Atelectatic tympanic membrane: histologic study.

This study aims to elucidate the morphological difference between the noncollapsible physiologic tympanic membrane (TM) and the collapsible atelectatic TM. Histologic examination of atelectatic TMs obtained at surgery from 16 ears revealed inflammatory changes and destruction of the pars tensa collagenous "backbone." The disappearance of the organized collagenous layer seen in atelectatic TMs explains their conversion from the stiff physiologic membrane to a flexible one. This in turn will convert the middle ear from a noncollapsible gas pocket to a partially collapsible gas pocket, in which minimal pressure of only a few millimeters of water can cause retraction or ballooning of the atrophic TM. These pressure differences are too small to equilibrate automatically the difference created with the atmospheric pressure. Integrity of the pars tensa collagenous layer thus appears to be essential for the proper mechanical functioning of the physiologic TM.