Cholesteatoma is classified as congenital, primary acquired or secondary acquired, with different origins and tympanic membrane associations.
Congenital cholesteatoma
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Congenital cholesteatoma arises from embryonic epidermal cell rests in the middle ear cleft or temporal bone. Important sites are the middle ear, petrous apex and cerebellopontine angle; symptoms depend on location.
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In the middle ear, it presents as a white mass behind an intact tympanic membrane and causes conductive hearing loss. It may be discovered during routine examination of children or during myringotomy.
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It may spontaneously rupture through the tympanic membrane and produce a discharging ear indistinguishable from chronic suppurative otitis media.
Primary acquired cholesteatoma
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Primary acquired cholesteatoma has no history of previous otitis media or a pre-existing perforation.
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The invagination theory describes persistent negative attic pressure producing a pars flaccida retraction pocket that accumulates keratin. Infection leads to expansion towards the middle ear; the attic perforation represents the proximal end of the expanding sac.
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The basal cell hyperplasia theory describes proliferation of the basal layer of pars flaccida following subclinical childhood infections. The expanding cholesteatoma breaks through pars flaccida to form an attic perforation.
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The squamous metaplasia theory describes replacement of normal attic pavement epithelium by keratinizing squamous epithelium due to subclinical infections. This change has also been demonstrated in otitis media with effusion.
Secondary acquired cholesteatoma
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A pre-existing pars tensa perforation is present, often posterosuperior marginal or sometimes large central.
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The migration theory describes keratinizing squamous epithelium from the external auditory canal or outer tympanic membrane surface entering the middle ear through the perforation.
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Perforations involving the tympanic annulus, as in acute necrotizing otitis media, are more likely to permit squamous epithelial ingrowth. Middle ear mucosal metaplasia is also introduced as a proposed mechanism.