title: Endolymphatic hydrops is prevalent in the first weeks following cochlear implantation.
abstract: OBJECTIVE
  To explore morphological or electrophysiological evidence for the presence of endolymphatic hydrops (EH) in guinea pig cochleae in the first 3 months after cochlear implantation.
  
  
  METHODS
  Dummy silastic electrodes were implanted atraumatically into the basal turn of scala tympani via a cochleostomy. Round window electrocochleography (ECochG) was undertaken prior to and after implantation. Animals survived for 1, 7, 28 or 72 days prior to a terminal experiment, when ECochG was repeated. The cochleae were imaged using micro-CT after post-fixing with osmium tetroxide to reveal the inner ear soft tissue structure. EH was assessed by visual inspection at a series of frequency specific places along the length of the cochlea, and the extent to which Reissner's membrane departed from its neutral position was quantified. Tissue response volumes were calculated. Using ECochG, the ratio of the summating potential to the action potential (SP/AP ratio) was calculated in response to frequencies between 2 and 32 kHz.
  
  
  RESULTS
  There was minimal evidence of electrode trauma from cochlear implantation on micro-CT imaging. Tissue response volumes did not change over time. EH was most prevalent 7 days after surgery in implanted ears, as determined by visual inspection. Scala media areas were increased, as expected in cases of EH, over the first month after cochlear implantation. SP/AP ratios decreased immediately after surgery, but were elevated 1 and 7 days after implantation.
  
  
  CONCLUSIONS
  EH is prevalent in the first weeks after implant surgery, even in the absence of significant electrode insertion trauma.
authors.affiliation: Department of Otolaryngology, University of Melbourne, 2nd Floor, Peter Howson Wing, Royal Victorian Eye and Ear Hospital, 32 Gisborne St, East Melbourne, Victoria 3002, Australia; Karolinska University Hospital, Stockholm, Sweden. Electronic address: henrik.smeds@karolinska.se.
authors.forename: H
authors.initials: H
authors.lastname: Smeds
authors.affiliation: Department of Otolaryngology, University of Melbourne, 2nd Floor, Peter Howson Wing, Royal Victorian Eye and Ear Hospital, 32 Gisborne St, East Melbourne, Victoria 3002, Australia. Electronic address: haydente@unimelb.edu.au.
authors.forename: H T
authors.initials: HT
authors.lastname: Eastwood
authors.affiliation: Department of Otolaryngology, University of Melbourne, 2nd Floor, Peter Howson Wing, Royal Victorian Eye and Ear Hospital, 32 Gisborne St, East Melbourne, Victoria 3002, Australia. Electronic address: ahampson@unimelb.edu.au.
authors.forename: A J
authors.initials: AJ
authors.lastname: Hampson
authors.affiliation: Department of Otolaryngology, University of Melbourne, 2nd Floor, Peter Howson Wing, Royal Victorian Eye and Ear Hospital, 32 Gisborne St, East Melbourne, Victoria 3002, Australia. Electronic address: phillip.sale@gmail.com.
authors.forename: P
authors.initials: P
authors.lastname: Sale
authors.affiliation: Department of Otolaryngology, University of Melbourne, 2nd Floor, Peter Howson Wing, Royal Victorian Eye and Ear Hospital, 32 Gisborne St, East Melbourne, Victoria 3002, Australia. Electronic address: lukejcampbell@yahoo.com.au.
authors.forename: L J
authors.initials: LJ
authors.lastname: Campbell
authors.affiliation: ARC Centre of Excellence for Advanced Molecular Imaging, Department of Physics, La Trobe University, Victoria 3086, Australia. Electronic address: b.arhatari@latrobe.edu.au.
authors.forename: B D
authors.initials: BD
authors.lastname: Arhatari
authors.affiliation: Department of Otolaryngology, University of Melbourne, 2nd Floor, Peter Howson Wing, Royal Victorian Eye and Ear Hospital, 32 Gisborne St, East Melbourne, Victoria 3002, Australia. Electronic address: stephaniemansour07@gmail.com.
authors.forename: S
authors.initials: S
authors.lastname: Mansour
authors.affiliation: Department of Otolaryngology, University of Melbourne, 2nd Floor, Peter Howson Wing, Royal Victorian Eye and Ear Hospital, 32 Gisborne St, East Melbourne, Victoria 3002, Australia. Electronic address: sjoleary@unimelb.edu.au.
authors.forename: S J
authors.initials: SJ
authors.lastname: O'Leary
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D001300:Audiometry, Evoked Response; D001309:Auditory Threshold; D003051:Cochlea / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D019929:Cochlear Implantation / Q000009:adverse effects* / Q000295:instrumentation; D003054:Cochlear Implants; D004195:Disease Models, Animal; D018159:Endolymphatic Hydrops / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D005071:Evoked Potentials; D006168:Guinea Pigs; D013997:Time Factors; D055114:X-Ray Microtomography