title: Tympanic membrane changes in experimental cholesteatoma in the gerbil.
abstract: OBJECTIVE
  The current study aimed to analyze changes of the acoustic stiffness properties and coincident morphologic changes of the tympanic membrane (TM) in early stages of cholesteatoma. The results were compared with those obtained in previous studies of otitis media with effusion and purulent otitis media.
  
  
  BACKGROUND
  The pathophysiology of the cholesteatoma development process remains unclear. Changes of the physical properties of the TM seem to play an important role. In chronic middle ear disease, atrophic regions and retraction pockets of the TM are often present. Such changes of the TM may facilitate 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 surgery. After completed measurements, the TMs were analyzed morphologically.
  
  
  RESULTS
  The acoustic stiffness of the TM was significantly increased in all cholesteatoma ears compared to normal control ears. A pronounced thickening and proliferative activity of the entire TM was observed in the early stage of cholesteatoma. The outer keratinizing epithelium showed an increased number of cell layers and an increased keratin production. The fibrous layer 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 was significantly increased in all cholesteatoma ears. The results of the acoustic admittance measurements are comparable with those obtained in previous studies on purulent otitis media and otitis media with effusion.
authors.affiliation: Department of Otorhinolaryngology, Karolinska Hospital and Karolinska Institute, Stockholm, Sweden.
authors.forename: C
authors.initials: C
authors.lastname: Larsson
authors.forename: M
authors.initials: M
authors.lastname: von Unge
authors.forename: D
authors.initials: D
authors.lastname: Bagger-Sjöbäck
mesh_terms: D000158:Acoustic Impedance Tests / Q000379:methods; D000818:Animals; D001284:Atrophy / Q000473:pathology; D002452:Cell Count; D018424:Cholesteatoma, Middle Ear / Q000150:complications / Q000473:pathology*; D004195:Disease Models, Animal; D005260:Female; D005347:Fibroblasts / Q000648:ultrastructure; D005849:Gerbillinae; D010034:Otitis Media with Effusion / Q000209:etiology; D012720:Severity of Illness Index; D014432:Tympanic Membrane / Q000473:pathology* / Q000648:ultrastructure*