surface osteoma

Surface osteomas are relatively uncommon, asymptomatic, benign slow- growing bony tumors usually affecting the calvaria and facial bones.

Some osteomas appear on the outer surface of the calvaria as circumscribed, ivory-like excrescences composed of mature lamellar bone.

Similar surface osteomas on the long or flat bones are very rare and most likely initially diagnosed as surface osteogenic sarcoma.

However, microscopic examination will reveal only mature bone without any associated low-grade fibrous component and usually only non-descript adipose tissue in the marrow spaces.

Localization

Osteomas seen on the face are generally associated with the frontal and ethmoid sinuses, and are formed of dense immature woven bone, often with a central area characterized by fibrosis with active osteoblasts and osteoclasts.

The etiology of these facial osteomas is obscure; however, microscopically the lesion has a close kinship with osteoblastoma.

The lesion does not recur after surgical excision, and it is not associated with malignant change.

Synopsis

 ivory exostosis
 well-circumscribed nodular growth
 the lesion is composed of mature lamellar bone
 irregular heavily mineralized mass
 The lesion has a dense appearance.
 The lession is well demarcated from the adjacent cancellous bone.
 compact cortical bone

Gardner syndrome

Very rarely, this latter type of osteoma is associated with colonic polyps (Gardner’s syndrome).

Other disorders characteristically grouped with this syndrome are odontomas, supernumerary and unerupted teeth, and soft tissue tumors, including fibromas and epidermal inclusion cysts.

Gardner syndrome is an autosomal dominant genetic disorder, and it is of particular importance because of the malignant change that frequently occurs in the adenomatous intestinal polyps.

Gardner syndrome is associated with mutations on the APC gene on chromosome 5.

Examples

 mandibular osteoma

See also

 bone-forming tumors

• lamellar bone-forming tumors
• spongious bone-forming tumors