A biopsy shows odontogenic epithelium with extensive squamous metaplasia and keratin pearl formation within the epithelial islands. Which lesion is this MOST easily confused with a squamous tumor?

Correct answer: C. Acanthomatous ameloblastoma

• A. A compound odontoma consists of denticles with organised enamel, dentin, cementum and pulp — it has no squamous appearance whatsoever.
• B. The Pindborg tumor (CEOT) has polyhedral epithelial cells with prominent intercellular bridges, marked nuclear pleomorphism, AMYLOID deposits and Liesegang ring calcifications — a distinctive picture. Its pleomorphism raises concern for malignancy, but not specifically for a squamous tumor.
• C. CORRECT. The ACANTHOMATOUS variant of ameloblastoma shows extensive SQUAMOUS METAPLASIA of the stellate reticulum-like centre of the epithelial islands, often with keratin pearls. Because the islands then look squamous rather than odontogenic, it is the ameloblastoma variant most commonly mistaken histologically for SQUAMOUS CELL CARCINOMA or for a squamous odontogenic tumor. The diagnostic clue is the retained peripheral layer of tall columnar cells with REVERSE POLARITY at the edge of the islands.
• D. The FOLLICULAR variant is the classic textbook pattern — discrete islands with peripheral palisading and a loose stellate reticulum-like centre. It looks unmistakably odontogenic and is not confused with a squamous tumor.

Note: Ameloblastoma histologic variants: follicular (most common), plexiform, acanthomatous, granular cell, basal cell, desmoplastic. Only the acanthomatous variant creates the squamous-lesion pitfall.