Osteoma

In some patients large, bulky osteomas may develop from the cortical surface of the clavicle, innominate bone and tubular bones (parosteal osteomas). Multiple osteomas of the mandible, calvaria or tubular bones can accompany Gardners syndrome. Osteomas can also develop in soft tissues, generally in the head (as in the posterior part of the tongue), but the tumours have been described in the thigh as well.

An osteoid osteoma is a benign osteoblastic tumour in which a central core of vascular osteoid tissue is surrounded by a peripheral zone of sclerotic bone. The femur and tibia are the most common sites of involvement; other sites include the bones in the hands and feet, vertebrae, innominate bone, skull, mandible or maxilla, clavicle, scapula, ribs and radius. In some patients involvement of the spine or adjacent ribs may result in scoliosis.

Osteoid osteoma has a classic radiographic appearance (centrally located, oval or round radiolucent area surrounded by a zone of uniform bone sclerosis) that is virtually diagnostic of this lesion (Fig.1). Nevertheless, modifications in this appearance occur according to the specific bone affected and the site within the involved bone. The appearance also varies according to whether the lesion occurs in the cortex, in cancellous bone or subperiosteally (Table 1).

Osteoma, Table 1. Radiographic appearance of osteoma and osteoid osteoma.

On bone scans, lesions of osteoid osteoma avidly accumulate bone-seeking radiopharmaceutical agents and exhibit a characteristic double density sign. CT scanning has largely replaced conventional tomography in the evaluation of osteoid osteomas. MR imaging, however, is generally considered less successful than CT scanning. On MR images findings of synovitis and joint effusion may accompany intra-articular osteoid osteomas.

DR