more frequently seen with polyostotic disease and is a relatively straightforward diagnosis once CT It is worth remembering the utility of CT imaging in the correlation is obtained. Although these entities are uncom- characterization of benign intrinsic bone abnormalities such mon in the temporal bone, they are an important differential as fibrous dysplasia and Paget’s disease, which may appear to consider in the MRI evaluation of patients with hearing bizarre at MRI with heterogeneous T2 signal intensity and loss, particularly with Paget’s disease, which may manifest contrast enhancement (Fig. 8.77 and Fig. 8.78). Petrous apex here with mixed SNHL and CHL (see Chapter 5).184–187

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Index

Note: Page numbers followed by f and t indicate figures and tables, respectively.

A Adenoma ABCs. See Aneurysmal bone cyst middle ear, 195–197, 224f Abducens nerve. See Cranial nerve(s), VI mucosal, 195 ABI. See Auditory brainstem implants papillary, 195 Abscess Adenoma/pleomorphic adenoma, of EAC, 43 in acute otomastoiditis, 79, 111 Aditus ad antrum, 60, 64f, 75, 299 Bezold, 80, 82–83 computed tomography, best projection for, 59f in acute otitis media, 9–10 Adolescent(s), computed tomography in, effective mAs for, 1 epidural, 86 ADOP. See Osteopetrosis, autosomal dominant in acute otitis media, 9–10 Adult, computed tomography in, effective mAs for, 1 extracerebral (perisinus), in acute otomastoiditis, 83 AER. See Anterior epitympanic recess intracerebral, in acute otomastoiditis, 83 AGs. See Arachnoid granulations intracranial, with necrotizing external otitis, 15 AICA. See Anterior inferior cerebellar artery (AICA) odontogenic, 34 Alagille’s syndrome, 332, 332f, 337–338 parenchymal, 85–86, 87f inner ear deformity in, 337 parenchymal/extracerebral, in acute otomastoiditis, 80 Albers-Schönberg disease, 45, 379–381. See also Osteopetrosis periauricular, 82 Alexander syndrome, 312, 312t petrous apex, 95f Ampulla, 300f subdural, 86 Ampulla (of semicircular ducts), 304 subperiosteal, 80, 82, 84f Amyloidosis in acute otomastoiditis, 79 in EAC, 51 Accessory regions, pneumatization, 73 of meatus and pinna, 51 Achondroplasia, 177–178 Aneurysm, thrombosed, 110 Acoustic aura, 528 Aneurysmal bone cyst, 193, 378 Acoustic coupling, 60 in petrous apex, 535 Acoustic neurinoma. See Schwannoma Angiofibrolipoma, 42 Acoustic neuroma. See also Schwannoma Angiography, conventional bilateral, and cochlear implantation, 399 of aneurysm of petrous ICA, 275, 280f retrosigmoid dissection, complications, 369 of dural arteriovenous fistula, 269, surgical approach for, 369 271, 272f Acrocephalosyndactyly, 176 of endolymphatic sac tumors, 287–288 type I. See Apert syndrome of ICA stenosis/occlusion, 275 Acute myelogenous leukemia (AML), granulocytic sarcoma in, of paraganglioma, 284 203–204 of paragangliomas, in recurrent disease, 286 Adenocarcinoma, in middle ear, 197 of venous sinus thrombosis, 254 Adenoid cystic carcinoma, 49–50 in work-up for pulsatile tinnitus, 262 559 index.qxd 9/24/08 7:25 PM Page 560

560 Index

Angiomyolipoma, 42 pathogenesis, 269 Annular ligament, 60–63 with subacute infarct, 271, 273f Anotia, 26 three-dimensional (3D) time of flight (TOF) MRA, Anterior epitympanic recess, 62f, 64f, 69, 69f, 133 22, 22f cholesteatomatous involvement, 133, 133f and tinnitus, 21 computed tomography, best projection for, 59f with transosseous collaterals, 271, 274f Anterior epitympanic (geniculate) sinus, 451–452 treatment, 269–270 Anterior inferior cerebellar artery (AICA), 284, 484, 484f type I, 269–270, 271f anatomic variant, 520 type II, 270, 271f aneurysm, 520–521 type III, 270 impingement on CN VIII, 22 work-up for, 262 labyrinthine branch, 304 extracranial, 269 loop, 275–276, 280f, 451f, 484, 484f imaging, 22 Anterior mallear ligament, 62f–63f, 64, 69f vertebral, 273–274 calcification, 161f Arteriovenous malformation computed tomography, best projection for, 59f in cerebellopontine angle, 521–524, 533f Anterior tympanic artery, 71, 71t, 73f of EAC, 41–43 Anterior tympanic fissure, 63, 64f imaging, 22 Anterior tympanic isthmus, 74 and tinnitus, 21 Anterior tympanic spine, 63, 64f, 68f Arteritis, stenotic lesions caused by, and pulsatile Antineutrophil cytoplasmic antibody, C-ANCA, in Wegener tinnitus, 274 granulomatosis, 37–38, 217 Ascending pharyngeal artery, 71, 73f, 284, 285f Antrum Aspergillosis, differential diagnosis, 203 computed tomography, best projection for, 59f Aspergillus, external otitis caused by, 35 embryology, 77 Astrocytoma AOM. See Otitis media, acute; Otomastoiditis, acute extraaxial, 515 Apert syndrome, 13–14, 176, 332 pilocytic, involving cerebellopontine angle, 515 inner ear anomalies in, 338 Ataxia, with schwannoma, 256 Apical cells, 75 Atherosclerosis Apical petrositis, 253, 531–532, 543f. See also Petrous apicitis stenotic lesions caused by, and pulsatile tinnitus, atypical, 542f 274, 278f confluent, 531–532 and tinnitus, 21, 262 Applebaum prosthesis, 165, 192f work-up for, 262 Arachnoid cyst(s), 94, 216, 491–492, 496f, 498, 502f Atresiaplasty coexistent with vestibular schwannoma, 498, 502f indications for, 32 of petrous apex, 111 preoperative imaging for, 13–14 Arachnoid granulations, 85, 91, 289 techniques for, 32 aberrant, 345, 349f Attic, 63f, 65f CT appearance, 345 computed tomography, best projection for, 59f differential diagnosis, 345 congenital fixation, 209f Arcuate eminence, 299 erosive debris in, 107f Arnold’s nerve, 26, 59, 251, 251t lateral wall, 64f glomus bodies associated with, 277, 281f new bone formation in, tympanosclerosis and, 164f AROP. See Osteopetrosis, autosomal recessive Attic block, 75, 96, 214f Arrectores pilorum, 43 Atticotomy, 148, 159f, 169f, 178f Arterial anatomy, normal, 251–253 anterior, 10 Arterial dissection, stenotic lesions caused by, Auditory agnosia, 525, 527–528 and pulsatile tinnitus, 274, 279f Auditory brainstem implants, 396 Arteriohepatic dysplasia. See Alagille’s syndrome Auditory cortex Arteriovenous fistula primary, 484–486, 486f, 488f direct, 273–274 lesions, otoneurologic manifestations, 528 extracranial, 273–274, 277f tonotopic organization, 484 intracranial, 273–274, 275f Auditory pathway dural, 91, 269–273, 272f–274f course, 488f angiographic findings, 271, 272f intracranial lesions along, 524–528 draining into vertebral venous plexus, 271, 275f normal anatomy, 480–486 imaging, 269 Aural atresia, congenital magnetic resonance angiography, 8 chromosome 18 and, 27 MRI appearance, 269–271 and EAC duplication anomalies, 27 index.qxd 9/24/08 7:25 PM Page 561

Index 561

hereditary syndromes associated with, 13–14 Branchial arch(es), 26, 266 imaging in, 13–14 anomalies, choristoma and, 198–199 interpretation, 13–14 first, 26 protocol for, 13 abnormalities, 207f report, 14 derivatives, 63f, 64, 66f, 78 surgery for, 13 maldevelopment, 27 Aural dysplasia, congenital. See also Aural atresia, congenital mesenchyme, 445, 446f hereditary syndromes associated with, 13–14 second, 26, 445, 445f imaging in, 13–14 abnormalities, 205f–206f Aural polyps, 41–42, 43f derivatives, 26, 58, 60, 64, 66f, 71, 78–79, 347 Auricle, 25 mesenchyme, 445, 445f–446f embryology, 26 Branchial cleft, first, type 2 anomaly, 29 Auricular mass(es). See Mass(es), temporal bone, auricular Branchial cleft cyst, 33–34 Auriculotemporal nerve, 26 computed tomography, 33, 33f Auto-atticotomy, 148 differential diagnosis, 34 Autoimmune inner ear disease, 17–18 endoscopic resection, 34 Automastoidectomy, 136, 148, 152f–153f, 170f ethanol injection sclerotherapy for, 34 Autophony, in superior semicircular canal dehiscence first syndrome, 332 associated anomalies, 33 Avascular osteonecrosis, of temporal bone, 234 clinical presentation, 33 AVMs. See Arteriovenous malformation incidence, 33 location, 33 B treatment, 33–34 Bacteroides, brain abscess, 86 magnetic resonance imaging, 33 BAHA. See Bone-anchored hearing aid malignant transformation, 33 Basal cell carcinoma management, 33–34 of EAC, 49 pathology, 33 in middle ear, 195 with superimposed infection, 34 Basilar artery, 484 Branchio-oto-renal syndrome, 13–14, 338, Basilar membrane, 301f, 309 338f–339f Battle’s sign, 51 Breast cancer BCC. See Branchial cleft cyst leptomeningeal seeding, 514 Beckwith-Wiedemann syndrome, 176 metastases Behçet’s disease, hearing loss in, 363 to EAC, 50 Bell’s palsy, 15, 464 to jugular foramen, 260f atypical, 471–472 to middle ear and mastoid, 201 imaging in, 15–17 to petrous apex, 534, 547f–548f clinical presentation, 471 Brown tumor, 193 diagnostic criteria for, 471 Bruit(s), paraganglioma and, 279 differential diagnosis, 15–16 B2-transferrin, 347–349 imaging, 459t–460t, 471–472, 471f–473f MRI appearance, 528f viral association, 471 C Benign paroxysmal positional vertigo (BPPV), 22, 369 CA. See Cochlear aqueduct Bill’s bar, 450, 482 CAD. See Aural dysplasia, congenital Bing-Siebenmann deformity, 312 Camurati-Engelmann dysplasia, 381, 381f Birbeck granules, 190 Canal, definition, 299 Black Oval-Top Prosthesis, 166, 192f, 201f Canaliculus chordae tympani, 65f, 69, 71 Bleomycin, for cystic hygroma/cystic lymphangioma, 34 Canalithiasis, 433 Blue-dome cyst, 106 Canal of Huguier, 450, 455 Bone-anchored hearing aid Canal of Rosenthal, 303f, 309 indications for, 32 Canal wall down (CWD) mastoidectomy. See Mastoidectomy, placement, 14 canal wall down (CWD) procedure Bone sequestra, with endolymphatic sac tumors, 287 Canal wall up (CWU) mastoidectomy. See Mastoidectomy, canal Bony spicule, 301f wall up (CWU) procedure BOR. See Branchio-oto-renal syndrome Cancer risk, from pediatric CT, 6 Brain, heterotopic, in middle ear, 216 Candida, external otitis caused by, 35 Brain injury, temporal bone fractures and, 438–439 Capillary telangiectasia, 528, 537f Brainstem tumor, involving cerebellopontine angle, 515, 524f Carcinoid, 195–196 index.qxd 9/24/08 7:25 PM Page 562

562 Index

Carcinoma inflammatory, 515–519 chronic stenosing external otitis and, 36 vascular, 520–524 of external auditory canal, 37 schwannoma, 495–510. See also Schwannoma, vestibular imaging, 47–48 MRI appearance, 356 mastoid/middle ear involvement in, 36 surgery for, labyrinthine ossification after, 356 of temporal bone, 47–50 tumors, 22 metastases, 48, 49f Cerebellopontine angle cistern treatment, 48–49 evaluation Caroticojugular spine, 249f, 250, 252–253 in tinnitus, 22 Caroticotympanic artery, 71, 71t, 73f, 252, 265–266, 266f, 268f in vertigo, 23 Caroticotympanic nerve, 250 facial nerve in, 448–449, 448f–449f Carotid artery Cerebritis, in acute otomastoiditis, 87f aberrant, and tinnitus, 21 Cerebrospinal fluid (CSF) aneurysm, and tinnitus, 21 leak, 75 petrous, pseudoaneurysm, postradiation, 212 in acute otomastoiditis, 111 stenosis, and tinnitus, 21 after surgical resection of vestibular schwannoma, 504–505 Carotid bruit, and tinnitus, 21 congenital defects causing, 345, 349f Carotid canal, 58, 70f, 249f, 252, 304f–306f imaging, 346, 349f fracture, 416, 422f, 438–439 posttraumatic, 434–438 horizontal segment, 249f in trauma patient, 51 CT appearance, 253 otorhinorrhea, 85 vertical segment, 268f congenital defects causing, 345, 349f hypoplasia/aplasia, 265 otorrhea, 85, 345f Carotid cancer, 251 longitudinal temporal bone fracture and, 418f, 434 Carotid-cavernous fistulas, 273, 276f pathophysiology, 346 Cataract(s), radiation-related, threshold dose for, 5–6 with petrous apex cephalocele, 216 Cavernoma posttraumatic, 434–438 in cerebellopontine angle, 521 rhinorrhea, 345f imaging characteristics, 528, 535f–536f pathophysiology, 346 otoneurologic manifestations, 528 posttraumatic, 435 Cavernous angioma. See Cavernoma Cerebrospinal fluid (CSF) fistula(s), 345f Cavernous sinus, 487f pathogenesis, 344, 345f Cellulitis, chronic stenosing external otitis and, 36 risk factors for, 344 Central mastoid tract, 75 Cerumen gland(s), tumors originating from, 49–50 computed tomography, best projection for, 59f Ceruminoma, 43, 196 Central nervous system (CNS) Cervical cyst(s), 13 hypertension, evaluation for, in sensorineural hearing loss, 18 Cervical fistula(s), 13 hypotension, evaluation for, in sensorineural hearing loss, 18 Cervical plexus Cephalocele greater auricular branch, 20 petrous apex, 94, 216 mastoid branch, 20 of petrous apex, 532, 545f Cervical root compression, otalgia caused by, 20–21 Cerebellopontine angle, 481f Cervico-oculo-acoustic syndrome. See Wildervanck syndrome arachnoid cyst, 491–492, 496f CG. See Cholesterol granuloma arteriovenous malformation, 521–524, 533f CH. See Cholesteatoma evaluation, in sensorineural hearing loss, 17–18 CHARGE association, 13–14, 331 hamartoma, 494, 498f–499f inner ear anomalies in, 338, 339f imaging, 486–553 CHD. See Hearing loss, conductive intraaxial masses involving, 515, 524f–526f Chiari I malformation lesions, 490 evaluation for, in sensorineural hearing loss, 18 lipoma, 492–494, 497f otoneurologic manifestations, 22–23 lymphoma in, 515, 523f Child(ren) magnetic resonance imaging, protocols, 489 aural polyps in, 42 masses, congenital, 490–494 computed tomography, radiation dose reduction techniques meningioma, 510–513, 519f for, 4–7 metastatic disease in, 513–515, 522f computed tomography in pathology effective mAs for, 1 acquired neoplastic, 495–515 protocols for, 7 acquired nonneoplastic, 515–524 facial swelling in, differential diagnosis, 34 infectious, 515–519 CHL. See Hearing loss, conductive index.qxd 9/24/08 7:25 PM Page 563

