Skull Base–Related Lesions at Routine Head CT from the Emer

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TRAUMA/EMERGENCY RADIOLOGY - - 1161 - - [email protected] Introduction radiographics.rsna.org RSNA, 2019 • RSNA, ologist’s search pattern, as the findings can be incompletely imaged. findings can be incompletely imaged. as the search pattern, ologist’s lack of recognition of skull base or misdiagnosis, diagnosis, Delayed This article care. impact patient pathologic entities can negatively and com the essential skull base anatomy reviews and illustrates are importantmon blind spots that radiologists to interpret who The imaging acute setting. nonenhanced head CT images in the lesions are emphasized characteristics“do not miss” of important within the skull base, and categorized by their cause and location An interpre are discussed. and the potential differential diagnoses diagnostic accuracy is provided. checklist to improve tation © Routine non–contrast material–enhancedRoutine non–contrast head CT is one of the studies in the emergencymost frequently ordered department. often depicted on the first or pathologic entities, Skull base–related in can be easily overlooked head CT study, last images of a routine the emergency setting if not incorporated in the interpreting radi Non–contrast material–enhanced is the primary CT of the head with neurologic patients imaging deficits modality used to evaluate who present to the emergency Routine head CT often department. and extracranial spaces, includes images of portions of the skull base, and pathologic is complex, Skull base anatomy upper cervical spine. There- conditions in this region can be subtle and easily overlooked. a must have in the acute care setting radiologists all working fore, CT and the at of normalthorough knowledge skull base anatomy manifest in this area. wide spectrum may of disease that ------

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ASB = anterior skull base, ASB = anterior skull base, LEARNING OBJECTIVES and Lessons Learned Skull Base–related Lesions at Emer the CT from Head Routine Pitfalls, gency Department: Pearls, See rsna.org/learning-center-rg. activity, participants will be able to: Characterize easily missed skull base Identify clinical or imaging red flags Discuss the complex anatomy of the Discuss the complex anatomy ■ ■ ■ RSNA, 2019 RSNA, SA-CME After completing this journal-based SA-CME Presented as an education exhibit at the 2017 exhibit at Presented as an education 30, March Received Meeting. Annual RSNA and received revision requested June 21 2018; this journal-based For accepted July 24. July 17; and re editor, the authors, SA-CME activity, relationships. relevant no disclosed have viewers Address correspondence to [email protected] pital, 550 Peachtree Rd, Atlanta, GA 30308 Atlanta, Rd, 550 Peachtree pital, Department of R.B.P.); M.V., J.A.G., (H.R.B., Medi of Massachusetts University Radiology, Department Mass (S.R.); Worcester, cal School, of Diagnostic and Interventional Imaging, Uni Hous Health Science Center at Texas versity of and Department of (J.M.); Tex Houston, ton, Arkansas for Medi of University Radiology, S.G.). Ark (R.V.H., Little Rock, cal Sciences, From the DepartmentIm of Radiology and Emory aging of School University Sciences, Emory Hos Medicine, University Midtown lesions on nonenhanced head CT images in the acute setting. further necessitate may workup. that skull base. © RadioGraphics 2019; https://doi.org/10.1148/rg.2019180118 Content Codes: Abbreviations: = cerebello- CCJ = craniocervical CPA junction, CSB = central skull base, pontine angle, IIH = idiopathic CSF = cerebrospinal fluid, MCF = middle cra intracranial hypertension, nial fossa, PNS = PCF = posterior cranial fossa, PPF = pterygopalatine fossa, paranasal sinuses, SIH = spontaneous intracranial hypotension, joint TMJ = temporomandibular Saurabh Rohatgi, MD Rohatgi, Saurabh MD Mona Vakil, MD McCarty, Jennifer MD Hemert, Van Rudy L. MD Stephen Geppert, MD Peterson, B. Ryan Hernan R. Bello, MD Bello, Hernan R. MD Graves, A. Joseph ■ ■ ■ 1162 July-August 2019 radiographics.rsna.org

greater than 5 mm. Studies have shown the supe- TEACHING POINTS riority of depicting findings on thinly collimated ■■ If there is discordance between the imaging findings and the spiral CT images (2). Obtaining thin-section im- clinical history, a more detailed investigation of the electronic ages of 3 mm or less is recommended in the setting medical record or a direct conversation with the clinician or consultation service members should be performed. of trauma, as use of thick-section images has been ■■ Any time that facial pain or paresthesia (in a trigeminal nerve found to miss a significant number of linear frac- distribution) manifests, the radiologist should interrogate the tures and skull base lesions, particularly when the PPF for evidence of abnormal soft tissue replacing the normal images are obtained in the horizontal plane (3,4). fatty contents, which could indicate extraosseous extension In addition to obtaining directly acquired axial of metastatic disease and compression of the pterygopalatine images, high-resolution multiplanar reformatted ganglion. images, including those obtained in the coronal ■■ The frontal sinus has bony dehiscences, structural abnor- and sagittal planes, may be constructed from the malities that can channel the spread of infection. Patients can present with headaches, photophobia, seizures, or focal neu- axial dataset to increase sensitivity in the acute rologic signs. Complications include subdural and epidural setting (2,5). At our trauma center, in addition to empyema, cerebritis, brain abscess, and meningitis, which are obtaining CT images with 5-mm section thick- often neurosurgical emergencies. ness, we routinely obtain 0.625-mm thin-section ■■ If there is any suggestion of temporal bone injury, evaluating images by using a bone algorithm with sagittal nonenhanced lung-window CT images of the head may allow and coronal reformatted images for all trauma identification of extra-axial pneumocephalus, which is a finding highly suggestive of injury. head CT protocols, thereby enhancing the depic- tion of complex skull base anatomy. ■■ When one encounters mastoid effusions (especially a unilateral effusion), the soft tissues along the eustachian tube and within the nasopharynx should be thoroughly investigated to Anatomy Review exclude an underlying obstructive mass. The anatomy depicted on the first few images of a routine nonenhanced head CT study can be categorized as being located in the skull base, craniocervical junction (CCJ), or extracranial soft tissues. In addition, using a systematic search pattern and having an overall awareness of the neurologic Skull Base manifestations of a skull base lesion can aid in The skull base separates the intracranial and increasing the diagnostic yield for the interpreting extracranial compartments. It is formed from radiologist. These neurologic manifestations are portions of the frontal, ethmoid, sphenoid, paired often referred to as red flags and include cranial temporal, paired parietal, and occipital bones nerve deficits, strokelike symptoms that are atypi- (Fig 1). Arteries, veins, and multiple cranial cal for a specific vascular territory, and progres- nerves traverse the skull base through a constel- sive and/or recurrent onset of symptoms. Delayed lation of canals and foramina. The bones and diagnosis, misdiagnosis, or lack of recognition foramina of the skull base can be segmented into of skull base conditions can negatively impact three main components: anterior, middle, and patient care, highlighting the importance of using posterior (Figs 2,3) (6–9). a mental checklist when interpreting studies of The ASB is formed by the ethmoid, frontal, and the skull base, especially the first few images of sphenoid bones. Laterally, the ASB is composed of the study. the orbital plates of the frontal bones and antero- In this article, we review and illustrate the es- medially by the cribriform plate, crista galli, and sential skull base anatomy and the common blind fovea ethmoidalis of the ethmoid bone. Posteri- spots important to radiologists interpreting a orly, the flat surface of the planum sphenoidale nonenhanced head CT study in the acute setting. separates the sphenoid sinus from the intracranial We review the imaging characteristics of impor- contents. The line dividing the anterior and middle tant “do not miss” lesions at the skull base on the skull base can be drawn along the posterior aspect basis of their anatomic location and manifesta- of the lesser sphenoid wing and along the posterior tions. An interpretation checklist to help improve aspect of the planum sphenoidale, which (depend- diagnostic accuracy is provided. ing on the source used) typically does not include the anterior clinoid processes (6–9). Imaging Parameters The CSB is formed predominantly by the According to the practice parameter for the per- sphenoid and temporal bones. Anteriorly, the formance of head CT developed by the American sphenoid tuberculum sellae, anterior clinoid College of Radiology, the American Society of processes, and greater sphenoid wings define the Neuroradiology, and the Society for Pediatric Ra- CSB. Laterally, the temporal bone squamosal diology (1), contiguous or overlapping axial images portion and parietal bone confine the CSB. The should be acquired with a section thickness of no petrous ridge of the petrous temporal bone seg- RG • Volume 39 Number 4 Bello et al 1163

Figure 1. Basic skull base anatomy. (a) Axial three- dimensional reconstructed CT image with color-coded overlay shows the skull base sections. Blue = central skull base (CSB), purple = posterior skull base, teal = anterior skull base (ASB). (b) Axial CT image with color-coded overlay shows the skull base bones. Blue = temporal bones, fuchsia = nasal bones, green = ethmoid bone, light pink = vomer, purple = occipital bones, teal = sphenoid bone, yellow = zygomatic bones. (c) Axial CT image with color-coded overlay shows the extracranial spaces. Blue = masticator space, dark yellow = parotid space, fuchsia = parapharyngeal space, green = nasal cavity, light yellow = maxillary sinus, pink = carotid space, purple = perivertebral space, red = spinal canal and spinal cord, teal = nasopharynx.

