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Osteoma

Osteoma is a benign bony outgrowth of membranous bones. They are found mostly on skull and facial bones. Large osteomas may develop on the clavicle, pelvis, and tubular bones (parosteal osteomas). Soft tissue osteomas may occur in the head, eye,and tongue,or in the extremities. Osteomas are slow growing lesions that are normally completely asymptomatic. They only present if their location within the head and neck region is causing problems with breathing, vision, or hearing.

The highest incidence is in the sixth decade. Some authors report that osteomas occur more often in women than men (3:1). Multiple osteomas are associated with Gardner's syndrome. The etiology of osteomas is unclear. They may be related to osteoblastomas or may simply be a developmental anomaly. The fact they are often found in the auditory canals of swimmers and divers who frequent cold water suggests that in some cases they are some type of inflammatory reaction.

The radiological appearance of osteomas depends on their location. Central osteomas are well delineated sclerotic lesions with smooth borders, without surface irregularities or satellite lesions. Dr. Enneking describes the lesion as having the appearance of "one-half of a billiard ball" attached to the underlying bone. The adjacent cortex is not involved or weakened. Peripheral osteomas are radiopaque lesions with expansive borders that may be sessile or pedunculated. Osteomas need to be differentiated from enostosis which also appear as densely sclerotic well-defined lesions on x-ray.

Bone scan will show increased uptake during the active phase of growth, which will diminish to background levels as the lesion becomes progressively less active.

There are two types of osteomas microscopically. Compact or "ivory" osteomas are made of mature lamellar bone. They have no Haversian canals and no fibrous component. Trabecular osteomas are composed of cancellous trabecular bone with marrow surrounded by a cortical bone margin. Trabecular osteomas can be found centrally (endosteal) or peripherally (subperiosteal).

Treatment of osteomas is only necessary if they are symptomatic. Large osteomas should be evaluated to rule out other diagnoses. '

i Bulloughs, Peter, Orthopaedic Pathologv (third edition), Times Mirror International Publishers Limited, London, 1997.

Huvos, Andrew, Bone Tumors: Diagnosis, Treatment and Prognosis, W.B.Saunders, Co.,
1991.

Some text adapted from Dr. Enneking's site.¶