Index 563

Chloroma. See Granulocytic sarcoma first branchial cleft cyst and, 33 Chocolate cyst, 106 and granulation tissue, differentiation, 99 Cholesteatoma, 37–41, 75, 79f, 170f–171f. See also Otitis media, histopathology, 40 chronic, active, with cholesteatoma imaging, 150 acquired, 141f, 143f–148f, 151f invasive, 217f in acute otomastoiditis, 79 labyrinthine involvement in, 362 CT appearance, 136, 185 large erosive, with extensive fistula, 150f etiology, 116, 116t longitudinal temporal bone fracture and, 418 growth patterns, 118 magnetic resonance imaging, 133 immigration theory, 117 middle ear, extensive, 149f in middle ear, 115–136, 115t MRI appearance, 185 MRI appearance, 138f–139f mural, 136 papillary proliferation theory, 117 origins, 26 primary, 115, 115t and otic capsule demineralization, 394 retraction theory, 116–117 pars flaccida (attic), 118–120, 126f–130f secondary, 115, 115t pars tensa, 120–123, 129, 130f–133f with sinus plate destruction, 139f petrosal, 135f, 185 squamous metaplasia theory, 117–118 acquired, 123, 185 age distribution, 38 congenital, 123, 185 aggressive, 133–136, 140f–142f, 152f definition, 123 surgical approach to, 136 of petrous apex, 133–134, 334, 532, 544f attic, 69, 137f, 149f recurrent, 180f atticoantral, 129f, 145f postradiation, 214 and aural polyps, 42 poststapedectomy, 157 in Camurati-Engelmann dysplasia, 381 posttraumatic, 423f causes, 40 primary, 180–185 and cholesterol granuloma, differentiation, 99 of jugular foramen, 259–260 in chronic otomastoiditis, 96 MRI appearance, 260 chronic stenosing external otitis and, 36 Prussak’s space, 118–120, 126f–130f, 136f clinical presentation, 38–40 invagination theory, 128f complications, 124–133, 125t, 136, 141f–150f recurrent, 150f–151f, 169f, 173f, 177f–180f, 194f–195f congenital, 41, 180–185, 212f–214f, 216f imaging, 40 in attic, 184–185 mimicking encephalocele, 179f atypical, 215f with superinfection, 175f bilateral, 180 sinus, 120 clinical presentation, 180–181 and tympanosclerosis, 160f–161f CT appearance, 185 Cholesterol granuloma, 75, 76f, 99–100, 289–291 differential diagnosis, 76 in acute otomastoiditis, 79 and epidermoid formation, 181–182 of cerebellopontine angle, differential diagnosis, 110–111 in geniculate ganglion, 184 cochlear involvement in, 362 in internal auditory canal, 184 CT appearance, 291 in mastoid, 185 differential diagnosis, 110–111 in middle ear, 115, 115t imaging, 109–110, 110f–111f, 150 of middle ear, 180–185 and intralabyrinthine hemorrhage, 364 posterior, 183–184, 214f in middle ear, 109f MRI appearance, 185 inner ear involvement in, 104 unilateral, 180 MRI appearance, 291 CT appearance, 185 and otic capsule demineralization, 394 with EAC atresia/microtia, 30, 30f, 40 of petrous apex, 104–105, 113f–115f, 530–531, 540f–541f evaluation for development, 109 in acute otitis media, 9–10 differential diagnosis, 110–111 in chronic otitis media/otomastoiditis, 10–11 treatment, 111, 119f of external auditory canal, 38–41 Chondritis, chronic stenosing external otitis and, 36 congenital, 41 Chondroblastoma, 216 imaging, 40–41, 40f–41f in EAC, 50 postoperative, 40 Chondrogenic tumor, 233f staging, 40 Chondroid chordoma, 216 facial recess, 130f Chondrosarcoma, 50, 216–217, 535, 550f–551f fibrous dysplasia and, 46, 377 of jugular foramen, 260 index.qxd 9/24/08 7:25 PM Page 564

564 Index

Chordal eminence, 68f, 69, 71 Cochlear-carotid interval, 399 Chordal ridge, 69 absent, 399, 399f Chorda tympani, 63f, 67f, 69, 70f, 448, 450, 451f, 455 variation, 334 embryology, 445, 446f Cochlear duct, 299, 300f–301f, 303f, 309 lesions, localization, 462–463, 463t embryology, 298, 298t Chordoma, 535, 549f–550f evolution, 298 chondroid, 216 Cochlear fossette of jugular foramen, 260 axial CT image, 2f physaliphorous, 216 evaluation Choristoma, 196–199 for atresiaplasty, 13–14 Choroid plexus, 484 for cochlear implantation, 12 papilloma, involving cerebellopontine angle, 515, 525f Cochleariform process, 60f, 64, 69, 305f, 453 Chromosome 11, and paragangliomas, 278 Cochlear implantation, 394–401 Chromosome 18q, and congenital aural atresia, 27 candidates for, 396 Chronic granulomatous disease (CGD), 37 contraindications to, 341, 397–400, 490 Chronic myelogenous leukemia (CML), 204 devices for and intralabyrinthine hemorrhage, 364 components, 396–397 CI. See Cochlear implantation CT appearance, 401f CISS. See Magnetic resonance imaging (MRI), constructive multichannel, 395, 397f interference in steady state images historical perspective on, 395 Cisternography, 456 imaging for Cleidocranial dysplasia, 177 interpretation, 12 Clivus, 58, 249f protocol, 11–12 COA. See Ossicles, congenital anomalies report, 12–13 Coalescence, in acute otomastoiditis, 79 indications for, 395 Cochlea, 58, 75, 249f–250f, 300f–301f, 455f, 481f–482f lead position in, confirmation of, imaging for, 8, 9f absence, 313, 313t mechanism of action, 395–396 anatomy, 307–309 MRI contraindicated after, 401 anterior turn, 306f otospongiosis and, 391 apical turn, 63f, 302f–303f, 305f–306f postoperative evaluation, 400–401, 400f–401f basilar turn, 65f, 303f–304f, 306f, 310f, 311 postoperative imaging, 310f dehiscence, 334 for posttraumatic hearing loss, 428 distal, 305f preoperative evaluation for, 356, 397–400 proximal, 302f, 305f surgical landmarks for, 12, 304 embryology, 330–331 surgical pitfalls, 12 evaluation, in sensorineural hearing loss, 18 Cochlear nerve, 67f, 301f, 303f, 307, 450, 451f, 480–482, 482f fistula, 148f absence, 398–399, 398f–399f, 490 fluid-filled spaces, 309 anatomy, 480 fractures, and cochlear implantation, 399 aperture, 302f–303f, 306f, 480, 481f function, 307–309 stenosis, 398f, 399 hypoplasia, 324f, 355, 398f aplasia, and IAC size, 340–341, 342f, 398–399 middle turn, 63f, 302f–303f, 305f–306f deficiency, classification, 341 and sensorineural hearing loss, 309 hypoplasia, 490 Cochlear aplasia, 313, 313t, 316f–317f, 355 imaging, 341 bilateral, 316f–317f and sensorineural hearing loss, 309 Cochlear aqueduct, 299, 303f–304f, 415f, 416 size, 481 abnormal patency, 344–345 Cochlear nerve deficiency, IAC morphology and, 31 accessory, 311 Cochlear neural foramen, 303f anatomy, 311 size, and IAC size, 341, 342f deformity, 172 Cochlear nuclear complex, 484, 485f dysfunction, 311 lesions involving, 525 function, 311 Cochlear nuclei labyrinthine segment, 311 evaluation, in sensorineural hearing loss, 18 large caliber, 344 and sensorineural hearing loss, 309 lateral orifice, 311 Cochlear recess, 299, 300f, 309 medial orifice, 311 Cochleovestibular aplasia, 313 otic capsule segment, 311 Cochleovestibular hypoplasia, 313, 313t, 314f, 315–317, 325f petrous apex segment, 311 Cochleovestibular malformation, cystic, 313–314 Cochlear canal, 480 Cockayne’s syndrome, 311 index.qxd 9/24/08 7:25 PM Page 565

Index 565

“Cog,” 69, 151f of malignant otitis externa, 37 Cogan’s syndrome, 362–363, 367f of mandibulofacial dysostosis, 13 Cold water exposure multidetector, 457 and exostoses in EAC, 44–45 advantages, 4 and osteoma in EAC, 45 performance, 4 Coloboma, 13–14 reformats, 4, 5f–6f COM. See Otitis media, chronic; Otomastoiditis, chronic in otalgia, 20–21 Common cavity, 313–314, 313t, 314f, 318f–320f in otitis externa, 14–15 and CSF fistula, 344 of paragangliomas, in recurrent disease, 286 Common crus, 299, 300f, 306f partial volume effect, 333 Computed tomographic angiography (CTA), multidetector row, patient positioning for, 1 of arterial dissection, 274–275, 279f in pediatric patient, cancer risk from, 6 Computed tomography (CT), 1–7. See also PET/CT Poschl projection, 308f in acute otitis media, 9–10 for posttraumatic facial nerve paresis, 15–17 axial images in soft tissue algorithm, 4 preoperative, for atresiaplasty, 13–14

of bony anatomy, 256f radiation dose. See also CTDIvol of cholesteatoma of EAC, 40, 40f–41f reduction in chronic otitis media/otomastoiditis, 10–11 strategy for, 7, 457 in chronic stenosing external otitis, 36 techniques for pediatric patients, 4–7 for cochlear implantation, 11–13 reformats collimation, 1 in axial plane, 4 in conductive hearing loss, 17–18 in coronal plane, 4 of congenital abnormalities, report, 30–31 resolution, 1 of congenital aural atresia, 13–14 of retrotympanic masses, 18–19 contrast-enhanced routine technique, 1–4, 2f–3f of CSF leakage, 346, 349f in sensorineural hearing loss, 486–488 in work-up for pulsatile tinnitus, 262–263 in children, 17–18 of craniofacial bones, in children, 13 source images, 4 dual field of view, 1, 4 of squamous cell carcinoma of EAC, 48f in dural sinus occlusive disease, 91 of squamous cell carcinoma of temporal bone, 47f effective mAs for, 1 standard axial dataset/reconstruction, 1–4, 2f and radiation dose, 7 standard coronal dataset/reconstruction, 1–4, 3f of endolymphatic sac tumors, 287 Stenver projection, 310f of eosinophilic granuloma, 38, 39f in superior semicircular canal dehiscence syndrome, 333, of exostoses in EAC, 44–45, 44f 333f–335f of external auditory canal, 25 of temporal bone, deterministic effects, 5–6 of external auditory canal stenosis, 13–14 of temporal bone fractures, 418 of facial nerve, normal anatomy, 452f–455f, 456 in tinnitus, 21–22 of foramen of Huschke, 35 of tuberculous otitis externa, 37, 38f gantry cycle time for, 1 in vertigo, 22 helical mode for, 1 of Wegener granulomatosis, 38, 38f high-resolution Computed tomography arteriography (CTA), 4 with bone algorithm, 283–284 indications for, 262 of cholesteatoma in middle ear and mastoid, 123 Computed tomography venography (CTV), 4 of DAVF, 271 indications for, 262 of paragangliomas, 283 Conductive hearing loss. See Hearing loss, conductive of temporal bone fractures, 416, 417f Contrast media, intravenous, for computed tomography, 1 in temporal bone trauma, 439–440 Cornelia de Lange syndrome, inner ear malformation in, 338 image noise, 7 Corticobulbar tract, 485f image quality, 7 Corticopontine tract, 485f and radiation dose, 7 Corticospinal tract, 485f indications for, 486–488 Cotton wool appearance, 370, 372f intravenous contrast for, 1 Cotugno’s canal, 311 of jugular foramen, 250–251 CPA. See Cerebellopontine angle of keratosis obturans, 41, 42f Cranial nerve(s) kilovolt peak (kVp), 1 V, 26 and radiation dose, 7 auriculotemporal branch, 20 of lesions of jugular foramen, 254–255 evaluation, in otalgia, 20 of lymphangioma, 34 mandibular segment, 249f index.qxd 9/24/08 7:25 PM Page 566

566 Index

Cranial nerve(s) (Continued) Cystic hygroma. See Hygroma, cystic VI Cystic lymphangioma. See Lymphangioma, cystic cavernous sinus segment, 487f Cytomegalovirus (CMV), inner ear infection, in HIV-infected cisternal segment, 487f (AIDS) patients, 353 course, 487f dysfunction, 337 D intraorbital segment, 487f DAVF. See Arteriovenous fistula, dural motor nucleus, 445 Deep auricular artery, 73f nucleus, 447f, 448, 448f Deep petrosal nerve, 251 petrous apex segment, 487f Dermoid, 42, 199–200 VII. See Facial nerve Desmoplastic fibroma, 220 VIII. See Vestibulocochlear nerve DFOV. See Dual field of view IX, 26, 250 Diabetes mellitus, malignant external otitis in, 36–37 deficits, 256 Digastric groove, 82 evaluation, in otalgia, 21 Digastric muscle, embryology, 26 Jacobson branch, 20, 250 DiGeorge syndrome, 13 paraganglia associated with, 281f inner ear deformity in, 337 tympanic plexus, 71 Dizziness X, 26, 250 differential diagnosis, 22 Arnold branch, 20, 250–251 imaging in paraganglia associated with, 281f interpretation, 22–23 in jugular foramen, 251, 251t protocol, 22 in malignant external otitis, 37 report, 23 Cranial neuropathy(ies) perilymphatic fistula and, 160 with giant cholesterol cyst, 106–109 poststapedectomy, 161 with leptomeningeal carcinomatosis, 514, 522f–523f sound-induced, 332–333 with meningioma of jugular foramen, 258 in superior semicircular canal dehiscence syndrome, 332 multiple, 462–463, 463t DLP. See Dose-length product in osteopetrosis, 380 Dorello’s canal, 487f paraganglioma and, 279 Dose-length product, 5 petrous apicitis and, 92 Down syndrome, inner ear anomalies in, 338 in sarcoidosis, 516 DSOD. See Dural venous sinuses, occlusive disease with vestibular schwannoma, 496 Dual field of view, in computed tomography, 1, 4 Craniofacial bone(s), imaging, in children, 13 Duane retraction syndrome, 176, 337 Craniofacial dysostosis, 332. See also Crouzon syndrome Duct, definition, 299 Craniometaphyseal dysplasia, 176, 381 Ductus reuniens, 299 Craniosynostoses, 13–14 Dural herniations, in acute otomastoiditis, 111 Crista falciformis, 250f, 305f, 450, 482, 482f–483f Dural venous sinuses Crouzon syndrome, 13–14, 332 asymmetry, 91 inner ear anomalies in, 338 mural thrombus, 86 Cryptococcus, inner ear infection, in HIV-infected (AIDS) occlusive disease, 86–91 patients, 353 in acute otomastoiditis, 79–80, 86–91 CT. See Computed tomography (CT) magnetic resonance imaging, 88–90, 88f–90f CTA. See Computed tomographic angiography (CTA); stenosis, 269 Computed tomography arteriography (CTA) in osteopetrosis, 380 CTDI , 4 vol and pulsatile tinnitus, 275 definition, 1 CTV. See Computed tomography venography (CTV) Cup ear deformity(ies), 27 E Cupulolithiasis, 305, 369, 433 Eagle syndrome, 21 Cyber Knife surgery, for paragangliomas, 286 EDS. See Endolymphatic duct system Cyst(s). See also Aneurysmal bone cyst; Arachnoid cyst(s); EF. See Epidermoid formation Branchial cleft cyst Effective mAs, for computed tomography, 1 blue-dome, 106 and radiation dose, 7 chocolate, 106 Ekman-Lobstein syndrome, 392 giant cholesterol, 106 ELD. See Endolymphatic duct lymphoepithelial, in HIV-infected (AIDS) patients, 34 ELDS. See Endolymphatic duct system in parotid tail region, 34 ELH. See Endolymphatic hydrops subarachnoid, in neurocysticercosis, 517–519 ELS. See Endolymphatic sac index.qxd 9/24/08 7:25 PM Page 567

