An osteochondroma-like lesion represents the beginning of juxtacortical osteosarcoma. This may be differentiated from simple osteochondroma by the irregular development of masses of connective tissue, fibrocartilage, and osteoid, in and on the cartilaginous cap of the lesion, and also by the appearance of more than a minimal amount of connective-tissue stroma in the marrow cavity of the bony stalk.