INTRAMEDULLARY SPINAL CORD LESIONS IN NF 1 AND

INTRAMEDULLARY SPINAL CORD LESIONS IN NF 1 AND NF 2 Sheila Kori

NF 1 Most common neurocutaneous disorder, autosomal dominant Pathophysiology: Mutation in or deletion of the NF 1 gene, which encodes neurofibromin, leads to tissue proliferation and tumor development. The oligodendrocyte myelin glycoprotein is embedded in this gene which may be the cause of white matter lesions. Incidence: 1: 3, 000 -5, 000

NF 1 Best Imaging Tool: MRI to evaluate for white matter lesions, visual pathway gliomas, and plexiform lesions Imaging Findings: Hyperintense lesions on T 2 W 1 White Matter lesions involve dentate nuclei of cerebellum, globus pallidus, thalamus, pons, midbrain, hippocampus Visual pathway gliomas Sphenoid wing dysplasia Aneurysms and moya

NF 2 “MISME”: Multiple intracranial schwannomas, meningiomas, ependymomas Pathophysiology: Mutations in the NF 2 gene that encodes merlin which functions as a tumor suppressor. Results in decreased function or production of this protein causing development of tumors in the central and peripheral nervous systems. 50% of patients have NF 2 as a result of a new gene mutation. Incidence: 1: 40, 000

NF 2 Best Imaging Tool: Contrast enhanced MR Imaging Findings: Bilateral vestibular schwannomas Meningiomas and schwannomas involving CNs Spinal manifestations: meningiomas, ependymomas, and nerve sheath tumors

Intramedullary Tumors Intramedullary lesions are rare, 4 -10% of CNS tumors Are found more commonly in patients with neurofibromatosis: NF 2 associated with ependymomas NF 1 associated with astrocytomas Some reports of intramedullary schwannomas

Astrocytomas 75% are well-differentiated grade I, 25% are grade III (anaplastic) lesions Usually eccentrically located within the cord, since it arises from cord parenchyma, infiltrative Poorly defined margins, no cleavage plane Patchy enhancement after intravenous contrast material administration. T 1 WI: Iso- to hypointense relative to the spinal cord T 2 WI: hyperintense Average number of vertebral segments involved = 7

Astrocytomas MR T 2 (left) and post Gd T 1 (right) images show small, cystic, and enhancing astrocytoma.

Ependymomas are slow growing, displace adjacent neural tissue, and arise from ependymal cells of central canal causing symmetric cord expansion. T 2 WI: lesions may be isointense or hyperintense Most cases (60%) show cord edema around the masses Average number of vertebral segments involved = 3. 6 78%– 84% of ependymomas have at least one cyst T 1 WI: Iso- or hypointense relative to the spinal cord 84% enhanced after administration of intravenous Gd-based contrasts and (89%) had well-defined margins on post Gd images NF 2 patients with nonsense and frameshift mutations when compared with those of other types of mutations are more likely to have intramedullary tumors but not any other type of tumor.

Ependymomas MR T 2 (left) and post Gd T 1 (right) images show relatively well-defined cervical ependymoma.

Schwannomas Most commonly found locations: extradural or intradural extramedullary, however there have been about 60 reports of intramedullary schwannomas. Pathogenesis is unknown. Some theories include: 1. Central inclusion of Schwann cells during embryological development 2. Aberrant Schwann cells around intramedullary myelin fibers 3. Extension of Schwann cells along the intramedullary perivascular nervous plexus 4. Transformation of pial cells originating from neuroectoderm into Schwann cells 5. Tumoral growth of Schwann cells on a dorsal root located in a critical area corresponding to the point where the dorsal root loses its cover and enters the pia mater

Intramedullary Schwannomas Characteristics on MRI Well defined margins Uniform contrast enhancement on post Gd T 1 WI Eccentrically located on axial and coronal images Treatment: complete resection, often likely to cure

Intramedullary Schwannomas MR sagittal (left) and axial (right) T 2 images show welldefined, eccentric schwannoma in mid thoracic spinal cord.

References 1. 2. 3. 4. 5. 6. Barkovich JA. Diagnostic Imaging Pediatric Neuroradiology. 2007; I-8 -2 – I-8 -9 Ozawa N, Tashiro T, et al. Subpial schwannoma of the cervical spinal cord mimicking an intramedullary tumor. Radat Med. 2006; 24: 690 -694 Patronas NJ, Courcoutsakis N, Bromley CM, et al. Intramedullary and spinal canal tumors in patients with neurofibromatosis 2: MR imaging findings and correlation with genotype. Radiology 2001; 218: 434 Egelhoff JC, Bates DJ, et al. Spinal MR finding in neurofibromatosis Types 1 and 2. AJNR. 1992; 13: 1071 -1077 Koeller K, Rosenblum, SR, Morrison AL. Neoplasms of the Spinal Cord and Filum Terminale: Radiologic-Pathologic Correlation. Radio. Graphics 2000; 20: 1721– 1749 Lee M, Rezai, A, Freed D, Epstein F. Intramedullary Spinal Cord Tumors in Neurofibromatosis. Neurosurgery. 1996; 38: 32 -37