ment forms the posterior extent of the CSB. The bone forms the bulk of the posterior skull base sella turcica, posterior clinoid processes, and the and creates the foramen magnum, which houses body of the sphenoid all reside centrally. the cervicomedullary junction. The cerebellar The CSB shapes the MCF, which houses the hemispheres sit atop the posterior portions of the anterior temporal lobes, pituitary gland, cavern- occipital bone. The other foramen and canals in- ous sinuses, and the exiting cranial nerves II cluded in the posterior skull base are the internal through VI. The optic canal traverses the sphe- auditory canal and its internal opening, the porus noid and houses the canalicular segment of the acusticus externus, as well as the jugular fora- optic nerve. This osseous canal courses medially men and the hypoglossal canal. The jugular spine to the optic struts and inferomedially to the ante- splits the jugular foramen into the pars nervosa rior clinoid processes (6–9). and pars vascularis (6–9). The posterior skull base is formed by the temporal, sphenoid, and occipital bones. The anterior CCJ and Upper Cervical Spine margin begins at the temporal bone petrous ridge Segments of the CCJ and the upper cervical spine and the dorsum sellae. Posteriorly, the occipital are depicted on every routine nonenhanced head 1164 July-August 2019 radiographics.rsna.org

Figure 2. Detailed skull base anatomy. (a) Coronal CT image: 1 = anterior clinoid process, 2 = optic canal, 3 = planum sphenoidale, 4 = sphenoid sinus, 5 = foramen rotundum, 6 = vidian canal, 7 = middle cranial fossa (MCF), 8 = nasal cavity. (b) Axial CT image: 1 = superior orbital fissure,2 = sphenoid sinus, 3 = greater sphenoid wing, 4 = squamosal temporal bone, 5 = MCF, 6 = internal auditory canal, 7 = clivus, 8 = facial nerve canal, 9 = petrous apex, 10 = tympanic cavity, 11 = mastoid air cells, 12 = posterior cranial fossa (PCF). (c) Axial CT image: 1 = inferior orbital fissure,2 = sphenoid sinus, 3 = foramen ovale, 4 = foramen spinosum, 5 = foramen lacerum, 6 = carotid canal, 7 = clivus, 8 = jugular foramen, 9 = PCF. (d) Coronal CT image: 1 = orbital plate, 2 = cribriform plate, 3 = fovea ethmoidalis, 4 = ethmoid sinus, 5 = lamina papy- racea, 6 = maxillary sinus, 7 = orbit, 8 = nasal cavity, 9 = anterior cranial fossa.

CT study, the extent of which varies depending Anteromedially, the occipital basion contrib- on the patient’s positioning and the CT protocol. utes to the cranial portion of the CCJ. Pos- The C1 (atlas) and C2 (axis) vertebrae of the cer- teriorly, the occipital opthision is the midline vical spine form the CCJ in conjunction with the osseous cranial landmark. Laterally, the occipital occipital bone and a multipart ligamentous com- condyles articulate with the lateral masses of the plex. Often, only a small portion of the C1 and C1 vertebra, forming the atlanto-occipital joints. C2 vertebrae are in the field of view, but because The lateral masses of the C1 and C2 vertebrae the CCJ houses the cervicomedullary junction, articulate to form the atlantoaxial joints (7–9). vertebral arteries, and various veins, these spinal The ligamentous complex of the CCJ can be structures are critically important to evaluate. directly identified on CT images by using sagittal RG • Volume 39 Number 4 Bello et al 1165

Figure 3. Detailed skull base anatomy. (a) Axial CT image: 1 = infratemporal fossa, 2 = orbit, 3 = ethmoid sinuses, 4 = sphenoid sinuses, 5 = foramen ovale, 6 = temporomandibular joint (TMJ), 7 = external auditory canal, 8 = foramen magnum and medulla. (b) Sagittal CT image: 1 = cribriform plate, 2 = planum sphenoidale, 3 = sella, 4 = basion, 5 = opthision, 6 = posterior arch of C1, 7 = sphenoid, 8 = dens, 9 = anterior arch of C1, 10 = basion-dental interval.

reformatted images and if they have been win- phragm—an ominous potential route for the dowed correctly. In addition, secondary findings spread of infection. of ligamentous injury such as atlanto-occipital or atlantoaxial joint space widening, ventral spinal Proposed Head CT Checklist canal collection and/or hematoma, or prevertebral The radiologist’s job in the emergency setting does effusion can be depicted on nonenhanced head not end after eliminating or confirming a diagnosis CT images. Any suspicious direct or secondary of acute intracranial abnormalities on head CT signs of CCJ trauma should be followed up with images. It is very important not to succumb to sat- nonenhanced MRI of the cervical spine, which is isfaction of search errors and to ensure adequate the optimal modality to evaluate these injuries. evaluation of the visualized portions of the skull base, CCJ, and extracranial soft-tissue structures. Extracranial Soft Tissues In this section, we provide a proposed checklist Portions of the orbits, paranasal sinuses (PNS), and guide for evaluating the skull base (Table). nasal cavity, and several suprahyoid neck spaces Bony sagittal reformatted images are great for abut the skull and are included at routine head evaluating the sella turcica, clivus, and CCJ on CT in varying degrees (Fig 1). bone-window CT images. Use soft-tissue win- The orbit contains the globe, extraocular dows in the sagittal plane to evaluate the mid- muscles, lacrimal gland, superior ophthalmic vein, line structures, including the foramen magnum, ophthalmic artery, optic nerve sheath complex, prepontine cistern, third and fourth ventricles,

and cranial nerves II, III, IV, VI, and V1. Cranial cerebellar tonsils, and upper cervical epidural nerve II traverses through the optic canal, while space. Coronal reformatted images may be help- cranial nerves III, IV, V1, V2 , and VI all converge in ful in assessing the included portions of the orbits the cavernous sinus, just lateral to the sella turcica. and reevaluating the ASB. The soft-tissue spaces of the suprahyoid neck continue from the skull base to the hyoid bone Clinical and Imaging Red Flags and are partially included on routine head CT Patients with primary skull base conditions can images (10). The pharyngeal mucosal space, present to the emergency department with symp- masticator space, parotid space, retropharyngeal toms such as focal neurologic deficits, altered space, danger space, and carotid space are the mental status, or headache. These symptoms are most commonly encountered. The danger space entirely nonspecific and are often attributed to is further posterior to the true retropharyngeal more common diagnoses such as a cerebrovascu- space and extends further caudally through the lar accident, intracranial trauma, hemorrhage, or posterior mediastinum all the way to the dia- uncomplicated infectious sinus conditions. 1166 July-August 2019 radiographics.rsna.org

Proposed Checklist for Evaluating the Skull Base

Structures Skull Base Segment and Specific Osseous Foramen, Canals, and Adjacent Imaging Tips Bones Components Traversing Structures Structures Anterior: Look Ethmoid, Cribriform plate Cribriform plate: CN I olfactory Nasal cavity, sep- for fractures, frontal, Crista galli fibers tum, bony arch osseous ero- sphenoid Lateral lamella Foramen cecum, emissary vein Orbital contents sions, dehis- Orbital walls Anterior ethmoid foramen, ante- PNS cence, and Fovea ethmoidalis rior ethmoid artery and vein Premalar and opacification Planum sphenoidale Posterior ethmoid foramen, pos- retroantral fat of the PNS. Lesser wing of the sphenoid terior ethmoid artery and vein pads

Middle: Turn Sphenoid, Tuberculum sellae Optic canal, CN II PPF, CN V2, to the lung temporal, Optic strut Superior orbital fissure, CN pterygoid gan-

window to parietal Anterior clinoid processes III, IV, V1, VI; superior and glion look for subtle Sella turcica inferior ophthalmic veins Masticator space

pneumocepha- Posterior clinoid processes Inferior orbital fissure, CN V2, Parotid space lus. Evaluate Dorsum sellae infraorbital artery and vein Carotid space

the middle ear Squamosal temporal bone Foramen rotundum, CN V2 TMJ, mandible for bony ero- Petrous temporal bone, pe- Vidian canal, vidian nerve and Middle and exter- sion, abnormal trous apices artery nal ear, ossicles

fluid, or soft Tympanic plates Foramen ovale, CN V3 Cavernous sinuses tissue. Greater wings of the sphenoid Foramen spinosum, middle Meckel cave Pterygoid plates meningeal artery Sphenoparietal recess Carotid canal, ICA Posterior: Look Sphenoid, Mastoid temporal bone Internal auditory canal, CNs VII Mastoid air cells for lytic or temporal, Clivus and VIII Nasopharynx and sclerotic bony occipital Occipital condyles Jugular foramen, pars nervosa retropharynx lesions. (CN IX, Jacobson nerve, Included portions inferior petrosal sinus), pars of the CCJ vascularis (CNs X and XI, Jugular fossa jugular bulb, posterior menin- CPA geal artery) Hypoglossal canal, CN XII Foramen magnum, medulla, anterior and posterior spinal arteries Note.—CN = cranial nerve, CPA = cerebellopontine angle, ICA = internal carotid artery, PPF = pterygopalatine fossa.

