The actual occurrence of true osteoma is so debatable that this tumor is not included in the overall statistical data. Reactive changes from trauma, infection, or an invading tumor such as a meningioma can cause osseous overgrowth. Some bony outgrowths may represent an ancient osteochondroma, the cartilaginous cap of which is completely involuted. Because these tumefactions produce the clinical manifestations of a neoplasm, they are often erroneously called “osteomas.”

Occasional tumors of the skull, especially those involving the paranasal sinuses, are the most nearly bona fide osteomas, and yet there is room for conjecture regarding these. The gamut of fibro-osseous dysplastic lesions that affect these bones runs from soft, purely fibrous lesions to lesions that are heavily ossified. A few of the dense “ivory” osteomas contain softer zones of fibro-osseous dysplasia. Hence, there is no clear line of distinction between obviously dysplastic lesions and completely osseous tumors that one wants to call “true osteomas” (Figs. 8.1, 8.2, 8.3 and 8.4).

Rarely, a sessile ossified neoplasm found on the surface of a bone has the radiographic and pathologic features that relate it closely to the malignant tumor called parosteal osteosarcoma. This benign counterpart is regarded as a parosteal osteoma.

Skeletal osteomas of various bones, but predominantly involving the skull and jaws, are associated with intestinal polyps, fibromatous and other lesions of connective tissue, and epidermal cysts in Gardner syndrome.

The appearance of some lesions regarded as “solid” odontomas is such that they may be osteomas, because formed elements of tooth structure cannot be absolutely identified. It seems probable that dentin can become ossified.

The dense body overgrowths of the torus palatinus and the torus mandibularis are of unknown cause but can hardly be considered neoplastic, because they have very restricted growth potential. Similar reasoning applies to hyperostosis cranii.

The list of osteomas seen at Mayo Clinic is not complete. However, 147 cases were coded as such through 2003. Of these, only four involved the long bones. The rest involved the skull, the jawbones, and the sinuses. These lesions of the head may produce symptoms through deformity or even proptosis or may be incidental findings on radiographs. As indicated above, some of these lesions may be related to fibrous dysplasia.