MRI of Conus Medullaris, Cauda Equina, and Filum Terminale Lesions Rami Eldaya, MD, MBA, Omar Eissa, MD, Gabriel Calles, MD, Jorge Lee-Diaz, MD, and Tomas Uribe, MD
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Volume 39 • Number 24 November 30, 2016 MRI of Conus Medullaris, Cauda Equina, and Filum Terminale Lesions Rami Eldaya, MD, MBA, Omar Eissa, MD, Gabriel Calles, MD, Jorge Lee-Diaz, MD, and Tomas Uribe, MD After participating in this educational activity, the radiologist should be better able to diagnose conus medullaris, cauda equina, and fi lum terminale lesions on MRI. Category: Neuroradiology Finally, the fi lum terminale, which is a fi ne strand of fi brous Modality: MRI tissue embedded in the cauda equina, is formed by a prolon- gation of the pia, and it extends from the conus medullaris to the termination of the thecal sac at the inferior border of S2. Key Words: Cauda Equina, Filum Terminale, Spinal Nerve Roots, Conus Medullaris Imaging Consideration Cauda equina is the Latin name for horse’s tail because The best way to assess the cauda equina is with MRI of the cauda equina resembles a horse tail. The cauda equina the lumbar spine with and without contrast medium. High- is a set of 10 paired dorsal and ventral nerve roots (20 nerve fi eld strength MR magnets (≥1.5 T) allow evaluation of the roots in total), corresponding to four lumbar (second to fi fth), nerves, their size, enhancement, and involvement by a path- fi ve sacral, and one coccygeal segments that originate from ologic process. the conus medullaris. These nerve roots are contained by the Pathology of the cauda equina can arise from a nerve root, thecal sac, which is an enclosed space formed by dura mater pia mater, or arachnoid space. The etiology can be primary and arachnoid extending from the head to the sacrum. The or secondary via direct or hematogenous spread of disease. conus medullaris is an expansion of the terminating distal Pathology can be classifi ed in multiple ways. A simple clas- thoracic spinal cord, typically located at the T12-L1 level. sifi cation into malignant, infl ammatory, vascular, infectious, and congenital is considered in this article. The purpose of As the cauda equina nerve roots exit the thecal sac at each this article is to review the most common pathologies of the level, they move in pairs to the lateral recess, which is a conus medullaris, cauda equina, and fi lum terminale with tubular refl ection of meninges located at the anterolateral emphasis on MRI fi ndings. portion of the thecal sac, and decline in number as they extend caudally from 20 nerve root pairs at L2-L3 to 11 nerve root Neoplastic pairs at L5-S1 and one coccygeal nerve root pair at S5-C1. Ependymoma. Ependymoma is the most common spi- nal intramedullary neoplasm in adults.1 The most common Dr. Eldaya is Resident, Dr. Eissa is Resident, Dr. Calles is Neuroradiology location is the cervical region, and only about 6.5% Fellow, Dr. Lee-Diaz is Resident, Department of Radiology, University of Texas Medical Branch, Galveston, Texas; and Dr. Uribe is Assistant Professor, involves the distal spinal cord or the conus medullaris. Department of Radiology, Baylor College of Medicine, One Baylor Plaza, Typically, patients initially present with mild symptoms MS360, Houston, RX 77555; E-mail: [email protected]. that often lead to a delay in diagnosis. Spinal cord ependymo- The authors and all staff in a position to control the content of this CME activity mas arise from ependymal cells that line the central canal, and their spouses/life partners (if any) have disclosed that they have no relation- ships with, or fi nancial interests in, any commercial organizations pertaining to which explains the central location and symmetrical appear- this educational activity. ance of ependymomas. Most spinal cord ependymomas Lippincott Continuing Medical Education Institute, Inc., is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. Lippincott Continuing Medical Education Institute, Inc., designates this enduring material for a maximum of 2 AMA PRA Category 1 Credits™. Physicians should only claim credit commensurate with the extent of their participation in the activity. To earn CME credit, you must read the CME article and complete the quiz and evaluation on the enclosed answer form, answering at least seven of the 10 quiz questions correctly. This continuing medical education activity expires on November 29, 2017. 