title: Impedance Changes and Fibrous Tissue Growth after Cochlear Implantation Are Correlated and Can Be Reduced Using a Dexamethasone Eluting Electrode.
abstract: BACKGROUND
  The efficiency of cochlear implants (CIs) is affected by postoperative connective tissue growth around the electrode array. This tissue formation is thought to be the cause behind post-operative increases in impedance. Dexamethasone (DEX) eluting CIs may reduce fibrous tissue growth around the electrode array subsequently moderating elevations in impedance of the electrode contacts.
  
  
  METHODS
  For this study, DEX was incorporated into the silicone of the CI electrode arrays at 1% and 10% (w/w) concentration. Electrodes prepared by the same process but without dexamethasone served as controls. All electrodes were implanted into guinea pig cochleae though the round window membrane approach. Potential additive or synergistic effects of electrical stimulation (60 minutes) were investigated by measuring impedances before and after stimulation (days 0, 7, 28, 56 and 91). Acoustically evoked auditory brainstem responses were recorded before and after CI insertion as well as on experimental days 7, 28, 56, and 91. Additionally, histology performed on epoxy embedded samples enabled measurement of the area of scala tympani occupied with fibrous tissue.
  
  
  RESULTS
  In all experimental groups, the highest levels of fibrous tissue were detected in the basal region of the cochlea in vicinity to the round window niche. Both DEX concentrations, 10% and 1% (w/w), significantly reduced fibrosis around the electrode array of the CI. Following 3 months of implantation impedance levels in both DEX-eluting groups were significantly lower compared to the control group, the 10% group producing a greater effect. The same effects were observed before and after electrical stimulation.
  
  
  CONCLUSIONS
  To our knowledge, this is the first study to demonstrate a correlation between the extent of new tissue growth around the electrode and impedance changes after cochlear implantation. We conclude that DEX-eluting CIs are a means to reduce this tissue reaction and improve the functional benefits of the implant by attenuating electrode impedance.
authors: Department of Otolaryngology, Hannover Medical School, Hannover, Germany.|Clinic for Exotic Pets, Reptiles, Pet and Feral Birds, University of Veterinary Medicine, Foundation, Hannover, Germany.
authors: Maciej
authors: M
authors: Wilk
authors: MED-EL GmbH, Innsbruck, Austria.
authors: Roland
authors: R
authors: Hessler
authors: MED-EL GmbH, Innsbruck, Austria.
authors: Kenneth
authors: K
authors: Mugridge
authors: MED-EL GmbH, Innsbruck, Austria.
authors: Claude
authors: C
authors: Jolly
authors: Clinic for Exotic Pets, Reptiles, Pet and Feral Birds, University of Veterinary Medicine, Foundation, Hannover, Germany.
authors: Michael
authors: M
authors: Fehr
authors: Department of Otolaryngology, Hannover Medical School, Hannover, Germany.|Cluster of Excellence "Hearing4all", Hannover Medical School, Hannover, Germany.
authors: Thomas
authors: T
authors: Lenarz
authors: Department of Otolaryngology, Hannover Medical School, Hannover, Germany.|Cluster of Excellence "Hearing4all", Hannover Medical School, Hannover, Germany.
authors: Verena
authors: V
authors: Scheper
mesh_terms: D000818:Animals; D001309:Auditory Threshold; D019929:Cochlear Implantation / Q000009:adverse effects / Q000379:methods*; D003054:Cochlear Implants; D003238:Connective Tissue / Q000254:growth & development*; D003907:Dexamethasone / Q000494:pharmacology*; D017097:Electric Impedance; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology*; D005260:Female; D006168:Guinea Pigs; D034381:Hearing Loss / Q000517:prevention & control*; D012405:Round Window, Ear / Q000601:surgery; D012533:Scala Tympani / Q000502:physiology; D013016:Sound
chemical_list: D003907:Dexamethasone