Pathogenesis of experimental aural cholesteatoma in the chinchilla

Histopathological observation of celloidin serial sections of the chinchill a middle ear after treatment with propylene glycol disclosed the developmen t of severe inflammation of the middle ear mucosa and tympanic membrane, pa pillary proliferation of the epidermis of the tympanic membrane and externa l auditory meatus, and retraction and adhesion of the tympanic membrane, Th e findings for the tympanic membrane, impedance testing and histopathologic al examination suggested that there were two types of acquired cholesteatom a formation, probably with a difference in the pathogenesis, In one type, t he proliferated epidermal layer of the tympanic membrane penetrated into th e middle ear cavity making tympanic perforations, In the other type, there was progressive retraction of the tympanic membrane forming a retraction po cket, We discuss the two different patterns of cholesteatoma development.