Figure 8a. Lateral radiograph (a), CT scan (b), and sagittal MR image (c) demonstrate a large destructive lesion that involves a long segment of the femoral diaphysis, with cartilage matrix (small arrows in a, arrow in b). There is evidence of a permeative pattern of cortical destruction (large white arrows in a, arrows in c) with periosteal new bone formation (black arrow in a). A massive associated soft-tissue mass (large arrowheads in b, arrowheads in c) with scattered punctate foci of cartilage matrix (small arrowheads in b) are also seen. Size of the soft-tissue mass relative to the extent of destruction in a and the large unmineralized areas within the mass should suggest dedifferentiation in a malignant cartilage tumor. The dedifferentiated component proved to be osteoblastic osteosarcoma.