Head and Neck Imaging

Cholesterol granuloma

expansile lesion arising from a pneumatized cavity which becomes closed; the subsequent decrease in air pressure causes oedema, fluid accumulation and intralesional bleeding; this will promote a granulomatous reaction leading to neovascularity and continuing haemorrhage. The most typical examples of cholesterol granuloma arise from a pneumatized petrous apex. On CT-images a well demarcated expansile lesion is seen, indistinguishable from congenital cholesteatoma. However, these entities have different MR characteristics: cholesteatomas commonly have essentially a low signal intensity on T1-weighted and a high signal intensity on T2-weighted images (cholesteatoma (VI:2), Fig. 5); cholesterol granulomas are typically hyperintense on both T1- and T2-weighted images (this being due to their haemorrhagic components) (Fig.1).

Smaller lesions, corresponding to cholesterol granuloma, are often found surgically and histologically within the middle ear cavity, in the context of chronic otitis media; on otoscopy, this may give rise to a blue tympanic membrane, suggesting the presence of a vascular mass lesion.

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Fig.1

Axial T2-weighted (a) and T1-weighted (b) spin-echo images of the temporal bones. Expansile lesion in the left petrous apex (arrow), hyperintense on both sequences. The inflammatory changes in the left middle ear and mastoid presumably also contain blood degradation products and/or cholesterol granuloma (patient previously operated on for middle ear cholesteatoma).
Cholesterol granuloma, Fig.1 (a)
Cholesterol granuloma, Fig.1 (b)