Etiology of the retraction pocket in the posterosuperior quadrant of the eardrum.
The tympanic membrane meets the posterosuperior bony canal wall at a wide angle and thus makes the posterosuperior quadrant of the eardrum the most vulnerable part against the thrust effect of the air column in the external auditory canal compared with the rest of the pars tensa. The air column thrust effect becomes active when there is a decrease in the middle ear pressure because of Eustachian tube obstruction. The medial displacement of the eardrum exposes the posterosuperior quadrant of the eardrum to the venturi effect in the isthmus tympanicus posticus and the region below. The retraction pocket is the end result.
D004427:Ear Diseases / Q000209:etiology; D004432:Ear, Middle / Q000033:anatomy & histology; D006801:Humans; D055585:Physical Phenomena; D010825:Physics; D014432:Tympanic Membrane