Monitoring Of Brainstem Auditory Evoked Potentials Research Articles

Intraoperative Monitoring During Microvascular Decompression

During microvascular decompression(MVD)for hemifacial spasm(HFS), trigeminal neuralgia(TN), and glossopharyngeal neuralgia(GPN), brainstem auditory-evoked potential monitoring is widely used to preserve hearing function. In MVD for HFS, abnormal muscle response monitoring is useful for identifying the offending vessels compressing the facial nerve and confirming the completion of decompression intraoperatively. The amplitude of facial motor-evoked potential by transcranial electrical stimulation in the orbicularis oculi muscle is reported to decrease after completing MVD. The Z-L response(ZLR)probably confirms the true offending vessels by stimulating the culprit vessels; then, the ZLR could disappear after decompressing the offending vessels away from the compression sites. Spontaneous electromyographic activities obtained from the mentalis muscles by injection of saline into the facial nerve reportedly decreased after MVD compared with those before MVD. In MVD for the GPN, glossopharyngeal motor-evoked potential by transcranial electrical stimulation is used to preserve swallowing function and not to assess the completion of MVD. Because MVD for both the TN and GPN can result in normalization of the hyperactivity of the sensory nerve, it may be difficult to develop any monitoring to confirm the completion of MVD during surgery.

Preliminary application of combined auditory monitoring technique in resection of vestibular neurinoma

Objective: To explore the value of electrically evoked auditory brainstem response (EABR) monitoring combined with brainstem auditory evoked potential (BAEP) and compound action potential (CAP) monitoring during vestibular schwannoma resection for the protection of the cochlear nerve. Methods: Clinical data from 12 patients with vestibular schwannomas who had useful hearing prior to surgery were analyzed at the PLA General Hospital from January to December 2021. Among them, there were 7 males and 5 females, ranging in age from 25 to 59 years. Before surgery, patients underwent audiology assessments (including pure tone audiometry, speech recognition rate, etc.), facial nerve function evaluation, and cranial MRI. They then underwent vestibular schwannoma resection via the retrosigmoid approach. EABR, BAEP, and CAP were simultaneously monitored during surgery, and patients' hearing preservation was observed and analyzed after surgery. Results: Prior to surgery, the average PTA threshold of the 12 patients ranged from11 to 49 dBHL, with a SDS of 80% to 100%. Six patients had grade A hearing, and six patients had grade B hearing. All 12 patients had House-Brackman grade I facial nerve function prior to surgery. The MRI indicated tumor diameters between 1.1 and 2.4 cm. Complete removal was achieved in 10/12 patients, while near-total removal was achieved in 2/12 patients. There were no serious complications at the one-month follow-up after surgery. At the three-month follow-up, all 12 patients had House-Brackman grade I or II facial nerve function. Under EABR with CAP and BAEP monitoring, successful preservation of the cochlear nerve was achieved in six of ten patients (2 with grade B hearing, 3 with grade C hearing, and 1 with grade D hearing). Successful preservation of the cochlear nerve was not achieved in another four patients (all with grade D hearing). In two patients, EABR monitoring was unsuccessful due to interference signals; however, Grade C or higher hearing was successfully preserved under BAEP and CAP monitoring. Conclusion: The application of EABR monitoring combined with BAEP and CAP monitoring during vestibular schwannoma resection can help improve postoperative preservation of the cochlear nerve and hearing.

Intraoperative Monitoring during Microvascular Decompression for Hemifacial Spasm

Brainstem auditory evoked potential(BAEP)and abnormal muscle response(AMR)monitoring are widely used during microvascular decompression(MVD)for hemifacial spasm(HFS). In BAEP monitoring, the intraoperative findings of wave V do not necessarily predict postoperative hearing function. However, if a warning sign as significant as wave V change appears, the surgeon must abort the operation or inject artificial cerebrospinal fluid into the VIII nerve. During MVD for HFS, BAEP monitoring must be performed to preserve hearing function. AMR monitoring is useful in identifying the offending vessels compressing the facial nerve and confirming the completion of decompression intraoperatively. During the operation of the offending vessels, AMR sometimes changes its onset latency and amplitude in real time. These findings allow surgeons to identify the offending vessels. Even if the AMRs remain after completion of decompression, a decrease in amplitude of more than 50% compared to baseline is predictive of postoperative loss of HFS in long-term outcomes. When the AMRs disappear after dural opening, the AMR monitoring should be continued because the AMRs sometimes reappear.