Sometimes the clinical picture does not co- Positional Headaches and/or incide with the imaging findings for these more Multiple Cranial Nerve Deficits common conditions. If there is discordance If a patient presents with positional headaches between the imaging findings and the clini- and/or multiple cranial nerve deficits, a diagnosis cal history, a more detailed investigation of the of spontaneous intracranial hypotension (SIH) electronic medical record or a direct conversa- should be excluded (Fig 4). Although infrequent tion with the clinician or consultation service (the annual incidence is five per 100 000 patients), members should be performed. Special atten- this diagnosis can be easily missed by a trainee or tion should be directed toward the clinical time radiologist who is unfamiliar with the condition, course of the symptoms, a detailed neurologic which can delay treatment. Symptoms of SIH examination should be performed, and past include nausea, vomiting, neck pain, visual and/ medical history including any prior imaging or hearing disturbances, or vertigo, likely result- should be reviewed. There are a number of clini- ing from the tension of the cranial nerve owing to cal scenarios or red flags in which the radiologist brain sagging (11). should consider performing a detailed inspec- Sagittal imaging can improve the sensitivity tion of the skull base to include or exclude an for identifying SIH; however, all trainees and alternative diagnosis. any radiologist reviewing neurologic images RG • Volume 39 Number 4 Bello et al 1167

Figure 4. SIH in a young woman who presented with dizziness. (a, b) Axial nonenhanced head CT images show crowding at the foramen magnum (arrowheads in a) and diffuse effacement (arrowheads in b) of the basal cisterns. (c) Axial T2-weighted MR image obtained at follow-up shows bilateral subdural collections (arrowheads). (d) Axial T1-weighted MR image obtained after the administration of contrast material (postcontrast) shows diffuse pachymeningeal enhancement (arrowhead). (e) Sagittal postcontrast T1-weighted MR image shows effacement of the prepontine cistern (arrowhead), sagging of the brainstem, and cerebellar tonsillar ectopia.

from the emergency department should be fa- Additional evaluation with contrast-enhanced miliar with the findings on axial cross-sectional MRI can confirm SIH, and its imaging features images. Routine nonenhanced imaging find- include diffuse non-nodular pachymeningeal ings that should raise the possibility of an SIH enhancement, decreased fluid in the optic nerve diagnosis include (a) bilateral subdural hemor- sheaths, engorgement of the pituitary gland, and rhages or subdural hygromas; (b) effacement of any of the previously noted signs of brain sagging. the skull basal cisterns, especially the suprasellar and prepontine cisterns; (c) engorgement of the Strokelike Symptoms with Nonacute Time dural venous system; (d) sagging of the brain Course or Facial Pain and/or Paresthesia parenchyma, including abutment of the optic The time frame for the onset of a patient’s apparatus on the sella turcica or cerebellar ton- symptoms can be unclear, especially if there is sillar ectopia; and (e) inferior orientation of the a history of prior cerebrovascular events and a splenium of the corpus callosum. lack of reliable past clinical history or imaging. In 1168 July-August 2019 radiographics.rsna.org these settings, a focal neurologic deficit related or intracranial mass. If the patient is a woman to a skull base lesion can be mistaken for a new of childbearing age and is obese, idiopathic vascular ischemic stroke. intracranial hypertension (IIH) should be the A key example is an osseous metastasis or preemptive diagnosis, especially if papilledema primary osseous tumor (eg, chordoma) close is noted at physical examination or the patient to skull base foramina, specifically the Dorello reports pulsatile tinnitus. (cranial nerve VI) or the hypoglossal (cranial Another CT finding of IIH includes en- nerve XII) canals. In these situations, patients largement of the skull base foramina (Fig 5). may present with the inability to laterally abduct Although there are few imaging findings of one or both eyes or with tongue deviation, a IIH identified at CT, an empty and expanded finding reflecting cranial nerve compression and sella turcica has been described in patients associated muscular atrophy. Also, any time that with IIH and can indicate underlying increased facial pain or paresthesia (in a trigeminal nerve intracranial pressure. The diagnosis is usually distribution) manifests, the radiologist should confirmed by the results of a lumbar puncture, interrogate the PPF for evidence of abnormal but additional findings can be seen at MRI, soft tissue replacing the normal fatty contents, including increased cerebrospinal fluid (CSF) which could indicate extraosseous extension of in the optic nerve sheaths, intraocular protru- metastatic disease and compression of the ptery- sion at the optic disc, optic nerve tortuosity or gopalatine ganglion. enhancement, flattening of the posterior globes, If the clinical time frame is in question or if transverse dural venous sinus stenosis, and slit- facial pain manifests, the radiologist should pay like ventricles (13). special attention to the mineralization pattern of the skull base and investigate any additional New Seizures, Facial Swelling, signs of metastatic disease outside the brain or Acute Change in Mental Status or interrogate the medical record. If there are A diagnosis of an occult skull base encephalo- additional questions, further evaluation with cele or CSF leak should be strongly considered contrast-enhanced MRI or skeletal scintigraphy if there is an acute change in mental status or may be considered. new seizures and a remote history of traumatic In addition, infectious processes of the skull brain injury or evidence of frontotemporal base can occur as an unusual acute strokelike traumatic encephalomalacia. Protrusion of brain manifestation. Infection or inflammation of the parenchyma through an osseous or dural defect petrous apex in the setting of acute otomastoid- from prior trauma typically occurs at the ante- itis can present with a unilateral cranial nerve VI rior cranial fossa (cribriform plate) and MCF palsy known as Gradenigo syndrome, first de- (tegmen tympani or tegmen mastoideum), dam- scribed in 1904. The classic triad of symptoms aging the underlying protruding brain paren- comprises acute suppurative otitis media, severe chyma and resulting in an epileptogenic focus. temporoparietal pain, and paresis or paralysis of These defects can also predispose a patient to the ipsilateral abducens nerve. CSF leaks that can result in meningitis or cere- Often, in addition to abducens nerve palsy, britis, leading to seizure activity. Visualization of ipsilateral facial pain owing to involvement of the defect is often difficult on axial images, so if the adjacent dura and trigeminal nerve in the there is concern, coronal images should be re- Meckel cave may manifest. Nonenhanced im- viewed as they are key to making the diagnosis. ages should depict opacities in the tympanic Traumatic cavernous carotid fistulas or pseu- cavity, mastoid air cells, and pneumatized doaneurysms can occur immediately following petrous apex, usually with lysis of the thin bony or soon after significant traumatic skull base septa. Contrast-enhanced MRI is more sensitive fractures. If there is any periorbital erythema or for the evaluation of dural or leptomeningeal new altered mental status, radiologists and clini- enhancement, and it aids in imaging of compli- cians need to have a low threshold for perform- cations such as adjacent cerebritis, intracranial ing vascular imaging such as CT angiography. abscess, and cavernous sinus thrombosis (12). In addition, a cavernous sinus thrombus can manifest in a similar fashion in the setting of Blurry Vision with Headaches more subacute trauma or infectious processes Acute or subacute changes in vision should like invasive sinus disease. In such cases, spe- always prompt an investigation with MRI, un- cial attention should be paid to exclude any less there is an acceptable alternative diagnosis asymmetric bulging of the cavernous sinuses or such as migraine. However, the first emergent enlargement of the superior ophthalmic vein, examination usually performed is nonenhanced which can be seen with a cavernous carotid head CT to exclude a subarachnoid hemorrhage fistula, pseudoaneurysm, or thrombus. RG • Volume 39 Number 4 Bello et al 1169

Figure 5. IIH in a woman with obesity who presented with eye pain. (a, b) Axial nonenhanced head CT images show an enlarged foramen ovale (arrowhead in a) and an empty sella (arrowhead in b). (c) Axial T2-weighted MR image shows increased CSF (arrowheads) in the optic nerve sheaths. (d) Axial postcontrast T1-weighted MR image shows stenosis (arrowheads) of the transverse venous sinuses bilaterally.

