Ameloblastoma

Synonym / Acronym

Adamantinoma, central epithelioma, cystoma, chorioblastoma, embryoplastic odontoma, central papilloma of the jaws, proliferating cysts of the jaws, and epithelial odontomas.

Definition

Ameloblastoma is a benign, slowly growing, locally aggressive epithelial odontogenic neoplasm that contains ameloblasts that have differentiated from ectodermal epithelium. It arises from remnants of the dental lamina and enamel organ (odontogenic epithelium). It is one of the most frequently encountered neoplasm and it accounts for approximately 11% of all odontogenic tumors and has a high recurrence rate after surgical treatment. It can also occur from the epithelial lining of a dentigerous cyst; in which case; it is called a mural ameloblastoma.

Clinical Features

The average age for ameloblastoma is the fourth decade, but it can occur at any age. It has equally male to female ratio. It can occur anywhere in the mandible or maxilla but is seen most frequently in the mandibular molar region. It is usually painless in 80% unless secondary inflamed. Ameloblastoma is usually detected as incidental finding during routine dental exam as the patient notices a gradual jaw expansion producing facial asymmetry. There are 5 histologic patterns of ameloblastoma: the follicular (most common), plexiform, acanthomatous, basal cell, and granular cell type. Most commonly found are unicystic type and desmoplastic variant.

Radiographic Features

A multilocular cystic appearance is by far the most commonly seen although it can appear unilocular as well with round, oval or scalloped outline. It can be either totally radiolucent or radiolucent with septa. The internal septa are most commonly coarse and curved in outline. The septa give it a honey comb (small loculations) appearance which has been associated with the solid form as opposed to the cystic form of the lesion, or soap bubble (large compartments) appearance. Most of ameloblastoma occurs in the mandibular molar region but it can occur in the maxillary third molar region where it extends into the maxillary sinus and nasal floor. The margins are well-defined, usually corticated, and could be ill-defined as in the maxilla. It causes extensive root resorption and displacement of teeth. Ameloblastoma has considerable potential for bone expansion and causes a thin “eggshell” of cortical bone without breaking the cortex. Unicystic type may cause extreme expansion of the mandibular ramus. Ameloblastoma is smaller in size in the anterior mandible and larger if it is located in the posterior mandible.

Recurrent Ameloblastoma

Ameloblastoma has a high recurrence rate after surgical treatment. Recurrent ameloblastoma appears as multiple small cystic like spaces surrounded by a band of sclerotic bone. These spaces may be separated by what appears to be normal bone.

Imaging Techniques

Although the appearance on cone beam computed tomography (CBCT) is essentially the same as in plain films, CBCT is highly recommended to help better define and assess the periphery and relationship to the surrounding structures. CBCT can detect also if there is perforation in the outer cortex. If soft tissue invasion is extensive, magnetic resonance imaging (MRI) can provide superior images of the extension and nature of the lesion. T1-weighted images have intermediate signal and T2-weighted images have intermediate to high.

Differential Diagnosis

The lesion can occur from the epithelial lining of a dentigerous cyst which surrounds the crown of tooth makes it hard to differentiate ameloblastoma from dentigerous cyst if no septa are present. Other lesions that might have septa include keratocystic odontogenic tumor, central giant cell granuloma, odontogenic myxoma, and ossifying fibroma. Cystic ameloblastoma causes expansion more than it is commonly seen in keratocystic odontogenic tumor as KCOT tends to grow along the bone rather than expanding it. CGCG has granular ill-defined septa, affect younger individuals group and usually located anterior to the molars. Odontogenic myxoma has less expansion than ameloblastoma and their septa are thin, sharp and straight. It is always important to examine the epithelial for removed dentigerous for possible presence of ameloblastoma. It differs from fibro-osseous lesions in that it retains thin cortical borders.

Treatment

Surgical resection is the most common treatment. Wide margins resection is usually carried out due to the tendency of the neoplasm to invade adjacent beyond what it is seen on radiographs and high recurrence rate. CBCT or MRI can help better delineate the true margins of the lesion. If the lesion is small then it can be removed without resecting the jaw. If the lesion invades the maxilla; it is treated more aggressively due to the tendency of the lesion to invade vital structures. Radiation therapy may be done for inoperable tumors in the posterior maxilla.

Case Reports

HISTORY: A 12-year-old male was referred for a Cone Beam CT scan to evaluate the extent of an anterior mandibular lesion.


FINDINGS: There is a well-defined radiolucent lesion. The lesion is corticated in some areas and extending from the inter-radicular area of teeth #28-29 to the distal aspect of #24. The lesion extends from the alveolar crest of teeth #24-25 superiorly to the middle length of the mandible inferiorly. There is facial expansion and thinning of the cortical plate. There are no signs of septations or an internal architecture. The lesion is close to the mental foramen but does not encroach on it. The lesion has caused teeth displacement.


IMPRESSION: The characteristic of the lesion is consistent with a moderately aggressive benign neoplastic process with cystic characteristics.





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HISTORY: A 29-year-old female was referred for a Cone Beam CT scan for evaluation of the right mandibular body and ramus for odontogenic cyst/tumor and relationship to the mandibular canal.


FINDINGS: There is a well-defined radiolucent lesion in the right posterior mandible. The lesion starts from the distal aspect of root for tooth #30 and extends posteriorly and superiorly to involve the ramus area. There appears to be slight root resorption associated with tooth #31. The right mandibular canal is displaced inferiorly and facially. The lesion is expansile and there is thinning of cortical borders.


IMPRESSION: The slight roots resorption and expansion favors ameloblastoma (unicystic or mural); however, KCOT can be included in the differential diagnosis. CGCG is a possibility but it is less likely.




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