Epiphyseal osteosarcoma: distinguishing features from clear cell chondrosarcoma, chondroblastoma, and epiphyseal enchondroma.

In a retrospective radiologic and histologic study of 286 osteosarcomas in files of a metropolitan hospital, four patients (three men and one woman) with osteosarcomas confined to the epiphysis were identified. In this series, there were also 16 metaphyseal osteosarcomas that extended to the epiphysis with penetration through the cartilaginous growth plate, a structure that ordinarily resists tumor growth. All tumors occurred in the femoral condyle. Characteristically, all four patients had histories of knee joint pain, and three reported antecedent trauma. Radiologically, the tumors showed predominantly lytic features. Histologically, three of the tumors were osteoblastic in type, and one was mostly chondroblastic. Purely epiphyseal osteosarcoma has overlapping radiologic features with clear cell chondrosarcoma, epiphyseal chondroblastoma, and epiphyseal enchondroma. The epiphyseal osteosarcomas of the distal femur reported here were characterized by a history of symptoms localized to the knee joint itself as a consequence of their epiphyseal location and joint involvement. This is in contrast to the usual metaphyseal osteosarcomas, which present with lower thigh pain and swelling. Because osteosarcomas may present as lytic tumors confined to the epiphysis, they should be included in the differential diagnosis of such lesions.