Tympanic membrane changes in experimental cholesteatoma in the gerbil

Hypothesis: The current study aimed to analyze changes of the acoustic stif fness properties and coincident morphologic changes of the tympanic membran e (TM) in early stages of cholesteatoma. The results were compared with tho se obtained in previous studies of otitis media with effusion and purulent otitis media. Background: The pathophysiology of the cholesteatoma development process re mains unclear. Changes of the physical properties of the TM seem to play an important role. In chronic middle ear disease, atrophic regions and retrac tion pockets of the TM are often present. Such changes of the TM may facili tate the development of cholesteatoma. Methods: Early stages of external ear canal cholesteatoma were produced in the Mongolian gerbil by closing the external meatus with a suture. Acoustic admittance measurements were performed after 1, 2, or 3 months after surge ry. After completed measurements, the TMs were analyzed morphologically. Results: The acoustic stiffness of the TM was significantly increased in al l cholesteatoma ears compared to normal control ears. A pronounced thickeni ng and proliferative activity of the entire TM was observed in the early st age of cholesteatoma. The outer keratinizing epithelium showed an increased number of cell layers and an increased keratin production. The fibrous lay er was thickened because of an increased amount of collagen fibers combined with minor edema. Conclusions: The thickness of the fibrous layer was almost doubled, mostly because of an increased amount of collagen fibers. The acoustic stiffness w as significantly increased in all cholesteatoma ears. The results of the ac oustic admittance measurements are comparable with those obtained in previo us studies on purulent otitis media and otitis media with effusion.