Mandibular ameloblastoma with classic radiologic findings

Clinical History

A 43-year-old Hispanic male patient presented to the emergency department with a three-year history of a slow-growing, painless mandibular mass disfiguring facial contours.

Imaging Findings

Figures 1a and 1b: AP and oblique mandibular radiographs showing an expansile, multicystic, radiolucent lesion, with well-demarcated borders and cortical thinning near the left third molar tooth in the body of the mandible, showing a 'soap-bubble' appearance.
Figures 2a and 2b: Coronal and axial non-contrast CT images depicting erosion of the thinned cortex and extension into adjacent soft tissues.
Figure 3: Ultrasound colour Doppler evaluation reveals a mixed solid and cystic jaw lesion with papillary projections that show increased internal vascularity.
Figure 4: MRI images demonstrate a multilocular mass with solid/cystic pattern and irregular margins (Fig 4a) showing vivid enhancement (Fig. 4b and 4c). The arrow in Fig. 4c reveals erosion of the adjacent dental root. The left mandibular lesion demonstrates abnormally low ADC values and high signal on DWI representing restricted diffusion within solid components (Fig. 4d).

Discussion

Ameloblastoma originates from residual odontogenic epithelium, mainly from dental lamina that fails to regress during the embryological period. They are commonly described as polymorphic tumours with a follicular/plexiform pattern in a mature fibrous stroma without odontogenic ectomesenchyme. [1, 2, 3]

The WHO classifies ameloblastoma in four main variants: 1. solid/multicystic ameloblastoma, 2. unicystic ameloblastoma (both central tumours that develop within the bone), 3. peripheral/extraosseous ameloblastoma that develop on the alveolar mucosa and 4. desmoplastic ameloblastoma. [1] Although malignant transformation may occur it is rare (2-5%). Recognised variants of malignant transformation include: ameloblastic carcinoma, ameloblastic fibrosarcoma and malignant ameloblastoma. [1, 3, 4] In total these lesions account for 1% of oral tumours and 9-11% of odontogenic tumours. [2]

Clinically characterised as slow growing disfiguring masses, they are usually located near the angle of the mandible (third molar region) with 20% arising from the maxilla. They are most common in the third to fifth decades of age with almost equal distribution between genders. [5, 6]

Depending on their radiological appearance four patterns are described: unicystic, spider-web, soap-bubble/honey-comb and solid. [7]
Classic findings include: expansile, lucent uni- or multilocular cysts with variable thickness septa giving rise to a honey-comb, soap-bubble or bunch-of-grapes appearance. [5, 6]
Lesions can cause cortical destruction, invade surrounding soft tissues and erode adjacent dental roots (a characteristic denoting aggressive and malignant behaviour). [4] Computed tomography may give a better appreciation of cystic and solid areas that strongly enhance with intravenous contrast fluid. Tumours are often 2-8mm larger than they appear radiographically and the diagnosis is usually made when their size is >2 cm. [4, 5, 6] Magnetic resonance imaging aids by evaluating intra and extraosseous extension, with avid contrast enhancement in solid components including papillary projections, the wall and internal septa. [8]
Features suspicious of malignancy include: large solid enhancing component, papillary projections and extraosseous extension. [8]

Surgery is the mainstay of treatment. Options vary from enucleation or curettage to wide local resection including marsupialisation, cryotherapy and/or instillation of Carnoy’s solution. [9] Recurrence is common in solid/multicystic types, therefore bony excision margins should be 1-1.5 cm for ameloblastoma and 2-3 cm for ameloblastic carcinoma. [9, 10, 11] Partial maxillectomy with prosthesis, and osteomyocutaneous free flap reconstruction are reserved for aggressive tumours. [9, 10] Patients who are not candidates for surgery or with incompletely resected tumours may be considered for radiotherapy. [10] Chemotherapy has been attempted and platinum-based agents may improve clinical symptoms in non-surgical patients. [11]

Differential Diagnosis List

Final Diagnosis

Solid multicystic ameloblastoma of the mandible

URL:	https://www.eurorad.org/case/15243
DOI:	10.1594/EURORAD/CASE.15243
ISSN:	1563-4086