INTRAMEDULLARY SPINAL CORD LESIONS IN NF1 AND NF2

Sheila Kori

NF1

Most common neurocutaneous disorder, autosomal dominant

Pathophysiology: Mutation in or deletion of the NF1 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

NF1

Best Imaging Tool: MRI to evaluate for white matter lesions, visual pathway gliomas, and plexiform lesions

Imaging Findings: Hyperintense lesions on T2W1

White Matter lesions involve dentate nuclei of cerebellum, globus pallidus, thalamus, pons, midbrain, hippocampus

Visual pathway gliomas Sphenoid wing dysplasia Aneurysms and moyamoya

 

NF2

“MISME”: Multiple intracranial schwannomas, meningiomas, ependymomas

Pathophysiology: Mutations in the NF2 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 NF2 as a result of a new gene mutation.

Incidence: 1: 40,000

NF2

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: NF2 associated with ependymomas NF1 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. T1WI: Iso- to hypointense relative to the spinal

cord T2WI: hyperintense Average number of vertebral segments involved

= 7

Astrocytomas

MR T2 (left) and post Gd T1 (right) images show small, cystic, and enhancing astrocytoma.

Ependymomas

Ependymomas are slow growing, displace adjacent neural tissue, and arise from ependymal cells of central canal causing symmetric cord expansion.

T1WI: Iso- or hypointense relative to the spinal cord T2WI: 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 84% enhanced after administration of intravenous Gd-based

contrasts and (89%) had well-defined margins on post Gd images NF2 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 T2 (left) and post Gd T1 (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 T1WI Eccentrically located on axial and coronal images

Treatment: complete resection, often likely to cure

Intramedullary Schwannomas

MR sagittal (left) and axial (right) T2 images show well-defined, eccentric schwannoma in mid thoracic spinal cord.

References

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2. Ozawa N, Tashiro T, et al. Subpial schwannoma of the cervical spinal cord mimicking an intramedullary tumor. Radat Med. 2006; 24:690-694

3. 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

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