title: Cochlear microphonics for hearing preservation in vestibular schwannoma surgery.
abstract: OBJECTIVE
  To determine whether cochlear function is beneficial in decision-making concerning the selection of hearing preservation surgery for vestibular schwannoma.
  
  
  METHODS
  Retrospective review of 44 patients undergoing tumor resection with a middle fossa approach.
  
  
  METHODS
  Cochlear microphonics in electrocochleography together with tumor size, pure-tone average (PTA), speech discrimination score (SDS), auditory brainstem response (ABR), and compound action potentials were examined. As acoustic stimuli, short tone-bursts with frequencies of 0.5, 1, and 2 kHz were employed to measure cochlear microphonics and a click was used to obtain compound action potentials. We determined detection thresholds of cochlear microphonics and action potentials.
  
  
  RESULTS
  The overall rate of preservation of serviceable hearing was 59.1% (26/44). There were significant differences between patients with and without serviceable postoperative hearing in PTA, SDS, finding of ABR, compound action potential detection threshold, and mean cochlear microphonic detection threshold (at 0.5, 1, and 2 kHz). However, tumor size was unrelated to hearing outcome. Serviceable hearing was preserved in 23 (76.7%) of 30 patients, with a mean cochlear microphonic detection threshold of 40 dB nHL or less, suggesting normal or slightly impaired cochlear function. Hearing recovery was recognized in three patients, who also had a mean cochlear microphonic detection threshold of 40 dB nHL or less. Of the three patients, two had lower cochlear microphonic detection thresholds than audiometric thresholds, demonstrating the existence of a retrocochlear component in their hearing loss.
  
  
  CONCLUSIONS
  The cochlear microphonic detection threshold predicts not only hearing preservation but also hearing improvement in patients with vestibular schwannomas.
authors.affiliation: Department of Otolaryngology, School of Medicine, Tokyo Medical and Dental University, Japan. noguchi.oto@med.tmd.ac.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Noguchi
authors.forename: A
authors.initials: A
authors.lastname: Komatsuzaki
authors.forename: H
authors.initials: H
authors.lastname: Nishida
mesh_terms: D000328:Adult; D001309:Auditory Threshold / Q000502:physiology; D003055:Cochlear Microphonic Potentials / Q000502:physiology*; D005260:Female; D006319:Hearing Loss, Sensorineural / Q000503:physiopathology* / Q000517:prevention & control; D006320:Hearing Tests; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D009464:Neuroma, Acoustic / Q000503:physiopathology / Q000601:surgery*; D011183:Postoperative Complications / Q000503:physiopathology* / Q000517:prevention & control; D011379:Prognosis; D012189:Retrospective Studies