Epithelioid Schwannoma of the acoustic nerve.

A 25-year-old woman presented with left progressive deafness due to an intracranial tumor of the cerebello-pontine angle. Biopsy and subsequent total surgical excision indicated origin from the acoustic nerve. Histologically, the tumor showed typical feature of Schwannoma associated with a population of epithelioid cells. Three years after surgery no local invasion, no relapse, and no metastasis were noted. Immunohistochemistry showed a strong positivity for S100 protein in the cytoplasm of Schwannian and epithelioid tumoral cell components. This positivity in the epithelioid cells correspond to a well differentiated cell population derived from a Schwann cell precursor explaining the benign course of the tumor. In the absence of similar cases of epithelioid Schwannoma of the acoustic nerve in literature, we will discuss the differential diagnosis, potential evolutivity, and origin of the epithelioid cells.