Index 567

ELST. See Endolymphatic sac tumors Epidermoid formation, and congenital cholesteatoma, Empty delta sign, 91 181–182 Empyema Epitympanum (attic), 65f, 71, 74, 74f, 75, 299 in acute otomastoiditis, 80 embryology, 77 petrous apicitis and, 92 pneumatization, 78 subdural, in acute otomastoiditis, 83 Eustachian tube, 58, 73f, 249f Encephalocele, 152–153, 179f dysfunction, 79–80, 96, 103 in acute otomastoiditis, 111 dysplasia, with EAC atresia/microtia, 30 CSF fistula with, 347f embryology, 77 differential diagnosis, 179f functions, 73 Endobones, in osteopetrosis, 380 obstruction, 80 Endolymph, 299, 309–310 by dermoid, 102f evolution, 298 and otomastoiditis, 79 Endolymphatic duct, 299, 310. See also Large endolymphatic Ewing sarcoma, 34 duct and sac syndrome Ewing’s sarcoma, 234 arterial supply, 311 Exophthalmos, pulsatile, 273 embryology, 298, 298t, 330–331 Exostoses isthmic (vertical) segment, 310 in EAC, 44–45, 44f sinus (horizontal) segment, 310 recurrence, 45 Endolymphatic duct system, 299, 310–311 in IAC/CPA, 490, 491f Endolymphatic hydrops, 364–369. See also Meniere disease External auditory canal, 25, 58, 70f, 250f idiopathic, 367–368. See also Meniere disease abnormalities, associated with microtia, 27–28, 28f epidemiology, 368 amyloidosis, 51 etiology, 368 anatomy, 25–26 genetics, 368 arterial supply to, 26 imaging, 368–369 atresia luetic, 351 chromosome 18 and, 27 posttraumatic, 434 grading system for, 27 secondary, 367. See also Meniere syndrome nonsyndromic, 28, 28f surgical treatment, 369 reconstructive surgery for, 32 Endolymphatic sac, 299, 301f, 310. See also Large endolymphatic complications, 32–33 duct and sac syndrome severity, classification, 28 arterial supply, 311 syndromic, 27 decompression/shunt, 369 type A (meatal), 28 distal (smooth) segment, 310 type B (partial), 28 dysfunction, pathophysiology, 324–326 type C (total), 28 embryology, 330–331 type D (hypopneumatic total), 28 proximal (rugose) segment, 310 benign osteonecrosis, 45 shunting, 324 canalization, 26 surgical obliteration, 324–326 failure, 28, 28f Endolymphatic sac tumors, 291f–292f carcinomas, 47–49 diagnosis, 288–289 development, 25 differential diagnosis, 288, 345 duplication anomalies, 27 imaging, 287–288 dysplasias, 27–33 and intralabyrinthine hemorrhage, 364 embryology, 26 and middle ear adenoma, differentiation, 196 evaluation mimics, 288–289 in chronic otitis media/otomastoiditis, 10–11 salt and pepper appearance, 287 in conductive hearing loss, 18 of temporal bone, 286–287 in otitis externa, 15 Endolymphatic sinus, 299, 310 in tinnitus, 21 Eosinophilic granuloma, 38, 39f, 190. See also Langerhans fibrocartilaginous, 25–26 cell histiocytosis Goldenhar syndrome, 27 Ependymoma granulation tissue in, 37 of fourth ventricle, 515, 526f imaging, techniques for, 25 involving cerebellopontine angle, 515 innervation, 26 Epibranchial placode, 184 intracranial masses extending into, 52, 52f Epidermoid lateral, 25–26 cerebellopontine angle, 490–491, 494f lymphatic drainage, 26 imaging, 490–491, 494f–495f lymphoma, 50 index.qxd 9/24/08 7:25 PM Page 568

568 Index

External auditory canal (Continued) descending segment, 249f, 251, 251f malformations, 27 disorders. See also Bell’s palsy, atypical; Multiple cranial melanoma, 50 neuropathy(ies) metastases to, 50 imaging in osseous, 26 interpretation, 15–17 pathology protocol, 15 embryologic, 27–35 report, 17 inflammatory, 35–41 dysfunction neoplastic, 41–50 cholesteatoma and, 130–131 postirradiation changes, 229f–230f in labyrinthitis, 353 stenosis, 27 otitis media and, 130 fibrous dysplasia and, 377, 378f in syphilis, 350–351 imaging, 13–14 embryology, 445–446, 445f–446f, 490 nonsyndromic, 28, 28f evaluation syndromic, 27 for atresiaplasty, 13–14 superficial, 26 and cochlear implantation, 12 trauma, 50–51, 51f in otalgia, 20 tumors, 41–50 extracranial, 444, 455 benign bony, 43–47 lesions affecting, 464–465, 464f benign soft-tissue, 41–43 extracranial (parotid) segment, 451f, 451t of cerumen gland origin, 49–50 computed tomography, 457–458, 458t malignant, 47–50 fibrous dysplasia and, 377 middle ear involvement in, 202–203 in first branchial cleft anomalies, 34 rare types, 50 functions, 444f, 447, 451f venous drainage, 26 hemangioma, 468–471, 469f–470f External carotid artery, 73f hypoplasia, 16f External ear imaging, 445, 456 embryology, 25 DRIVE (driven equilibrium) sequence, normal appearance, 16f innervation, 26 in EAC disease, 35–36 External otitis. See Otitis externa protocols for, 457–462 Extramedullary hematopoiesis, middle ear debris with, 204 injury in BCC surgery, 33–34 F in EAC atresia surgery, 33 Fabry disease, otoneurologic manifestations, 23 temporal bone trauma and, 419f, 422–427, 425f–426f, 450 Facial clefts, 13–14 intracanalicular (internal auditory canal) segment, Facial colliculus, 448, 448f 450, 451f, 451t Facial expression, muscles lesions affecting, 463, 464t embryology, 26 intracranial, 444 facial nerve and, 451f intratemporal, 444, 447, 447f Facial hiatus, 451–452, 452f computed tomography, 457–458, 458t Facial nerve, 26, 302f, 482f–483f lesions affecting, 463–464, 464t in acute otomastoiditis, 80, 91, 91f, 111 involvement in acute otitis media, 9–10 anatomy, 447–456, 447f–455f, 481f, 482 labyrinthine segment, 61f, 450, 451f, 451t, 452, 452f, 481f anomalies, choristoma and, 199 distal, 453–454, 453f anterior (first) genu, 450, 454f lesions, preimaging localization, 462–463, 463t aplasia, 16f magnetic resonance imaging arterial supply to, 456 axial CISS (constructive interference in steady state) axonotmesis, 423 image, 16f brainstem causes, 463, 464t protocols for, 458–461, 459t–460t branches, 451f, 455 in malignant external otitis, 37 cisternal (intracranial) segment, 449–450, 449f, 451f, 451t mastoid segment, 72f, 450, 451f, 451t, lesions affecting, 463, 464t 454–455, 454f–455f computed tomography, protocols for, 457–458, 458t and posterior margin of glenoid fossa, anteroposterior course, 444 distance between, evaluation, 14 in EAC atresia/microtia, 31, 32f mastoid (descending) segment, 451f, 451t cystic schwannoma, 34 motor nucleus, 447, 447f–448f, 448t dehiscence neurapraxia, 423 choristoma and, 199 neuromas, 468 postsurgical, 181f neurotmesis, 423 index.qxd 9/24/08 7:25 PM Page 569

Index 569

normal bony dehiscences, 446 computed tomography, 452f–455f, 456 congenital malformations, 446 magnetic resonance imaging, 456–457, 456f coronal CT image, 3f nuclei, 447–448, 447f–448f defects, 345 functions, 447–448, 448t dehiscence, 76 lesions affecting, 463, 464t embryology, 79, 490 palsy first genu, 302f central, 462 imaging, 133 clinical presentation involvement in cholesteatoma, 133, 134f and etiology, 461–462 labyrinthine segment, 302f and location, 461–462 distal, 305f in osteopetrosis, 380 mastoid segment, 68f, 70f, 307f peripheral, 462 normal defects, 446 preimaging localization of lesions causing, 462–463, 463t in otosclerosis, 383, 384f postirradiation, 232f postmastoidectomy, 153 postmastoidectomy, 181f second genu, 68f, 72f postoperative, 181f postsurgical defect, 181f posttraumatic, 422–427 tympanic segment, 65f, 69f, 302f, 308f imaging, 426–427 proximal, 302f, 305f magnetic resonance imaging, 427 Facial recess, 67f–68f, 69, 70f, 454, 455f management, 427 cholesteatoma, 130f recurrent, 462 computed tomography, best projection for, 59f paresis evaluation, and cochlear implantation, 12 cisternal causes, 463, 464t Facioacoustic primordium, 445, 445f clinical presentation Falciform crest. See Crista falciformis and etiology, 461–462 Fallopian canal and location, 461–462 anatomy, 450 extracranial causes, 464–465, 464t dehiscence, in chronic otitis media/otomastoiditis, 10–11 idiopathic. See Bell’s palsy development, 445–446 intracanalicular causes, 463, 464t FD. See Fibrous dysplasia intratemporal causes, 463–464, 464t Fetal alcohol syndrome, and lymphangioma, 34 miscellaneous causes, 464t Fibroinflammatory pseudotumor, of inner ear, 360 postmastoidectomy, 181f Fibromuscular dysplasia, stenotic lesions caused by, and pulsatile posttraumatic, 51, 422–427 tinnitus, 274, 279f differential diagnosis, 16 Fibrosarcoma imaging in, 15–17 of auricle/pinna/EAC, 50 of unknown etiology, imaging in, 15–17 radiation-related, 215 pathology, imaging, 462–475 Fibrosis, postoperative, IAC/CPA involvement in, 515 posterior (second) genu, 450, 452f, 454, 454f–455f Fibrous dysplasia, 45–47, 220, 375–379, 551f–552f, 553 Ramsey-Hunt branch, 20 bone involvement, 375 schwannoma, 508–510, 518f and cholesteatoma, 377 schwannomas, 465–468, 466f–468f clinical presentation, 375 second genu, 67f cystic, 375, 375t, 376f, 377–378 segments, 449, 451f, 451t epidemiology, 375 somatic motor output, 444, 444f, 447, 448f etiology, 375 terminal branches, 451f, 455–456 facial nerve involvement in, 377 tympanic segment, 61f–62f, 64f, 68f, 250f, 450, hearing loss in, 375–377 451f, 451t, 452–454, 452f–454f imaging, 375, 376f–380f dehiscence, 76, 77f, 144, 166f malignant degeneration, 377 in otosclerosis, 383, 384f–385f in middle ear, 234f protrusion/prolapse, 76, 77f, 144, 166f, 446 monostotic, 45–46, 375 in otosclerosis, 383–384, 385f MRI appearance, 378–379 proximal, 69 pagetoid, 375, 375t, 376f, 377 tympanic (horizontal) segment, 250f, 451f, 451t pathology, 375 visceral afferent fibers, 444, 444f polyostotic, 45–46, 375 visceral efferent fibers, 444, 444f postoperative, 378f Facial nerve canal, 60f, 63f sclerotic, 375, 375t, 376f, 377–378, 378f, anatomy, 450 380f–381f anterior tympanic segment, enlargement, 269 subtypes, 375, 375t, 376f index.qxd 9/24/08 7:25 PM Page 570

570 Index

First pharyngeal arch syndrome. See also Mandibulofacial GJB2 gene, mutations, 328–330 dysostosis Glandular tumor(s), of EAC, 43 zygomatic deficiency in, 14 Glaserian fissure, 68f. See also Anterior tympanic fissure; Fissula antefenestram, 18, 389–390, 394f Petrotympanic fissure Fissures of Santorini, 26 Glenoid fossa, posterior margin, and mastoid segment Fistulography, preoperative, 33 of facial nerve, anteroposterior distance between, Fistulous communications, otogenic, 344–349, 345f evaluation, 14 FLAIR. See Magnetic resonance imaging (MRI), fluid attenuated Glioblastoma, extraaxial, 515 inversion recovery (FLAIR) images Glioma Floating cochlea, 417 brainstem, involving cerebellopontine angle, 515 Flocculus (of cerebellum), 481f, 484 mixed, extraaxial, 515 Foramen lacerum, 249f, 253 Glomus formations, 180, 251, 276 Foramen of Huschke, 26, 35 near skull base, 281f congenital persistence, 154 Glomus tumor(s). See Paraganglioma(s) imaging, 35 Glossopharyngeal ganglion patent, 35 inferior, 250 persistent, 35 superior, 250 surgery for, 35 Glossopharyngeal meatus, 311 Foramen of Luschka, 484, 485f Glossopharyngeal nerve. See Cranial nerve(s), IX Foramen ovale, 70f, 249f Glossopharyngeal sulcus, 70f, 305f, 415f, 416 Foramen spinosum, 70f, 249f GNT. See Granulation tissue absent, 268f, 269, 270f Goldenberg prosthesis, 166, 193f–194f, 199f Foramen tympanicum. See Foramen of Huschke Goldenhar syndrome, 27, 30, 176, 210f, 332, 337 Foreign body(ies), in ear, 15, 51, 51f, 432, 436f Gorlin-Goltz syndrome, 49 Fossa incudis, 60, 62f, 454 Gradenigo syndrome, 93, 531 computed tomography, best projection for, 59f Granulation tissue, 106f, 124f Fossula postfenestram, in otosclerosis, 382 in acute otomastoiditis, 79 Foveate impression, 310 chronic intractable, 80 Fracture(s), of temporal bone. See Temporal bone, fractures chronic otitis and, 128f Friedreich ataxia, evaluation for, 23 in chronic otomastoiditis, 98–99, 106f–109f Fusobacterium, brain abscess, 86 hemorrhagic, 112f imaging, 150 pale, 80 G Granulocytic sarcoma, 203–204 Gamma Knife surgery Greater superficial petrosal nerve, 253, 451–452, 452f intralabyrinthine hemorrhage after, 364 embryology, 445, 446f for paragangliomas, 286 lesions, localization, 462–463, 463t for vestibular schwannoma, 500–501 Griesinger’s sign, 82 complications, 508 Ground-glass appearance, with fibrous dysplasia, 378, 381f posttreatment changes/response, 507–508, 514f–515f Guillain-Barré syndrome, 527f Gastric cancer, metastases, to middle ear and mastoid, 201 Gastroesophageal reflux disease (GERD), otalgia caused by, 20 Geniculate fossa, 450, 452 H Geniculate ganglion, 445, 446f, 450, 452f Haemophilus, drug-resistant, acute otomastoiditis caused by, 80 congenital cholesteatoma in, 184 Haemophilus influenzae hemangioma, and petrous apex, 536 acute otomastoiditis caused by, 80 Gentamycin, transtympanic perfusion, for endolymphatic meningitis, 344 hydrops, 369 Hair cells, 302–304, 309 Giant apical air cell, 345 Hallucination(s), auditory, 528 Giant cell granuloma, 193 Hamartoma, 197 Giant cell reparative granuloma, 217 in CPA/IAC, 494, 498f–499f Giant cell tumor, 192–193, 223f, 378 in middle ear, 234 epidemiology, 193 Hand-Schüller-Christian disease, 190 histologic grades, 193 Head and neck cancer, squamous, metastases, to middle ear of mastoid, 45, 46f and mastoid, 201 in petrous apex, 535 Hearing, anatomical substrate, 307 postoperative recurrence, 193 Hearing aid(s) treatment, 193 and chronic stenosing external otitis, 36 Giant cholesterol cyst, 106 limitations, 394 index.qxd 9/24/08 7:25 PM Page 571

Index 571

Hearing disorders, congenital fibrous dysplasia and, 375 genetic causes, 311, 312t imaging in, 17–18, 480, 486–488 nongenetic causes, 312, 312t intralabyrinthine schwannoma and, 358 Hearing loss. See also X-linked progressive mixed deafness in labyrinthitis, 92, 159 with aberrant ICA, 265 in large vestibular aqueduct syndrome, 319–326 after aneurysm surgery, 311 with lateral semicircular canal malformation, 335 after EAC atresia surgery, 32–33 with longitudinal temporal bone fractures, 418–419 after subarachnoid hemorrhage, 311 in multiple sclerosis, 526, 534f asymmetric, 17–18 neural (retrocochlear), 309 in Camurati-Engelmann dysplasia, 381 in osteogenesis imperfecta, 392 chronic stenosing external otitis and, 36 in Paget disease, 371, 371t conductive, 75–76 perilymphatic fistula and, 92, 346 congenital, 215f poststapedectomy, 157 with EAC atresia and stenosis, 25 posttraumatic, 434 fibrous dysplasia and, 375–377 progressive/fluctuating, differential diagnosis, 369 with floating cochlea, 417 retrocochlear, 17–18 imaging in, 17–18 in retrofenestral otosclerosis, 388 intralabyrinthine schwannoma and, 358 sensory (cochlear), 309 with isolated congenital ossicular anomalies, 168 sudden, 17–18, 346, 353 with lateral semicircular canal malformation, 335 syndromic, 335–336 with neurofibroma, 43 temporal bone trauma and, 427–433 nonneoplastic congenital, 167–178 with transverse temporal bone fractures, 421 in osteogenesis imperfecta, 392 in trauma patient, 51 otodystrophies causing, 381 traumatic, 527 in otosclerosis, 382 unilateral, 480 in Paget disease, 371–372, 371t intraaxial lesions causing, 525 paraganglioma and, 279 with vestibular schwannoma, 496 postinflammatory noncholesteatomatous, 136–144, 137t in superior semicircular canal dehiscence syndrome, 332 poststapedectomy, 157 syndromic, 335–338 syndromal (congenital), 173–178 temporal bone trauma and, 427–433 with temporal bone fractures, 417–418 with vestibular schwannoma, 496 temporal bone trauma and, 427–433 Heart murmur, and tinnitus, 21 CPA lipoma causing, 493 Helicotrema, 300f–301f, 309 hemolabyrinth and, 311 Helix imaging in embryology, 26 interpretation, 17–18 upper, absence, 27 protocol, 17 Hemangioendothelioma, 207–208 report, 18 Hemangioma, 34 with lateral semicircular canal malformation, 335 cavernous, pathology, 34 with meningioma of jugular foramen, 258 of EAC, 41, 43 with microtia and EAC dysplasia, 27 facial nerve, 468–471, 469f–470f mixed, temporal bone trauma and, 427–433 of geniculate ganglion, and petrous apex, 536 in multiple sclerosis, 526, 534f and intralabyrinthine hemorrhage, 364 in osteopetrosis, 380 ossifying, 227f in Paget disease, 46, 371, 371t of temporal bone, 286 in Pendred syndrome, 336–337 and tinnitus, 21 perilymphatic fistula and, 160 Hematoma, perivascular, with ICA dissection, 274 postinflammatory noncholesteatomatous, 136–144, 137t Hemifacial microsomia, 30, 31f radiation-related, 215 Hemifacial spasm, 493 in Ramsay Hunt syndrome, 35 causes, 473–475 rapid, 17–18 imaging in, 461, 461f–462f, 472–475 with schwannoma, 256 management, 475 sensorineural Hemolabyrinth, 311 asymmetric, 480 Hemorrhage, intralabyrinthine, 363–364, 368f bilateral, intraaxial lesions causing, 525 Hemotympanum, 417f, 422f, 425f, 428 causes, 480 cholesterol granuloma and, 99–100 in children, 480 Hennebert’s sign, 333 cochlear, 17–18 Herpes zoster oticus. See Ramsay Hunt syndrome congenital, 311–312, 312t, 335–336 Herpetic facial paralysis, 471 index.qxd 9/24/08 7:25 PM Page 572

