Non-tumor

  • Stress fracture
  • Fracture callus
  • Myositis ossificans

Benign

  • Osteochondroma
  • Periosteal chondroma

Malignant

  • Parosteal osteosarcoma
  • Periosteal osteosarcoma
  • Parosteal chondrosarcoma

Notes

  • 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.

Other Differential Diagnoses by Anatomic Location