Nearly always histologically benign tumor consisting of ameloblast-like epithelial cells.

Is characterized by a high rate of recurrence. An ameloblastoma with histopathological malignant characteristics such as cellular or nuclear polymorphism, mitotic activity, and invasive growth is extremely rare. A histologically benign ameloblastoma may in rare instances metastasize to the cervical lymph nodes or to sites elsewhere in the body, being referred to as metastasizing ameloblastoma.

There are no known etiologic factors.

The estimated incidence is one per million population per year. Sometimes diagnosed at a young age. The average age at the time of diagnosis is around 30 years.

The tumor nearly always develops in the jaw bone (intraosseous ameloblastoma), probably from residual epithelium of the dental lamina. Occasionally the tumor arises from odontogenic epithelium of the alveolar mucosa (peripheral ameloblastoma).

An ameloblastoma is often diagnosed after histopathological evaluation of a lesion that clinicoradiographically looked like a cyst. Sometimes an ameloblastoma presents as an intraoral or extraoral swelling (Fig. 7.25a, b). Occasionally causes disturbed tooth eruption.

Unilobular or multilobular radiolucency, sometimes surrounded by a cortical line. May cause resorption of teeth (Fig. 7.26). Often expansion of the jaw bone. May mimic, a.o., a residual cyst, a follicular cyst, or a keratocystic odontogenic tumor (Fig. 7.27). Particularly in the upper jaw but also in the mandible, additional CT scans are required in order to get better information about the extent of the lesion and the integrity of the cortical plates of the jaw bones.

Almost all ameloblastomas are histopathologically benign. The diagnosis “malignant” ameloblastoma is justified only in case of cellular and nuclear polymorphism and/or mitotic activity. Most ameloblastomas are histopathologically easy to diagnose, especially in case of the common follicular type (Fig. 7.28). However, some histopathologic subtypes, such as the plexiform type and the granular cell type, may be difficult to recognize as such (Fig. 7.29). Furthermore, it may be difficult to distinguish an acanthomatous ameloblastoma from a squamous odontogenic tumor, another extremely rare but less aggressive odontogenic tumor.

The unicystic ameloblastoma is a rare variant, being characterized macroscopically as a cystic lesion and microscopically by a lining with ameloblastomatous epithelial cells (Fig. 7.30). The diagnosis “unicystic ameloblastoma” cannot be made on the basis of radiographic aspects.

The histopathological differential diagnosis of an ameloblastoma may include a number of other odontogenic, somewhat ameloblastoma-like tumors, such as the already mentioned squamous odontogenic tumor, the ameloblastic fibroma (Fig. 7.31), the ameloblastic fibrodentinoma, and the ameloblastic fibro-odontoma, having generally a less aggressive behavior than an ameloblastoma.

Note: in follicular tissue of impacted teeth, epithelial proliferations may occur that might be misdiagnosed histopathologically as part of an ameloblastoma (Fig. 7.32).

Preferably wide surgical excision with a margin of surrounding clinically normal bone, if necessary sacrificing the continuity of the mandible. In children a more conservative approach is perhaps justified; this possibly also applies to ameloblastomas that are located in the anterior part of the mandible or maxilla. Especially when located in the dorsal part of the mandible and the maxilla, radical removal has to be pursued, since a recurrence in that location will be difficult to treat successfully. Most recurrences after enucleation do so within a few years. Therefore, strict annual follow-up is indicated for, e.g., 10 years.

A benign tumor consisting of cementum.

Rare tumor; the estimated incidence is less than one per million population per year. Is usually diagnosed before the age of 25 years.

Usually relates to the mandibular molars. Fast-growing swelling, painful.

Well-circumscribed opacity attached to the root of a tooth (Fig. 7.33).

Cementum and cementum-like tissue attached to the root of a tooth (Fig. 7.34a, b).

Extraction or surgical removal of the tooth together with the attached cementoblastoma. Recurrences are not uncommon.

The diagnosis keratocystic odontogenic tumor (KCOT) is based exclusively on histopathologic criteria. In the past, the lesion was classified as an odontogenic cyst. Worldwide there is a debate among (oral) pathologists about the correctness of “upgrading” the odontogenic keratocyst to a keratocystic odontogenic tumor.

Intraoral or extraoral swelling; sometimes an incidental finding on a radiograph.

Unilobular or multilobular well-defined radiolucency (Fig. 7.35); sometimes expansion of the bone (Fig. 7.36). A KCOT rarely causes tooth resorption. The radiographic aspect is not pathognomonic and may resemble, a.o., a residual cyst, an ameloblastoma, a central giant cell lesion, and other odontogenic and non-odontogenic lesions.

Multiple KCOTs, not necessarily present simultaneously, are indicative of the hereditary basal cell nevus syndrome (Gorlin syndrome); the other aspects of this syndrome are, a.o., the presence of one or more bifid ribs, pits in the skin of the hand palms, calcifications of the falx cerebri, and, most important, multiple basal cell carcinomas of the skin, often located in the head and neck area and occurring already at an early age (Figs. 7.37, 7.38, and 7.39).

KCOT has characteristic histopathologic aspects consisting among others of an epithelial lining of 6–8 cell layers thick, palisade arrangement of the basal cells, corrugated surface of the epithelium, and a parakeratotic, often corrugated surface (Fig. 7.40a, b). The characteristic features may partly disappear when the cyst becomes secondary inflamed. In case of distinct hyperkeratosis, one is most likely dealing with a keratinizing odontogenic cyst (see before).

Enucleation and, if possible, removal of the overlying mucosa. In some cases marsupialization or decompression is to be preferred, usually requiring enucleation at a later stage. Some clinicians use the “fixation before and/or after enucleation technique,” applying Carnoy’s fixative solution before and/or after enucleation.

The recurrence rate of KCOTs depends on the extent of the surgical removal and may be up to 25 % or more during a follow-up period of five years after just enucleation. Because of the risk of recurrence, annual follow-up is advised for at least five years. Although the recurrence rate after enucleation is lower than in ameloblastomas, one may consider to perform radical surgery for KCOTs located in the posterior part of the jaws, particularly when located in the ascending ramus of the mandible since recurrences at that side may be difficult to treat successfully.

In case of suspicion of the basal cell nevus syndrome, referral to a department of clinical genetics is indicated.

Odontogenic tumor of mesenchymal tissue of the tooth bud.

The estimated incidence is less than one per million population per year. The tumor is usually diagnosed at the age of 20–30 years.

The odontogenic myxoma almost exclusively occurs within the bone of the upper or the lower jaw. Sometimes, the tumor gives rise to an intraoral or extraoral swelling, usually being asymptomatic otherwise.

Unilobular or multilobular radiolucency with sometimes a “honeycomb” aspect (Fig. 7.41); sometimes associated with an impacted tooth. The radiographic differential diagnosis includes, among others, ameloblastoma, keratocystic odontogenic tumor, central giant cell lesion, and a central arteriovenous malformation.

Circumscribed loose, fibromyxoid tissue containing stellate or sometimes rounded cells (Fig. 7.42). Cellular and nuclear polymorphism or mitotic activity is rarely observed. Sometimes the presence of nests of odontogenic epithelium, but this is not a requirement for the diagnosis of odontogenic myxoma.