Intraoperative brainstem auditory evoked potential monitoring during cerebellopontine angle surgery via retrosigmoid approach.

Brainstem auditory evoked potential (BAEP) monitoring was used to identify the influence of auditory function during cerebellopontine angle (CPA) surgery for cranial neuropathy via the retrosigmoid approach. This prospective study included 20 patients who underwent CPA surgery for cranial neuropathy via the retrosigmoid approach with intraoperative BAEP monitoring and pure tone audiometry (PTA). The latency and interpeak latency were analyzed at each surgical step in combination with the pre- and postoperative PTA. Follow-up data were available for 17 patients. The mean pre- and postoperative PTA values were 25.65 dB and 20.70 dB, respectively. Two patients (2/17, 11.76%) developed hearing loss postoperatively. The latency of wave І significantly changed during direct auditory nerve manipulation and at the end of the surgery, while that of wave III only changed during direct auditory nerve manipulation. The appearance of wave V peak was delayed during CPA surgery. CPA surgery for cranial neuropathy via the retrosigmoid approach can cause hearing loss to varying degrees, and intraoperative BAEP monitoring can reduce the occurrence of hearing loss. Intraoperative hearing function can be estimated by the latency of wave I. Hearing loss due to stretching of the brainstem can be estimated by the latency of wave III, and wave V is an early indicator of intraoperative hearing loss. Waves I and III remained stable both pre- and postoperatively, whereas wave V was unstable despite no surgery. Therefore, a precise operation and well-defined operative steps for surgeons during CPA surgery could facilitate maximal preservation of the anatomical structure and function.

Exploring brainstem auditory evoked potentials and mental development index as early indicators of autism spectrum disorders in high-risk infants.

This study of infants from Hubei Province, China examined brainstem auditory evoked potentials (BAEP) and mental development index (MDI) as possible early indicators associated with autism spectrum disorders (ASD). The 34 ASD cases and 102 controls who had recovered from perinatal conditions were matched for age, sex, gestational age, birth weight and maternal age. BAEP absolute latencies (AL) I, III, V and interpeak latencies (IPL) I-III, III-V, I-V were compared in ASD cases and controls at ages 1, 3 and 6months. MDI scores were compared in these infants from 1month to 2 years old. Multiple logistic regression analysis was performed to test associations among ASD, BAEP and MDI. Results showed BAEP AL I, V and IPL III-V prolonged in the ASD group (p < 0.001), and MDI scores in ASD cases sharply declining from 12 to 24 months (p < 0.001). Regression analysis revealed odds ratios (OR) indicating that ASD was likely associated with abnormal values of BAEP AL I at 1 and 3months (ORAL I : 4.27; ORAL I : 4.13), and AL V at 6months (ORAL V : 7.85). Lower MDI scores (MDI < 80) in infants at 1, 3, and 6months were likely associated with ASD (ORMDI : 2.58; ORMDI : 3.83; ORMDI : 4.87). These data show that abnormal BAEP values and low MDI scores are independent factors associated with ASD, and that monitoring of BAEP and MDI during infancy might facilitate screening for ASD development.

WS5.3. Brainstem Auditory Evoked Potential Monitoring

Brainstem auditory evoked potentials (BAEP) are obtained by stimulating the vestibulocochlear nerve. As the stimulation volley ascends in the brainstem, BAEP waveforms can be obtained from various neurologic structures. BAEPs are frequently used during surgery to monitor the integrity of the distal auditory pathways. It is useful when the integrity of the cochlea, vestibulocochlear nerve, or brainstem auditory structures is at risk. In this presentation, the basics of the anatomy of the auditory pathways will be discussed. This will be followed by a discussion of the methodology and technical challenges of obtaining BAEPs in the operating room. The types of changes in BAEP waveforms that may occur in the operating room will be described. Finally, a summary of the clinical applications of BAEP monitoring will be reviewed.

