Teaching Case

A 75-year-old man presented with a visible painless bulge over the anterior right mandible, which had been growing for several years, causing slight facial asymmetry. There was no past history of head and neck malignancy or surgery, including dental surgery.

The orthopantomogram shows a large lucent expansive lesion with lobulated margins in the mandibular body (Fig.1). There is no root resorption of adjacent teeth.
CT bone window images (Fig. 2), demonstrate an expansile hypodense lesion in the body of the mandible, with thinning of the cortex and at least two loculations. The more anterior loculation causes disruption of cortical bone and protrudes into vestibular soft tissues. Soft tissue window images (Fig. 3) show the anterior loculation/cystic extension to better advantage, allowing the visualization of a peripheral enhancing septum.
MRI could unfortunately not be performed as the patient was claustrophobic.
The lesion was biopsed which allowed a definitive diagnosis.

Lesions developing within the jaw can develop from any tissue including dental elements, bone, nerves, or blood vessels. Odontogenic tumours represent 9% of all tumours of the oral cavity [1]. Odontogenic tumours are designated according to their origin, namely, from the crown (epithelial origin) or apex (ectomesenchymal origin).
An ameloblastoma is a benign epithelial odontogenic tumour that arises from ameloblasts (enamel-forming cells) [1, 2]. It has no gender predilection and demonstrates a peak incidence in the 3rd and 4th decades of life. Two-thirds occur before 40 years of age.
Ameloblastomas comprise 18% of odontogenic tumours; 81% are located in the mandible, and the remaining 19% in the maxilla. Half of the mandibular lesions are located in the molar regions.
These tumours are slow-growing, painless and can reach a considerable size; swelling is the most common symptom. Small lesions can be asymptomatic.
In the WHO classification published in 2005, ameloblastomas are classified into 4 types: solid/multicystic type, extraosseous/peripheral type, desmoplastic type, and unicystic type [1].
Although rare, the solid/multicystic ameloblastoma is the most common type and constitutes the second most common odontogenic tumour (after odontoma). They occur almost exclusively in the jaw, 80% in the mandible. These tumours tend to recur but there is no tendency to metastasize. Long-term follow-up is needed, as recurrence can occur more than 10 years after initial treatment [1].
Radiographically, an ameloblastoma is radiolucent and either multilocular or unilocular. The unilocular lesions occur most often in the maxilla. The multilocular form often has a bubble-like appearance. These tumours can vary in size from a small to a large cyst that causes extensive destruction of the jaw. The tumour tends to break through the cortex of the bone, with extension into adjacent soft tissues. There can be bony expansion, but there is no periosteal bone formation. Loss of the lamina dura, erosion of the tooth apex, and displacement of teeth are also common [3].
MR imaging findings include mixed patterns of solid and cystic components, irregularly thick walls, papillary projections, and marked enhancement of the walls and septa [4].
Treatment strategies remain predominantly surgical and vary from curettage to large en bloc excisions.
A malignant form of ameloblastoma accounts for 1% of lesions. They are classified as metastasizing ameloblastoma, which has no specific imaging features, and ameloblastic carcinomas, which can show irregular margins, rapid growth, cortical expansion with perforation and invasion of adjacent structures [1].