Pathologic Entities of the Skull Base patients (15,16). CT is often the first modality performed to diagnose bony involvement and Anterior Skull Base intracranial extension (15,17), which can result Common pathologic conditions in the ASB in- either from direct extension or by valveless com- clude intracranial extension of sinonasal malignan- municating veins. In addition, the frontal sinus cies and infections, as well as congenital lesions has bony dehiscences, structural abnormalities and conditions secondary to trauma (6,14,15). that can channel the spread of infection (16,17). Neoplasms of the nasal cavity and PNS can Patients can present with headaches, photo- involve the ASB, with many of these aggressive le- phobia, seizures, or focal neurologic signs (16). sions demonstrating overlapping imaging features, Complications include subdural and epidural which are discussed in the section on the “Sinona- empyema, cerebritis, brain abscess, and men- sal Region.” The role of the radiologist interpret- ingitis (Fig 6), which are often neurosurgical ing the initial CT study is to identify the presence emergencies (16). Osteomyelitis of the frontal of an extracranial lesion and recommend further bone can spread outward and form a subgaleal imaging with enhanced brain MRI to determine abscess described as Pott puffy tumor (16,17). the full extent of involvement from a resectability Polyposis with secondary fungal infections can and staging standpoint (6,14,15). erode into the ASB, which can develop into Sinonasal infections caused by bacteria such meningitis or cause CSF leaks (15,18). as Pseudomonas aeruginosa or invasive fun- During an acute trauma assessment, the radi- gal agents like Aspergillus or Zygomycetes are ologist is at the forefront of interpreting injuries commonly diagnosed in immunocompromised of the face and ASB, as performing a physical 1170 July-August 2019 radiographics.rsna.org

Figure 6. Invasive bacterial and/or fungal sinusitis in an immunocompromised woman who presented with headache and facial pain. (a) Axial nonenhanced head CT image shows opacification throughout the PNS and osseous erosions (arrowheads). (b) Axial postcontrast T1-weighted MR image obtained at follow-up shows abnormal sinus wall enhancement, with extrasinus extension (white arrowhead), and an enhancing extra-axial collection (black arrowhead) in the left CPA, a finding compatible with an abscess.

examination alone is insufficient (19). Craniofacial injuries are frequently associated with fractures of the ASB, and fractures of the facial bones and sinus walls can lead to CSF leak, dural laceration, and herniation, with the ASB being the most common location for traumatic CSF leak (6,14). In the pediatric population, normal sutures, ac- cessory or variant sutures, and wormian bones can mimic calvarial fractures in both accidental and nonaccidental trauma (20). Coup or contrecoup traumatic intraparenchymal contusions commonly occur along the inferior frontal and anterior temporal lobes where the brain has the greatest chance of impact against the rigid bone (20,21). Meningoencephaloceles are a congenital herniation of meninges and brain parenchyma, which are further subdivided as sincipital or basal, dependent on the site of herniation (6,14). MRI is performed to delineate the extent of the Figure 7. Schwannoma in a young man who presented with lesion, but high-resolution CT with multiplanar right-sided facial numbness. Axial nonenhanced CT image of reformatted images helps delineate bony anat- the head shows marked asymmetric expansion of the right omy and differentiate meningoencephaloceles foramen ovale (red arrowhead) when compared with that of from other congenital masses such as nasal der- the normal left foramen ovale (white arrowhead). There are no overlying erosions to suggest an aggressive process. The moids, sinus cysts, and nasal gliomas (6,14,15). findings on MR images (not shown) were compatible with a Pitfalls in the ASB include areas of arrested trigeminal (V3) schwannoma. pneumatization in the basisphenoid, which are incidental “do not touch” findings that are often mistaken for malignancy. These are nonexpansile include unossified frontal, nasal, and ethmoid fat-containing geographic lesions with calcifica- bones, which can be mistaken for skull base de- tion and sclerotic margins (6). Additional pitfalls fects, especially in infants (14). RG • Volume 39 Number 4 Bello et al 1171

Middle Cranial Fossa motor deficits (eg, ptosis, diplopia, anisocoria, or The MCF is an easily overlooked segment of the ophthalmoplegia) (24). skull base on nonenhanced CT images and has a Patients with tumors of the anterior clivus close anatomic relationship with temporal bone often present with signs and symptoms related and CSB entities. The main structures in this re- to local invasion (Fig 8). These include cranial gion are the temporal lobe with its accompanying nerve palsies, brainstem compression, or hydro- dura and the sphenoparietal dural venous sinus cephalus (25). Clival metastases are often aggres- along the lesser wing of the sphenoid bone. sive soft-tissue masses and usually manifest in Subtle traumatic injury in this region can be patients with a known history of malignancy. easily obscured at imaging by significant beam- Chordomas of the skull base are uncommon hardening artifacts from the adjacent dense but malignant. They can arise at the midline cli- bone. Lung windows may help identify punctate vus and are typically well-circumscribed expans- extra-axial pneumocephalus, which can suggest ile soft-tissue masses that may contain irregular underlying injury. Extra-axial hematomas (epi- intratumoral calcifications. The differential dural and subdural) are common in this loca- diagnosis for clival and spheno-occipital lesions tion, with 10.5% localized to the MCF (22). A includes chondrosarcomas, metastases, and plas- venous epidural hematoma is an entity specific macytomas (26). to this location. It is likely the result of trauma Pituitary adenomas are benign lesions and can to the sphenoparietal sinus, often following a vary in size and location. Usually macroadeno- benign clinical course as compared with that of mas manifest with symptoms owing to local mass an arterial epidural hematoma, and does not re- effect. They arise from the anterior lobe of the quire surgical intervention. Coup or contrecoup pituitary gland and are the most common cause traumatic intraparenchymal contusions are also of sellar masses from 20 years of age, but they frequent owing to the underlying rough contour account for only up to 10% of all intracranial of the temporal and sphenoid bones. neoplasms (27,28). Neoplastic processes in this region usually fol- Care should be taken not to overlook inflam- low a benign course. The differential diagnosis of matory or infectious processes, as they can spread a mass in the MCF region includes meningioma rapidly and have deadly consequences. Involve- and epidermoid cysts, which usually arise in the ment of the CSB can occur from the extension of CPA but can arise from the parasellar region in sinusitis from the sphenoid sinus and can infil- 10%–15% of cases and extend into the MCF trate the cavernous sinus, leading to cavernous (23). Epidermoid cysts can be easily mistaken sinus thrombosis (16). for arachnoid cysts and can be differentiated on Trauma in the region of the CSB is not usually MR images, where epidermoid cysts demonstrate an isolated finding but is typically seen with ASB marked restricted diffusion at imaging. or temporal bone trauma. Important structures to evaluate in the traumatic setting include the carotid Central Skull Base canals (for which performing CT angiography may The anatomy of the CSB is complex and com- be warranted), sphenoid bone (for assessing for pact. As previously stated, using thin-section CSF leak), and pterygoid plates (for assessing for bone algorithms and obtaining coronal or sagit- Le Fort–type fractures). It is important to recog- tal reformatted images are useful for identify- nize CSB trauma, as performing additional imaging subtle skull base conditions (2). Important ing, including facial CT, temporal bone CT, CT structures are housed in the CSB, including the angiography, and/or MRI, may be warranted. pituitary gland, cavernous sinuses, and basal foramina, which contain an array of vital neuro- Temporal Bone vascular structures (6–9). Neoplastic, infectious, Similar to the CSB, the temporal bone is a inflammatory, and traumatic processes can af- complex region that houses many of the cranial fect the CSB. nerve foramina, the auditory apparatus, and Slow-growing tumors such as schwannomas carotid vascular inflow, and it articulates with can expand the skull base foramina (Fig 7). the CSB and mandible. The crucial techniques However, more aggressive tumors will demon- used to identify pathologic conditions in this strate a destructive process. Tumors affecting the region involve evaluating symmetry (eg, com- cavernous sinus may cause neurologic symptoms paring the side with the finding to the contralat- related to the neurovascular structures involved, eral temporal bone) and using thin-section bone including trigeminal nerve dysfunction (eg, facial algorithms with reformatted images. Pathologic numbness or pain), visual field deficits owing to conditions in this region can be categorized compression of the optic nerve, ischemic deficits as having traumatic, neoplastic, infectious, or owing to carotid artery compression, and ocular inflammatory causes. 1172 July-August 2019 radiographics.rsna.org

Figure 8. Metastatic disease in a middle-aged man with no significant medical history who presented with isolated tongue deviation. (a) Axial nonenhanced CT image of the head shows a focal lytic lesion (arrowhead) in the left aspect of the clivus near the hypoglossal nerve canal. (b) Axial CT image of the neck obtained at follow-up shows fatty atrophy (arrowhead) of the left base of the tongue owing to hypoglossal nerve involvement. The patient was later diagnosed with metastatic prostate cancer.

