ANIMAL-MODEL FOR PERSISTENT TYMPANIC MEMBRANE PERFORATIONS

Topically applied hydrocortisone was used to develop an animal model f or persistent tympanic membrane (TM) perforations. Hydrocortisone susp ension was applied on the margins of TM perforations of standardized s ize in rats once daily for 10 days. The healing patterns of the TMs we re mapped weekly and, when the perforations were about to close, daily . After 50 days, all hydrocortisone-treated perforations were open, wh ereas the controls closed within 9 to 12 days. At 3 months, when one t hird of the perforations still were open, the TMs were studied by otom icroscopy and light microscopy. All TMs were thickened and covered by keratin and wax. The thickened epidermal layer at the border of the TM perforations that remained open also draped the surface of the perfor ation facing the middle ear cavity. The thickened connective tissue la yer contained abundant fibroblasts with their axes of length oriented at random. Both application of 1.4% hyaluronan and wounding of the per foration border enhanced the healing rate of the hydrocortisone-induce d chronic TM perforation.