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Neuroradiology Case of the Week

Case 90

Ravinder Sidhu MD, Lawrence Buadu MD, and P-L Westesson MD, PhD, DDS

Clinical Presentation: A 44-year-old male presented with history of numbness in both legs.

Radiological Findings:  Sagittal T1-weighted MR image of the lumbar spine showed a well-defined isointense lesion in the region of filum terminale (Fig.1A). Sagittal T2-weighted MR image showed heterogeneous hyperintense nature of the lesion (Fig. 1B). Axial T2-weighted MR image revealed the central location of the lesion (Fig. 2).

Diagnosis: Spinal ependymoma (myxopapillary ependymoma)

Discussion: Spinal intramedullary neoplasms account for 4-10% of all central nervous system (CNS) tumors and about 2-4% of CNS glial tumors. Most spinal cord neoplasms are malignant, and 90-95% are classified as gliomas, which constitute ependymomas or astrocytomas. Ependymomas are the most common intramedullary glial tumor in adults, whereas astrocytomas are most common in children. Non-glial neoplasms constitute hemangioblastoma, paraganglioma, metastases, and lymphoma. Primitive neuroectodermal tumors are much less common. Cord ependymomas most commonly occur in the cervical region followed by the thoracic and lumbar region, respectively. However, the myxopapillary variant that contains abundant mucin is virtually always located along the filum terminale. Clinical symptom includes back or neck pain depending upon the site of tumor, sensory deficits, motor weakness and bladder or bowel dysfunction [1,2].
     Plain films of the spine may reveal scoliosis or canal widening with associated pedicle erosion. Myelography frequently reveals partial or complete block to the flow of contrast media. On CT scan, ependymomas may appear as iso to hyperdense lesions and enhance intensely after contrast administration [3]. Most spinal cord ependymomas are seen as centrally located, well-defined, iso-or hypointense relative to the spinal cord on T1-weighted and hyperintense on T2-weighted MR images. Enhancement is virtually almost always seen after the contrast administration. Myxopapillary ependymomas may appear hyperintense on T1-weighted MR image due to presence of abundant mucin and also are more prone to hemorrhage. Cysts may be seen in about 78-84% of ependymomas. Three distinct types of cysts have been described: (a) tumoral cysts; (b) rostral or caudal cysts; and (c) reactive dilatation of the central canal. The tumoral cysts are seen within the tumor itself as a result of degeneration, necrosis, and liquefaction, and show peripheral rim enhancement. The rostral and caudal cysts occur above and/or below the tumor and do not show rim enhancement. The reactive dilatation causing cyst-like appearances are most likely related to partial obstruction of the central canal by the tumor mass [4,5].
     Radiologically, astrocytoma is a close mimicker of ependymoma. Ependymomas are central in location since they arise from central canal ependymal cells, whereas astrocytomas are eccentric with infiltrating borders as they originate from the cord parenchyma. Findings such as hemorrhage within the tumor and hemosiderin deposition or calcification are more frequent in ependymomas due to rich connective tissue stroma. Contrast enhancement is also intense and homogenous in ependymomas whereas it is patchy and irregular in astrocytomas. Ependymomas especially the myxopapillary variety have particular predilection for conus medullaris which is not so in the case of astrocytomas. Ependymomas can be differentiated from hemangioblastoma by virtue of enhancing mural nodule, which is the hallmark of hemangioblastoma.

References:

1. Constantini S, Houten J, Miller DC et al. Intramedullary spinal cord tumors in children under the age of 3 years. J Neurosurg.1996; 85:1036-1043.
2. Epstein FJ, Farmer JP, Freed D. Adult intramedullary spinal cord ependymomas: the result of surgery in 38 patients. J Neurosurg. 1993; 79:204-209.
3. Ferrante L, Mastronardi L, Celli P, Lunardi P, Acqui M, Fortuna A. Intramedullary spinal cord ependymomas- a study of 45 cases with long-term follow-up. Acta Neurochir 1992; 119:74-79.
4. Kahan H, Sklar EM, Post MJ, Bruce JH. MR characteristics of histopathologic subtypes of spinal ependymoma. AJNR Am J Neuroradiol. 1996; 17:143-150.
5. Koeller KK, Rosenblum RS, and Morrison AL. Neoplasms of the spinal cord and filum terminale: radiologic-pathologic correlation. Radiographics 2000; 20:1721-1749.