Approximately 18%–22% of patients with major predict facial nerve palsies and various types of head trauma have involvement of the temporal bone hearing loss, as well as help guide management. (29). Patients will often present with stark clinical Management examples include further evalua- signs of focal trauma such as Battle sign, postau- tion with CT angiography if the carotid canal is ricular ecchymosis, vertigo, or hearing loss. Physi- involved or treatment with antibiotics to prevent cal findings include facial nerve palsy, otorrhagia, meningitis if the fracture crosses the PNS or tem- hemotympanum, tympanic membrane perforation, poral bone tegmen. stroke, and nystagmus. Subtle nondisplaced tem- One fracture that is often overlooked is the poral bone fractures can be easily missed. However, tympanic plate fracture involving the posterior if there is soft-tissue swelling overlying the temporal wall of the glenoid fossa of the TMJ. With direct bone and hyperattenuating fluid in the mastoid air injury to the jaw, either by motor vehicle collision cells and tympanic cavity, a close interrogation of or ground-level fall onto the chin, the energy is the temporal bone at thin-section imaging should either transmitted to the mandibular condyle or be repeated. transferred to the tympanic plate. The tympanic As described previously, if there is any sugges- plate fracture can be incorrectly identified as a tion of temporal bone injury, evaluating nonen- normal adjacent squamotympanic fissure and hanced lung-window CT images of the head may can lead to misdiagnosis, external auditory canal allow identification of extra-axial pneumocephalus, atresia, and subsequent conductive hearing loss, which is a finding highly suggestive of injury. unless bolstered by packing material by a trauma When a temporal bone fracture is identified, the or otorhinolaryngology surgeon. extent and distribution of the fracture can predict There is a plethora of neoplastic processes that morbidity and prognosis. Classically, a temporal can involve the temporal bone region, includ- bone fracture is described as either longitudinal ing paraganglioma, schwannoma, neurofibroma, (most common) or transverse but can be a combi- endolymphatic sac tumor, and metastasis. nation (described as mixed, complex, or commi- Infectious or inflammatory involvement of nuted) (29). A newer classification system uses the the temporal bone can include disease processes involvement of the otic capsule (otic capsule–spar- that appear masslike such as cholesteatomas and ing vs otic capsule–violating fracture) (30). The petrous apex cholesterol granulomas (Fig 9) involvement of the ossicular chain, PNS, tegmen or infiltrative such as petrous apicitis and otitis tympani and/or mastoideum, carotid canal, and media. Fluid accumulation in the mastoid air cranial nerve foramina can help explain and/or cells is among the first findings of infection in RG • Volume 39 Number 4 Bello et al 1173

Figure 9. Cholesterol granuloma in a patient who presented with tinnitus and left facial pain. (a) Axial nonenhanced CT image of the head shows an expansile well-marginated lesion (arrowheads) in the left petrous apex. Note the nor- mally pneumatized right petrous apex (arrows). (b) Axial T2-weighted MR image shows a focal lesion (arrowhead) with high signal intensity. (c) Axial postcontrast T1-weighted MR image shows no significant enhancement of the lesion (arrowhead). (d) Coronal T2-weighted MR image shows T2-hyperintense debris (arrowhead) with a sedimentation level (arrow). this region. When one encounters mastoid effu- tibular schwannomas are by far the most common sions (especially a unilateral effusion), the soft CPA tumor, accounting for over 85% of all CPA tissues along the eustachian tube and within the tumors, followed by meningiomas (31,32). The nasopharynx should be thoroughly investigated key to visualizing an isoattenuating CPA mass is to to exclude an underlying obstructive mass. In carefully evaluate the CPA cistern for effacement addition, complications of a temporal bone in- and asymmetry, abnormal soft-tissue opacification, fection should be excluded, including coalescent or expansion of the internal auditory canal. otomastoiditis; associated dural venous sinus Vascular abnormalities can be easily overlooked dehiscence or thrombosis; and subperiosteal, owing to the limitations of imaging the PCF. sternocleidomastoid muscular, or intraparenchy- Posterior inferior cerebellar artery aneurysms mal brain abscess. can sometimes be visualized on nonenhanced CT images if they are large, partially calcified, Posterior Cranial Fossa or hyperattenuating. Dural arteriovenous fistulas The PCF is the most posterior aspect of the skull are an uncommon collection of conditions that base and is home to the brainstem and cerebel- share arteriovenous shunts from dural vessels lum, as well as other important extra-axial struc- (Fig 10). Diagnosing dural arteriovenous fistulas tures (eg, dural venous sinuses, internal acoustic can certainly be challenging at nonenhanced CT, meatuses, foramen magnum, jugular foramina, but a red flag should be raised if the intracranial hypoglossal canals, and the vestibular aqueducts) hemorrhage pattern is in an unusual location or (6–9). Owing to bone-induced beam-hardening is visualized in a patient outside the typical age of artifacts depicted on images, the evaluation of the manifestation (33). PCF is often compromised. Dural venous thrombosis is a critical diagno- The most common neoplasms in the PCF are sis that could have dire consequences if missed. CPA tumors, which are almost all benign. Ves- Classically, patients with dural venous sinus 1174 July-August 2019 radiographics.rsna.org

Figure 10. Dural arteriovenous fistula in a patient who presented with altered mental status experienced while driving. (a) Axial nonenhanced CT image of the head shows enlargement and tortuous course of the left middle meningeal artery (arrows), arising from the foramen spinosum. (b) Axial nonenhanced CT image of the head shows multiple intraosseous vascular structures (arrowheads), with pitting of the inner table. (c) Time-resolved MR angiogram obtained at follow-up shows a Borden type III dural arteriovenous fistula (arrowheads). Note the prominent middle meningeal artery (arrow). thrombosis will present with headache, with or without neurologic deficits. On nonenhanced CT images, the affected sinuses or vein will be hyperattenuating, with or without venous hemorrhage or infarction. This has been described as the “dense cord” or “dense vein” sign. The results of a study by Buyck et al (34) show that sinus attenuation more than 62 HU and a Hounsfield unit to hematocrit ratio greater than 1.52 support a diagnosis of cerebral venous sinus thrombosis. If this diagnosis is suspected, Craniocervical Junction CT venography should be performed for confir- The extent of the CCJ depicted on routine head CT mation (34). In the setting of trauma, skull base images can vary. Pathologic conditions involving the fractures involving the dural venous sinus place CCJ and included portions of the cervical spine are the patient at risk for dural venous thrombosis, most often caused by trauma. However, incidental and CT venography should be considered. findings of upper cervical spine neoplasms, includ- The PCF houses a number of neurovascular ing metastatic disease, should not be overlooked. It structures. Radiologists must inspect the internal is important to identify primary or secondary find- auditory canals and hypoglossal canals for masses ings that indicate cervical spine injury, as the next like schwannomas along cranial nerves VII, VIII, step would include spine surgery consultation and and XII, respectively. The jugular foramen is an performing CT and/or MRI of the cervical spine to important landmark that can be divided into the assess for brainstem, cord, and ligamentous injury. pars nervosa and the pars vascularis. Although the Craniocervical dissociation or atlanto-occipital foramen can be asymmetric in size, it is important dissociation refers to subluxation, distraction, or to make sure the walls are well corticated. complete dislocation at the atlanto-occipital joint, RG • Volume 39 Number 4 Bello et al 1175 which is primarily stabilized by the tectorial mem- terval that is greater than 3 mm in adults suggests brane and paired alar ligaments. Atlanto-occipital atlantoaxial dissociation, with injury to the trans- dissociation results from the disruption of these verse ligament (2). A transverse ligament injury ligaments, usually caused by extreme hyperexten- is usually associated with a C1 or dens fracture sion and lateral flexion in high-velocity trauma. but can occur in isolation or with nontraumatic These injuries are often associated with severe causes such as rheumatoid arthritis. Atlantoaxial neurologic deficits and high mortality, particularly dissociation may result in the posterior displace- from vascular and brainstem injuries (2,35). ment of the C2 vertebra and compression of the The basion-dens interval should be assessed spinal cord between the dens and the posterior on sagittal images. A basion-dens interval greater arch of the C1 vertebra. than 10 mm as measured on the sagittal plane is Various causes can result in craniocervical highly suggestive of atlanto-occipital dissociation extra-axial hemorrhage, most commonly trauma, (5). Secondary findings include occipital condyle including the various fractures described previ- fractures and subarachnoid or subdural hemor- ously. Additional causes include aneurysmal and rhage, which should be included on the radiolo- nonaneurysmal subarachnoid hemorrhage, dural gist’s imaging checklist. arteriovenous fistula, and extension of epidural or Occipital condyle fractures are often visualized intrathecal hemorrhage from the cervical spine. on routine head CT images and are classified The most common intramedullary spinal cord into three types: (a) isolated impaction fracture lesion is ependymoma, although its CT appear- (type I), (b) skull base fractures that extend into ance is nonspecific. The differential diagno- the occipital condyles (type II), and (c) alar liga- sis includes astrocytoma, hemangioblastoma, ment avulsion fractures (type III) that extend metastasis, lymphoma, or myelitis. Spinal cord into the foramen magnum. Type I and II injuries tumors typically expand the spinal cord and are are stable, and type III injuries are potentially isoattenuating or slightly hyperattenuating on unstable, dependent on the degree of fracture nonenhanced CT images, especially if hemor- fragment displacement (2,35,36). rhage is present. A syrinx is any cavity within the Injuries associated with occipital condyle cord with CSF attenuation that may or may not fractures include cervical spine or facial fractures, communicate with the central canal. This can be as well as vascular trauma to the vertebral or congenital, most commonly from Chiari malfor- carotid arteries (36). Lower cranial nerve palsies mations (Fig 11), or acquired from trauma or may also be diagnosed, most commonly of the spinal cord tumors obstructing the normal flow hypoglossal nerve, if there is fracture extension of CSF. Extramedullary intradural lesions typi- through the hypoglossal canal (35). cally have a CSF cleft between the lesion and the Atlas fractures account for one-fourth of CCJ spinal cord and may result in cord compression. injuries and are often associated with C2 ver- Meningiomas and nerve sheath tumors make up tebra fractures. Fractures are divided into five a majority of intradural lesions and can be dif- types according to their location: (a) posterior ficult to distinguish at CT. arch (type I), (b) anterior arch (type II), (c) an- Osseous metastasis may be osteoblastic, terior and posterior arches (type III or Jefferson osteolytic, or mixed and should be considered in burst fracture), (d) lateral masses (type IV), and the differential diagnosis for any bone lesion in a (e) avulsion injuries (type V) (27). On coronal patient over 40 years of age. The most common images, the displacement of the lateral masses lytic vertebral body metastases include those of C1 in relation to the lateral aspect of C2 is an found in the breast, lung, renal cells, and thyroid, indicator of atlas fracture (2). (although metastases in the breast and lung may Odontoid fractures account for over one-half have a mixed appearance), as well as melanoma of C2 fractures, with a greater prevalence in the and lymphoma. The prostate and bladder are the older population. They can be divided into three most common sites of sclerotic metastasis. Multi- types, dependent on location: (a) tip of dens ple myeloma manifests as diffuse osseous infiltra- fracture from avulsion of the alar ligament (type tion, with multiple well-defined lytic lesions. I), (b) junction of the odontoid process and body of C2 (type II), and (c) extension into the body Pathologic Entities of the (type III) (36). Fractures of the odontoid process Extracranial Structures are best depicted on coronal and sagittal reformatted images. It is important not to mistake an Masticator Space unfused os odontoideum or the subdental basilar The masticator space contains the mandible, synchondrosis with a dens fracture. TMJ, muscles of mastication (temporalis, masse- The atlanto-dens interval should always be ter, medial pterygoid, and lateral pterygoid), and assessed on sagittal images. Widening of the in- V3 branch of the trigeminal nerve (10). 1176 July-August 2019 radiographics.rsna.org

