Congenital cholesteatomas are identical to epidermoid cysts, differing only in name and location.
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Pathology
They are intraosseous inclusions of the ectoderm and are therefore comprised of keratin debris and cholesterol. Characteristically, they are located at the petrous apex. In contrast, middle ear cholesteatomas tend to be acquired, secondary to tympanic membrane perforation.
Radiographic features
MRI
Unsurprisingly, congenital cholesteatomas have imaging characteristics similar to those of epidermoid cysts.
MRI shows sharply demarcated margins with smooth bony erosions.
T1: low signal
-
T2
high signal (usually slightly brighter than CSF)
usually will not attenuate on FLAIR imaging, however partial or heterogeneous attenuation may occur; this is in contrast to cholesterol granulomas which never attenuate
T1 C+ (Gd): no enhancement of the mass itself; thin linear enhancement confined to the margins may be seen
DWI/ADC: characterized by diffusion restriction 3
A white epidermoid variant is also recognized in bone, in which case it becomes indistinguishable from a cholesterol granuloma, as both are bright on both T1 and T2 due to the high cholesterol component.
Differential diagnosis
chronic otitis media: may be complicated by granulation tissue formation and development of an acquired cholesteatoma ref
aberrant internal carotid artery: MRI shows signal flow void, and postcontrast images demonstrate avid arterial enhancement ref
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