Secretory cells in adenomatoid odontogenic tumour - induction or metaplastic mineralisation?

Objectives: The adenomatoid odontogenic tumor (AOT) has long been the subject of controversy with regard to its nature and classification. It has recently been reclassified with those odontogenic tumors arising from epithelium and which do not show inductive phenomena. It has been concluded that the dental matrix material arose as a result of metaplastic mineralization. The aim of this study was to review the histology of a large series of cases of AOT in order to document the frequency and histomorphology of secretory cells, which might indicate an inductive capacity. Methods: Hematoxylin and eosin stained sections of fifty-one archival cases of AOT were reviewed. Those cases showing the presence of dental matrix material were stained with PAS and Congo red. Results: Dental matrix material is found in various forms in the AOT. Well documented are PAS positive small hyaline droplets or globules, smaller foci of calcified material present within solid rests of cells as well as larger amorphous globular masses which also contain an amyloid-like material. None of these extracellular deposits are associated with secretory cells. Less well recognized are round secretory structures, which consist of a single layer of tall columnar ameloblasts-like cells showing secretory activity surrounding a central lumen, containing an eosinophilic secretory product which is almost likely enameloid. The layer of columnar cells is not always complete, being continuous with smaller cuboidal cells. These circular secretory structures were present in five of our cases and have not been previously adequately described. Conclusion: It seems likely that most of the dental matrix material in AOT occurs as a result of metaplastic mineralization. However, the presence of circular secretory structures with an orderly arrangement of tall columnar cells showing secretory activity raises the possibility that in some cases, dental matrix material deposition is the result of tissue induction.