Cholesteatoma represents keratinizing squamous epithelium in the middle ear or mastoid, where this lining is normally absent.
Normal middle ear lining
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The anterior and inferior regions have ciliated columnar epithelium, the middle region has cuboidal epithelium, and the attic has pavement-like epithelium.
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No region of the normal middle ear is lined by keratinizing squamous epithelium.
Definition and terminology
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The presence of keratinizing squamous epithelium in the middle ear or mastoid constitutes cholesteatoma, described as skin in the wrong place.
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The name is a misnomer because cholesteatoma neither contains cholesterol crystals nor is a tumour. The term persists because of its widespread use.
Structural components
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The matrix consists of keratinizing squamous epithelium resting on a thin stroma of fibrous tissue.
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The central white mass consists of keratin debris produced by the matrix.