Figure 11. Chiari malformation in a young woman with recurrent headache. (a) Axial nonenhanced CT image of the head shows crowding (arrowheads) at the foramen magnum. (b) Sagittal T2-weighted MR image of the brain obtained at follow-up shows a peglike configuration of the cerebellar tonsils with downward displacement (line) through the foramen magnum, resulting in crowding of the medulla. Note the decreased CSF level at the foramen magnum (arrowhead), resulting in mild hydrocephalus.

Traumatic abnormalities include mandibular Carotid Space fracture and TMJ dislocation. These are often The carotid space is formed from all three layers clinically evident and easy to visualize at CT. of cervical fasciae (superficial, middle, and deep), TMJ arthritis related to degenerative joint dis- and encases the carotid artery, jugular vein, sym- ease usually causes flattening and widening of the pathetic plexus, lymph nodes, and cranial nerves mandibular condyle with peripheral osteophytes, IX, X, XI, and XII (10). and periarticular erosions in rheumatoid arthritis Traumatic abnormalities in the space include give rise to a characteristic “sharpened-pencil” carotid dissection and pseudoaneurysm (Fig 12). appearance of the mandibular condyle, often with Both can cause patients to present with anterior additional findings from secondary degenerative circulation strokelike symptoms. On nonenhanced joint disease. head CT images, carotid dissection can be seen Infectious and inflammatory conditions are as a long segment luminal irregularity, an abrupt common in the masticator space, with infection change in caliber, or displacement of calcified often arising from periodontal disease. Phleg- plaque in an atherosclerotic arterial wall. Occa- mon and abscess can both manifest similarly, sionally in acute dissection, there will be a hyperat- with trismus or jaw pain. Loss of normal fat tenuating crescentic mural hematoma. Pseudoan- planes and well-defined fluid collections are eurysm is often depicted along with dissection and obvious signs of infection, but it is important to appears as focal dilatation of the vessel, usually identify if the source of infection is from peri- just proximal to the entrance to the carotid canal. odontal abscesses or dental caries. The radiolo- In practice, the two may be indistinguishable. The gist should evaluate for focal cortical break- dissection will frequently start in the proximal in- through or periosteal inflammation. ternal carotid artery, often below the field of view The most commonly encountered neoplas- on a head CT image, and usually stops before the tic lesion in this region involves the mandibular intracranial internal carotid artery. branch (V3) of the trigeminal nerve, which may The classic infectious abnormality to occur in be affected by a primary nerve sheath tumor or the carotid space is septic thrombophlebitis of by perineural spread, either from an oropharyn- the internal jugular vein, also known as Lemierre geal malignancy or from an intracranial malig- syndrome. Unlike noninfectious causes of throm- nancy. Clinically, patients often present with bophlebitis, this commonly occurs in young neuropathy in the V3 distribution. Widening of patients after being diagnosed with bacterial the mandibular foramen is the most important pharyngitis. On nonenhanced head CT images, diagnostic clue and should prompt a search for the thrombosed vein will be enlarged and hyper- the primary site of malignancy. attenuating, with surrounding soft-tissue edema. RG • Volume 39 Number 4 Bello et al 1177

Figure 12. Internal carotid artery pseudoaneurysm in an older man with a recent history of trauma. Axial nonenhanced CT image of the head shows a periph- erally calcified mass, a finding suspicious for left -in ternal carotid artery pseudoaneurysm (green arrowhead), compared to the normal right internal carotid artery (red arrowhead). The diagnosis was confirmed at CT angiography (not shown).

The most common neoplastic lesions in inciting a risk of aspiration, or may distend the the carotid space are glomus tumors (carotid retropharyngeal space. body tumor and glomus vagale) and schwanno- Inflammatory and/or infectious processes range mas. Both manifest as mass lesions, but glo- from pharyngitis to retropharyngeal abscess. At im- mus tumors are more likely to be pulsatile. On aging, pharyngitis will appear as ill-defined thick- nonenhanced CT images, they both appear as ening of the mucosal space. However, this finding soft-tissue masses similar in attenuation to that of should raise a red flag when depicted in adults, as muscle. Schwannomas often displace the internal benign nasopharyngeal inflammation can be dif- carotid artery, whereas glomus vagale tumors ficult or even impossible to distinguish from early splay the internal carotid artery and the external stage primary nasopharyngeal carcinoma (37). carotid artery. While both can be familial lesions, A further review of the patient’s history or direct glomus vagale tumors are more likely to be bilat- examination of the mucosa may be necessary. eral and are often seen with glomus tympanicum Retropharyngeal edema is depicted as an area and glomus jugulare tumors. Performing a search of ill-defined low attenuation. In contrast, a retro- pattern that includes the contralateral carotid pharyngeal abscess will appear well defined on im- space, jugular foramen, and middle ear could ages and often will distend the space to a greater help with differentiation. degree than that of an edema. Given that both retropharyngeal edemas and abscesses can continue Nasopharyngeal and caudally to the T3 level, where the retropharyngeal Retropharyngeal Spaces space ends, and owing to the potential for epidural The nasopharyngeal space includes the mucosal extension in the case of an abscess (10), perform- surface, lateral pharyngeal recess (fossa of Ros- ing additional imaging of this region is imperative. senmüller), torus tubarius, constrictor muscles, Malignancies of the nasopharynx include na- pharyngeal lymphatic tissue (adenoids of Waldeyer sopharyngeal carcinoma (Fig 13), non-Hodgkin ring), minor salivary glands, and the eustachian lymphoma, and minor salivary gland tumors. The tube openings (8–10). The retropharyngeal space clinical presentations for these malignancies may contains mostly fat. While the boundaries of these be vague. Nasopharyngeal carcinoma is a nonke- spaces are indistinguishable at normal nonen- ratinizing carcinoma that arises from the lateral hanced head CT, they may be elucidated by the pharyngeal recess, and it is related to an Epstein- type and extent of the pathologic processes. Barr virus infection (38). Asymmetry, masslike Traumatic injury in this region varies widely, invasion of adjacent structures, and (potentially) from gunshot wounds to embedded ingested for- CSB destruction will clue the radiologist into eign bodies, and it can be iatrogenic or idiopathic. considering a nasopharyngeal carcinoma diagno- Lines and tubes can potentially cause iatrogenic sis. Radiologists should always be on high alert trauma or may be malpositioned and included in if they encounter asymmetric nasopharyngeal the field of view on CT or scout CT images. Hem- fullness and unilateral persistent tympanomastoid orrhage from trauma can spill into the pharynx, effusion on CT images of the head in adults. 1178 July-August 2019 radiographics.rsna.org

Figure 13. Nasopharyngeal carcinoma in a patient with no significant medical history who presented with arm pain. (a) Axial nonenhanced CT image of the head shows an incidental asymmetric soft-tissue mass (white arrowhead) in the right posterior nasopharynx, effacing the fossa of Rossenmüller. Note the normal left side (black arrowhead), which contains an aerated eustachian tube (arrow). (b) Axial postcontrast fat-saturated T1-weighted MR image obtained at follow-up shows a homogeneously enhancing mass (white arrowhead) in the right nasopharynx, compared to the normal left nasopharynx (black arrowhead).

