Epithelioid schwannomas of the acoustic nerve

Epithelioid schwannomas occur predominantly in relation to peripheral nerves and are associated with histological and clinical malignancy. However, a variant of the epithelioid schwannoma involving cranial nerves is extremely rare. In this study we report three cases of epithelioid schwannomas originating from the acoustic nerves and located in the cerebello-pontine angles. In the first case, the tumor was histopathologically entirely solid and demonstrated biphasic pattern with both spindle-shaped cells and a population of round or polygonal epithelioid cells. The second one consisted of the smaller part exhibiting typical Antoni B and A tissue and large areas containing clusters and bundles of epithelioid cells. Purely epithelioid schwannoma composed predominantly of cords or nests of round and polygonal epithelioid cells were observed in the third case. All schwannomas revealed marked polymorphism and nuclear hyperchromasia. Immunohistochemical studies showed a diffuse, strong positivity for S-100 protein in the cytoplasm of the spindle and epithelioid tumor cells. These two populations of cells were positively stained for vimentin, but were negative for EMA, cytokeratin and HMB45. Patchy GFAP-immunoreactivity was also noticed at the peripheral parts of the tumors. The authors discuss differential diagnosis of this unusual variant of schwannoma in relation to malignant transformation of the epithelioid component.