Malignant epithelioid schwannoma arising in a benign schwannoma. A case report.

A case of malignant epithelioid schwannoma arising in a benign schwannoma is described. The findings were supported by morphologic criteria as well as by a clinical history of recent growth of a long-standing mass adherent to the sciatic nerve, accompanied by evidence of metastatic spread. The light microscopic, ultrastructural, and immunohistochemical features are described, and the three previous cases of malignant change in benign neurilemmomas reviewed.