A congenital cholesteatoma is identical to an epidermoid cyst, differing only in name and location.
They are intraosseous inclusions of 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.
Unsurprisingly congenital cholesteatomas have imaging characteristics similar to those of epidermoid cysts
Shows sharply demarcated margins with smooth bony erosions.
- T1 : low signal
- T2 : high signal (usually slightly brighter than CSF)
- T1 C+ (GAD) : no enhancement of the mass itself ; thin linear enhancement confined to the margins may be seen
A white epidermoid variant is also recognised 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.