Myositis ossificans is generally distinct from the cortex of the underlying bone. This may be best appreciated with cross-sectional imaging, such as CT.
In osteochondromas, the cortex of the exostosis blends with the cortex of the underlying bone; the marrow cavity of the lesion is continuous with the underlying bone marrow.
Parosteal osteosarcoma arises on the surface of the bone like a lump of plastacene.
Periosteal chondroma seems to arise within the cortex, erodes into the cortex, and expands outward into the soft tissues.
Periosteal osteosarcoma and chondrosarcoma generally have a soft tissue mass with matrix formation.