Role of Intraoperative Neurophysiologic Monitoring in Internal Carotid Artery Injury During Endoscopic Endonasal Skull Base Surgery

In the present study, we investigated the role of intraoperative neuromonitoring (IONM) in internal carotid artery (ICA) injury during endoscopic endonasal skull base surgery (EESBS). The study group included all 13 patients who had experienced an ICA injury during EESBS with IONM from 2004 to 2017. The medical records were reviewed for the perioperative data. The IONM reports were reviewed to evaluate the baseline somatosensory evoked potentials (SSEP), electroencephalography (EEG), and brainstem auditory evoked potentials (BAEP) and their significant changes related to ICA injury and/or the subsequent surgical/endovascular interventions. All 13 patients had undergone SSEP and 7 patients had BAEP monitoring during surgery. EEG was added during emergent angiography following the surgery for 5 patients. Two patients showed significant SSEP changes, and one showed significant SSEP and EEG changes, indicating cerebral hypoperfusion. Of these 3 patients, patient 1 had experienced irreversible SSEP loss with postoperative stroke. Patients 2 and 3 had SSEP and/or EEG changes that had recovered to baseline after interventions without postoperative deficits. Despite ICA injury, 10 patients showed no significant SSEP and/or EEG changes, and all 7 patients with BAEP monitoring showed no significant BAEP changes, indicating adequate cerebral and brainstem perfusion, respectively. The injured ICA was sacrificed in 4 patients, of whom 3 showed stable SSEP and 1 had experienced irreversible SSEP loss. IONM correlated with the postoperative neurologic examination findings in all cases, adequately predicting the neurologic outcomes after ICA injury. SSEP and EEG monitoring can accurately detect cerebral hypoperfusion and provide real-time feedback during surgery. SSEP and EEG changes predicted forneurologic outcomes and guide surgical decisions regarding the preservation or sacrifice of the ICA. Comprehensive multimodality monitoring according to the surgical risks can serve to detect and guide the management of ICA injury in EESBS.

Delayed hearing loss after microvascular decompression for hemifacial spasm.

This study aimed to analyze cases of delayed hearing loss after microvascular decompression (MVD) for hemifacial spasm and identify the characteristic features of these patients. We retrospectively reviewed the medical records of 3462 patients who underwent MVD for hemifacial spasm between January 1998 and August 2017. Among these, there were 5 cases in which hearing was normal immediately postoperatively but delayed hearing loss occurred. None of the 5 patients reported any hearing disturbance immediately after the operation. However, they developed hearing problems suddenly after some time (median, 22days; range 10-45days). On examination, sensorineural hearing loss was confirmed. High-dose corticosteroid treatment was prescribed. Preoperative hearing levels were restored after several months (median duration from the time of the operation, 45days; range 22-118days). Interestingly, the inter-peak latency of waves I-III in the brainstem auditory evoked potential (BAEP) was prolonged during the surgery, but recovered within a short time. Delayed hearing loss may occur after MVD for HFS. Prolongation of the inter-peak latency of waves I-III seems to be associated with the occurrence of delayed hearing loss. It is possible that BAEP changes may predict delayed hearing loss, but confirmatory evidence is not available as yet. Analysis of more cases is necessary to determine the utility of BAEP monitoring to predict delayed hearing loss after MVD and to identify its exact cause.

Posterior Fossa Re-Exploration for Recurrent Trigeminal Neuralgia: Operative Findings and Surgical Techniques.

Microvascular decompression (MVD) is considered the first choice for the surgical treatment of trigeminal neuralgia (TN). However, recurrence after MVD is still a problem and a challenge for neurosurgeons. In this study, we share our experience in the posterior fossa re-exploration of the recurrent cases. From January 2014 to January 2015, 15 recurrent TN patients who received fossa re-exploration were retrospectively studied. Surgeries were performed by retrosigmoid suboccipital approach. Brainstem auditory evoked potentials (BAEP) were monitored throughout the operation. Intraoperative findings and surgical techniques were recorded. Postoperative outcomes and complications were analyzed. Among the 15 patients, Teflon adhesion was found in 14. Teflon felt displacement was found in 4 patients, and additional Teflon felt was used to interpose. New offending vessels were found in 5 patients. Three of them were small arteries and the other 2 were petrosal veins. After dissected, small pieces of wet gelatin sponge and Teflon felt were implanted respectively to ensure complete decompression. The remaining 6 patients had no vascular compression except severe adhesion, and nerve combing was performed. After surgery, 12 achieved complete pain relief, 2 gained partial pain relief, and 1 failed. Six patients experienced facial numbness postoperatively. There was no hearing impairment or other complications. During the mean 26-month follow-up, no recurrence occurred and all of 6 cases with facial numbness after surgery improved. Teflon adhesion is a significant cause of recurrent TN. Wet gelatin-assisted method is good for Teflon interposition. If no vascular compression is found during re-exploration, trigeminal nerve combing can be used. Intraoperative BAEP monitoring is helpful to reduce the incidence of hearing loss.

