Solitary enchondroma to chondrosarcoma: Malignant degeneration

Observe the grossly expansile, primarily lytic lesion of the metaphysis and proximal diaphysis of the femur. There is characteristic stippled matrix calcification throughout the lesion (arrows). There is disruption of the cortex with the presence of a soft tissue mass on the medial surface of the femur (arrowheads). The radiographic signs of cortical disruption, a poor zone of transition surrounding the lesion, and a large soft tissue mass support the biopsy diagnosis of malignant degeneration of a pre-existing benign enchondroma to a secondary chondrosarcoma. Malignant degeneration of benign cartilaginous tumors occurs in bones closest to the axial skeleton and is much more common in the long tubular bones than in the small bones of the hands or feet.