​Cholesteatoma is an abnormal collection of skin cells behind the ear drum in the middle ear space, which may eventually result in destruction to the bony structures in the middle ear, such as the middle ear bones (ossicles), the hearing organ (cochlear), the balance organ (labyrinth), the base of the skull (tegmen tympani) and even the bony covering of the facial nerve. Uncommonly, cholesteatoma can also occur in the deeper structures such as the petrous apex and the cerebellopontine angle.