Ans. is'd' i.e., Primary cholesteatoma Retraction pockets are more common in the postero-superior poion of pars-tensa of ear-drum (tympanic membrane). Two reasons have been attributed to this features :- This area is more vascular, hence could be subjected to intense inflammatory reaction. Middle fibrous layer in this area is incomplete, lackin circular fibers. Long term effects ofprogressive retraction may be :- Fixation of atrophic sigment to bony wall of middle ear cavity. Erosion of ossicles, most commonly long process of incus. Formation of cholesteatoma (primary acquired cholesteatoma). "A posterior superior retraction pocket, if allowed to progress, leads to primary acquired choleastoma". Acquired cholesteatoma In majority of cases cholesteatoma is acquired. Acquired cholesteatoma may be either primary acquired or secondary acquired :? A. Primary acquired cholesteatoma There is no history of previous otitis media or a pre-existing perforation. Theories for its genesis are : - Retraction pocket (wittmaack's theory) : - It is the most accepted theory. There is invagination of pars flaccida in the form of retraction pocket due to negative pressure in middle ear as a result of Eustachian tube dysfunction. There is in growth (migration) of squamous epithelium from the outer layer of tympanic membrane (outer layer of TM is lined by squamous epithelium) through this retraction pocket. Infection supervenes on the impacted squamous epithelium/keratin. Basal cell hyperplasia (Ruedi's theory) : - There is proliferation of the basal layer of pars flaccida induced by subclinical childhood infections. These proliferating basal cells lay down keratinizing squamous epithelium. Squamous metaplasia (Sade's theory) : - Pavement epithelium of attic undergoes metaplasia and transforms into squamous epithelium due to subclinical infections. B. Secondary acquired cholesteatoma There is pre-existing perforation in pars tensa. Theories on its genesis include : - Epithelial invasion (Habermann's theory) : - The epithelium from the meatus or outer drum surface grows into the middle ear through a pre-existing perforation especially of the marginal type where pa of annulus tympanicus has already been destroyed. Metaplasia : - Middle ear mucosa undergoes metaplasia due to repeated infections of middle ear through the pre-existing perforation.