title: Brainstem auditory evoked potentials: intraoperative monitoring technique in surgery of posterior fossa tumors.
abstract: Brainstem auditory evoked potentials (BAEPs) were used to monitor eight neurosurgical procedures involving posterior fossa tumors to assist the neurosurgeon in preservation of hearing postoperatively. The technique included placement of recording electrodes over the Cz (vertex) and both earlobes. Stimulation was accomplished intraoperatively with a specifically designed intraauricular click stimulator that did not interfere with surgical access to the suboccipital region. Continuous BAEP recording was performed with particular attention to the sequence of preincision, opening of the dura, tumor mobilization, tumor excision, and closure. Absolute latencies and interpeak latencies of all five waves were recorded when possible. In three patients BAEPs were not significantly altered intraoperatively, and hearing was preserved postoperatively. In another three patients the acoustic nerve was severed during surgery and intraoperative monitoring was discontinued. In the remaining two patients medical complications arose intraoperatively, and significant irreversible changes in BAEP were observed despite no gross anatomical damage to the acoustic nerve. Both of these patients experienced postoperative hearing loss. These two cases illustrated some of the BAEP abnormalities that occurred during surgery. Difficulties during the procedures included electrical noise and interference, use of a bipolar cautery device, and unclear wave forms. Solutions for these difficulties were braiding the electrodes and using extra ground electrodes and a spike suppressor; switching off the evoked potential equipment when the bipolar cautery device was in use; and increasing repetitions and changing click intensity and polarity, respectively. Monitoring BAEPs in posterior fossa surgery can be accomplished with presently available equipment and may aid the neurosurgeon in preserving or minimizing injury to auditory pathways and adjacent structures.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000328:Adult; D001932:Brain Neoplasms / Q000601:surgery*; D001933:Brain Stem / Q000502:physiology; D003388:Cranial Fossa, Posterior; D005072:Evoked Potentials, Auditory; D005260:Female; D006311:Hearing Disorders / Q000517:prevention & control*; D006801:Humans; D007430:Intraoperative Care / Q000379:methods; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods; D011183:Postoperative Complications / Q000517:prevention & control*; D012306:Risk; D000159:Vestibulocochlear Nerve / Q000502:physiology