Cholesteatoma is defined as keratinising epithelium in the middle ear cleft.  Cholesteatoma is thought to develop from retractions of the tympanic membrane.  Migratory epithelium becomes trapped in retraction pockets; it then expands and gets infected, producing osteolytic enzymes as well as local pressure effects that destroy local structures. Cholesteatomas are characterised by a waxy debris trapped in a retraction pocket which may become infected and discharge.