Dedifferentiated parosteal osteosarcoma with rhabdomyosarcomatous differentiation

Dedifferentiated parosteal osteosarcomas are characterized histologically b y the combination of low-grade fibroblastic osteosarcoma admired with a hig h-grade component that typically has the appearance of malignant fibrous hi stiocytoma or osteosarcoma. Herein we report a case of dedifferentiated par osteal osteosarcoma of the distal femur, in which the high-grade component consisted of rhabdomyosarcoma. To our knowledge, a rhabdomyosarcomatous com ponent has not been described previously in a dedifferentiated parosteal os teosarcoma. The clinical, radiologic, and pathologic features of this rare type of surface osteosarcoma are described.