Ameloblastoma

Findings

CT images demonstrate an expansile cystic “bubbly” mass within the right mandibular body and extending into the ramus. Thin bony septations are seen within the lesion (Figure 1 and Figure 2). Marked thinning of the cortical margins is noted with focal areas of dehiscence (Figure 3). The margins are relatively well-defined with no significant infiltration of adjacent soft tissues. The tongue and medial soft tissue structures are displaced and pushed by this large soft tissue mass in the mandible (Figure 4).
Ill-defined enhancement is seen in the anteromedial aspect of the mass on postcontrast CT (Figure 5).


Diagnosis: Ameloblastoma


Ameloblastoma is a histologically benign, locally aggressive tumor arising from the odontogenic ectoderm. It arises from the enamel-forming cells of the odontogenic epithelium that have failed to regress during embryonic development. Ameloblastoma is the most common odontogenic tumor (representing 10% of all tumors in the maxillomandibular region).

The tumor most commonly occurs in the posterior mandible, typically in the third molar region, with associated follicular cysts or impacted teeth. The mandible is affected four times more frequently than the maxilla. Patients typically present in the third to fifth decades of life with a slow-growing, painless mass.

Ameloblastoma typically presents as a mixed cystic-solid mass in the posterior mandibular ramus associated with an unerupted 3rd molar tooth. The expansile, radiolucent tumor can be unilocular (20%) or multilocular (80%), with a characteristic "soap bubble–like" appearance. The slow growth of the tumor can lead to significant expansion of the mandible with an osseous shell that represents involved bone. The tumor can perforate the lingual cortex and spread to adjacent soft tissues. Erosion of the roots of adjacent teeth is unique to ameloblastoma and indicates aggressive behavior of the tumor.

MRI best defines the extra osseous extension and shows the multilocularity, mixed solid and cystic components, irregularly thickened walls, papillary projections, and marked enhancement of the walls and septa. Presence of nodular enhancement distinguishes ameloblastoma from large dentigerous cyst and odontogenic keratocyst.

The treatment of ameloblastoma is surgical excision with wide free margins. Appropriate reconstruction may be performed at the same time. Solid lesions show high recurrence rates (50% to 90%), necessitating tumor excision or partial resection of the jawbone. Although malignant transformation is rare (1%), repeated recurrences increase the likelihood of malignancy.