Keratin-filled cysts that grow medial to the tympanic membrane are considered to be congenital if they fulfill the following criteria: mass medial to the tympanic membrane,
normal tympanic membrane, no previous history of ear discharge, perforation or ear surgery.
Congenital cholesteatomas occur at three important sites: the middle ear, the Petrous apex, and the cerebropontine angle. They are most often found deep to the anterior aspect of the ear drum, and a vestigial structure, the epidermoid formation, from which congenital cholesteatoma may originate, has been identified in this area.