Osteochondroma (also known as exostosis) is the most common bone
tumor. This osseous excrescence often arises from the metaphyseal region of a
long tubular bone, such as the femur (70%) and tibia. This lesion can be
pedunculated or sessile in morphology. An osteochondroma characteristically
demonstrates marrow continuity with the underlying bone. Exostoses are rarely
symptomatic in an adult and are usually an incidental finding radiographically.
They are usually sporadic, but can be part of:
- hereditary multiple exostoses (HME): also known as diaphyseal aclasis
- Trevor disease: also known as dysplasia epiphysealis hemimelica
All osteochondromas have a cartilage cap, although this is typically thin. This cartilage cap provides the source of malignant degeneration and can be accurately assessed by MRI. A cartilage cap of >2 cm is indicative of malignant transformation and should be surgically resected. Radiographically, an interval increase in chondroid matrix, or the dissipation of previously seen chondroid matrix can indicate malignant transformation.