Small-cell osteosarcoma.

Small-cell osteosarcoma, a subtype of osteogenic sarcoma, consists of sheets of round cells that produce an osteoid matrix. It may be confused with Ewing sarcoma if the osteoid matrix is not included in the biopsy. The distinctive radiographic features of an osteoblastic tumor and a pattern of permeative destruction will confirm the histologic diagnosis or indicate the true nature if tumor osteoid is not included in the histological sections. We add 13 patients to the 32 previously reported in the literature. Fourteen (31%) of the 45 are living and well, though three have been followed for only 2 months (Tables 1 and 2). The treatments have been so varied that a statistically significant evaluation cannot be developed. The radiographic features are not distinctive, but the diagnosis may be suggested when a tumor has osteoblastic features in the metaphysis and extends well down into the shaft with a pattern of permeative destruction. The radiographic features are especially important when limited biopsies reveal only sheets of round cells, thus suggesting Ewing sarcoma. The presence of an osteoid-producing tumor as evidenced by osteoblastic new bone formation will lead to the correct diagnosis.