A New Score to Predict the Risk of Hearing Impairment After Microvascular Decompression for Hemifacial Spasm.

Intraoperative monitoring of brainstem auditory evoked potentials (BAEPs) has been implemented to reduce the risk of hearing impairment during microvascular decompression for hemifacial spasm. To evaluate intraoperative monitoring of BAEPs during microvascular decompression in patients with hemifacial spasm for predicting the risk of hearing impairment after surgery. This prospective study included 100 patients. BAEPs were recorded for all patients. We established a scoring system for the changes in wave I amplitude, I-III interpeak latency, and wave V amplitude and latency. For each change, total points were calculated, and a score out of 6 was assigned to every patient. We classified the patients based on the points scored into 3 risk groups: low-risk (0-3), medium-risk (4-5), and high-risk (6). Further, the correlation between the score and the hearing outcome was evaluated to detect the incidence and degree of hearing impairment. Eighty-seven patients scored 0 to 3, 10 scored 4 to 5, and 3 scored 6. The degree of hearing impairment was proportionate to the score recorded at the end of surgery, and patients in the low-risk group showed no impairment; medium-risk group, deterioration of maximum 2 grades according to World Health Organization classification of hearing impairment; and high-risk group, deterioration of 3 to 4 grades. Intraoperative monitoring of BAEPs evaluated through our scoring system was valuable in predicting hearing impairment after surgery.

Brainstem Auditory Evoked Potentials' Diagnostic Accuracy for Hearing Loss: Systematic Review and Meta-Analysis.

Background Microvascular decompression (MVD) utilizes brainstem auditory evoked potential (BAEP) intraoperative monitoring to reduce the risk of iatrogenic hearing loss. Studies report varying efficacy and hearing loss rates during MVD with intraoperative monitoring. Objectives This study aims to perform a comprehensive review and study of diagnostic accuracy of BAEPs during MVD to predict hearing loss in studies published from January 1984 to December 2013. Methods The PubMed/MEDLINE and World Science databases were searched. Studies performed MVD for trigeminal neuralgia, hemifacial spasm, glossopharyngeal neuralgia or geniculate neuralgia and monitored intraoperative BAEPs to prevent hearing loss. Retrospectively, BAEP parameters were compared with postoperative hearing. The diagnostic accuracy of significant change in BAEPs, which includes loss of response, was tested using summary receiver operative curve and diagnostic odds ratio (DOR). Results A total of 13 studies were included in the analysis with a total of 2,540 cases. Loss of response pooled sensitivity, specificity, and DOR with 95% confidence interval being 74% (60-84%), 98% (88-100%), and 69.3 (18.2-263%), respectively. The similar significant change results were 88% (77-94%), 63% (40-81%), and 9.1 (3.9-21.6%). Conclusion Patients with hearing loss after MVD are more likely to have shown loss of BAEP responses intraoperatively. Loss of responses has high specificity in evaluating hearing loss. Patients undergoing MVD should have BAEP monitoring to prevent hearing loss.

Microvascular decompression for hemifacial spasm: how can we protect auditory function?

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). Conclusion. 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.

Appropriate time to establish baseline responses for brain stem auditory evoked potentials during microvascular decompression for hemifacial spasm.

To evaluate the appropriate time to establish baseline responses for brain stem auditory evoked potentials (BAEPs) during microvascular decompression for hemifacial spasm and its implications on the alarm criteria and outcomes. Overall, 61 patients who had intraoperative monitoring with BAEP during microvascular decompression were retrospectively identified. The latencies and amplitudes of wave V before skin incision and at dura opening (before major manipulation) were compared with the latency and amplitude of wave V at change start (first alarm reported to the surgeon). Also, the results with respect to postoperative outcomes were evaluated. More alarms would have been communicated to the surgeon when baseline values were set at the beginning of the procedure, when compared with baseline values reset at dura opening (before major manipulation). Significant variations in BAEP latency exist before any major manipulations during microvascular decompression. Despite a false-negative case, baselines can be set before any major manipulations (e.g., just before dura opening), with an understanding of the etiology of changes to BAEPs during microvascular decompression. This is the first study to establish that during intraoperative BAEP monitoring, baselines that are reset before any significant manipulations are performed, rather than at the beginning of the procedure, have a higher level of sensitivity with regards to hearing outcomes.

