Extraskeletal osteosarcoma of the scalp.

A rare case of extraskeletal osteosarcoma of the scalp in a 56-year-old woman is described. At presentation she was found to have an 8-cm diameter, tender, firm, exophytic scalp tumor. MRI scan confirmed absence of underlying skeletal origin and showed extension along the subcutaneous plane. The tumor was excised and the patient received post-operative chemotherapy. Histologically, the tumor showed classical features of an osteogenic osteosarcoma with focal fibroblastic areas. In addition, there were rhabdoid cells present, which showed paranuclear cytoplasmic immunoreactivity for epithelial membrane antigen. The patient developed metastatic disease 6 months after surgical excision.