Learning Objectives: The objective of this presentation is to critically evaluate the different theories of cholesteatoma pathogenesis and to discuss the evidence for and against various theories.

It is clear that cholesteatomas arise due to a number of different mechanisms. Clinical and experimental observations support the etiologies of cholesteatoma formation. Cholesteatomas clearly can arise by the ingrowth of keratinizing epithelium from the lateral surface of the tympanic membrane and ear canal into the middle ear. These so-called secondary cholesteatomas arise from implantation of keratinizing epithelium or ingrowth of a perforation. Experimental and clinical evidence supports this etiology.

Cholesteatomas may also arise by formation of retract pockets in the pars tensa or pars flaccida. The retraction pockets develop because of Eustachian tube malfunction and inflammatory degradation and weakening of the tympanic membrane. These retraction pockets are sometimes benign, but sometimes accumulate keratin debris. Once the keratin debris accumulates in a retraction pocket, expansion of the retraction pocket into a cholesteatoma is usually relentless.

Experimental and human temporal bone evidence has shown that cholesteatomas may arise by perforation of the basal lamina of the keratinizing epithelium of the tympanic membrane and the development of micro-cysts in enlarging intramural cholesteatomas.

A theory of mucosal traction by ciliated cells of an attic retraction pocket has been proposed. However, the epithelium of most of the middle ear and attic regions does not contain ciliated cells (Chole & Lim). Furthermore, recent evidence (Thompson & Tucker) has shown that the epithelium of the attic and around the ossicles is of neural crest origin and the area near the Eustachian tube is of endodermal origin. Neural crest derived epithelium does not form cilia.