Osteochondroma

The solitary osteochondroma may be regarded as a true tumour; the lesion tends to be a painless, slowly growing mass and occurs most commonly in the long tubular bones, especially the femur, humerus and tibia; the small bones of the hand and foot; the innominate bone; and the spine and scapula.

On radiographs the tumour appears as a sessile or pedunculated bone protuberance arising from the external bone surface and containing spongiosa and cortex that are continuous with those of the parent bone (Fig.1). Typically, osteochondromas tend to point away from the nearby joint and toward the diaphysis. Widening of the metaphysis of tubular bones may be evident. At its tip the osteochondroma is covered by a cap composed of hyaline cartilage with a variable degree of calcification. A large and poorly defined cap with irregular calcification may indicate the possibility of malignant transformation. CT scanning and ultrasonography also may be useful in evaluating osteochondromas. Similarly, MR imaging can allow idenfitication of the cartilaginous tissue in the cap of an osteochondroma through its high signal intensity in T2-weighted spin-echo MR images, which may supply information relating to the likelihood of malignant change.

Among the complications of osteochondromas are fracture, bone deformity, vascular injury (arterial or venous stenosis), pseudoaneurysms, neurologic compromise such as from compression of the spinal cord or neve roots, bursa formation arround the tip of the lesion and malignant transformation.

DR/RB