"Undifferentiated" cerebral primitive neuroectodermal tumor in a young adult--case report.

A 21-year-old female presented with a cerebral primitive neuroectodermal tumor (PNET) without either glial or neuronal differentiation, who has survived for 27 months without neurological deficit following total removal of the tumor, radiotherapy, and intensive chemotherapy. Both immunohistochemical and ultrastructural studies are important for the diagnosis of PNET. "Undifferentiated" PNET may be a distinct entity from common PNET which shows either glial or neuronal differentiation or both.