Teaching Case

Pain, hypostenia hypothermia and paresthesia of left leg. CT and MR of lumbar spine

Hypostenia and pain of left leg, lasting 2 years. Aggravation of the symptoms in the last six months and onset of paresthesia and hypothermia. MR of lumbar spine was performed to establish the origin of the symptoms.

We present here a case of purely extradural schwannoma of the left L4 nerve root. Schwannomas (also known as neurinoma or neurilemmoma)are bening tumors arising from schwann cells. They represent the most common intradural extramedullary spinal neoplasm, accounting for 25%-30% of all the cases. Schwannomas are usually isolated tumors, with multiple tumors seen in 1%-55% of patients, mainly affected by neurofibromatosis type 2. They are more frequent in adults, usually between the age of 40 and 50 years old, rather than in children, and both sexes are equally affected, with only a slight predominance of the female gender. Schwannomas are lobulated, grossly encapsulated usually round or oval tumors. They grow eccentrically from the nerve they arise in, with the nerve fibers confined to the capsule. They mostly arise from the dorsal sensory roots, and can have an intradural (70%-75%), extradural (15%) or combined intradural and extradural localization (15%). They arise throught the spine, with a slight lumbar prevalence. The symptoms are often indistinguishable from disk herniation, with pain and radiculopathy being the most frequent symptoms; other symptoms are paresthesia and limb weakness. Schwannomas have a varying MR appearance: nearly 75% are isointense to spinal cord on T1 weighted images, 25% are hypointense, while the vast majority are hyperintense on T2 weighted images as it is the contrast enhancement. A cystic, hemorragic, or necrotic area can be seen. The differential diagnosis is with meningioma (especially with an intradural nerve root tumor. Conus and filum terminale ependymomas are sometimes indistinguishable from schwannoma, and other extramedullary neoplasm like epidermoid or dermoid tumor or metastasis should be considered. Causes of diffuse nerve root enlargement (benign hypertrophic neuropathies, metastasis, or non-Hodgkin lymphoma) can mimic a nerve root schwannoma, as can some benign conditions such as conjoined nerve roots, ganglion cysts, and disk herniation.