Tympanostomy tubes were inserted in 16 chinchillas to study the effect on tympanic membrane morphology. Tympanic membranes were examined with an operating microscope after 72 hours and at weekly intervals thereafter. Three ears developed postoperative otorrhea. Except for the ears with otorrhea, all tympanic membranes remained gray and translucent. Histologically, granulation tissue and polymorphonuclear leukocyte infiltration occurred around the tympanostomy tube by 7 days. With time this was replaced by a mature fibrous ring, which explained the tissue band observed otoscopically. In those tympanic membranes where the tympanostomy tube had extruded, healing occurred with an overly developed membrana propria. The middle ears of all experimental animals remained free of pathologic changes except for the three ears with otorrhea.
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