1 CCDRv39n24.inddDRv39n24.indd 1 119/10/169/10/16 66:58:58 PPMM Figure 2. Schwannoma in a 43-year-old woman who pre- sented with chronic lower Figure 1. Ependymoma in a back pain. Sagittal, contrast 26-year-old woman with paresthe- en hanced, T1-weighted MR sia. Sagittal, contrast enhanced, image demonstrates an intra- T1-weighted MR image demon- dural, extramedullary, periph- strates intense enhancing mass erally enhancing cystic mass with enlargement and infi ltration (arrow) without evidence of a of the conus medullaris and cauda dural tail. Given location, equina fi lling and distending the cystic appearance, and lack of thecal sac at the upper lumbar dural tail, schwannoma was spine (arrow). Given location, suggested and confi rmed at appearance, and age of patient, surgery. myxopapillary ependymoma should be the primary considera- tion. Findings were confi rmed at Schwannoma. Schwannoma is the most common intra- surgery. dural, extramedullary spinal mass. It can present as an intra- dural, extramedullary mass (70%); transforaminal mass (15%); or extradural mass (15%). Most schwannoma are solitary are iso- or hypointense relative to the spinal cord on T1- (90%) and present within the fi fth or sixth decade. However, weighted sequences and iso- to hyperintense on T2-weighted when schwannomas are associated with neurofi bromatosis sequences. About 20% to 33% demonstrate the “cap sign,” type 2 (NF-2), they tend to present at a younger age. Imaging a hypointense rim (hemosiderin) seen at the poles of the depends on the cellular content of Antoni A (densely packed tumor on T2-weighted sequences. The cap sign is thought and arranged in fascicles) and Antoni B (loosely packed and to be secondary to hemorrhage. Most ependymomas more prone to cystic degeneration)2 (Figure 2). On T1-weighted exhibit enhancement on MR images. A special variant of images, schwannomas are typically iso- to hypointense relative ependymoma, the myxopapillary ependymoma (Figure 1), 1 to the spinal cord and nerve root. Typically, schwannomas are constitutes about 13% of all spinal ependymomas, and it hyperintense on T2-weighted sequences, and they can be cystic has been reported at all ages, with peak age at 30 to 40 and can contain blood products. years. These mucoid tumors arise from the ependymal glia of the fi lum terminale, and constitute the most common neoplasm in this region. Myxopapillary ependymomas are Spinal schwannomas present as an intradural, typically isointense relative to the spinal cord on extramedullary mass (70%); transforaminal T1-weighted images and hyperintense on T2-weighted mass (15%); or extradural mass (15%). images. Enhancement always is present on MR images. The cervical spinal cord is the most common Neurofi bromaրNeurofi bromatosis Type 1 site of spinal intramedullary ependymomas. Commonly related to neurofi bromatosis type 1 (NF-1), von Recklinghausen disease is an autosomal dominant The continuing education activity in Contemporary Diagnostic Radiology is intended for radiologists. EDITOR: Robert E. Campbell, MD, Clinical Professor of Radiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania Contemporary Diagnostic Radiology (ISSN 0149-9009) is published bi-weekly by Lippincott Williams & Wilkins, Inc., 16522 Hunters Green Parkway, Hagerstown, MD 21740-2116. Customer Service: Phone (800) 638-3030; Fax (301) 223-2400; E-mail: [email protected]. Visit our website at LWW.com. Publisher, Randi Davis. EDITORIAL BOARD: Teresita L. Angtuaco, MD Mary C. Mahoney, MD Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved. Priority Postage paid at Hagerstown, MD, and at George S. Bisset III, MD Johnny U. V. Monu, MBBS, Msc additional mailing offi ces. 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All comments are for general guidance only; professional coun- Radiology are protected by copyright. Reproduction, photocopying, and storage or transmission by magnetic or sel should be sought for specifi c situations. Indexed by Bio-Science Information electronic means are strictly prohibited. Violation of copyright will result in legal action, including civil and/or Services. criminal penalties. Permission to reproduce in any way must be secured in writing; go to the journal website (www.cdrnewsletter.com), select the article, and click “Request Permissions” under “Article Tools,” or e-mail [email protected]. Reprints: For commercial reprints and all quantities of 500 or more, e-mail reprint- [email protected]. For quantities of 500 or under, e-mail [email protected], call 866-903-6951, or fax 410-528-4434. 2 CCDRv39n24.inddDRv39n24.indd 2 119/10/169/10/16 66:58:58 PPMM Figure 3. NF-1 that had been clinically diagnosed in a 24-year-old man with lower extremity neuropathy. A: Sagittal, contrast enhanced, T1-weighted MR image dem- onstrates nodular enhancement of the enlarged nerve roots (arrows) at the cauda equina and the subcutaneous neurofi broma (circle).