Silent otitis media: an animal study.

Recent clinical and laboratory observations suggest that otitis media can occur in the absence of visible tympanic membrane changes (silent otitis media). Temporal bone histopathology was studied in 38 chinchillas that had been subjected to conditions known to predispose these animals to otitis media. Morphological changes were compared to a control group of 25 nonmanipulated animals. The tympanic membranes were examined at intervals and during the immediate premortem period with the operating microscope. Thirty-one tympanic membranes in the experimental group and all tympanic membranes in the control group were judged to be normal (gray and translucent) throughout the study period. The middle ears from the experimental group histologically manifested varying amounts of effusion, mucosal edema, granulation tissue, hyperemia of the subepithelial space, hemorrhage in the middle ear space, and abundant polymorphonuclear leukocytes in the middle ear cleft. These findings were not present in the control group.