This site is targeted at medical and radiology professionals, contains user contributed content, and material that may be confusing to a lay audience. Use of this site implies acceptance of our Terms of Use.

Ameloblastoma

Dr MT Niknejad and Dr Frank Gaillard et al.

An ameloblastoma (previously known as an adamantinoma of the jaw) is a benign but locally agressive tumour arising from the mandible, or less commonly from the maxilla.

Epidemiology

Ameloblastomas are the second most common odontogenic tumour (odontoma is the most common) and account for up to a 3^rd of such cases.

They are slow growing and tend to present in the 3^rd to 5^thdecades 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 3^rd molar tooth (48 and 38) although they can occur anywere along the alveolus of the mandible (80%) and maxilla (20%). When the maxilla is involved, the tumour is located in the premolar region, and can extend up in 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 unerrupted teeth.

Pathology

Ameloblastomas (not surprisingly) arise from ameloblasts, (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

Radiographic features

Plain film and CT

It is classically seen as a multilocualted (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.

MRI

In general ameloblastomas demonstrate a mixed solid and cystic pattern, with a thick irregular wall, often with papillary solid structures projecting into the lesion. These components tend to vividly enhance.

Treatment and prognosis

Ameoloblastomas tend to be treated by surgical en-bloc resection. Local curettage is associated with a high rate of local recurrance (45 - 90%).

Simple unicystic lesions are less common but have a better prognosis. Simple (no nodule) variant will not be diagnosable on radiography, as it will be indistinguishable form 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 behaviour is seen in two forms ⁵:

ameloblastic carcinoma
- frankly malignant histology
malignant ameloblastoma
- metastases despite well differentiated 'benign' histology

Differential diagnosis

Considerations include

dentigerous cyst : the relationship between ameloblastomas and dentrigerous 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 indistiguishable
aneurysmal bone cyst (ABC)
fibrous dysplasia