5-year-old boy with a clival mass.

Epithelioid sarcoma is a rare tumor originating from mesenchymal cells, usually involving the extremities of young adults and is found only sporadically in the head and neck region. Only one case involving the central nervous system has been described so far. We report a 5 year-old boy with a large solid, osteolytic lesion of the clivus with a wide soft tissue component expanding into the intracranial compartment and obliterating the prepontine cistern. Histopathological examination revealed epithelioid neoplastic cells with abundant eosinophilic cytoplasm, rounded nuclei and prominent nucleoli. Areas of geographic necrosis and numerous mitoses were present. Neoplastic cells immunostained for vimentin, cytokeratin, and epithelial membrane antigen (EMA). No immunostaining was observed for glial fibrillary associated protein (GFAP), S-100, PLAP, α-fetoprotein, CD 117, CD 34, CD 31, BAF-47 (INI1). The Ki67 proliferation index exceeded 40%. These histological findings favor a diagnosis of epithelioid sarcoma. This report adds epithelioid sarcoma to the differential diagnosis of both clival tumors and pediatric skull base tumors.