Appropriate Time to Establish Baseline Responses for Brain stem Auditory Evoked Potentials During Microvascular Decompression for Hemifacial Spasm

OBJECTIVE The aim of this study was to define a new protocol for intraoperative monitoring (IOM) of brainstem auditory evoked potentials (BAEPs) during microvascular decompression (MVD) surgery to treat hemifacial spasm (HFS) and to evaluate the usefulness of this new protocol to prevent hearing impairment. METHODS To define the optimal stimulation rate, estimate the number of trials to be averaged, and identify useful warning criteria in IOM of BAEPs, the authors performed a preliminary study of 13 patients with HFS in 2010. They increased the stimulation rate from 10.1 Hz/sec to 100.1 Hz/sec by 10-Hz increments, and they elevated the average time from 100 times to 1000 times by 100-unit increments at a fixed stimulus rate of 43.9 Hz. After defining the optimal stimulation rate and the number of trials that needed to be averaged for IOM of BAEPs, they also identified the useful warning criteria for this protocol for MVD surgery. From January to December 2013, 254 patients with HFS underwent MVD surgery following the new IOM of BAEPs protocol. Pure-tone audiometry and speech discrimination scoring were performed before surgery and 1 week after surgery. To evaluate the usefulness of the new protocol, the authors compared the incidence of postoperative hearing impairment with the results from the group that underwent MVD surgery prior to the new protocol. RESULTS Through a preliminary study, the authors confirmed that it was possible to obtain a reliable wave when using a stimulation rate of 43.9 Hz/sec and averaging 400 trials. Only a Wave V amplitude loss > 50% was useful as a warning criterion when using the new protocol. A reliable BAEP could be obtained in approximately 9.1 seconds. When the new protocol was used, 2 patients (0.8%) showed no recovery of Wave V amplitude loss > 50%, and only 1 of those 2 patients (0.39%) ultimately had postoperative hearing impairment. When compared with the outcomes in the pre-protocol group, hearing impairment incidence decreased significantly among patients who underwent surgery with the new protocol (0.39% vs 4.02%, p = 0.002). There were no significant differences between the 2 surgery groups regarding other complications, including facial palsy, sixth cranial nerve palsy, and vocal cord palsy. CONCLUSIONS There was a significant decrease in postoperative hearing impairment after MVD for HFS when the new protocol for IOM of BAEPs was used. Real-time IOM of BAEPs, which can obtain a reliable BAEP in less than 10 seconds, is a successful new procedure for preventing hearing impairment during MVD surgery for HFS.

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Delayed and Progressive Hearing Loss after Microvascular Decompression of Cranial Nerves

Annals of Otology Rhinology & Laryngology ◽

10.1177/000348949610500212 ◽

1996 ◽

Vol 105 (2) ◽

pp. 158-161 ◽

Cited By ~ 12

Author(s):

Takeo Fuse ◽

Margareta B. Møller

Keyword(s):

Hearing Loss ◽

Evoked Potentials ◽

Brain Stem ◽

Microvascular Decompression ◽

Cranial Nerve ◽

Auditory Evoked Potentials ◽

Cranial Nerves ◽

Reflex Response ◽

Eighth Cranial Nerve ◽

Progressive Hearing Loss

An unusual case of unilateral delayed and progressive hearing loss following a microvascular decompression operation on cranial nerves V, VII, and VIII on the left side is reported. Preoperative and postoperative audiologic evaluation revealed a mild high-frequency hearing loss for both ears, normal thresholds for the acoustic middle ear reflex response, and normal brain stem auditory evoked potentials. Three years after this microvascular decompression procedure, the patient noticed slowly decreasing hearing in her left ear, and subsequent serial audiograms revealed a progressive sensorineural hearing loss and a decrease in her speech discrimination score. Brain stem auditory evoked potentials showed progressive changes. Because of the patient's increasing symptoms of vertigo and tinnitus in the left ear, reexploration of the eighth cranial nerve was performed 5½ years after the initial procedure. This second operation revealed reactive tissue around the eighth cranial nerve that was atrophic and yellow. We interpret the delayed and progressive hearing loss to be a result of reactive scar tissue and progressive atrophy of the auditory nerve.

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Does Intraoperative Monitoring of Auditory Evoked Potentials Reduce Incidence of Hearing Loss as a Complication of Microvascular Decompression of Cranial Nerves?

Neurosurgery ◽

10.1227/00006123-198902000-00017 ◽

1989 ◽

Vol 24 (2) ◽

pp. 257-263 ◽

Cited By ~ 70

Author(s):

Aage R. Møller ◽

Margareta B. Møller

Keyword(s):

Hearing Loss ◽

Evoked Potentials ◽

Hemifacial Spasm ◽

Microvascular Decompression ◽

Auditory Evoked Potentials ◽

Cranial Nerves ◽

Hearing Threshold ◽

Speech Discrimination ◽

Compound Action Potentials

Abstract During a 14-month period, 129 individuals underwent 140 operations for microvascular decompression to relieve hemifacial spasm, disabling positional vertigo, tinnitus, or trigeminal neuralgia at our institution. Seven patients were operated upon twice on the same side and 4 were operated upon on both sides at different times. In each case, the brainstem auditory evoked potentials were monitored intraoperatively by the same neurophysiologist. In 75 of these operations, compound action potentials were also recorded from the exposed 8th nerve. Comparison of speech discrimination scores before the operation and at the time fo discharge showed that at discharge, discrimination had decreased in 7 patients by 15% or more and increased in 4 patients by 15% or more, in 2 patients by as much as 52%. Essentially similar results were obtained when preoperative speech discrimination scores were compared with results obtained from the 87 patients who returned for a follow-up visit between 3 and 6 months after discharge. Only one patient lost hearing (during a second operation to relieve hemifacial spasm). Another patient (also operated upon to relieve hemifacial spasm) suffered noticeable hearing loss postoperatively, but had recovered nearly normal hearing by 4 months after the operation. Nine patients had an average elevation of the hearing threshold for pure tones in the speech frequency range (500 to 2000 Hz) of 11 dB or more at 4 to 5 days after the operation; 8 of these had fluid in their middle ears that most likely contributed to the hearing loss. Threshold elevations occurred at 4000 Hz and 8000 Hz in 19 and 29 ears, respectively.

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Monitoring Auditory Nerve Potentials during Operations in the Cerebellopontine Angle

Otolaryngology ◽

10.1177/019459988409200412 ◽

1984 ◽

Vol 92 (4) ◽

pp. 434-439 ◽

Cited By ~ 29

Author(s):

Aage R. Øller ◽

Peter J. Jannetta

Keyword(s):

Hearing Loss ◽

Evoked Potentials ◽

Brain Stem ◽

Microvascular Decompression ◽

Auditory Nerve ◽

Cerebellopontine Angle ◽

Auditory Evoked Potentials ◽

Cranial Nerves

Direct monitoring of auditory nerve potentials was performed in 19 patients undergoing retromastoid craniectomy and microvascular decompression of cranial nerves. In addition, brain stem auditory evoked potentials (BSEPs) were monitored in these patients. No patient suffered significant hearing loss. Direct monitoring of auditory nerve potentials complements the recording of BSEPs because the auditory nerve potentials can be visualized without averaging many responses. Therefore the effect of any intraoperative manipulation that is harmful to the auditory nerve can be detected instantaneously.

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