The origin of cholesteatoma is debated. Proposed mechanisms must explain the appearance of squamous epithelium in the middle ear cleft. Cholesteatoma is also called epidermosis or keratoma.
Congenital rests and invagination
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Congenital cell rests are one proposed origin.
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Wittmaack's theory describes invagination of the tympanic membrane from the attic or posterosuperior pars tensa to form retraction pockets.
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The outer tympanic membrane is lined by stratified squamous epithelium. After invagination, this epithelium forms the cholesteatoma matrix and deposits keratin in the pocket.
Basal cell hyperplasia
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Ruedi's theory proposes that infection stimulates proliferation of basal cells in the skin's germinal layer, which lay down keratinizing squamous epithelium.
Epithelial invasion
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Habermann's theory proposes that epithelium from the meatus or outer drum surface grows into the middle ear through a pre-existing perforation.
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This occurs especially through marginal perforations where part of the annulus tympanicus has already been destroyed.
Metaplasia
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Sade's theory proposes that repeated infections cause middle ear mucosa to undergo metaplasia and transform into squamous epithelium.