Brainstem auditory evoked potential monitoring and neuro-endoscopy: Two tools to ensure hearing preservation and surgical success during microvascular decompression

BackgroundThe effectiveness of microvascular decompression (MVD) has made trigeminal neuralgia (TN), hemifacial spasm (HFS), glossopharyngeal neuralgia, and other cranial nerve rhizopathy diseases treatable by surgery. To ensure hearing preservation and surgical success, we have presented our experience in the application of brainstem auditory evoked potential (BAEP) monitoring and neuro-endoscopy during MVD. MethodsFrom July 2007 to October 2012, a total of 93 patients in our institution received MVD for cranial nerve rhizopathies. Among these patients, 43 had both BAEP monitoring and endoscope-assisted microsurgery for their MVD. None of the patients had undergone previous surgical treatment. Postoperative outcomes were assessed based on the medical records and clinical follow-up. ResultsThis study included 32 women and 11 men. There were 36 HFS cases and seven TN cases, and the median patient age at the time of MVD was 48 years. The median duration of symptoms before MVD was 4.2 years, and the median follow-up duration was 3.5 years (range 1.5 months–5 years). All of the patients had either immediate or delayed complete relief from the symptoms after MVD. One TN patient underwent gamma knife radiosurgery 3 years after MVD, and two HFS cases had recurrent slight spasms, which warranted no further treatment. There was no surgical mortality. The major complications included one HFS patient with delayed and permanent hearing loss and facial palsy, which occurred 1 week after MVD. The surgical success rate was 100%, and the hearing complication rate was 2%. ConclusionThe results of this retrospective study emphasized the importance of BAEP monitoring and neuro-endoscopy during MVD. It is well known that BAEP monitoring can preserve hearing function, and the endoscope offers neurosurgeons a second look to identify the nerve root entry zone and confirms the position of the Teflon felt. These two tools are especially useful in difficult cases.

Value of multimodality monitoring using brainstem auditory evoked potentials and somatosensory evoked potentials in endoscopic endonasal surgery

Objectives: To evaluate the value of intraoperative neurophysiological monitoring (IONM) using brainstem auditory evoked potential (BAEP) and somatosensory evoked potential (SSEP) monitoring to predict and/or prevent postoperative neurological deficits during endoscopic endonasal surgery (EES).Methods: We retrospectively identified 138 consecutive patients who had BAEP monitoring in addition to SSEP monitoring during EES at our institution. We reviewed the postoperative clinical outcomes and neurophysiological changes independently.Results: The total of number of patients with any IONM changes was 10. The incidence of BAEP changes was 3·62%. The incidence of SSEP changes was 3·62% as well. One patient had changes in both BAEPs and SSEPs. Majority of the changes were observed during changes in mean arterial pressure (MAP) without any postoperative neurological deficits. There were two postoperative neurological deficits.Discussion: BAEPs and SSEPs provide unique information about integrity of brainstem function during EES procedures involving tumors in the and around clival region. We advocate a comprehensive multimodality approach to IONM during EESs including BAEPs and SSEPs depending on the location of the neural structures at risk.

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

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%. 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. 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. 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 patterns and risk factors of hearing loss following microvascular decompression for hemifacial spasm

The aim of this study was to reveal the risk factors including intraoperative brain stem auditory evoked potential (BAEP) changes and to define parameter and warning values of BAEP beyond which the probability of hearing impairment rises significantly. From April 1997 to February 2009, 1156 patients underwent microvascular decompression (MVD) for hemifacial spasm (HFS) and their medical records and audiologic data. The intraoperative BAEP monitoring was performed in all operations during surgery from the time of administration of general anesthesia until the time of skin closure. Pure tone audiometry (PTA) and Speech Discrimination Score (SDS) were performed on all patients before and after surgery for categorizing the patterns of hearing loss. There were 825 females and 331 males with a mean age of 48.7 years (range 17-75 years). The mean symptom duration was 67.8 months (range 1-420 months). At the 1-year follow-up examination, 1091 (94.4%) patients of the total 1156 patients exhibited a cured state, and 65 (5.6%) patients had residual spasms. Hearing loss occurred in 46 patients (3.9%). In 26 patients, PTA was decreased more than 15 dB with a proportional decrease of the SDS. In 10 patients, poor SDS without hearing loss occurred. Total deafness was developed in 10 patients. A higher incidence of BAEP change and a poor recovery especially amplitude in wave V during surgery was observed in patients with poor SDS (eight patients) and total deafness (seven patients) (p = 0.000). Reduction of amplitude more than 50% in wave V was a strong indicator for a worse outcome of the hearing capacity. The difference in other risk factors according to hearing loss pattern was not statistically significant (p > 0.05). Only female was significant (p = 0.005). The intraoperative BAEP change and a poorer recovery, especially reduction of amplitude more than 50% in wave V, was a strong indicator for a worse outcome of the hearing capacity. Vigilant intraoperative monitoring of the BAEP and adequate steps for recovery of the BAEP change could prevent hearing loss after MVD for HFS.