572 Index

Heschl’s gyrus, 484, 486f disruption, in temporal bone trauma, 428, 430f–431f Heterotopia, 197–198 embryology, 170 Heterotopic brain, 216 Incus, 59, 454 Histiocytosis, mastoid/middle ear involvement in, 36 absent, postinflammatory, 206f HIV-infected (AIDS) patients ankylosis, 170 lymphoepithelial cysts in, 34 body, 60, 62f–65f, 74, 308f mastoiditis in, 80 computed tomography, best projection for, 58t necrotizing external otitis in, 15, 36–37 congenital anomaly, 207f neurotologic findings in, 353 embryology, 78 otitis media in, 79–80 erosions, 139 otosyphilis in, 351 dislocation, in temporal bone trauma, 420f, 428, 430, HMC syndrome, 13 433f–435f Horizontal canal fistula, in chronic otitis media/otomastoiditis, embryology, 26 10–11 erosions, 138–139 Horner’s syndrome, incomplete, 252, 274 noncholesteatomatous, 154f House syndrome, 384 evaluation, for atresiaplasty, 13–14 Human herpesvirus (HHV), HHV-1, and sudden hearing loss, 353 fracture, in temporal bone trauma, 428, 432 Hygroma, 83–84 isolated congenital fixation, 170 cystic, 34–35 lenticular process, 60, 62f, 63, 63f, 65f–66f, 68f clinical presentation, 34 computed tomography, best projection for, 58t imaging, 34 erosions, 139 Hyoid artery, 266f long process, 60, 62f, 63, 63f–66f embryology, 266 computed tomography, best projection for, 58t Hyoid bone, embryology, 26 erosions, 139, 156f Hypertelorism-microtia-clefting syndrome. See HMC syndrome pressure necrosis, with stapes prosthesis, 157 Hypoglossal canal, 249f, 305f malformations, 29, 29f Hypotympanum, 70f, 71, 72f, 74, 74f short process, 60, 62f–63f Hyrtl’s fissure, 85, 311, 345 embryology, 78 anomalously patent, 311 subluxation, Y deformity caused by, 430, 433f defects, 345 Incus interposition procedure, 162, 188f–191f Infection(s) dental, otalgia caused by, 20 I intracranial, and otitis externa, 15 ILH. See Hemorrhage, intralabyrinthine of nasopharyngeal carotid space, 253 ILSS. See Schwannoma, intralabyrinthine odontogenic, 34 Imaging, 1–24. See also Computed tomography (CT); retropharyngeal, 254f Magnetic resonance imaging (MRI) Inferior cochlear vein, 311 modalities, 1 Inferior colliculus, 484, 486f technical parameters, 1 focal bilateral hemorrhagic contusions, 527 temporal bone lesions involving, 525 indications for, 8–9 postoperative injury, 527 referrals for, 8–9 Inferior petrosal sinus, 249f, 250 strategies for, 8–9 Inferior tympanic annulus, 65f Immunocompromised patient(s), necrotizing external Inferior tympanic artery, 71, 71t, 73f, 250, 266f, 268f, 284 otitis in, 15, 36–37 Inferior tympanic canaliculus, 60f, 71, 250, 416 Implants, otologic, MRI safety, 155–156 enlarged, 265 Incomplete partition, 313 enlargement, 266f–268f type 1 (IP-1), 313, 313t, 314, 314f, 320f–322f widening, schwannoma and, 187 hybrid, 323f–324f Inferior tympanic cancer, 415f with modiolar deficiency and semicircular canal dysplasia, 322f Inferior vestibular nerve, 67f, 299, 301f, 303f, 305, 450, type 2 (IP-2, Mondini), 313, 313t, 314f, 317–319, 325f–327f 451f, 481–482, 482f, 483 Incudomallear joint aperture, 302f ankylosis, isolated congenital, 171 saccular branch, 299 fixation, in otosclerosis, 384 Inflammatory histiocytic proliferation, 209 separation, in temporal bone trauma, 428 Inflammatory lesions, of temporal bone, local, 289–292 Incudomallear ligaments, 60 Inflammatory myofibroblastic tumor, 209 Incudostapedial joint (ISJ), 62f, 63, 66f–68f Inner ear, 58 abnormalities, 139 anatomy, 299–311, 300f–301f computed tomography, best projection for, 58t congenital disorders, 311–330 congenital deformity, 169–170, 205f–207f classification, 313 index.qxd 9/24/08 7:25 PM Page 573

Index 573

embryology, 298–299, 298t stenosis development phase, 298 acquired, 340–341, 490, 491f growth phase, 298 bony lesions and, 490, 491f ossification phase, 298 congenital, 340–341, 490 evaluation Internal auditory meatus, 480 for atresiaplasty, 13–14 Internal carotid artery, 73f, 248f and cochlear implantation, 12 aberrant, 19, 263, 265–266, 266f–267f in sensorineural hearing loss, 18 CT appearance, 265, 267f in tinnitus, 22 differential diagnosis, 265 evolution, 298 and persistent stapedial artery, 265 function, 299–311 bilateral agenesis, 269 pathology, 311–394 cervical, normal anatomy, 266f terminology for, 302t dissection, 274, 279f Inner ear–middle ear communication, aberrant, 344, 345f. clinical presentation, 274 See also Perilymphatic fistula genu (posterior loop), 252, 252f Internal auditory artery, 456 horizontal segment, 252, 252f, 253 Internal auditory canal, 58, 248f, 250f, 301f–302f, 305f hypoplasia/aplasia, with EAC atresia/microtia, 30 anatomy, 480–482, 481f laterally displaced, 265–266, 268f anomaly, 338–344 magnetic resonance angiography, 252f, 253 aplasia, 490 petrous, 248f, 250f, 251–252 asymmetric widening, 340 aneurysm, 269, 275, 280f, 536 bilateral widening, 340, 340f narrowing, in infection, 254f block, 360 normal anatomy, 266f bulbous, 172 segments, 252, 252f caliber stenosis, in osteopetrosis, 380 in cochlear nerve deficiency, 340–341, 398–399 stenosis, 269 reduced, 340–341 imaging, 274 congenital cholesteatoma in, 184 unilateral agenesis/hypoplasia, 269, 271f congenital malformations, 490 vertical segment, 252–253 diameter, 340 vertical (ascending) segment, 252, 252f distal, 482f Internal jugular bulb/vein, thrombosis, 253, 257f embryology, 490 Internal jugular vein, 247f–248f, 250 enlarged, 490, 492f Internal maxillary artery, 73f evaluation Interohyale, 79 for atresiaplasty, 13–14 Interscalar septum, 303f, 306f, 309 for cochlear implantation, 12 lateral, 303f in sensorineural hearing loss, 18 medial, 303f in tinnitus, 22 Intervestibulocochlear groove, 450 in vertigo, 23 Intracranial hypertension fundus, 306f, 453f, 480, 481f benign, and tinnitus, 21 nerves at, 481, 482f DAVF and, 270 hamartoma, 494, 498f–499f otitic, 91 hypoplasia, 340–341, 341f in acute otomastoiditis, 80 imaging, 486–553 IOP. See Osteopetrosis, intermediate lesions, 490 IP. See Incomplete partition lipoma, 492–494, 497f–498f ISJ. See Incudostapedial joint (ISJ) magnetic resonance imaging, protocols, 489 ISS. See Interscalar septum masses, congenital, 490–494 ITC. See Inferior tympanic canaliculus morphology, and cochlear nerve deficiency, 31 nerves in, 481–483, 482f–483f in osteopetrosis, 380–381 J pathology Jacobson’s nerve, 59, 60f, 251, 251t acquired neoplastic, 495–515 glomus bodies associated with, 276–277, 281f acquired nonneoplastic, 515–524 Jervell syndrome, 312 infectious, 515–519 Jugular bulb, 71, 247, 247f, 248, 248f, 250 inflammatory, 515–519 asymmetrically enlarged, 252f, 263 vascular, 520–524 venous flow alterations in, differential diagnosis, 252f, 257f, schwannoma 259f, 263 MRI appearance, 356 asymmetry, 254–255 surgery for, labyrinthine ossification after, 356 mimicking thrombus, 255f–256f index.qxd 9/24/08 7:25 PM Page 574

574 Index

Jugular bulb (Continued) malformations, 28, 312, 312t dehiscence, 76, 263 membranous (endolymphatic), 300f, 302t, 309, 482f, 485f imaging, 22 abnormal, 363f and tinnitus, 21 embryology, 298–299, 298t, 330–331 diverticulum, 263–264, 264f enhancement, miscellaneous causes, 363 high-riding, 19, 76, 263 malformations, 312, 312t definition, 263 combined with malformations of bony labyrinth, 312–313, 313t dehiscent, 263–264, 264f nontumorous enhancement, 360 nondehiscent, 263, 263f osseous (bony), 299, 300f, 302t position malformations, combined with malformations and cochlear implantation, 12 of membranous labyrinth, 312–313, 313t and mastoidectomy, 11 ossification, 298, 298t, 353–355 variants/anomalies, 262–265 after labyrinthectomy, 369, 371f Jugular foramen, 70f, 248, 249f, 250, 250f–251f, bilateral, 356f 305f–306f causes, 355–356 asymmetrically enlarged, 252f differential diagnosis, 355 asymmetry, 255 diffuse, 355 congenital hypoplasia, 256f localized, 355 contents, 251t in otosclerosis, 390, 395f CT appearance, 251 postoperative, 356 endocranial opening, 250 secondary to meningitis, 360f enlargement, schwannoma and, 257, 258f perilymphatic, 299, 309 lesions, 254–260, 257t postmastoidectomy, 153 “do not touch,” 255, 257t static, 302 imaging, 254–255 vasculitis, imaging, 363 MRI appearance, 251–252 Labyrinthectomy, 369 pars nervosa, 249f, 250, 251t, 311 CT appearance after, 369, 370f pars vascularis, 249f, 250–251, 251t indications for, 369 permeative destruction, with paraganglioma, 257f labyrinthine ossification after, 356, 369, 371f size, 251 Labyrinthine concussion, 433–434 symmetry, 251 imaging, 363 Jugular foramen syndrome, 37 Labyrinthine fistula, tympanosclerosis and, 161f Jugular fossa, 58 Labyrinthine fistulas, 146f, 350 Jugular spine, 249f in acute otomastoiditis, 111 Jugular vein, 247 cholesteatoma and, 125–129 in chronic otomastoiditis, 125 facial nerve involvement in, 128 K Labyrinthine ossification, 313 Kaposi angiosarcoma, of auricle/pinna/EAC, 50 Labyrinthitis, 22, 349–356 Keratosis obturans, 37–38 in acute otomastoiditis, 79–80, 91–92, 92f age distribution, 38 autoimmune, 349t, 350 of external auditory canal, 38, 41, 42f bacterial, 349t, 350 Klippel-Feil syndrome, 173–176 classification inner ear deformity in, 337 by agent, 349, 349t, 350 KO. See Keratosis obturans by route of spread, 349–350, 349t Koerner’s septum, 58, 65f, 69, 69f, 75, 77–78, 412, 413f clinical presentation, 349 large, 96 evaluation for KS. See Koerner’s septum in tinnitus, 22 Kurz K piston, 184f–185f in vertigo, 23 facial nerve involvement in, 353 fibroosseous, 355f, 357f L fibrous stage, 353–354, 355f–358f Labyrinth hematogenic, 349, 349t, 350, 355 acquired disorders, 349–364 imaging findings in dysplasia, with EAC atresia/microtia, 30 acute/subacute stage, 353, 353f–355f erosive changes in, 362 chronic stage, 353–356, 355f–362f hypersignal on T1W1 or FLAIR MRI, 364, 366t intermediate stage, 358f ischemia, imaging, 363 luetic (syphilitic), 349t, 350–351, 350f kinetic, 304 and meningitis, 311 index.qxd 9/24/08 7:25 PM Page 575

Index 575

meningogenic, 349, 349t, 350, 355, 356f Lateral tympanic sinus, 71 MRI findings in, 18 Laterohyale, 79 ossific stage, 354–355, 357f LCH. See Langerhans cell histiocytosis poststapedectomy, 161–162 LEDS. See Large endolymphatic duct and sac syndrome poststapedectomy serofibrinoid, and intralabyrinthine Leiomyoma, of EAC, 43 hemorrhage, 364 Lens, radiation dose to, in computed tomography, 5–6 posttraumatic, 349, 349t, 350 LESA. See Large endolymphatic sac anomaly serous, 142, 351 Lesser superficial petrosal nerve, 250, 253, 452 poststapedectomy, 159 Letterer-Siwe syndrome, 190 suppurative, 9–10, 351 Lingual nerve, 450 toxic, 353 Lipoma tympanogenic, 91–92, 349, 349t, 350, 355, 359f CT appearance, 493, 497f viral, 349t, 350, 354f of external auditory canal, 42, 43f and intralabyrinthine hemorrhage, 364 in IAC/CPA, 492–494, 497f–498f Labyrinthitis ossificans, 358f, 360f–361f, 398f, 432f, 490 intravestibular, 362, 493–494 and cochlear implantation, 12 MRI appearance, 493, 497f–498f differential diagnosis, 313, 316f Liposarcoma, 42 MRI findings in, 18 LO. See Labyrinthitis ossificans tympanogenic, 359f, 361f–362f Loose wire syndrome, 157 Lacrimal drainage, congenital abnormalities, 13–14 LSCC. See Semicircular canal(s), lateral Lacrimation Lung cancer facial nerve and, 451f leptomeningeal seeding, 514 facial nerve lesions affecting, 462–463, 463t metastases, to middle ear and mastoid, 201 Lacrimo-auriculo-dento-digital (LADD) syndrome, 13–14 Lupus, mastoid/middle ear involvement in, 36 LADD syndrome. See Lacrimo-auriculo-dento-digital (LADD) LVAS. See Large vestibular aqueduct syndrome syndrome Lymphangioma, 34 Lagena, 298 capillary, pathology, 34 Lange-Nielsen syndrome, 312 clinical presentation, 34 Langerhans cell histiocytosis, 34, 37–38, 39f, 222f–223f cystic, 34–35 and aural polyps, 42 CT appearance, 34 clinical presentation, 190–192 magnetic resonance imaging, 34 CT appearance, 192 MRI appearance, 34 epidemiology, 190 staging, 34 etiology, 190 differential diagnosis, 34 of head and neck, 190 embryology, 34 imaging characteristics, 190, 192 pathology, 34 infantile, 190 recurrence, 35 metastatic, inner ear involvement in, 360 spontaneous resolution, 35 in petrous apex, 535 treatment, 34–35 petrous apex involvement in, 192 Lymphangiomatosis, primary, fistulas caused by, 345–346 temporal bone involvement in, 190–191 Lymphoma(s) treatment, 191–192 in cerebellopontine angle, 515, 523f type 2, 190 in ear, 50 Large endolymphatic duct and sac syndrome, 313t, 319–330 external auditory canal involvement in, 50 historical perspective on, 319–326 Hodgkin, 34 imaging characteristics, 326–328, 328f–330f metastatic, inner ear involvement in, 360 pathophysiology, 319–326 non-Hodgkin, 34 Large endolymphatic sac anomaly, 322 leptomeningeal seeding, 514 Large vestibular aqueduct syndrome, 313t, 314f, 319–330, 347 perivascular spread, 253 genetics, 319, 328–330 petrous apex involvement in, 534 and hearing loss, 319–326 historical perspective on, 319–326 imaging characteristics, 326–328, 328f–330f M intralabyrinthine hemorrhage in, 364 Macewen’s triangle, 82 with modiolar deficiency, 314f Maculae (of utricle and saccule), 302–304 pathophysiology, 319–326 Madelung’s dyschondroosteosis, 176 Laryngitis, otalgia caused by, 21 Magnetic resonance angiography (MRA), 8 Lateral mallear ligament, 60f–61f, 64, 69 of aberrant ICA, 265, 267f computed tomography, best projection for, 59f of dural AVFs, 22, 271–273 index.qxd 9/24/08 7:25 PM Page 576

