Congress of Neurological Surgeons Systematic Review and Evidence-Based Guidelines on Intraoperative Cranial Nerve Monitoring in Vestibular Schwannoma Surgery.

Question 1: Does intraoperative facial nerve monitoring during vestibular schwannoma surgery lead to better long-term facial nerve function? Target Population: This recommendation applies to adult patients undergoing vestibular schwannoma surgery regardless of tumor characteristics. Recommendation: Level 3: It is recommended that intraoperative facial nerve monitoring be routinely utilized during vestibular schwannoma surgery to improve long-term facial nerve function. Question 2: Can intraoperative facial nerve monitoring be used to accurately predict favorable long-term facial nerve function after vestibular schwannoma surgery? Target Population: This recommendation applies to adult patients undergoing vestibular schwannoma surgery. Recommendation: Level 3: Intraoperative facial nerve can be used to accurately predict favorable long-term facial nerve function after vestibular schwannoma surgery. Specifically, the presence of favorable testing reliably portends a good long-term facial nerve outcome. However, the absence of favorable testing in the setting of an anatomically intact facial nerve does not reliably predict poor long-term function and therefore cannot be used to direct decision-making regarding the need for early reinnervation procedures. Question 3: Does an anatomically intact facial nerve with poor electromyogram (EMG) electrical responses during intraoperative testing reliably predict poor long-term facial nerve function? Target Population: This recommendation applies to adult patients undergoing vestibular schwannoma surgery. Recommendation: Level 3: Poor intraoperative EMG electrical response of the facial nerve should not be used as a reliable predictor of poor long-term facial nerve function. Question 4: Should intraoperative eighth cranial nerve monitoring be used during vestibular schwannoma surgery? Target Population: This recommendation applies to adult patients undergoing vestibular schwannoma surgery with measurable preoperative hearing levels and tumors smaller than 1.5 cm. Recommendation: Level 3: Intraoperative eighth cranial nerve monitoring should be used during vestibular schwannoma surgery when hearing preservation is attempted. Question 5: Is direct monitoring of the eighth cranial nerve superior to the use of far-field auditory brain stem responses? Target Population: This recommendation applies to adult patients undergoing vestibular schwannoma surgery with measurable preoperative hearing levels and tumors smaller than 1.5 cm. Recommendation: Level 3: There is insufficient evidence to make a definitive recommendation. The full guideline can be found at: https://www.cns.org/guidelines/guidelines-manage-ment-patients-vestibular-schwannoma/chapter_4.

Emprical factors associated with Brainstem auditory evoked potential monitoring during microvascular decompression for hemifacial spasm and its correlation to hearing loss.

BACKGROUND: Cranial nerve VIII is at risk during microvascular decompression (MVD) for hemifacial spasm (HFS). The primary aim of this study is to evaluate the empirical factors associated with brainstem auditory evoked potential monitoring and its correlation to post operative hearing loss (HL) after MVD for HFS. METHODS: Pre-operative and post-operative audiogram data and BAEP from ninety-four patients who underwent MVD for HFS were analyzed. Pure tone audiometry (PTA) and Speech Discrimination Score (SDS) were performed on all patients before and after surgery. Intraoperative neurophysiological data were reviewed independently. HL was assessed using the AAO-HNS classification system for non-serviceable hearing loss (Class C/D), defined as PTA >50 dB and/or SDS <50% within the speech range of frequencies. RESULTS: Patients with HL had higher rates of loss in the amplitude of wave V and prolongation in the interpeak latency of peak I-V latency during MVD. Gender, age, side, and MVD duration did not increase the risk of HL. There was no correlation between successive number of BAEP changes (reflective of the number of surgical attempts) and HL. There was no association between the speed of recovery of BAEPs and HL. CONCLUSIONS: Patients with new post-operative HL have a faster rate of change in the amplitude of wave V and the interpeak I-V latency during intraoperative BAEP monitoring for HFS. Our alarm criteria to inform the surgeon about impending nerve injury might have to be modified and prospectively tested to prevent rapid change in BAEPs.

Analysis of interpeak latencies of brainstem auditory evoked potential waveforms during microvascular decompression of cranial nerve VII for hemifacial spasm.

OBJECT: Microvascular decompression (MVD) of the facial nerve is an effective treatment for patients with hemifacial spasm. Intraoperative monitoring of brainstem auditory evoked potentials (BAEPs) during MVD can reduce the incidence of hearing loss. In this study the authors' goal was to evaluate changes in interpeak latencies (IPLs) of Waves I-V, Waves III-V, and Waves I-III of BAEP Waveforms I, III, and V during MVD and correlate them with postoperative hearing loss. To date, no such study has been performed. Hearing loss is defined as nonuseful hearing (Class C/D), which is a pure tone average of more than 50 dB and/or speech discrimination score of less than 50%. METHODS: The authors performed a retrospective analysis of IPLs of BAEPs in 93 patients who underwent intraoperative BAEP monitoring during MVD. Patients who did not have hearing loss were in Class A/B and those who had hearing loss were in Class C/D. RESULTS: Binary logistic regression analysis of independent IPL variables was performed. A maximum change in IPLs of Waves I-III and Waves I-V and on-skin change in IPLs of Waves I-V increases the odds of hearing loss. However, on adjusting the same variables for loss of response, change in IPLs did not increase the odds of hearing loss. CONCLUSIONS: Changes in IPL measurements did not increase the odds of postoperative hearing loss. This information might be helpful in evaluating the value of IPLs as alarm criteria during MVD to prevent hearing loss.

The efficacy of N-acetylcysteine to protect the human cochlea from subclinical hearing loss caused by impulse noise: a controlled trial.

In military outdoor shooting training, with safety measures enforced, the risk of a permanent, noise-induced hearing loss is very small. But urban warfare training performed indoors, with reflections from walls, might increase the risk. A question is whether antioxidants can reduce the negative effects of noise on human hearing as it does on research animals. Hearing tests were performed on a control group of 23 military officers before and after a shooting session in a bunker-like room. The experiments were repeated on another group of 11 officers with peroral adminstration of N-acetyl-cysteine (NAC), directly after the shooting. The measurements performed were tone thresholds; transient-evoked otoacoustic emissions, with and without contralateral noise; and psycho-acoustical modulation transfer function (PMTF), thresholds for brief tones in modulated noise. Effects from shooting on hearing thresholds were small, but threshold behavior supports use of NAC treatment. On the PMTF, shooting without NAC gave strong effects. Those effects were like those from continuous noise, which means that strict safety measures should be enforced. The most striking finding was that the non-linearity of the cochlea, that was strongly reduced in the group without NAC, as manifested by the PMTF-results, was practically unchanged in the NAC-group throughout the study. NAC treatment directly after shooting in a bunkerlike room seems to give some protection of the cochlea.