Sinonasal Region immunocompromised patients to determine The sinonasal region contains the nasal cavity if there is any evidence of extrasinus exten- and PNS. Traumatic abnormalities in this region sion or invasive features. Prompt diagnosis include a host of facial fractures, including zy- and treatment are essential, as acute invasive gomaticomaxillary complex, Le Fort, and naso- fungal sinusitis infection has a mortality rate of orbitoethmoid fractures (Fig 14). Radiologists 50%–80% (40). Abnormal soft tissue or inflam- should evaluate for skull base involvement, as mation in the premalar, retroantral, and PPF skull base fractures have the potential for com- fat and subtle erosions of the PNS wall or any plications of CSF leaks and meningitis, as well as significant mucosal irregularities in the nasal other complications. cavity can indicate an invasive fungal or aggres- Inflammatory and infectious conditions include sive bacterial sinusitis. Early detection before sinusitis, granulomatosis with polyangiitis (GPA, significant intracranial extension or vascular formerly known as Wegener granulomatosis), and compromise could result in improved outcomes. sarcoidosis. Sinusitis is a clinical diagnosis. Imag- Importantly, not all sinus low-attenuation ing features can include mucosal thickening, frothy opacification represents secretions or sinusitis. secretions, and air-fluid levels as depicted in cases Patients with encephaloceles and CSF leaks of typical bacterial sinusitis; hyperattenuating ex- may have water-attenuation–filled isolated PNS pansile material in cases of allergic fungal sinusitis; that abut the skull base at imaging. Multiplanar and the ominous invasive extrasinus soft tissue reconstructions are invaluable in differentiating a depicted in cases of invasive fungal sinusitis. GPA sinus entity from an intracranial entity protruding manifests with clinical features of chronic rhinitis into the sinuses. and renal failure and histologic features of granu- Sinonasal cavity malignancies include squa- lomatous necrotizing inflammation. Imaging may mous cell carcinoma (SCC), lymphoma, sino- show mucosal nodularity of the nasal cavity, septal nasal undifferentiated carcinoma, and esthesio- destruction, erosions, and osteoneogenesis (39). neuroblastoma. The clinical symptoms of nasal Sarcoidosis may show similar nonspecific findings stuffiness, nasal discharge, and headache overlap on nonenhanced head CT images. with the symptoms of benign sinonasal entities. Special care should be taken to evaluate SCC is the most common sinonasal malignant the PNS on nonenhanced head CT images in tumor and will manifest as a masslike destruc- RG • Volume 39 Number 4 Bello et al 1179

Figure 14. Axial nonenhanced CT images of the head show various traumas in four patients. (a) Image shows a type III left occipital condyle fracture (arrowheads). (b) Image shows hyperattenuating blood products (arrowhead) in the prepontine cistern in a patient with no other intracranial hemorrhage. (c) Image shows a tympanic plate fracture (arrowhead). (d) Image shows a dislocated right mandibular condyle (arrowhead) in a patient who was found unconscious. Note the normal position of the left mandibular condyle within the mandibular fossa.

tive soft-tissue lesion. Esthesioneuroblastoma is tine foramen, with the propensity to reoccur. CT a neuroectodermal neoplasm, most commonly images classically depict widening of the PPF and located in the nasal cavity olfactory recess, sphenopalatine foramen, with anterior bowing of which may be isolated to the nasal cavity. Its the posterior maxillary sinus wall (Holman-Miller findings include olfactory recess widening and sign). In addition, these masses can extend into cribriform plate extension, which help differen- the orbit and MCF (14,15,42). tiate it from other benign nasal entities (41). Olfactory groove meningiomas may extend Juvenile nasopharyngeal angiofibromas are through the cribriform plate into the ethmoid si- benign locally aggressive tumors diagnosed in nuses and nasal cavity. On CT images, classic fea- adolescent boys that arise from the sphenopala- tures include depict hyperostosis, dural thickening, 1180 July-August 2019 radiographics.rsna.org and bone remodeling (6,14,15). Benign osseous lesions include fibrous dysplasia, a fibro-osseous lesion that can affect any bone, can be mono- or polyostotic, and can have a ground-glass appearance at CT. Osteomas are slow-growing osteogenic lesions composed of mature bone. They are hyperattenuating at CT and most commonly manifest in the frontal and ethmoid sinuses (14,42,43).

Orbit The contents of the orbit and the potential for complications are extensive. Traumatic entities should not be missed at emergent imaging. They include subtle traumatic globe rupture, radiopaque or lucent ocular foreign bodies, lens dislocation, intraorbital hemorrhage or detach- ments (retinal, choroidal, or vitreous), retrobul- bar hematomas, and orbital floor fractures. Orbital infection is usually apparent clinically, Figure 15. Parotid gland mass in a patient who pre- but the identification of postseptal extension or sented with seizure. Axial nonenhanced CT image of the head shows an incidental small left parotid mass (ar- subperiosteal abscess is extremely important, rowhead), later diagnosed as a benign Warthin tumor. although these can be difficult to visualize on routine nonenhanced head CT images. Exophthal- mos, PNS opacities, sinus wall thinning or dehis- evaluations with contrast-enhanced MRI of the cence, and postseptal orbital fat inflammation are orbits are critical for a correct diagnosis. findings that can help direct the identification of Vascular lesions are common, accounting for these sometimes-thin abscesses and determine if up to 20% of orbital masses (44). Most of these additional imaging is needed. are incidental slow-growing lesions, with a sub- Acute manifestations of thyroid orbitopathy can acute to chronic time course. The main vascular mimic periorbital cellulitis. Usually, the patient lesions the radiologist should not overlook are has a clinical history of thyroid orbitopathy, and orbital varices or enlargement of the superior nonenhanced head CT is performed for other ophthalmic vein from a cavernous carotid fistula reasons. Therefore, it is important to avoid incor- or cavernous sinus thrombosis. rectly diagnosing this population with cellulitis. The radiologist should remember the mnemonic Parotid Space for expected extraocular muscle involvement, The parotid space houses the parotid gland, “I’M SLO,” with enlargement progressing from lymph nodes, retromandibular vein, and cranial the inferior rectus, medial rectus, superior rectus, nerve VII (7–10). lateral rectus, and oblique muscles, in that order Parotid gland inflammation will appear as (44). A normal muscle thickness ranges from 3 to an area of abnormal attenuation and indistinct 6 mm (45). borders, with stranding of the adjacent fat planes Orbital and ocular neoplastic processes include and possible thickening of the deep cervical fascia. primary neoplasms such as choroidal melanoma, Parotitis has many possible causes, including optic nerve sheath meningiomas, lacrimal gland systemic infectious processes such as mumps (eg, lymphoma, and adenoid cystic carcinomas. the epidemic form that most commonly manifests Intraorbital metastasis should not be overlooked, in children), HIV infection, catscratch disease, and especially if the patient has been diagnosed with syphilis. Often, this finding will be bilateral. basal cell or squamous cell skin cancer or breast or Acute bacterial sialadenitis is usually unilat- renal carcinomas (44). eral and can be a result of sialoliths blocking the Orbital pseudotumor or immunoglobulin G4– gland’s ducts, which will appear dilated on CT related orbitopathy classically manifests with pain- images. Parotid gland abscesses are hypoattenu- ful exophthalmos. However, an incomplete patient ating fluid collections within the gland. Nonin- history or history of headaches can misguide the fectious parotitis can be secondary to sarcoid- radiologist. The appearance of orbital pseudotumor osis, radiation therapy, and Sjögren disease. In can mimic other neoplastic processes of the orbit these chronic conditions, the gland may appear but can be as understated as ill-defined soft tissue atrophied and replaced by fat. at the orbital apex, which can easily be missed. Re- Parotid gland neoplasms are difficult to dif- viewing the clinical history and performing further ferentiate on nonenhanced CT images (46). RG • Volume 39 Number 4 Bello et al 1181