576 Index

Magnetic resonance angiography (MRA) (Continued) flow-related artifacts, mimicking venous thrombosis, 255 in dural sinus occlusive disease, 90–91 fluid attenuated inversion recovery (FLAIR) images dynamic, of dural AVFs, 271–273 axial, 7 in hemifacial spasm, 475 labyrinthine hypersignal on, 364, 366t indications for, 8 full balanced steady-state coherent imaging (FBSSC), 489 of internal carotid artery, 252f, 253 functional, of auditory cortex, 486, 488f maximum intensity projections (MIP), 8 gradient echo (GRE), 489 parameters for, 8 gradient-recalled acquisitions in the steady state (GRASS) three-dimensional (3D) parallel imaging, 273 images, 109–110 three-dimensional (3D) time of flight (TOF) in hemifacial spasm, 475 of dural arteriovenous fistula, 22, 22f in herpes zoster oticus, 35–36 of facial nerve, 460t, 461, 462f high-resolution, of facial nerve, 459t–460t, 460–461 in tinnitus, 21–22 indications for, 488 Magnetic resonance imaging (MRI), 7–8 of internal auditory canal, protocols, 489 in acute otitis media, 9–10 of jugular foramen, 251 of arterial dissection, 274 of lesions of jugular foramen, 254–255 of arteriovenous malformation of EAC, 42–43 of lymphangioma, 34 of auricular/periauricular masses, 18–20 of malignant otitis externa, 37 axial FLAIR, indications for, 25 of meningitis, 436 axial T1-weighted images in middle ear disease, 187t indications for, 25 in otalgia, 20–21 parameters for, 7 of paragangliomas, 283 postcontrast, indications for, 25 in recurrent disease, 286 axial T2-weighted images, 7 patient positioning for, 7 indications for, 25 in Ramsay Hunt syndrome, 472, 474f in Bell’s palsy, 459t–460t, 471–472, 471f–473f of recurrent cholesteatoma, 40 brain–IAC study, 488 of retrotympanic masses, 18–19 protocols, 488 routine technique, 7–8 of cerebellopontine angle, protocols, 489 safety considerations in, 8, 155–156 of cholesteatoma in middle ear and mastoid, 124, 136f–141f sagittal T1-weighted images, 7 of cholesterol granuloma, 109–110, 110f–111f indications for, 25 in chronic stenosing external otitis, 36 screening internal auditory canal protocols, 489 constructive interference in steady state images in sensorineural hearing loss, 480, 488 axial, parameters for, 7 in adults, 17–18 indications for, 25 in children, 17–18 contraindications to, 401 signal-to-noise ratio, 489–490 contrast-enhanced and stapes prostheses, 8 indications for, 25 surface coils, 489 in otitis externa, 14–15 of temporal bone fractures, 418 coronal T1-weighted images three-dimensional (3D) constructive interference in steady high-resolution, parameters for, 8 state (CISS), 489 parameters for, 7 three-dimensional (3D) fast asymmetric spin echo (FASE), 489 postcontrast, indications for, 25 three-dimensional (3D) FIESTA (fast imaging employing of cranial nerve VIII, for cochlear implantation, 12–13 steady-state acquisition), parameters for, 7 of CSF leakage, 346 three-dimensional (3D) gradient recalled echo (GRE), of facial diffusion weighted images, axial. See Magnetic resonance nerve, 449f, 451f, 460–461, 460t imaging (MRI), fluid attenuated inversion recovery three-dimensional (3D) segment interleaved motion (FLAIR) images compensated acquisition in the steady state in dural sinus occlusive disease, 88–90, 88f–90f (3D-SIMCAST), 489 of endolymphatic sac tumors, 287 three-dimensional (3D) spoiled gradient recalled (3D SPGR), 488 of eosinophilic granuloma, 38 three-dimensional (3D) T2 FSE, 489 of exostoses in EAC, 45 with fast recovery (FRFSE), 489 of external auditory canal, 25 three-dimensional (3D) true-fast imaging with steady-state of facial nerve precisions (FISP), 489 axial CISS (constructive interference in steady state) image, 16f in tinnitus, 21–22 normal anatomy, 456–457, 456f T1-weighted, labyrinthine hypersignal on, 364, 366t of facial nerve disorders, 15–17, 16f ultra-high field (3T), 489–490 fast spin echo (FSE), 489 of venous sinus thrombosis, 254, 254f–255f of facial nerve, 459t, 460–461 in vertigo, 22 index.qxd 9/24/08 7:25 PM Page 577

Index 577

in work-up for pulsatile tinnitus, 262 internal auditory canal, 490 zero-fill interpolated (ZIP) fast recovery 3D FASE, 489 intraaxial, involving cerebellopontine angle, 515, Magnetic resonance venography (MRV) 524f–526f indications for, 263, 416–417 middle ear, 178–211 maximal intensity projection image, 247f temporal bone of normal anatomy, 247f auricular of paragangliomas, 283 anatomical relations, 19–20 of venous sinus thrombosis, 254, 255f density/signal characteristics, 19 Malignancy, upper aerodigestive, otalgia caused by, 20–21 imaging, 18–20 Malignant fibrous histiocytoma, 50, 50f, 208 imaging, interpretation, 19–20 Malignant melanoma. See Melanoma imaging, protocol, 18–19 Malleal prominence, 59 imaging, report, 20 Malleoincudal articulation, 60, 62f, 63, 63f measurement, 19 computed tomography, best projection for, 58t imaging congenital fixation, 170–171 interpretation, 19–20 Malleoincudal complex protocol, 18–19 dislocation, in temporal bone trauma, 419f–420f, 428, 431, 432f lateral temporal bone resection for, 19 in otosclerosis, 382 otoscopic findings with, 19 Malleoincudal dislocation, with stapes prosthesis, 158 pearly white, 19 Malleus, 59, 63–64, 250f periauricular, imaging, 18–20 anterior process, 60 retrotympanic congenital fixation, 208f anatomical relations, 19 embryology, 26 density/signal characteristics, 19 evaluation, for atresiaplasty, 13–14 imaging, 18–19 fractures/dislocations, in temporal bone trauma, 428, imaging, interpretation, 19 432–433, 437f imaging, protocol, 18–19 handle, 59, 59f, 60, 62f–64f imaging, report, 20 head, 60, 60f–64f, 74 measurement, 19 computed tomography, best projection for, 58t sleeve resection, 19 congenital anomaly, 207f subtotal temporal bone resection for, 19 embryology, 78 surgery for, 19 erosions, 139 total temporal bone resection for, 19 isolated congenital fixation, 170 vascular retrotympanic. See Vascular lateral (short) process, 59–60, 62f, 65 retrotympanic mass computed tomography, best projection for, 58t Mastication, muscles, embryology, 26 malformations, 29, 29f Mastoid manubrium, 59–60, 60f congenital cholesteatoma, 216f computed tomography, best projection for, 58t debris in, 80 development, EAC and, 29 evaluation osteoma, 205, 227f for atresiaplasty, 13–14 neck, 60, 60f–61f, 66f–68f, 69 in chronic otitis media/otomastoiditis, 10–11 computed tomography, best projection for, 58t in otitis externa, 15 Malleus bar, 170 in tinnitus, 21 Mandible giant cell tumor, 45, 46f embryology, 26 metastases to, 200–203 evaluation, 14 opacification, on computed tomography, 10–11 Mandibular artery, fetal, 266 osseous margins, computed tomography, 9–10 Mandibular condyle, 65f osteoblastoma in, 207 dysplasia, with EAC atresia/microtia, 30 osteoma, 227f embryology, 79 pneumatization, 73, 77 Mandibular nerve, 59, 249f on computed tomography, 10–12 Mandibulofacial dysostosis, 13–14 and imaging of facial nerve, 455 EAC atresia with, 28 in otosclerosis, 386 imaging, 13 poor, with EAC atresia/microtia, 29–30 oculo-auriculo-vertebral spectrum, 13–14 pneumocele, 75 Marble bone disease, 45 sclerosis, 10–11 Mass(es) size, 73 bony, and congenital conductive hearing loss, 207f on computed tomography, 10–11 cerebellopontine angle, 490 xanthoma, 228f index.qxd 9/24/08 7:25 PM Page 578

578 Index

Mastoid air cells, 58, 248f Melanoma antrum, 251f of ear, treatment, 50 embryology, 77 of external auditory canal, 50 infection, and secondary thrombosis, 254 leptomeningeal seeding, 514 size, 73 metastatic, inner ear involvement in, 360 Mastoid antrum, 64f–65f, 75 prognostic factors for, 50 effusion, 101f Meniere disease, 17–18, 22, 364–369, 434 Mastoid canaliculus, 414f, 416 definition, 367 Mastoidectomy, 144–154, 177f, 179f, 182f, 194f epidemiology, 368 canal wall down (CWD) procedure, 10–11, 147t, 148–150, genetics, 368 167f, 173f, 176f, 178f imaging in, 368–369 canal wall up (CWU) procedure, 10–11, 145–148, 147t, morphological features, 368–369 166f–169f postoperative, 369 endolymphatic sac decompression, 171f Meniere syndrome, definition, 367 cavity Meningioma, 43–44, 52 CT appearance, 150 cerebellopontine angle, 490, 510–513, 519f–520f debris in, 151 MRI appearance, 356 MRI appearance, 150 characteristics, 256 closed cavity, 145 CT appearance, 513 complications, 181f differential diagnosis, 289 facial recess approach, 145 of internal auditory canal, 360, 512, 520f with fat packing, MRI appearance, 174f intracanalicular, 512 intact canal wall, 147t, 160f, 166f, 168f intralabyrinthine, imaging, 360 modified radical, 147t, 149, 173f, 176f of jugular foramen, 256, 258 open cavity, 145, 148 clinical presentation, 258 postoperative imaging for, 147t, 151 imaging characteristics, 259, 260f radical, 147t, 149–150, 150f, 174f, 179f–180f, 183f, 195f primary, 259 Silastic tube, 169f secondary, 258–259, 260f simple (cortical), 145 treatment, 259 surgical landmarks for, 11 with malignant/atypical features, 513 Mastoiditis MRI appearance, 513 coalescent, 9, 80–82, 82f–85f, 87f and otic capsule demineralization, 394 postirradiation, 230f–231f and petrous apex, 536 and dural sinus thrombosis, 254f porus, 512, 521f fungal, 80 of temporal bone, 360 in HIV-infected (AIDS) patients, 80 and tinnitus, 21 postirradiation, 229f Meningitis Pseudomonas, in HIV-infected (AIDS) patients, 80 in acute otitis media, 9–10 tubercular, 37 in acute otomastoiditis, 79–80, 83–86, 111 Mastoid region, 75 cancer, 202 Mastoid tegmen. See Tegmen carcinomatous, 350 Mastoid tip, pneumatization, 82 and cochlear implantation, 12 Maxilla, embryology, 26 congenital inner ear malformations and, 344 Mayer-Rokitansky-Küster-Hauser syndrome, 176 evaluation for, in sensorineural hearing loss, 18 McCune-Albright syndrome, 46 fistulous communications and, 345f MDP. See Technetium-99m methylenediphosphonate (MDP) scan IAC/CPA involvement in, 515 MEA. See Middle ear, adenoma and labyrinthitis, 311, 350 MEC. See Middle ear cavity (MEC) osteoradionecrosis and, 212 Meckel’s cartilage, 78 perilymphatic fistula and, 160 Meckel’s cave, 92 petrous apicitis and, 92 schwannoma, and petrous apex, 536 posttraumatic, 434–438 Medial geniculate body imaging, 436 lesions involving, 525 risk factors for, 436–438 postoperative injury, 527 syphilitic, 350–351 Medial geniculate nucleus, 486f Meningocele, 94 Medial longitudinal fasciculus, 307, 485f of middle ear, 215–216 Medulloblastoma, cerebellar, involving cerebellopontine posttraumatic, 436 angle, 515 Meningoencephalocele, 120f, 345 MEE. See Middle ear, effusion posttraumatic, 436–438, 438f index.qxd 9/24/08 7:25 PM Page 579

Index 579

Mesotympanum, 59, 74, 74f neoplasia, 178–211 posterior, 78 normal variations, 76–77 [131I]Metaiodobenzylguanidine scintigraphy, of paragangliomas, pathology, magnetic resonance imaging, 187t 284–286, 290f pneumatization, 73 Metastatic disease primary neoplasms, metastases, 203 in cerebellopontine angle, 513–515, 522f pseudoneoplasia, 178–211 differential diagnosis, 378 recesses, 65–71 external auditory canal involvement in, 50 ridges, 65–71 hematogenous, 200–202 schwannoma, 218f–219f inner ear involvement in, 360 teratoma, 200 of jugular foramen, 260, 260f vascular supply, 71, 71t, 73f leptomeningeal spread, 200, 202, 514, 522f–523f Middle ear cavity (MEC), evaluation meningeal, 202 in acute otitis media, 9–10 in middle ear and mastoid, 200–203 for atresiaplasty, 13–14 and Paget disease, differentiation, 373, 374f–375f in chronic otitis media/otomastoiditis, 10–11 perineural spread, 200 and cochlear implantation, 12 in petrous apex, 117f–118f, 225f–226f, 534, 546f–549f in conductive hearing loss, 18 of pinna, 50 in otitis externa, 15 vascular, of temporal bone, 286 Middle meningeal artery, 249f Metencephalon, 445 branches, 71 MFH. See Malignant fibrous histiocytoma embryology, 269 Michel aplasia, 313, 313t, 314f–316f, 490 Migraine, 22 differential diagnosis, 355–356 Mini-ear, 27 Michel deformity. See Michel aplasia MIP. See Magnetic resonance angiography (MRA), maximum Microtia, 26–33 intensity projections (MIP) and EAC abnormalities, 27–28 Mitochondrial disorder, evaluation for, 23 epidemiology, 27 Modiolus, 301f–303f, 306f, 307–309, 480, 481f severity, classification, 27 axial CT image, 2f surgery for, 32 congenital malformation, 322f, 331f Midbrain, 486f MOE. See Otitis externa, malignant Middle cranial fossa, 58, 69, 71 “Molar tooth” configuration, 63, 64f abscess, 84 Mondini malformation, 312–313 low-lying, 77, 79f classic (IP-2), 313, 313t, 314f, 317–319, 325f–327f Middle ear, 58 Moraxella, drug-resistant, acute otomastoiditis adenocarcinoma in, 197 caused by, 80 adenoma, 195–197, 224f MRA. See Magnetic resonance angiography (MRA) imaging characteristics, 196 MRI. See Magnetic resonance imaging (MRI) types, 195–196 Mucocele atelectasis, 111–114 hydrated, 110 cholesteatoma petrous apex, 111, 119f, 529, 539f–540f acquired, 115–136, 115t sublingual, 34 congenital, 115, 115t Mucoepidermoid carcinoma, 49–50 compartments, 74, 74f Multiple cranial neuropathy(ies), imaging in, 15–17 dermoid, 200 Multiple endocrine neoplasia, type 2, and paragangliomas, 278 effusion, 159f Multiple sclerosis (MS), hearing loss in, 526, 534f in acute otomastoiditis, 79–80 Mycobacteria, atypical, and granulation tissue, 80 chronic, and cholesterol granuloma, 103–104 Mycobacterial infection, and aural polyps, 42 in chronic otomastoiditis, 80, 96–111, 97f–102f Mycotic disease(s), 80 in nasopharyngeal carcinoma, 96, 102f types, 80 embryology, 77–79 Myelination disorders evaluation, in tinnitus, 21 evaluation for fibrous dysplasia, 234f in sensorineural hearing loss, 18 hemorrhage in, 292 in vertigo, 23 infection, and cochlear implantation, 399 inherited, 23 inflammatory disease, 79–144 Myeloma, petrous apex involvement in, 534 surgical treatment, 144–166 Mylohyoid muscle, embryology, 26 innervation, 71 Myoclonus metastases to, 200–203 middle ear, 22 myoclonus, 22 palatal, 22 index.qxd 9/24/08 7:25 PM Page 580

