Cholesteatoma (膽脂瘤)

A ball of keratinizing stratified squamous epithelium in the middle ear cleft or mastoid which enlarges and can destroy or erode local structures. It is a feature of the unsafe type of chronic middle ear disease.

Aetiology:
The most widely accepted theory of its development is the immigration-retraction pocket theory: in response to Eustachian tube obstruction and negative middle ear pressure an inward retraction of the tympanic membrane occurs, usually in the attic region. 
Desquamated epithelium normally shed from the membrane into the meatus collects in the pocket, the continued enlargement of which results in the formation of a cholesteatoma sac. Congenital cholesteatoma is very rare and results from congenital squamous cell rests within the temporal bone.

Clinical features:
Presents as progressive conductive hearing loss with purulent, and often offensive, otorrhoea. Pain or vertigo due to bong erosion may also occur. Otoscopy reveals a retraction pocket or perforation in the attic or posterior marginal region of the tympanic membrane with flaky white debris visible in the defect. Nystagmous and other evidence of neurological involvement should be sought.

Management:
Radical mastoidectomy involves removal of the cholesteatoma, middle ear structures and bone of the bony external meatus, producing a smooth exteriorized mastoid cavity accessible for inspection. The operation may be modified in order to conserve hearing by retaining part of the ossicular chain and tympanic membrane.