They include benign neoplasms such as pleo- diagnostic intracranial angles. AJR Am J Roentgenol 2013;200(2):400–407. morphic adenoma (the most common salivary 12. Som PM, Curtin HD. Head and neck imaging. St Louis, gland tumors) and lymphomatous papillary Mo: Mosby, 2003. cystadenomas (Warthin tumor), a well-defined 13. Degnan AJ, Levy LM. Pseudotumor cerebri: brief review of clinical syndrome and imaging findings. AJNR Am J heterogeneous solid and cystic lesion that can Neuroradiol 2011;32(11):1986–1993. be multifocal and bilateral in up to 20% of cases 14. Parmar H, Gujar S, Shah G, Mukherji SK. Imaging (Fig 15). Malignant parotid neoplasms include of the anterior skull base. Neuroimaging Clin N Am 2009;19(3):427–439. mucoepidermoid carcinoma and adenoid cystic 15. Raut AA, Naphade PS, Chawla A. Imaging of skull base: carcinoma, which may affect the intraparotid pictorial essay. Indian J Radiol Imaging 2012;22(4): facial nerve and cause perineural spread (46). 305–316. 16. Mafee MF, Tran BH, Chapa AR. Imaging of rhinosinusitis Purely cystic parotid gland lesions include and its complications: plain film, CT, and MRI. Clin Rev first branchial cleft cysts, simple sialocysts, and Allergy Immunol 2006;30(3):165–186. benign lymphoepithelial lesions, commonly seen 17. Dankbaar JW, van Bemmel AJ, Pameijer FA. Imaging findings of the orbital and intracranial complications of acute bac- in patients with HIV infection and in association terial rhinosinusitis. Insights Imaging 2015;6(5):509–518. with cervical lymphadenopathy and adenoid tis- 18. Aggarwal SK, Bhavana K, Keshri A, Kumar R, Srivastava sue enlargement. A. Frontal sinus mucocele with orbital complications: management by varied surgical approaches. Asian J Neurosurg 2012;7(3):135–140. Conclusion 19. Ludi EK, Rohatgi S, Zygmont ME, Khosa F, Hanna TN. Pathologic entities located in and around the Do radiologists and surgeons speak the same language? A retrospective review of facial trauma. AJR Am J Roentgenol skull base can be easily overlooked on non- 2016;207(5):1070–1076. enhanced head CT images in the emergency 20. Bhatt AA, Hunsaker J, Kalina P. Pearls and pitfalls of pe- department. Understanding the patient’s clini- diatric head trauma imaging. Applied Radiology. https:// www.appliedradiology.com/articles/pearls-and-pitfalls-of- cal history and identifying discordant patient pediatric-head-trauma-imaging. Published 2014. Accessed symptoms or red flags can prompt the radiolo- January 17, 2018. gist to rereview the first few images of a CT 21. Karantanas AH, Komnos A, Paterakis K, Hadjigeorgiou G. Differences between CT and MR imaging in acute closed examination. A systematic checklist will aid in head injuries. CMIG Extra Cases 2005;29(1):1–8. identifying alternative diagnoses related to the 22. Gean AD, Fischbein NJ, Purcell DD, Aiken AH, Manley skull base, and every attempt should be made to GT, Stiver SI. Benign anterior temporal epidural hematoma: indolent lesion with a characteristic CT imaging appearance incorporate this process into routine practice. after blunt head trauma. Radiology 2010;257(1):212–218. 23. Osborn AG, Preece MT. Intracranial cysts: radiologic- pathologic correlation and imaging approach. Radiology References 2006;239(3):650–664. 1. American College of Radiology. ACR–ASNR–SPR practice 24. Bron LP, Traynor SJ, McNeil EB, O’Brien CJ. Primary and parameter for the performance of computed tomography metastatic cancer of the parotid: comparison of clinical be- (CT) of the brain. https://www.acr.org/-/media/ACR/Files/ havior in 232 cases. Laryngoscope 2003;113(6):1070–1075. Practice-Parameters/CT-Brain.pdf. Published March 24, 25. Géhanne C, Delpierre I, Damry N, Devroede B, Brihaye P, 2018. Accessed January 17, 2018. Christophe C. Skull base chordoma: CT and MRI features. 2. Riascos R, Bonfante E, Cotes C, Guirguis M, Hakimelahi JBR-BTR 2005;88(6):325–327. R, West C. Imaging of atlanto-occipital and atlantoaxial 26. Erdem E, Angtuaco EC, Van Hemert R, Park JS, Al-Mefty traumatic injuries: what the radiologist needs to know. O. Comprehensive review of intracranial chordoma. Radio- RadioGraphics 2015;35(7):2121–2134. graphics 2003;23(4):995–1009. 3. Maetani K, Namiki J, Matsumoto S, et al. Routine head 27. Keil MF, Stratakis CA. Pituitary tumors in childhood: update computed tomography for patients in the emergency room of diagnosis, treatment and molecular genetics. Expert Rev with trauma requires both thick- and thin-slice images. Neurother 2008;8:563–574. Emerg Med Int 2016;2016:5781790. 28. Jesser J, Schlamp K, Bendszus M. Pituitary gland tumors 4. van Straten M, Venema HW, Majoie CB, Freling NJ, Grim- [In German]. Radiologe 2014;54:981–988. bergen CA, den Heeten GJ. Image quality of multisection 29. Juliano AF, Ginat DT, Moonis G. Imaging review of the CT of the brain: thickly collimated sequential scanning versus temporal bone: part II—traumatic, postoperative, and thinly collimated spiral scanning with image combining. noninflammatory nonneoplastic conditions. Radiology AJNR Am J Neuroradiol 2007;28(3):421–427. 2015;276(3):655–672. 5. Connor SE, Flis C. The contribution of high-resolution 30. Little SC, Kesser BW. Radiographic classification of temporal multiplanar reformats of the skull base to the detection of bone fractures: clinical predictability using a new system. Arch skull-base fractures. Clin Radiol 2005;60(8):878–885. Otolaryngol Head Neck Surg 2006;132(12):1300–1304. 6. Policeni BA, Smoker WR. Imaging of the skull base: anatomy 31. Singh K, Singh MP, Thukral C, Rao K, Singh K, Singh and pathology. Radiol Clin North Am 2015;53(1):1–14. A. Role of magnetic resonance imaging in evaluation of 7. Netter FH. Atlas of human anatomy. Philadelphia, Pa: cerebellopontine angle schwannomas. Indian J Otolaryngol Elsevier Health Sciences, 2010. Head Neck Surg 2015;67:21–27. 8. Harnsberger HR. Diagnostic imaging: head and neck. Salt 32. Springborg JB, Poulsgaard L, Thomsen J. Nonvestibular Lake City, Utah: Amirsys, 2011. schwannoma tumors in the cerebellopontine angle: a 9. Harnsberger HR, Macdonald AJ. Diagnostic and surgical structured approach and management guidelines. Skull imaging anatomy: brain, head and neck, spine. Salt Lake Base 2008;18(4):217–227. City, Utah: Amirsys, 2006. 33. Kasliwal MK, Moftakhar R, O’Toole JE, Lopes DK. 10. Warshafsky D, Goldenberg D, Kanekar SG. Imaging High cervical spinal subdural hemorrhage as a harbinger anatomy of deep neck spaces. Otolaryngol Clin North Am of craniocervical arteriovenous fistula: an unusual clinical 2012;45(6):1203–1221. presentation. Spine J 2015;15(5):e13–17. 11. Shah LM, McLean LA, Heilbrun ME, Salzman KL. 34. Buyck PJ, De Keyzer F, Vanneste D, Wilms G, Thijs V, Intracranial hypotension: improved MRI detection with Demaerel P. CT density measurement and H:H ratio are 1182 July-August 2019 radiographics.rsna.org

useful in diagnosing acute cerebral venous sinus thrombosis. 40. Aribandi M, McCoy VA, Bazan C 3rd. Imaging features AJNR Am J Neuroradiol 2013;34(8):1568–1572. of invasive and noninvasive fungal sinusitis: a review. Ra- 35. Deliganis AV, Baxter AB, Hanson JA, et al. Radiologic spec- dioGraphics 2007;27(5):1283–1296. trum of craniocervical distraction injuries. RadioGraphics 41. Peckham ME, Wiggins RH 3rd, Orlandi RR, Anzai Y, Finke 2000;20(Spec issue):S237–S250. W, Harnsberger HR. Intranasal esthesioneuroblastoma: CT 36. Dreizin D, Letzing M, Sliker CW, et al. Multidetector CT patterns aid in preventing routine nasal polypectomy. AJNR of blunt cervical spine trauma in adults. RadioGraphics Am J Neuroradiol 2018;39(2):344–349. 2014;34(7):1842–1865. 42. Das S, Kirsch CF. Imaging of lumps and bumps in the 37. King AD, Wong LYS, Law BKH, et al. MR imaging criteria nose: a review of sinonasal tumours. Cancer Imaging for the detection of nasopharyngeal carcinoma: discrimina- 2005;5(1):167–177. tion of early-stage primary tumors from benign hyperplasia. 43. Earwaker J. Paranasal sinus osteomas: a review of 46 cases. AJNR Am J Neuroradiol 2017 Dec 28 [Epub ahead of print]. Skeletal Radiol 1993;22(6):417–423. 38. Glastonbury CM, Mukherji SK, O’Sullivan B, Lydiatt WM. 44. Grech R, Cornish KS, Galvin PL, et al. Imaging of adult Setting the stage for 2018: how the changes in the American ocular and orbital pathology: a pictorial review. J Radiol Joint Committee on Cancer/Union for International Cancer Case Rep 2014;8(2):1–29. Control Cancer Staging Manual eighth edition impact radi- 45. Ozgen A, Ariyurek M. Normative measurements of ologists. AJNR Am J Neuroradiol 2017;38(12):2231–2237. orbital structures using CT. AJR Am J Roentgenol 39. Pakalniskis MG, Berg AD, Policeni BA, et al. The many 1998;170(4):1093–1096. faces of granulomatosis with polyangiitis: a review of the 46. Yousem DM, Kraut MA, Chalian AA. Major salivary gland head and neck imaging manifestations. AJR Am J Roentgenol imaging. Radiology 2000;216(1):19–29. 2015;205(6):W619–W629.

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