580 Index

Myokymia, 473 O Myringitis, 96 OAV. See Mandibulofacial dysostosis, oculo-auriculo-vertebral Myringostapediopexy, 112, 122f–123f spectrum Myxoma OAVD. See Oculoauriculovertebral dysplasia cardiac, temporal bone metastasis, 201 Obersteiner-Redlich zone, 473, 520 of EAC, 41 Obturator foramen, 63 ossifying, 220 Occipital artery, 73f, 284 in petrous apex, 535 Occipital bone, 58, 249f Occipitomastoid fissure, 414f N Occipitomastoid suture, 412, 413f Nasopharyngeal carcinoma Octreotide scintigraphy, of paragangliomas, 286 metastases in recurrent disease, 286 to jugular foramen, 260 Oculoauriculovertebral dysplasia, 176. See also Goldenhar syndrome to petrous apex, 534, 546f–547f Oculosympathetic palsy, 252 metastatic, inner ear involvement in, 360 OE. See Otitis externa and middle ear effusion, 96, 102f OI. See Osteogenesis imperfecta middle ear involvement in, 202–203 OK-432, for cystic hygroma/cystic lymphangioma, 34 perivascular spread, 253, 253f Oligodendroglioma, extraaxial, 515 Nature’s myringostapediopexy, 112, 122f–123f Operculum, 310 Necrotizing external otitis, 15. See also Otitis Orbit(s), evaluation, 14 externa, malignant Organ of Corti, 309, 480 in immunocompromised patients, 15 embryology, 298, 312 NEO. See Necrotizing external otitis OSL. See Osseous spiral lamina Neonate(s), computed tomography in, effective mAs for, 1 Osseous erosion Nervus intermedius, 447f, 449–450, 450f with cholesteatoma, 124–133, 141f–150f embryology, 445 with endolymphatic sac tumors, 287 Neurilemmoma. See Schwannoma evaluation for Neurinoma. See Schwannoma in acute otitis media, 9–10 Neuroblastoma with temporal bone masses, 19–20 metastatic, 34 in necrotizing external otitis, 15 petrous apex involvement in, 534 Osseous spiral lamina, 303f, 306f, 309, 400 Neurocysticercosis, 517–519 Ossicles Neurodegenerative disorders, evaluation for, 23 abnormalities, 28–29 Neurofibroma, 34 accessory, 29 of EAC, 41, 43 anatomy, 25, 59–65 malignant degeneration, 43 computed tomography, best projection for, 58t plexiform, 43 congenital anomalies, 205f–207f Neurofibromatosis (NF), type II isolated (without external ear malformation), 168–172 bilateral vestibular schwannomas in, 496–497, 499f classification, 169 and intralabyrinthine schwannoma, 357 with mobile stapes, 169 new diagnosis in adult, 514 embryology, 79 and paragangliomas, 278 erosion, 156f Neuroma in acute otomastoiditis, 79 facial nerve, 468 cholesteatoma and, 125, 144f–145f postlabyrinthectomy, 369 CT appearance, 140, 154f–156f Neurosarcoidosis, 516, 529f noncholesteatomatous, 154f–155f Neurosyphilis, parenchymal, 350 postinflammatory, 153f, 164f Nevoid basal cell carcinoma syndrome, 49 erosions, 137–140, 153f–156f Noonan’s syndrome, and lymphangioma, 34 focal, 136 Notched incus with long process procedure, 164 evaluation Notched incus with short process procedure, 163–164 for atresiaplasty, 13–14 Notch of Rivinus, 26, 74, 79 in conductive hearing loss, 18 Nuclear imaging, of paragangliomas, 284–286, 290f evolution, 298 Nucleus solitarius, 447f, 448, 448f, 448t fibroosseous sclerosis, 143, 165f Nystagmus fibrous tissue fixation, 156f with pressure applied in EAC, 333 fixation produced by Valsalva maneuver, 333 in acute otomastoiditis, 79 sound-induced, 333 lateral attic wall, 165f index.qxd 9/24/08 7:25 PM Page 581

Index 581

new bone formation and, 143, 162f, 165f Osteopathia striata, 381 postinflammatory, 136, 140–144, 165f Osteopetrosis, 379–381. See also Albers-Schönberg disease fusion, 30, 32f autosomal dominant, 380 EAC atresia and, 29, 29f imaging characteristics, 381 injuries, in temporal bone trauma, 420f, 423f, 428–432 otoneurologic manifestations, 45 noncholesteatomatous disruption, 155f type I, 380 phylogeny, 60 type II, 380 postinflammatory resorption, 387 autosomal recessive, 380 Ossicular chain, 62f otoneurologic manifestations, 45 anatomy, 66f benign, 380 embryology, 78 CT appearance, 380–381, 381f evaluation, in chronic otitis media/otomastoiditis, 10–11 intermediate, 380 residual, postmastoidectomy, 153 malignant (autosomal recessive), 380 Ossicular coupling, 60 otoneurologic manifestations, 45 Ossicular implants, 162 types, 380 Ossicular reconstructions, 155–162 Osteoporosis circumscripta, in Paget disease, 372 Ossiculoplasty, 162–166 Osteoradionecrosis, 47, 51, 211–215, 394 postoperative evaluation, 166, 194f, 201f Osteosarcoma, of auricle/pinna/EAC, 50 Ossification Otalgia labyrinthine, 298, 298t causes, 20 of otic capsule, 298 imaging in Ossification centers, 298 interpretation, 20–21 Ossifying fibroma, 220, 377 protocol, 20 Ossifying myxoma, 220 report, 21 Os suprapetrosum of Meckel, 75 postmastoidectomy, 182f Osteitis primary, 59 in otosyphilis, 351 causes, 20 and petrous apicitis, 92 referred, 59 postirradiation, 232f causes, 20 Osteitis deformans. See Paget disease Otic capsule, 66f, 79, 304, 445–446, 455f Osteoblastoma, 220–234 anatomy, 25 in temporal bone, 207 demineralization Osteogenesis imperfecta, 391–392, 396f–397f in Camurati-Engelmann disease, 393 clinical features, 391–392 differential diagnosis, 392–394, 394f CT appearance, 392 diffuse thinning, 392–393 differential diagnosis, 351 inflammation and, 394 genetics, 391–392 localized, 392–394 hearing loss in, 392 moth-eaten, 392–393 pathophysiology, 391–392 neoplasia and, 394 type I (tarda), 392 in osteogenesis imperfecta, 392 type II (congenital), 392 in otosclerosis, 392 type III, 392 in otosyphilis, 351, 351f–353f, 393 type IV, 392 in Paget disease, 393 Osteogenic sarcoma, 34 plaque-like, 392–393 radiation-related, 215 embryology, 298 Osteoma endochondral layer, 382 compact, 204–205 endosteal (labyrinthine) layer, 382 CT appearance, 204 evaluation, for cochlear implantation, 12 in EAC, 45, 45f, 204 malformations, 312 histologic types, 204 ossification, 298, 298t in mallear manubrium, 227f periosteal (tympanic) layer, 382 of malleus manubrium, 205 Otic pit, 298, 298t in mastoid, 204, 227f Otic placode, 298, 298t Osteoma cancellare, 204 Otic vesicle, 298, 298t, 312, 331, 445, 445f, 490 Osteomalacia, X-linked hypophosphatemic, 311 dorsal pouch, 298, 298t Osteomyelitis ventral pouch, 298, 298t and petrous apicitis, 92 Otitic hydrocephalus, 91 of skull base, and internal carotid artery, 254f in acute otomastoiditis, 80 index.qxd 9/24/08 7:25 PM Page 582

582 Index

Otitis externa, 35–37 radiation-related, 211 acute uncomplicated, 35–36 tuberculous, 80, 81f clinical presentation, 35 Otomycosis, risk factors for, 35 microbiology, 35 Otopalatodigital syndrome, 172, 176 chronic, 36 Otorrhea chronic stenosing, 36 with endolymphatic sac tumors, 286 surgical treatment, 36 salivary, 35 fungal, 35, 80 from patent foramen of Huschke, 35 imaging in Otosclerosis, 46–47, 353, 382–391 interpretation, 15 classification, 389t protocol, 14–15 and cochlear implantation, 399, 400f report, 15 epidemiology, 382 malignant, 15, 36–37 evaluation for, in conductive hearing loss, 18 chronic stenosing external otitis and, 36 fenestral, 382–388 complications, 37 CT appearance, 384–385, 385f–388f differential diagnosis, 37, 203 differential diagnosis, 143, 168, 385–387 imaging in, 37 with incus subluxation, 382, 383f staging, 37, 37f obliterative, 382–383, 383f tuberculous, 37, 38f treatment, 387–388 Otitis media fenestral and cochlear, 389, 389f, 392f–394f acute genetics, 382 clinical presentation, 9 new bone formation in, 390, 395f complications, 9–10 and otospongiosis, 382 imaging in pathogenesis, 382 interpretation, 9–10 preoperative CT evaluation, 382–383, 382t protocol for, 9 retrofenestral (cochlear), 382, 388–391 report, 10 cochlear implantation for, 399, 400f adhesive, 113, 125f CT appearance, 388–389, 389f–392f chronic, 37, 73, 111, 304 hearing loss in, 388 active MRI appearance, 390–391, 395f–396f with cholesteatoma, imaging in, 10 pathogenesis, 388 without cholesteatoma, imaging in, 10–11 Otospongiosis, 353, 382 and aural polyps, 42 and cochlear implantation, 12, 399–400 with cholesteatoma, 37 evaluation for, in conductive hearing loss, 18 and cochlear implantation, 399 imaging, 22 imaging in and otosclerosis, 382 interpretation, 10–11 and tinnitus, 21 protocol for, 10 Otosyphilis, 350–351, 351f–353f report, 11 Ototoxic drugs, 353 inactive Oval window, 63, 67f, 70, 72f, 300f, 305f–306f, 309 with frequent reactivation, imaging in, 11 absence, with EAC atresia/microtia, 30 imaging in, 11 atresia, 29, 167–168, 202f–204f, 209f–210f with tympanic membrane retraction, 123f–124f defects, 344 in osteopetrosis, 381 dysplasia, 169 and perilymphatic fistula, 92 evaluation postradiation, 214 for atresiaplasty, 13–14 serous, unilateral, 345 in conductive hearing loss, 18 tubercular, 37 fistula, 129 Otocyst. See Otic vesicle normal, 383f Otodystrophy(ies), 369–394 in otosclerosis, 382–383, 383f–384f Otoliths, 304 size, 31 Otomastoiditis tympanosclerosis and, 163f–164f acute, 79–94, 82f Oval window niche, 302f, 310f bacterial, 80 CNS complications, 111 P complications, 79, 79t, 80 Paget disease, 45–47, 178, 369–375, 552f, 553 facial nerve involvement in, 91, 91f, 111 bone involvement, 370–371, 371f chronic, 79, 94–114 and cochlear implantation, 12 imaging in, 10–11 CT appearance, 372–373, 372f–374f index.qxd 9/24/08 7:25 PM Page 583

Index 583

differential diagnosis, 46–47, 351, 373, 374f–375f site of origin, 281f epidemiology, 369–370 treatment, 282, 286 evaluation for, in conductive hearing loss, 18 glomus vagale, 277–278, 285f hearing loss in, 371, 371t clinical presentation, 279 imaging in, 46 local invasion and recurrence, 278, 291f malignant degeneration, 370 imaging, 180, 283–286 management, 373–375 intracranial invasion, 278 mixed phase, 370 irradiated, residual mass on CT or MRI, 286 monostotic, 369 of jugular foramen, 256 MRI appearance, 373 local invasion, 278 osteoblastic phase, 370 malignant transformation, 278, 287f osteolytic phase, 370, 372 of middle ear, 179–180 polyostotic, 369–370 differential diagnosis, 265 remodeled phase, 370 MRI appearance, 256 Papilloma, inverting, 195–196 multicentric, 278 Paraganglia, 276 nonchromaffin (nonsecretory), 276 anterior jugular, 281f and normal vascular variants, differentiation, 282 carotid body, 281f recurrence, 278, 286, 291f glomus body, 281f salt and pepper appearance, 256, 258f, 283 inferior laryngeal, 281f scintigraphic appearance, 284–286, 290f locations, 281f secretory, 276 posterior jugular, 281f and tinnitus, 21 superior laryngeal, 281f treatment, 286 tympanic, 281f vascular supply to, 284 vagale, 281f Parietal bone, 58 Paraganglioma(s), 19, 251, 276–286 Parotid gland tumors angiographic appearance, 284 middle ear involvement in, 202–203 avascular, 284 temporal bone involvement in, 50 carotid body, 278, 286f Parotid plexus, 455 clinical presentation, 279 Parotitis, chronic stenosing external otitis and, 36 local invasion and recurrence, 278 Pars inferior, 129, 299, 330 characteristics, 256 Pars superior, 129, 299, 330 chromaffin, 276 Partial ossicular replacement prostheses, 164–165, clinical presentation, 279 193f–194f, 197f–198f, 200f. See also CT appearance, 256 specific prosthesis distant metastases, 278 extrusion, 198f familial, 278 lateralized, 198f–199f Glasscock-Jackson classification, 283, 290t and MRI safety, 8 glomus jugulare, 74f, 180, 258f, 277, 284 Patient size, and radiation dose in computed tomography, 7 angiography, 284 Pediatric patient(s). See Child(ren) Glasscock-Jackson classification, 290t Pendred syndrome, 328–330, 336–337, 337f imaging characteristics, 283 clinical findings in, 336 local invasion and recurrence, 278 inner ear deformity in, 337 site of origin, 281f Perchlorate discharge test, 336–337 treatment, 286 Periarterial sympathetic plexus, 251 glomus jugulotympanicum, 257f, 276–278, 283f, 455 Perilabyrinthine cells, 75 angiography, 284 Perilabyrinthine pneumatization, 73 differential diagnosis, 282 Perilabyrinthine tract, 75 involving CN VII, 288f Perilymph, 298–299, 309–311 site of origin, 281f leak, 311 treatment, 282, 286 Perilymphatic fistula, 22, 92, 159–160, 344, 345f glomus tympanicum, 19, 74f, 179–180, 211f, 276–277, causes, 346 282f, 289f in chronic otitis media/otomastoiditis, 10–11 clinical presentation, 279 congenital, 346, 349f differential diagnosis, 282 congenital stapes deformity and, 172 Glasscock-Jackson classification, 290t CT appearance, 160 imaging characteristics, 283 evaluation for, in vertigo, 23 MRI appearance, 212f imaging, 22, 346–347, 346f, 349f with secondary attic block, 289f–290f pathophysiology, 346 index.qxd 9/24/08 7:25 PM Page 584

