Does occurrence of keratinizing stratified squamous epithelium in the middle-ear cavity always indicate a cholesteatoma?

Abstract

The origin and behaviour of keratinizing stratified squamous epithelium, anessential component of cholesteatoma occurring in the middle-ear cavity, has puzzled otologistsfor decades. In this experimental study in 16 cats, central (n = 23) and peripheral (n = 9) tympanic membrane perforations were observed for up to 63 days before sacrifice. The tympanic membranes with bony rim were excised, decalcified and embedded in Epon 812. Sections werestained with toluidine blue and examined using a light microscope. The perforation had been sealed by meatal epithelium exhibiting pronounced hyperplasia and keratin formation, lying on abedof granulation tissue. Subtotal central perforations healed within 14 days, forming a bowl-shaped tympanic membrane and leaving parts of the handle of the malleus (with meatal epithelium) protruding freely into the middle-ear cavity. Stratified squamous epithelium, morphologicallyidentical with that of external ear canal epidermis, could be observed on the malleus even 63 days after operation. This meatal epithelium was non-keratinizing, non-invasive, and showed no destructive properties typical of acquired cholesteatoma. During certain circumstances, the cellcycle of hyperplastic epidermal epithelium within the middle-ear cavity can evidently be arrested and inactivated by a local defence mechanism.