summary Neurilemmoma, also known as Schwannoma, are benign, encapsulated nerve sheath tumors composed of Schwann cells that occur on the surface of peripheral nerves. The condition usually presents in patients in the 3rd to 6th decades of life with paresthesias in the distribution of the peripheral nerve. Diagnosis is made with biopsy showing a lesion that is well encapsulated in a nerve sheath with histology showing verocay bodies. Immunostaining is positive for S100. Treatment is usually observation for asymptomatic lesions. Marginal resection is recommended in cases of progressive symptoms. Epidemiology Demographics peak incidence is in the 3rd to 6th decades previous test question ages: 40, 45 affect males and females equally Anatomic location tumor is well encapsulated on the surface of a peripheral nerve often occurs on flexor surfaces of extremities and head and neck larger lesions may occur in the pelvis Etiology Pathoanatomy can affect motor or sensory nerves Genetics often associated with mutations affecting NF2 gene Malignant transformation extremely rare Presentation Symptoms usually asymptomatic may have paresthesia in the distribution of the peripheral nerve Physical exam may have positive Tinel’s sign in the distribution of the nerve affected may be present Imaging MRI sequences low intensity (dark) T1 high intensity (bright) on T2 diffuse enhancement with gadolinium findings may show “string sign” difficult to differentiate from neurofibroma Histology Gross pathology the lesion is well encapsulated in a nerve sheath gray in color Histology Antoni A structure a pattern of spindle cells arranged in intersecting bundles (spindle cell battle formation) Antoni B areas with less cellularity with loosely arranged cells Verocay bodies pathognomonic composed of two rows of aligned nuclei in a palisading formation Immunochemistry strongly uniform S100 antibody staining Treatment Nonoperative observation indications asymptomatic lesions Operative marginal excision indications symptoms or interfering with quality of life technique nerve function may be preserved by careful dissection, excising the lesion parallel to the nerve fascicles so the lesion may be extruded. complications small risk of sensory deficits outcomes recurrence is rare
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