A cholesteatoma is a benign cyst that grows in the ear. Most cholesteatomas occupy the middle ear space, which is behind the tympanic membrane (eardrum). Some occur in the external ear canal, and they are referred to as canal cholesteatomas. Cholesteatomas typically occur in children and adults who have chronic eustachian tube dysfunction (ETD), a problem with ventilating or "popping" the ears. When ETD is present for many years, it can lead to development of a cholesteatoma. Although most cholesteatomas are acquired, some patients are actually born with the cholesteatoma; this is called a congenital cholesteatoma.

Cholesteatomas usually grow very slowly, but they cause damage to any structure in the ear that they come in contact with. This can lead to infection, chronic ear discharge, ear pain, hearing loss, dizziness, facial paralysis, or in the rarest cases brain injury. Due to the seriousness of these complications, cholesteatomas need to be surgically removed. The operation is called a mastoidectomy, and the goal is to remove the entire cholesteatoma and, if possible, reconstruct the hearing. Following surgery, patients are usually seen on a regular basis to clean the ear and make sure the cholesteatoma does not return.