Ameloblastoma (Adamantinoma)

General: Comprising approximately 1% of all jaw tumors & cysts, it affects males and females of all ages (mean of ~35yo) and is slow growing but locally aggressive (~30% recurrence) with rare metastases to lungs or CNS. The unicystic variant more commonly affects a younger population, mean age 25yo., and is more common in males. The peripheral variant is the most rare, occurring in the oldest population (mean of ~50yo), are entirely extraosseous, and have been successfully treated with simple excision with a soft-tissue margin. Arises from ameloblast of dental lamina, dentigerous cysts, or basal layer of oral mucosa.

Gross: Solid and cystic; solid areas are white to gray with minimal or no hemorrhage or necrosis. May be multicystic, more rarely unicystic. May be intraosseous or extraosseous. Usually associated with an impacted tooth.

Radiology: Multiloculated lytic, expansile, radiolucent lesion. Approximately 80% are located in the posterior mandible, while ~20% are in the posterior maxilla and make for difficult surgical excision.

Microscopic: Composed of palisading columnar basal cells with vacuolated cytoplasm, hyperchromatic nuclei polarized away from basement membrane, suprabasal cells that are loosely textured and noncohesive, resembling stellate reticulum, and no enamel or dentin formation. Mitoses are rare or absent. Presence of an infiltrative border is a significant negative prognostic feature. There are several distinct microscopic patterns of arguable clinical significance, though potentially confusing diagnostically:

• Acanthomatous - Squamous metaplasia and variable keratinization of stellate reticulum.
• Desmoplastic - Extensive desmoplasia, more common in anterior jaw. More common in Asians, particularly Malaysians and Chinese.
• Follicular - Most common, with islands of odontogenic epithelium in fibrous connective tissue. Epithelium resembles peripheral ameloblastic columnar cells surrounding stellate reticulum-like cells.
• Plexiform - Irregular masses and cords of epithelial cells with minimal stroma and occasional osteoclast-like giant cells. Associated with sinonasal origin tumors.

Stains:

• Positive:
• Negative:
• Suggested, focused panel:

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