title: Elevated summating potential in a case of posterior fossa meningioma was normalized by tumor removal.
abstract: OBJECTIVE
  A change in the summating potential (SP) obtained from a patient with posterior fossa meningioma associated with surgical removal of the tumor was reported and possible mechanisms underlying the change are discussed.
  
  
  METHODS
  This paper is a retrospective case review. A tertiary care referral center was the setting for the study. The authors present a 46-year-old female patient with posterior fossa meningioma, which was removed surgically. Pure tone audiometry and electrocochleography (ECoG) were performed before and after surgical removal of the tumor.
  
  
  RESULTS
  Pure tone audiogram showed normal hearing levels before surgery, and there were no apparent postoperative changes in hearing levels. ECoG showed a normal compound action potential (AP) level and an elevated SP/AP ratio (0.53) before surgery. After the tumor removal, the SP/AP ratio became 0.16, which was a normal level in our department.
  
  
  CONCLUSIONS
  The increased SP/AP ratio was normalized after surgery. Possible mechanisms underlying the increase in SP/AP ratio are an inhibition of the olivocochlear bundle function and endolymphatic hydrops.
authors.affiliation: Department of Otolaryngology, Kochi Medical School, Nankoku, Kochi 783-8505, Japan. kakigia@kochi-ms.ac.jp
authors.forename: Akinobu
authors.initials: A
authors.lastname: Kakigi
authors.forename: Shoichi
authors.initials: S
authors.lastname: Sawada
authors.forename: Taizo
authors.initials: T
authors.lastname: Takeda
authors.forename: Shunji
authors.initials: S
authors.lastname: Takeuchi
authors.forename: Kasumi
authors.initials: K
authors.lastname: Higashiyama
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Azuma
mesh_terms: D001300:Audiometry, Evoked Response; D001301:Audiometry, Pure-Tone; D003388:Cranial Fossa, Posterior; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008279:Magnetic Resonance Imaging; D008577:Meningeal Neoplasms / Q000175:diagnosis* / Q000503:physiopathology / Q000601:surgery; D008579:Meningioma / Q000175:diagnosis* / Q000503:physiopathology / Q000601:surgery; D011183:Postoperative Complications / Q000175:diagnosis / Q000503:physiopathology; D012815:Signal Processing, Computer-Assisted; D014057:Tomography, X-Ray Computed