Tympanosclerosis in the Rat Tympanic Membrane: An Experimental Study

OBJECTIVES/HYPOTHESIS: Tympanosclerosis is a pathologic condition affecting the middle ear and tympanic membrane. It is a common condition in humans, most notably after grommet insertion. However, the pathogenesis of this disease is unclear. The aim of this study was to investigate the development and progression of tympanosclerosis in the pars tensa of rat tympanic membranes at various time intervals after inducing sterile middle ear effusions. METHODS: Fifty-six male-specific, pathogen-free CD Wistar rats (100-170 g) underwent unilateral eustachian tube obstruction. Contralateral ears served as controls. Only specimens from animals with sterile effusions were included in this study. Light and electron microscopic analysis was performed on the pars tensa of rats with induced effusions ranging from 1 to 12 months. RESULTS: Histologic changes consistent with tympanosclerosis were seen in the majority of animals with effusions from 3 months and greater. The process started in the submucosal connective tissue layer and progressed to involve all connective tissue sublayers. The extent of calcium deposition and fibrosis across the membrane was related to the duration of otitis media with effusion. Atrophy was not found in any specimens. CONCLUSIONS: Tympanosclerosis is a progressive disorder, which appears to be the main response of the rat pars tensa to prolonged sterile otitis media with effusion. The extent of involvement of the different sublayers of the pars tensa was closely related to the duration of otitis media with effusion. We propose that this new rat model for prolonged otitis media with sterile effusion is therefore a suitable animal model for the study of tympanosclerosis in the pars tensa.