Revision 72 for 'Ameloblastoma'

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Ameloblastoma

Ameloblastomas are locally aggressive benign tumors that arise from the mandible, or, less commonly, from the maxilla. Usually present as a slowly but continuously growing hard painless lesion near the angle of the mandible in the 3rd to 5th decades of life, which can be severely disfiguring if left untreated. 

Terminology

The most common form of ameloblastomas - the multicystic form - were formerly known as adamantinomas of the jaw. However, ameloblastomas are unrelated histologically to adamantinomas of the bone, and this terminology should be avoided to avoid confusion.

Epidemiology

Ameloblastomas are the second most common odontogenic tumor (odontoma is the most common overall, but ameloblastoma is the most common lucent lesion) 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.

Clinical presentation

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.

Pathology

Unsurprisingly, ameloblastomas arise from ameloblasts, which are part of the odontogenic epithelium, responsible for enamel production and eventual crown formation. Four forms have been described in the literature: unicystic, solid (multicystic), desmoplastic, and peripheral (extraosseous).

Histology

There are no specific histological features to differentiate between ameloblastomas and craniopharyngiomas, with only location differentiating between two tumors 6.

Radiographic features

Panoramic radiograph and CT

Multicystic ameloblastomas account for 80-90% of cases which are classically expansile "soap-bubble" lesions, with well-demarcated borders and no matrix calcification. Occasionally erosion of the adjacent tooth roots can be seen. When larger it may also erode through cortex into adjacent soft tissues.

MRI

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 which is very helpful to distinguish them from other lucent lesions of the mandible.

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 and can be treated only by curettage:

  • 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:

  1. ameloblastic carcinoma
    • frankly malignant histology
  2. malignant ameloblastoma
    • metastases despite well differentiated 'benign' histology

Differential diagnosis

General imaging differential considerations include:

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