584 Index

Perilymphatic fistula (Continued) Pharyngitis, otalgia caused by, 21 postoperative, 346 Phlegmon, subperiosteal, 85f with cochlear implantation, 401 Phylogeny, of ear, 298 posttraumatic, 346, 426f, 427–428, 429f Physaliphorous chordoma, 216 spontaneous, 346, 349f PICA. See Posterior inferior cerebellar artery (PICA) and vertigo, 434 Picibanil. See OK-432 Perilymphatic gusher, 172, 344, 345f, 384 Pierre Robin syndrome, 30 Perilymphatic space, 298 Pineal tumor(s), otoneurologic manifestations, 527 Peripheral mastoid area, 75 Pinna, 25 Peritubal cells, 75 embryology, 26–27 Peritubal tract, 75 malformations, 26–27 Persistent stapedial artery, 172, 263, 266–269, 268f–270f trauma to, 51 CT appearance, 269, 269f–270f Plain film radiography, 8, 9f developmental anatomy, 268f Stenvers projection, 8, 9f embryogenesis, 266 Planum temporale, 486 imaging, 21 Plasma cell granuloma, 208–209 not associated with aberrant ICA, 268f Plasmacytoma, extramedullary, 234 PET. See Positron emission tomography (PET) PLF. See Perilymphatic fistula PET/CT, 8 PMC. See Petromastoid canal Petromastoid canal, 84, 302f, 304, 305f, 308f, 412–416, 414f Pneumatization, 75 defects, 345 accessory, 75 wide, 304, 308f asymmetric, 111 vascular cause, 334 developmental tracts, 75 Petrooccipital fissure, 58, 249f, 412, 413f diploic, 73 Petrosal artery, 73f pattern Petrosquamosal fissure, 412, 413f computed tomography, best projection for, 59f Petrosquamous suture, 58, 84 and migration of cholesteatoma to petrous apex, 133–134 Petrotympanic fissure, 58, 58f, 71, 412, 450, 455 pneumatic, 73 Petrous apex, 58, 75 regions, 74t abducens nerve in, 487f sclerotic, 73 air cells, disease, 528–532, 538f–541f types, 74t arachnoid cysts, 111 Pneumatocele, 75 asymmetric marrow, 528, 537f–538f Pneumocele, mastoid, 75 cephalocele, 94, 216, 532, 545f Pneumocephalus, 75, 436 cholesteatoma, 532, 544f temporal bone trauma and, 422f, 429f cholesterol granuloma, 113f–115f, 530–531, 540f–541f Pneumolabyrinth, 160, 346f, 426f, 428, 429f destructive lesions, 111, 117f–118f Pneumovestibule, 423f, 426f effusion, 93–94, 96f Pocket ear, 27 fluid, 93, 95f, 111, 528–529, 538f–539f Polyp(s), aural, 41–42, 43f infection. See Apical petrositis Pons inflammatory disease, 532–536 lateral lemniscus, 484, 485f lesions, 480 lesions involving, 525 meningioma and, 536 medial lemniscus, 485f metastatic disease in, 117f–118f, 225f–226f, 534, 546f–549f Ponticulus, 69–70, 70f, 72f, 454 mucocele, 111, 119f, 529, 539f–540f computed tomography, best projection for, 59f neoplastic disease, 532–536 Pontine nuclei, 485f nonpneumatized, 111, 117f Pontocerebellar tracts, 485f pneumatization, 73, 75, 76f, 528 PORP. See Partial ossicular replacement prostheses asymmetric, 111, 116f Porus acusticus, 480, 481f unusual upward angulation, 177–178 meningioma, 512, 521f Petrous apicitis, 92f–94f Pöschl reformat, 4, 6f in acute otomastoiditis, 79–80, 92–94 Positron emission tomography (PET), 8. See also PET/CT differential diagnosis, 94 of rhabdomyosarcoma, 189 imaging, 94 Posterior ampullary nerve. See Singular nerve tubercular, 37 Posterior auricular artery, 73f, 284 Petrous pyramid. See Petrous apex Posterior cranial fossa, 58 Pfeiffer syndrome, 27, 30 Posterior fossa, 311 Pharyngeal arch(es), 26. See also Branchial arch(es) abscess, 84 Pharyngeal pouch, first, 77 Posterior hypotympanum, 248 index.qxd 9/24/08 7:25 PM Page 585

Index 585

Posterior incudal ligament, 63f, 64 Radiation dose

Posterior inferior cerebellar artery (PICA), 284, 304 in computed tomography. See also CTDIvol Posterior tympanic artery, 71t, 73f application-related factors affecting, 7 Posterior tympanic isthmus, 74 equipment-related factors affecting, 6–7 Posterior tympanic sinus, 71 factors affecting, 6–7 Posterior tympanum, 68f, 69–70, 70f, 71, 74, 74f head study, 5 Posteromedial cell tract, 75 as low as reasonable achievable (ALARA), 6 Postviral syndrome, 527f patient-related factors affecting, 7 Preauricular cyst(s), 26, 27f reduction Pressure equalization tube(s), extruded, 51, 51f strategy for, 7, 457 Primitive neuroectodermal tumors, EAC involvement in, 52, 52f techniques for pediatric patients, 4–7 Progressive diaphyseal dysplasia, 381 effective, in computed tomography, 4 Prominent ear, 27 definition, 4 Promontory, 65f, 303f–304f, 306f estimation, 5 Prostatic carcinoma, metastases, 374f–375f for head study, 5 to EAC, 50 for temporal bone scan, 4 to middle ear and mastoid, 201 Radiation therapy Proteus for paragangliomas, 286 acute otomastoiditis caused by, 80 temporal bone complications, 211–215, 229f–232f meningitis, 84–85 Ramsay Hunt syndrome, 35, 353, 519, 531f Protympanum, 74, 74f with brainstem enhancement, 36 Prussak’s space, 61f, 65–69, 77–78 imaging in, 472, 474f cholesteatoma, 118–120, 126f–130f, 136f MRI findings in, prognostic significance, 36 computed tomography, best projection for, 59f Rasmussen syndrome, 27 coronal CT image, 3f Red nucleus, 486f Pseudoaneurysm, 274–275 Refsum’s syndrome, 311 posttraumatic, 275 Reissner’s membrane. See Vestibular membrane Pseudomonas Reiter’s syndrome, cysts in, 34 acute otomastoiditis caused by, 80 Renal cell carcinoma, metastases meningitis, 84–85 to EAC, 50 Pseudomonas aeruginosa to middle ear and mastoid, 201 chronic otomastoiditis caused by, 96 to temporal bone, 286 external otitis caused by, 35 Restiform body, 485f and malignant external otitis, 36 Reticular formation, 307 Pseudootosclerosis, 143 Retinal disorders, congenital, 311 Pseudotumor Retinoic acid, and microtia, 27 fibroinflammatory, 210 Retrocochlear lesion(s) inflammatory, 208–209 definition, 18 in middle ear and mastoid, 208–210 hearing loss caused by, 17–18 nonpulmonary, 208–209 Retrotympanic mass(es). See Mass(es), temporal bone, xanthomatous, 209 retrotympanic Pseudotumor cerebri Retrotympanum, 69 imaging, 21 Rhabdomyosarcoma, 34, 50, 187–190, 219f–221f, 378 otoneurologic manifestations, 22 alveolar, 188 PT. See Tinnitus, pulsatile clinical presentation, 189 Pterygopalatine ganglion, 444f, 446f, 451 CT appearance, 189–190 Pyknodysostosis, 381 embryonal, 188–189 Pyle’s disease, 176, 381 epidemiology, 187–188 Pyramidal eminence, 65, 67f–68f, 69–70, 70f, 71, 79, 454, 455f of head and neck computed tomography, best projection for, 59f classification, 188–189 prevalence, 188 Q of middle ear, 189–190 MRI appearance, 189–190 Q-Tip injury, 432 orbital, 188 prognosis for, 189 R parameningeal Radiation cranial, 188 deterministic effects, 5–6 nonorbital, 188 stochastic effects, 5–6 prognosis for, 189 index.qxd 9/24/08 7:25 PM Page 586

586 Index

Rhabdomyosarcoma (Continued) clinical presentation, 256 in petrous apex, 535 CT appearance, 257 pleomorphic, 188 cystic, 34 prognosis for, 189 with cystic changes, 258, 259f staging, 189 differential diagnosis, 76 Rhombencephalon, 445 dumbbell-shaped, 258, 258f–259f, 468, 499, 505f Richards prosthesis, 166, 199f, 201f–202f of EAC, 43 RMS. See Rhabdomyosarcoma of eighth cranial nerve, 105, 508–509, 517f Round window, 72f, 300f, 303f, 305f–306f, 309, 311 facial nerve, 465–468, 466f–468f, 508–510, 518f absence, with EAC atresia/microtia, 30 IAC/CPA atresia, 28 bilateral, in NF2, 496–497, 499f computed tomography, best projection for, 59f imaging characteristics, 497–498, 500f–501f defects, 344 imaging, 255, 258f–259f dysplasia, 169 impaction in IAC, 503, 508f evaluation, and cochlear implantation, 12 internal auditory canal fistula, 147f MRI appearance, 356 in otosclerosis, 382–383, 384f surgery for, labyrinthine ossification after, 356 rupture, poststapedectomy, 157 intervestibulocochlear, 365f Round window niche, 70, 70f, 72f, 304f, 310f intralabyrinthine, 357–360, 357t Rugby jersey spine, in osteopetrosis, 380 with IAC involvement transmacular, 357, 357t transmodiolar, 357, 357t, 365f S imaging, 359–360, 365f–366f Saccular duct, 299, 310 intracochlear, 357, 357t Saccule, 298–299, 301f, 482f intravestibular, 357, 357t embryology, 298, 298t, 330–331 intravestibulocochlear, 357, 357t function, 302 with middle ear involvement innervation, 305, 482–483 transotic, 357–358, 357t Saccus anticus, 69, 77, 133 tympanolabyrinthine, 357t, 358 Saccus medius, 69, 77–78, 131–133 of jugular foramen, 256–258 Saccus posticus, 77–78 labyrinthine, 499, 506f Saccus superior, 77–78 localized to cochlea, 499, 506f SAF. See Subarcuate fossa of Meckel’s cave, and petrous apex, 536 Salicylates, transtympanic perfusion, for endolymphatic in middle ear, 185–187 hydrops, 369 nerves of origin, 185–187 Salivary gland(s), minor, malignancy, perivascular spread, 253 of middle ear, 218f–219f Salivary gland tissue, heterotopic, 33 MRI appearance, 258, 258f–259f Salivary otorrhea, 35 of ninth cranial nerve, 508–509, 517f Salivary tissue, ectopic, in middle ear, 197–198 and otic capsule demineralization, 394 Salivation, facial nerve lesions affecting, 462–463, 463t small intracanalicular, 499, 507f Sarcoidosis trigeminal, 508–509, 516f CNS involvement in, 516, 529f vestibular, 490, 495–508 in petrous apex, 535 in children, 497 Sarcoma, 52 clinical presentation, 496–497 granulocytic. See Granulocytic sarcoma coexistent with arachnoid cyst, 498, 502f Scala communis, 309 with cystic change, 498, 501f–502f Scala media, 299, 303f, 309 evaluation for, in tinnitus, 22 Scala tympani, 299, 300f–301f, 303f, 309, 310f, 311 Gamma Knife radiosurgery for, 500–501 Scala vestibuli, 299, 300f–301f, 303f, 309, 310f complications, 508 Scarpa’s ganglion. See Vestibular ganglion posttreatment changes/response, 507–508, 514f–515f SCC. See Semicircular canal(s) and hearing loss, 480 SCCA. See Squamous cell carcinoma hemorrhagic, 498–499, 503f–504f Scheibe syndrome, 312, 312t magnetic resonance imaging, 488 Schwannoma, 34 postoperative, 504–506 cerebellopontine angle postoperative changes seen on, 507, 509f–513f MRI appearance, 356 recurrence, 505–506 nerves of origin, 508–509, 516f–517f surgical management, 501–504 surgery for, labyrinthine ossification after, 356 complications, 504–505 characteristics, 256 follow-up, 505–506, 509f–510f index.qxd 9/24/08 7:25 PM Page 587

Index 587

postoperative care for, 504 Semicircular ducts, 298t, 299, 301f residual tumor after, 506–507, embryology, 330–331 509f–510f function, 302–304 treatment, 500–504 posterior, innervation, 305 Schwartze sign, 388 Sensorineural hearing loss. See Hearing loss, sensorineural Scutum, 60f, 63f, 65f, 69 Sickle cell disease, and intralabyrinthine hemorrhage, 364 ankylosis, 170 Sievert (Sv), definition, 4 computed tomography, best projection for, 59f Sigmoid notch, position, and cochlear implantation, 12 SDE. See Empyema, subdural Sigmoid plate, 247, 249f Seessel epipharyngeal pouch, 184 Sigmoid sinus, 247–248, 247f–248f, 308f Semicircular canal(s), 58, 299, 300f, absence, 248 481f–482f asymmetry, 248, 251f, 254 anatomy, 299 diverticulum, 265, 265f anomalies, 330–335 dural AVF, 270 embryogenesis, 330–331 hypoplasia, 256f aplasia, 331–332 normal anatomic variants, 76–77, 77f, 248, 251f and cochlear development, 331 occlusive disease, in otomastoiditis, 87, 88f, 90f congenital malformation, 322f position dysplasia, 316f–317f, 331–332, 331f and cochlear implantation, 12 sporadic, 331 and mastoidectomy, 11 syndromic, 331 thrombosis, 83, 253, 257f embryology, 298, 298t, 299, 330, 445 in acute otitis media, 9–10 evolution, 298 in acute otomastoiditis, 88f–89f function, 302–304 and recanalization, 269 horizontal, innervation, 482–483 Sigmoid sinus groove, computed tomography, best projection innervation, 305–307 for, 59f lateral, 65f, 68f, 72f, 250f, 299, 300f, 302f, 305f–308f, Sigmoid sinus plate, 64f 310f, 453f, 454 Sigmoid sulcus, 247, 249f axial CT image, 2f Single-photon emission computed tomography (SPECT), dysplasia, 332 gallium-67, of malignant otitis externa, 37 and hearing loss, 18 Singular canal, 302f–303f, 305, 412–416, 414f, 417f, 483f embryology, 330 Singular cancer, 483–484 fenestration, 162 Singular nerve, 299, 301f, 305, 483 fistula, 129, 146f Singular neurectomy, 305 hyperplasia, 335 Sinus cholesteatoma, 120 hypoplasia, 335 Sinusiitis, subdural empyema in, 83 isolated deformity, 335, 336f Sinusitis, 34 normative measurements, 335 otalgia caused by, 20 sagittal CT image, 2f Sinus tympani, 67f–68f, 69, 69f, 70, 70f, 71, 72f, 454, 455f ossification, 330 computed tomography, best projection for, 59f posterior, 63, 67f, 300f, 302f–308f deep, 77, 78f aplasia, 332, 332f Sjögren’s syndrome, parotid cysts in, 34 dehiscence, 334 Skull, thickness, evaluation, 12, 14 embryology, 330 Smooth muscle tumor(s), of EAC, 43 innervation, 305, 483 SNHL. See Hearing loss, sensorineural superior, 250f, 299, 300f, 302f, 305f–308f, 310f Sound waves, movement in cochlea, 301f, 309 anterior-posterior excursion, CT image, 6f SPECT. See Single-photon emission computed tomography aplasia, 332 (SPECT) cross-sectional CT image, 5f Sphenoid bone, 58 dehiscence. See also Superior semicircular canal dehiscence Sphenopetrosal fissure, 412, 413f syndrome Spine of Henle, 12 and conductive hearing loss, 18, 332 Spinocerebellar ataxia, 23 imaging, 4 Spiral ganglia, 482f and vertigo, 22–23, 332 Spiral ligament, 309 embryology, 330 cystic degeneration, in Paget disease, 371 fistula, 179f in retrofenestral otosclerosis, 388 imaging, 22 Squamous cell carcinoma innervation, 482–483 of EAC, 48–49 vascular supply, 304 imaging, 48, 48f index.qxd 9/24/08 7:25 PM Page 588

