Pathology of the Head and Neck

Maxillofacial Skeleton and Teeth Chapter 4 111Fig. 4.11. Large epithelial areas of loosely structured spindle epitheliumenclosing liquefacting stromal areas are typical of a plexiformameloblastoma. The epithelial cells facing the stroma showpalisadingFig. 4.13. Desmoplastic ameloblastoma consists of denselypacked spindle cells lying in a fibrous stroma. Palisading of peripheralcells is not a conspicuous feature in this type of ameloblastomaFig. 4.12. In cases of follicular ameloblastoma, the tumour consistsof epithelial islands with a loose oedematous centre and a peripheralrim of palisading cells. Liquefaction of their centre resultsin cyst formationFig. 4.14. In unicystic ameloblastoma, the tumour consists ofcyst-lining epithelium that still shows the typical features of ameloblastoma:loose epithelium and a rim of palisading cells facingthe stromaAcanthomatous and granular cell type ameloblastomaare variants of follicular ameloblastoma with squamousmetaplasia and granular cells respectively. If keratinisationis abundant, leading to large cavities filledwith keratin, lesions are called keratoameloblastoma[135]. In these tumours acantholysis may lead to a pseudopapillarylining that characterises the variant calledpapilliferous keratoameloblastoma.The basal cell ( basaloid) ameloblastoma is composedof nests of basaloid cells with a peripheral rim of cuboidalcells and does not display a well-developed, loose oedematouscentre.Desmoplastic ameloblastoma shows a dense collagenousstroma, the epithelial component being reduced tonarrow, compressed strands of epithelium. When thesestrands broaden to form larger islands, a peripheral rimof dark staining cuboidal cells and a compact centre inwhich spindle-shaped epithelial cells assume a whorlingpattern may be discerned (Fig. 4.13). Within the stromalcomponent, active bone formation can be observed[119].Unicystic ameloblastoma represents a cyst that islined by ameloblastomatous epithelium (Fig. 4.14) [115].This epithelium may proliferate to form intraluminalnodules with the architecture of plexiform ameloblastoma.Downward proliferation of this epithelium may leadto infiltration of the fibrous cyst wall by ameloblastomanests. Sometimes, the cyst lining itself lacks any featuresindicative of ameloblastoma, these being confined to intramuralepithelial nests [47]. Inflammatory alterationsmay obscure the specific histologic details to such an extentthat none are left.Ameloblastomas may also contain clear cells as wellas mucous cells [100, 184].Epithelial nests resembling ameloblastoma may befound in calcifying odontogenic cysts and ameloblas-