Ameloblastomas are benign, locally aggressive tumors that arise from the mandible, or less commonly from the maxilla. Usually presented as a hard painless lesion near the angle of the mandible in the 3rd to 5th decades of life.
On imaging, they are commonly identified as a well-defined, expansive, and multiloculated ("soap bubble") lesion in the posterior mandible
Ameloblastomas were previously known as adamantinomas of the jaw, although both conditions are unrelated histologically and the latter terminology should be avoided.
Ameloblastomas are the second most common odontogenic tumor (odontoma is the most common) and account for up to one-third of such cases.
They are slow growing and tend to present in the 3rd to 5th decades of life, with no gender predilection 4.
Ameloblastomas typically occur as hard painless lesions near the angle of the mandible in the region of the 3rd molar tooth (48 and 38) although they can occur anywhere along the alveolus of the mandible (80%) and maxilla (20%). When the maxilla is involved, the tumor is located in the premolar region, and can extend up into the maxillary sinus.
Although benign, it is a locally aggressive neoplasm with a high rate of recurrence. Approximately 20% of cases are associated with dentigerous cysts and unerupted teeth.
Unsurprisingly, ameloblastomas arise from ameloblasts, which are part of the odontogenic epithelium, responsible for enamel production and eventual crown formation.
Three variants are described:
- simple (no nodule): best prognosis
- luminal: single nodule projecting into the cyst
- mural: multiple nodules (often only microscopic) in the wall of the cyst
There are no specific histological features to differentiate between ameloblastomas and craniopharyngiomas, with only location differentiating between two tumors 6.
Panoramic radiograph and CT
It is classically seen as a multiloculated (80%), expansile "soap-bubble" lesion, with well-demarcated borders and no matrix calcification. Occasionally erosion of the adjacent tooth roots can be seen which is highly specific. When larger it may also erode through cortex into adjacent soft tissues.
In general, ameloblastomas demonstrate a mixed solid and cystic pattern, with a thick irregular wall, often with solid papillary structures projecting into the lesion. These components tend to enhance vividly.
Treatment and prognosis
Ameoloblastomas tend to be treated by surgical en-bloc resection. Local curettage is associated with a high rate of local recurrence (45-90%).
Simple unilocular lesions are less common but have a better prognosis. Simple (no nodule) variant will not be diagnosable on radiography, as it will be indistinguishable from other more common cysts. Luminal variant, has a single nodule projecting into the cyst. Mural variant has multiple nodules (often only microscopic) in the wall of the cyst. The latter has an elevated risk of recurrence.
Malignant behavior is seen in two forms 5:
- frankly malignant histology
- metastases despite well differentiated 'benign' histology
General imaging differential considerations include:
- dentigerous cyst: the relationship between ameloblastomas and dentigerous cysts is a controversial one, 20% of ameloblastomas thought to arise from pre-existing dentigerous cysts
- odontogenic keratocyst (OKC): usually unilocular with thin poorly enhancing walls
- odontogenic myxoma: can be almost indistinguishable
- aneurysmal bone cyst (ABC)
- fibrous dysplasia