Hamartomas are tumorlike malformations characterized by the presence of a cellular proliferation that is native to the part but that manifests growth cessation without potential for further growth.On the one hand, hamartomas are to be distinguished from malformations such as extra digits, supernumerary teeth, and ectopic salivary gland tissue, in which excessive tissue is present in its usual histologic relationship. On the other hand, hamartomas are to be distinguished from true benign tumors that have a relatively unlimited capacity for expansive growth (which may continue after the exciting agent has ceased to operate).
Hamartomas are usually congenital and have their major period of growth when the rest of the body is growing. Once they have achieved their adult dimensions, they do not extend to involve more tissue and rarely increase in size unless trauma, thrombosis, or infection cause edema, inflammatory infiltration, and filling of new vascular channels. They are also to be distinguished from the excessive proliferation of reparative tissue described earlier in this chapter (see “Inflammatory [Reactive] Hyperplasias”) and are usually easily separated histologically from such lesions. Hamartomas are found in many tissues of the body, and a tendency to such malformations is often hereditary. Individual oral hamartomas, therefore, often occur in association with other gross and microscopic developmental abnormalities that assist considerably in their diagnosis.
Hemangioma (both solitary and when found in association with other developmental anomalies in the various angiomatosis syndromes), lymphangioma, glomus tumor, nevi, granular cell tumor of the tongue and granular cell epulis, neuromas of the type III multiple endocrine neoplasia (MEN III) syndrome, fibrous dysplasia of bone, cherubism, various odontomas, some odontogenic tumors, and (possibly) the melanotic neuroectodermal tumor of infancy are all examples of hamartomatous development in the oral region. To a greater or lesser extent, these lesions all possess the characteristics of hamartomas. These variants aside, the treatment of hamartomas is essentially a cosmetic problem, and the complete removal of these lesions is often neither desirable nor possible. Neoplastic and malignant transformation are unusual in hamartomas although some have a greater tendency in this regard (eg, neurofibromas; see “Nerve Sheath Tumors and Traumatic Neuroma,” below).
Teratomas (which are often thought of as malformations but which are actually neoplasms of developing tissues) are mentioned at the end of this section, in comparison with hamartomas (see “Teratomas and Dermoid Cysts,” below).