PRIMARY INTRACEREBELLAR OSTEOSARCOMA ARISING WITHIN AN EPIDERMOID CYST

The authors report a case of a primary extraskeletal osteosarcoma aris ing within an epidermoid cyst in the parenchyma of the cerebellum in a 64-year-old woman. On initial presentation, the tumor involved the mi dline cerebellum without attachment to the surrounding dura mater or c alvarium. Complete medical and radiologic evaluation failed to reveal a primary skeletal or other extraskeletal osteosarcoma. To our knowled ge, this is the first reported case of a primary extraskeletal osteosa rcoma within the cerebellum. Osteosarcoma as a primary brain tumor is exceedingly rare, and only three cases (all occurring within the cereb ral hemispheres) have been reported previously. The histogenesis of pr imary sarcomas of the brain is not evident. The associated finding of an epidermoid cyst suggests the tumor originated from a teratoma.