Cholesteatoma is commonly caused by:

Tubotympanic type (safe or benign type)It is associated with central perforation of tympanic membrane and involves the anterior inferior pa of middle ear cleft (eustachian tube and mesotympanum).There is no association with cholesteatoma.Tubotympanic type is also called safe or benign type as there is no risk of serious complicatiions.Attico-antral type (unsafe or dangerous type)It is associated with an attic or a marginal perforation of the tympanic membrane and involves postero-superior pa of middle ear cleft (attic, antrum and mastoid).The attico-antral disease is characterized with cholesteatoma which erodes the bone.Risk of intracranial extension of infection, and thus the risk of complication, is very high, therefore it is called dangerous or unsafe ear.