Tympanic membrane changes in experimental otitis media with effusion.

A tympanometric in vitro model was used to measure the mechanoacoustic properties of the tympanic membrane. Impedance measurements were made during the early course (1-21 days) of experimentally induced otitis media with serous effusion in the Mongolian gerbil. A more severe form of otitis media with mucoid effusion was produced by electrocauterization of the nasopharyngeal orifice of the eustachian tube. The dynamic peak values of the acoustic susceptance were significantly reduced early in the course of serious otitis media, indicating increased stiffness of the tympanic membrane. In mucoid otitis media, the same reaction of the tympanic membrane was predominant, but the reverse reaction also was recorded in a few ears. These results indicate that alterations of the mechanoacoustic stiffness of the tympanic membrane occur during otitis media with effusion. Such changes may play an important role in the further course of the disease. The clinical implications of the tympanic membrane stiffness changes are discussed. Significant histopathologic changes were encountered in all cell layers, whereas the collagen fiber layer of the pars tensa appeared intact until 4 weeks of disease.