Intraoperative Neurophysiologic Monitoring in 80 Patients with Chiari I Malformation: Role of Duraplasty

Neurophysiologic intraoperative monitoring of the brainstem auditory evoked potentials (BAEPs) is a widely used method to assess the functional integrity of the central auditory system during surgery involving the brainstem or the cranial nerves. The purpose of this study is to describe our experience with neurophysiologic intraoperative monitoring of BAEPs during posterior fossa decompression (PFD) surgery for the management of Chiari I malformation. Although suboccipital craniectomy is the standard surgical technique applied in all cases undergoing PFD, the role of dural patch grafting (duraplasty) remains controversial. In most cases, the PFD was supplemented by duraplasty only when the Chiari I malformation was complicated by the presence of syringomyelia. Our study reviewed the intraoperative BAEP changes during the different surgical stages of Chiari repair and correlated these with clinical and radiological findings present. Our data revealed that for both groups of patients, with or without associated syringomyelia, the predominant improvement in central conduction in most cases occurred during the period of bony decompression without significant additional improvement after the duraplasty procedure.

Monitorage peropératoire des potentiels évoqués auditifs précoces dans la chirurgie de décompression microchirurgicale des nerfs crâniens de l’angle pontocérébelleux

Brainstem auditory evoked potentials (BAEP) monitoring is a useful tool to decrease the danger of hearing loss during pontocerebellar angle surgery, particularly in microvascular decompression (MVD). Critical complications arising during MVD surgery are the stretching of the VIII nerve - the main cause of hearing loss - labyrinthine artery manipulation, direct trauma with instruments, or a nearby coagulation, and at end of the surgery neocompression of the cochlear nerve by the prosthesis positioned between the conflicting vessel(s) and the VIIth-VIIIth nerve complex. All these dangers warrant the use of BEAP monitoring during the surgical team's training period. Based on delay in latency of peak V, we established warning thresholds that can provide useful feedback to the surgeon to modify the surgical strategy: the initial signal at 0.4 ms is considered the safety limit. A second signal threshold at 0.6 ms (warning signal for risk) corresponds to the group of patients without resultant hearing loss. The third threshold characterized by the delay of peak V is at 1 ms (warning signal for a potentially critical situation). BAEP monitoring provides the surgeon with information on the functional state of the auditory pathways and should help avoid or correct manoeuvres that can harm hearing function. BAEP monitoring during VIIth-VIIIth complex surgery, particularly in MVD of facial nerves for HFS is very useful during the learning period.

Intraoperative electrophysiological monitoring in microvascular decompression for hemifacial spasm

We aimed to determine the reliability of (i) intraoperative monitoring by stimulated electromyography (EMG) of the facial nerve to predict the completeness of microvascular decompression (MVD) for hemifacial spasm (HFS), and (ii) brainstem auditory-evoked potential (BAEP) to predict postoperative hearing disturbance. We conducted a prospective study of 36 patients who received MVD for HFS. We confirmed the disappearance of an abnormal muscle response in the facial nerve EMG to predict the completeness of MVD, and performed BAEP monitoring to predict postoperative hearing disturbance. The sensitivity, specificity and accuracy of facial nerve EMG and BAEP monitoring were evaluated. The sensitivity, specificity and accuracy of facial nerve EMG were 0.97, 1.0 and 0.97, respectively, and that for BAEP monitoring were 1.0, 0.94 and 0.94 respectively. There was one false positive result for facial nerve EMG, and two false positive results for BAEP monitoring. No false negative result was encountered for either EMG or BAEP monitoring. Facial nerve EMG correctly predicted whether MVD was successful in 35 out of 36 patients, and BAEP correctly predicted whether there was postoperative hearing disturbance in 34 out of 36 patients. Intraoperative facial nerve EMG provides a real-time indicator of successful MVD during an operation while BAEP monitoring may provide an early warning of hearing disturbance after MVD.