588 Index

Squamous cell carcinoma (Continued) malformations, 29, 167–168, 172, 204f–205f metastases, intranodal necrotic, 34 monopod, 172, 204f, 209f–210f metastatic, inner ear involvement in, 360 posterior crus, 60, 62f, 67f in middle ear, 195 Stapes footplate, axial CT image, 2f nasopharyngeal, metastases, to jugular foramen, 260 Stapes gusher, 311, 344–345, 384 perivascular spread, 253 X-linked, 490 of temporal bone, staging, 47, 47f Stapes prostheses, 156–162, 185f. See also Stapedectomy, SSC. See Semicircular canal(s), superior prosthetic SSCD. See Semicircular canal(s), superior, dehiscence graft lateralization, 184f, 187f Stapedectomy imaging, 157 complications, 311, 350 Kurz K piston, 184f–185f CT appearance after, 370f metallic intralabyrinthine hemorrhage after, 364 dislocated, 186f in otosclerosis, 387–388 medial subluxation, 188f partial, 157 in normal position, 186f prosthetic, 156–162 MRI safety, 155–156 complications, 157–161 and MRI safety, 8 for osteogenesis imperfecta, 392 protrusion into vestibule, 160–161 in otosclerosis, 387–388 subluxation, 157–158, 187f Stapedial ankylosis wire, 183f isolated, 169 Stapes superstructure, 60, 63, 66f–67f, 70f with other ossicular anomalies, 169 computed tomography, best projection for, 58t Stapedial artery, 63, 79 congenital fixation, 169 embryology, 266 Staphylococcus, meningitis, 84–85 Stapedial nerve, lesions, localization, 462–463, 463t Staphylococcus aureus Stapedial reflex chronic otomastoiditis caused by, 96 facial nerve and, 451f external otitis caused by, 35 facial nerve lesions affecting, 462–463, 463t Stenvers reformat, 4, 5f Stapedial ring, embryology, 170 Sternocleidomastoid muscle, 82 Stapediovestibular articulation, 63 Steroids, transtympanic perfusion, for endolymphatic Stapediovestibular dislocation, in temporal bone hydrops, 369 trauma, 428, 431 Streptococcus pneumoniae Stapediovestibular region, computed tomography, acute otomastoiditis caused by, 80 best projection for, 58t drug-resistant, acute otomastoiditis caused by, 80 Stapedius muscle, 64–65, 68f, 454 meningitis, 344 embryology, 26, 78–79 Stria vascularis, 309 Stapedius nerve, 451f, 455 String sign, 275 Stapedius tendon, 66f–67f, 70f Stroke, 22–23 congenital ossification, 172 Stylohyoid ligament, embryology, 26 embryology, 78–79 Stylohyoid muscle, embryology, 26 Stapedotomy, 157 Styloid eminence, 71 Stapes, 65f, 300f, 309 Styloid process, 58 anatomy, 59–60 embryology, 26, 79 anterior crus, 60, 62f, 67f fracture, 422 capitulum (head), 60 Stylomastoid artery, 71, 71t, 73f, 284, 311, 456 congenital deformity, 209f–210f, 344 Stylomastoid foramen, 68f, 71, 72f, 305f, 444f, 454, congenital fixation, 167–168, 205f 454f, 455, 455f embryology, 26, 79 Subarachnoid space, 311 erosions, 139 Subarachnoid space–inner ear communication, aberrant, evaluation, for atresiaplasty, 13–14 344, 345f–347f footplate, 62f, 63, 67f Subarachnoid space–middle ear communication, 349f computed tomography, best projection for, 58t aberrant, 344–345, 345f congenital fixation, 169 Subarcuate artery, 304 embryology, 79, 347 Subarcuate cell tract, 75 tympanic portion, 60, 62f Subarcuate fossa, 304 vestibular portion, 60, 62f Subiculum, 68f, 69–70, 70f, 72f fracture, in temporal bone trauma, 428, 432, 436f computed tomography, best projection for, 59f head, 62f, 67f–68f Submandibular ganglion, 444f implosion, 432, 436f Superficial petrosal artery, 71, 71t, 456 index.qxd 9/24/08 7:25 PM Page 589

Index 589

Superficial siderosis, 516–517, 530f avascular osteonecrosis, 234 Superior mallear ligament, 60f–61f, 64 congenital malformations, 446 computed tomography, best projection for, 59f extrinsic fissures and sutures and, 412, 413f Superior olivary nucleus, 485f fractures, 50–51 Superior orbital fissure, 487f causes, 412 Superior petrosal sinus, 247 classification Superior sagittal sinus, 247f alternate systems, 421–422 Superior salivatory nucleus, 447f, 448, 448f, 448t traditional, 416–421 Superior semicircular canal dehiscence syndrome, 332–335, Yanahigara, 421–422 332f–333f complex (mixed), 416, 417f, 420f–421f, bilateral, 332 423f, 425f clinical presentation, 332 complications, 412 differential diagnosis, 369 epidemiology, 412 epidemiology, 332 facial nerve involvement in, 421 imaging, 333, 333f–335f imaging, 416 Superior temporal gyrus, 486f longitudinal, 416–419, 418f–422f, 421 Superior tympanic artery, 71, 71t, 73f anterior (oblique), 416, 418f, 421f Superior vestibular nerve, 299, 301f–302f, 305, 450, complications, 416–417 451f–452f, 481–482, 482f and CSF otorrhea, 418f branches, 482–483 and facial nerve injury, 427 utricular branch, 299 imaging, 418–419 Supratubal recess. See Anterior epitympanic recess posterior, 416, 419f Surfer’s ear, 44 subtypes, 416 Suspensory ligaments, of middle ear, anatomy, 59–65 oblique, 421 Sv. See Sievert (Sv) transverse, 416, 419–421, 420f–421f, 423f–425f Swimmer’s ear. See Otitis externa, acute uncomplicated and facial nerve injury, 427 Synkinesis, 473 lateral, 421 Syphilis, 47. See also Otosyphilis medial, 421, 423f–424f mastoid/middle ear involvement in, 36 mixed medial and lateral, 425f–426f meningovascular, 350 subtypes, 421 Systemic lupus erythematosus (SLE), and intralabyrinthine with/without otic capsule involvement, 421 hemorrhage, 364 imaging, 1–24. See also Computed tomography (CT); Magnetic resonance imaging (MRI) T injury Taenia solium, 517–519 complications, 412 Taste epidemiology, 412 in anterior two thirds of tongue, facial nerve and, 451f intrinsic channels, 412–416 facial nerve lesions affecting, 462–463, 463t intrinsic fissures, 412, 413f Technetium-99m methylenediphosphonate (MDP) scan, mastoid segment, 58, 58f of malignant otitis externa, 37 oncologic surgery, 19 Tectorial membrane, 309 osteoblastoma in, 207 Tegmen osteoradionecrosis, 211–215 ankylosis, 170 petrous, 58, 58f computed tomography, best projection for, 59f pneumatization, 71–75 defects, 75, 345 pseudofractures, 412–416, 413f–415f imaging, 215–216 radiation-related disorders, 211–215, 229f–232f temporal bone trauma and, 420f–421f squamous, 58, 58f dehiscence, in chronic otitis media/otomastoiditis, 10–11 embryology, 26 position pneumatization, 78 and cochlear implantation, 12 styloid, 58, 58f and mastoidectomy, 11 trauma Tegmen mastoideum, 75 high-resolution CT in, 439–440 Tegmental air cells, 60f, 63f pathology associated with, 422–439 Tegmen tympani, 63f, 69, 71, 75, 79f tympanic, 58, 58f defects, 120f, 137f vascular lesions, 253 erosion, with cholesteatoma, 136 zygomatic, embryology, 26 Temporal bone, 249f Temporal fossa, 58 anatomy, normal, 58, 58f, 412–416, 413f–415f Temporal lobe, venous infarction, 254 aneurysmal bone cyst, 193 Temporomandibular fossa, 58 index.qxd 9/24/08 7:25 PM Page 590

590 Index

Temporomandibular joint (TMJ), 58 venous causes, 21–22 arthropathy, otalgia caused by, 20 in Wegener granulomatosis, 38 degenerative disease, tinnitus caused by, 21 TM. See Tympanic membrane dysfunction, postmastoidectomy, 182f TOM. See Otomastoiditis, tuberculous fractures, 422 Tonsillitis, otalgia caused by, 20–21 glenoid fossa, fractures, 416, 421f TORP. See Total ossicular replacement prostheses herniation into external auditory canal, 154 Total ossicular replacement prostheses, 164–165, 192f, 194f–195f, Temporoparietal suture, 412, 413f 197f–198f, 201f. See also specific prosthesis Tendons, of middle ear, anatomy, 59–65 dislocation, 166, 201f Tensor tympani muscle, 60f–61f, 64, 67f, 70f, 249f and MRI safety, 8 computed tomography, best projection for, 59f Tragus dysplasia, with EAC atresia/microtia, 30 absence, 27 embryology, 26, 78 embryology, 26 Tensor tympani tendon, 60f–61f, 63f, 64–65, Transverse sinus, 247f 66f–67f, 453 asymmetry, 254 computed tomography, best projection for, 59f occlusive disease, in otomastoiditis, 87 embryology, 78 thrombosis, 253, 257f Tensor veli palatini muscle, embryology, 26 in acute otitis media, 10 Teratogens, 312 and recanalization, 269 Teratoma, 199–200, 225f, 234 Trapezoid body, 485f, 488f Thalidomide, and microtia, 27 lesions involving, 525 Third mobile window, 332, 334 Trauma. See also Temporal bone, trauma Thyroid cancer, metastases to external auditory canal, 50–51, 51f intranodal necrotic, 34 and extracranial direct AVF, 273 to temporal bone, 286 fistulas caused by, 345 Tic convulsif, 472–473 hearing loss caused by, 527 Tinnitus and ICA dissection, 274 arterial causes, 21 and intralabyrinthine hemorrhage, 364 asymmetric, 21 Trautmann triangle, 84 CPA lipoma causing, 493 Treacher Collins syndrome, 27, 30 evaluation for, magnetic resonance angiography for Trigeminal nerve. See Cranial nerve(s), V data acquisition in, 8 Trigeminal neuralgia, 492 parameters for, 8 Trotter’s syndrome, 96 placement of venous saturation bands for, 8 Tuberculosis postprocessing in, 8 differential diagnosis, 203 imaging in external auditory canal involvement in, 37, 38f interpretation, 21–22 mastoid/middle ear involvement in, 36 protocol, 21 Tuberculous otomastoiditis, 80 report, 22 Tubotympanic recess, 26 nonpulsatile, 21 Tullio phenomenon, 333 characterization, 21 Tumor(s) work-up for, imaging algorithm for, 262, 262f chondrogenic, 233f with other symptoms, 21 fistulas caused by, 345–346 pulsatile, 21 and intralabyrinthine hemorrhage, 364 arterial, 260–261, 261t laryngeal, otalgia caused by, 21 arteriovenous high-flow, 261, 261t perivascular spread, 253, 253f causes, 261, 261t, 262–292 pharyngeal, otalgia caused by, 21 pathological categories for, 262 radiation-related, 215 characterization, 21 of temporal bone, 276–289 congenital anomalies and, 262–269 Turner’s syndrome, and lymphangioma, 34 differential diagnosis, 261t Tympanic annuli, 59 objective, 260 Tympanic cavity, 63f, 67f, 300f paraganglioma and, 279 anterior, fracture, 422f subjective, 260 embryology, 77 vascular causes, 21 pneumatization, 78 vascular variants and, 262–269 Tympanic isthmi, 183 venous, 260–261, 261t Tympanic membrane, 300f work-up for, 260–262 anatomy, 25–26, 59, 59f imaging in, 262 computed tomography, best projection for, 59f index.qxd 9/24/08 7:25 PM Page 591

Index 591

embryology, 26, 79 van der Hoeve–de Kleyn syndrome, 392 epidermal (squamous) layer, 59 Vascular anatomy epithelial (ectodermal) layer, 79 normal, 247–253, 247f–252f evaluation, in conductive hearing loss, 18 variants fibrous (mesodermal) layer, 59, 79 and pulsatile tinnitus, 262–269 inner (mucosal) layer, 59, 79 and vascular-appearing tympanic membrane, 262–269 innervation, 26, 59 Vascular injury(ies), temporal bone fractures and, 422f, 438–439, layers, 79 439f–440f pars flaccida, 26, 59, 59f–62f, 65 Vascular lesion(s) retraction, 112, 121f acquired, and pulsatile tinnitus, 269–276 pars tensa, 26, 59, 59f, 61f, 63f, 70f stenotic, and pulsatile tinnitus, 274–275 retraction, 112, 120f, 122f, 183 Vascular malformation(s), 34 perforations, 96 Vascular retrotympanic mass retraction, 120f–124f with aberrant ICA, 265 in acute otomastoiditis, 79, 111–114 causes, 262–292 clinical classification, 113 cholesterol granuloma and, 289–291 and granulation, 124f congenital anomalies and, 262–269 superior recess, 65–69 differential diagnosis, 282 vascular. See Vascular tympanic membrane evaluation of patient with, 260–262 Tympanic ring, 182 paraganglioma and, 279–282 embryology, 79 pathological categories for, 262 fractures, 422 vascular variants and, 262–269 Tympanomastoid fissure, 58f, 412, 414f Vascular tympanic membrane, 261 Tympanomastoid suture, 75 differential diagnosis, 261, 262t Tympanomeningeal fissure, 311 and normal vascular variants, differentiation, 261 Tympanoplasty, 154–155 Vasculolymphatic malformations, pathology, 34 for tympanic membrane retractions, 113 Vein of Labbé, 247, 247f, 254 types, 154–155, 183f Venous anatomy, normal, 247–251, 247f–252f Tympanosclerosis, 141, 157f–161f, 176f Venous sinus thrombosis, 253–254 atypical, 177f with necrotizing external otitis, 15 and cholesteatoma, 160f–161f, 177f Venous stenosis, and pulsatile tinnitus, 275 CT appearance, 162f Vertebrobasilar dolichoectasia, 269, 276, 280f differential diagnosis, 386 Vertebrobasilar system, evaluation, 23 and labyrinthine fistula, 161f Vertigo and oval window, 163f–164f benign positional, treatment, 305 true, 142, 158f–164f causes, 307, 433 Tympanosquamous fissure, 58f, 412, 413f central causes, 22, 307 Tympanosquamous suture, 58, 74–75 characterization, 22 Tympanostomy tube(s), 97–98, 103f–105f clinical presentation, 307 placement, 103f CPA lipoma causing, 493 retained, and aural polyps, 42 definition, 433 differential diagnosis, 22, 369 U imaging in Ultrasound, 8 interpretation, 22–23 of lymphangioma, 34 protocol, 22 Umbo, 59, 59f report, 23 Unusual cholesteatoma shell, 136 in labyrinthitis, 92, 159 Usher’s syndrome, 311 perilymphatic fistula and, 160 Utricle, 298–299, 301f, 482f peripheral, 307 embryology, 298, 298t, 330–331 poststapedectomy, 157 function, 302 posttraumatic innervation, 483 causes, 433 Utricular duct, 299, 310 clinical course, 434 Utriculosaccular duct, 299 in Ramsay Hunt syndrome, 35 recurrence, after labyrinthine ablation, 369 V with schwannoma, 256 VA. See Vestibular aqueduct sound-induced, 332–333 Vagus nerve. See Cranial nerve(s), X in superior semicircular canal dehiscence syndrome, 332 Valsalva maneuver, nystagmus produced by, 333 true, definition, 22 index.qxd 9/24/08 7:25 PM Page 592

592 Index

Vestibular aqueduct, 299, 303f, 306f, 308f, 310, 416. See also Large microvascular compression, 275–276 vestibular aqueduct syndrome schwannoma and, 256 anatomy, 309–310 vascular impingement on, 22 canaliculi, 310–311 Vestibulospinal tract, 307 enlarged, and hearing loss, 18 Vidian canal, 249f function, 309–310 Vogt-Koyanagi-Harada syndrome, 363

imaging, 309–310 Volume CT dose index. See CTDIvol length, 309 von Hippel-Lindau (VHL) disease Vestibular crest, 299, 300f and choristoma, 199 Vestibular ganglia, 301f, 482f endolymphatic sac tumors in, 286 Vestibular ganglion, 307 and paragangliomas, 278 Vestibular membrane, 309 Voorhoeve disease, 381 Vestibular nerve, 307 section, for endolymphatic hydrops, 369 W Vestibular neuritis, 22 Waardenburg’s syndrome, 332, 338 Vestibular nuclei, 307, 484, 485f inner ear deformity in, 337 Vestibule, 58, 72f, 250f–251f, 299, 302f–303f, Wegener granulomatosis, 37–38, 217 305f–306f, 455f imaging in, 38, 38f anatomy, 299 Wildervanck syndrome, 176 dysplasia, 316f–317f inner ear deformity in, 337, 337f embryology, 445 function, 302–304 X innervation, 305–307 Xanthoma, 210–211 medial wall intracranial, 210 elliptical recess, 299, 300f clinical presentation, 210–211 spherical recess, 299, 300f CT appearance, 211 posterior wall, 299, 300f MRI appearance, 211 vascular supply, 304 mastoid, 228f Vestibulocerebellar tract, 307 systemic, 210 Vestibulocochlear nerve, 305, 309, 448f, 449, 449f, 485f Xanthomatous pseudotumor, 209 absence, 490, 491f X-linked disorders, 311 anatomy, 480, 481f, 482, 483f X-linked hypophosphatemic osteomalacia, 311 compression, by bony lesions, 490 X-linked progressive mixed deafness, 342–344, 343f–344f congenital deficiency, 398 X-linked stapes gusher, 490 dysfunction, in syphilis, 350 XLPMD. See X-linked progressive mixed deafness embryology, 490 evaluation, in vertigo, 23 Z function, 480 Zygoma, 58 imaging, 486–553 evaluation, 14 for cochlear implantation, 12–13 Zygomatic arch, defects, with EAC atresia/microtia, 30