Middle ear as a gas pocket.

An analysis of 45 adult ears that underwent a modified radical mastoidectomy for cholesteatoma and remained with an intact unperforated pars tensa is described. 1) While in practically all these ears some air was present behind the tympanic membrane, its amount varied considerably. 2) The air present behind the tympanic membrane was always in communication with the eustachian tube. 3) The regions in the middle ear devoid of air presented a deep atelectasis that was found predominantly in the posterior-superior part of the middle ear. Topographically the regions of air and atelectasis corresponded to the distribution of ciliated and flat epithelia in the middle ear, respectively. The presence of air in the middle ears obliges us to view these ears as being aerated gas pockets. The aeration difference between such an atelectatic ear and one in a physiologic state is probably a difference of degree. This difference can result from reduction in aeration through the eustachian tube or from excessive absorption of gases into the circulation, or from deficient normal diffusion of carbon dioxide or nitrogen from the circulation into the middle ear, or from a combination of these factors. The analogy with the respiratory system is emphasized.