Ameloblastoma

Ameloblastomas, also known as adamantinoma, are the second most common odontogenic tumor, accounting for up to a third of cases (odontoma is the most common odontogenic tumour of the mandible (see mandibular lesions)- almost two thirds of cases). They are benign locally aggressive neoplasms arising from ameloblasts, which typically occur at the angle of the mandible in the region of the third molar (48 and 38), often associated with dentigerous cysts and unerrupted teeth. Being slow growing they tend to present in the 3rd to 5th decade of life.

When in the maxilla (less common) it is located in the premolar region, and can extend up in the maxillary sinus.

It is classically multilocualted (80%), expansile bubbly "soap-bubble" lesion, with well demarcated borders and no matrix calcification. It erodes the adjacent tooth roots, a feature that is essentially unique to this entity. It may also erode through cortex into adjacent soft tissues.

Unicystic lesions are less common, and 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 later has an elevated risk of recurrence.

Smaller lesions demonstrate a characteristic enhancing mural nodule, best seen on MRI. Larger lesions have more prominent enhancing soft tissue.

Malignant degeneration into ameloblastic carcinoma (malignant histology) & malignant ameloblastoma (metastases with benign histology) is rare.

Differential diagnosis

• Dentigerous cyst - of note 20% of ameloblastomas are thought to arrise from preexisting dentigerous cysts. Dentigerous cyst will be centered around the crown.
• Odontogenic keratocyst
• Aneurysmal bone cyst
• Fibrous dysplasia