Radiographic hallmarks of peripheral chondrosarcoma.

Ten peripheral chondrosarcomas, nine arising in the cap of an osteochondroma and one developing as a primary periosteal tumor, are reported. The radiological and histological features of these tumors are compared with those of 203 benign osteochondromas and two soft-tissue chondrosarcomas. In 3 of the 10 cases, cytological evidence of malignancy could not be demonstrated, although the size of the tumors and the presence of extension into adjacent soft tissues indicated that they were low-grade chondrosarcomas. In all of the 10 cases there was radiological evidence of scattered calcifications in the cartilaginous part of the tumor, and this is regarded as an important radiological indication of malignancy. Histological studies indicate that calcification of tumor cartilage, followed by replacement of the calcified cartilage by endochrondral bone, is responsible for the opacities that, in clinical radiographs, are characteristic of chondrosarcoma.