title: Rat model of chronic tympanic membrane perforation: A longitudinal histological evaluation of underlying mechanisms.
abstract: OBJECTIVE
  To evaluate histologically the progressive development and underlying mechanisms of chronic tympanic membrane perforation (TMP) in a rat model using a two-weeks ventilation tube (VT) treatment combined with topical application of mitomycin C/dexamethasone (VT-M/D), compared with normal tympanic membrane and acute TMPs.
  
  
  METHODS
  Fifty male Sprague-Dawley rats were divided into three experimental groups: a normal control group (n = 5), an acute TMP group (n = 5) (i.e. 3 days post-myringotomy) and a VT-M/D group (n = 40). The TMs were regularly assessed by otoscopy. The normal control animals were sacrificed on day 0 and the acute TMP group was sacrificed 3 days post-myringotomy for histological and immunohistochemical evaluations. The VT-M/D group was sacrificed at various time points - 14 and 17 days, 3, 4, 6, 8 and 10 weeks.
  
  
  RESULTS
  On longitudinal histological examination, compared with normal TM and acute TMP, the perforation edges at the later time points illustrated thickened stratified squamous epithelium rimming around the edges, significant increase in keratin and collagen deposition, increased macrophage infiltration as well as reduced cellular proliferation. Three phases of TMP healing process were identified - the acute healing phase (3-17 days), the transition phase (3-4 weeks) and the chronic phase (6-10 weeks).
  
  
  CONCLUSIONS
  Based on the histological results of this study, the progressive development of chronic TMPs appeared to be associated with increased epidermal thickening, collagen and keratin deposition, macrophage infiltration and reduced cellular proliferation. After the 3-4 weeks of transition phase, the TMPs seemed to have transformed into a non-healing chronic TMP between 6 and 10 weeks.
authors.affiliation: Ear Sciences Centre, School of Surgery, The University of Western Australia, Perth, Western Australia, Australia; Ear Science Institute Australia, Perth, Western Australia, Australia; Department of Otolaryngology, Head and Neck, Skull Base Surgery, Sir Charles Gairdner Hospital, Perth, Western Australia, Australia. Electronic address: allen.wang@earscience.org.au.
authors.forename: Allen Y
authors.initials: AY
authors.lastname: Wang
authors.affiliation: Ear Sciences Centre, School of Surgery, The University of Western Australia, Perth, Western Australia, Australia; Ear Science Institute Australia, Perth, Western Australia, Australia.
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Liew
authors.affiliation: Ear Sciences Centre, School of Surgery, The University of Western Australia, Perth, Western Australia, Australia; Ear Science Institute Australia, Perth, Western Australia, Australia; Department of Otolaryngology, Head and Neck Surgery, Ningbo Lihuili Hospital (Ningbo Medical Centre), Ningbo, Zhejiang, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Shen
authors.affiliation: Ear Sciences Centre, School of Surgery, The University of Western Australia, Perth, Western Australia, Australia.
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Wang
authors.affiliation: Akershus University Hospital and University of Oslo, Norway; Center for Clinical Research Västerås, University of Uppsala, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: von Unge
authors.affiliation: Ear Sciences Centre, School of Surgery, The University of Western Australia, Perth, Western Australia, Australia; Ear Science Institute Australia, Perth, Western Australia, Australia; Department of Otolaryngology, Head and Neck, Skull Base Surgery, Sir Charles Gairdner Hospital, Perth, Western Australia, Australia.
authors.forename: Marcus D
authors.initials: MD
authors.lastname: Atlas
authors.affiliation: Ear Sciences Centre, School of Surgery, The University of Western Australia, Perth, Western Australia, Australia; Ear Science Institute Australia, Perth, Western Australia, Australia.
authors.forename: Rodney J
authors.initials: RJ
authors.lastname: Dilley
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D049109:Cell Proliferation; D002908:Chronic Disease; D018450:Disease Progression; D004848:Epithelium / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D008264:Macrophages; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D014432:Tympanic Membrane / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D018058:Tympanic Membrane Perforation / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D014945:Wound Healing / Q000502:physiology*
chemical_list: D015415:Biomarkers
keywords: Animal model; Chronic; Histology; Rat; Tympanic membrane perforation; Ventilation tube