title: Microvascular decompression for hemifacial spasm: how can we protect auditory function?
abstract: OBJECTIVE
  The nerve function of the VIIIth nerve is at risk during microvascular decompression (MVD) for hemifacial spasm (HFS). Intraoperative monitoring of brainstem auditory evoked potentials (BAEPs) can be useful in decreasing the danger of hearing loss. This study assessed the intraoperative BAEP findings related to the surgical process to clarify the optimum maneuvers of MVD surgery to avoid hearing impairment.
  
  
  METHODS
  Hundred consecutive patients undergoing MVD for HFS with intraoperative BAEP monitoring were retrospectively reviewed. Patients were classified into four groups based on the greatest intraoperative latency prolongation and amplitude reduction of wave V of BAEP. Postoperative hearing function and surgical procedures including use of the brain retractor, preservation of arachnoid membrane along the VIIIth nerve, and duration of microscopic manipulation were analyzed in relation to the BAEP findings.
  
  
  RESULTS
  Three patients complained of hearing loss after the surgery, but two had complete recovery and only one suffered permanent moderate hearing impairment. Longer duration of microscopic manipulation and greater use of the brain retractor tended to have negative effects on the BAEP findings, whereas preservation of arachnoid membrane along the VIIIth nerve had a positive effect. Statistical analysis showed significant difference in preservation of arachnoid membrane along the VIIIth nerve in Groups 2 and 4 (p = 0.013).
  
  
  CONCLUSIONS
  Stretching of the VIIIth nerve should be avoided to prevent postoperative hearing impairment. Adequate exposure of the lower cranial nerve roots and lateral medulla oblongata from the caudal side without using the brain retractor gives enough space for decompression with minimum stretching of the VIIIth nerve. Maximum preservation of the arachnoid membrane along the VIIIth nerve and shortening of the duration of microscopic manipulation may help in avoiding postoperative hearing impairment.
authors: Department of Neurosurgery, Mitsui Memorial Hospital , Tokyo , Japan.
authors: Kenichi
authors: K
authors: Amagasaki
authors: Saiko
authors: S
authors: Watanabe
authors: Kazuaki
authors: K
authors: Naemura
authors: Hiroshi
authors: H
authors: Nakaguchi
mesh_terms: D003391:Cranial Nerves / Q000601:surgery*; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology*; D034381:Hearing Loss / Q000601:surgery*; D019569:Hemifacial Spasm / Q000601:surgery*; D006801:Humans; D061145:Microvascular Decompression Surgery / Q000379:methods; D016343:Monitoring, Intraoperative / Q000379:methods; D012189:Retrospective Studies; D016896:Treatment Outcome
keywords: brainstem auditory evoked potentials; complication; hearing preservation; hemifacial spasm; surgical technique