Extraskeletal Ewing's sarcoma of the scalp.

A 15-year-old boy had an extraskeletal Ewing's sarcoma arising in the soft tissues of the scalp. The tumor was rapidly growing, subcutaneous mass unattached to the underlying bony structures. Histologic examination revealed a proliferation of primitive-appearing, round to oval cells adopting a lobular configuration. Immunohistochemical studies confirmed the undifferentiated mesenchymal nature of the neoplasm.