Intraoperative Brainstem Auditory Evoked Potentials Monitoring Research Articles

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.

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.

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.

Value of Intraoperative Brainstem Auditory Evoked Potential Monitoring in Reducing the Auditory Morbidity Associated with Microvascular Decompression of Cranial Nerves

The present study was performed to determine whether the intraoperative monitoring of brainstem auditory evoked potentials (BAEPs) during microvascular decompression operations is effective in preventing profound hearing loss or deafness in the ipsilateral ear. The authors retrospectively compared the auditory morbidity of posterior fossa microvascular decompression surgery for the treatment of tic douloureux and hemifacial spasm before and after the introduction of routine intraoperative BAEP monitoring in 1984. Each patient underwent a similar procedure performed by the same surgeon. The two patient groups were comparable with regard to age, sex, and indications for surgery, Auditory morbidity did not decline with the increasing experience of the surgeon prior to 1984; 10 (6.6%) of 152 primary operations (151 patients) in which monitoring was not performed were followed by a profound ipsilateral hearing loss or deafness. In the monitored group, none of 109 operations (104 patients) caused profound hearing loss or deafness. This significant decline in auditory morbidity is attributed by the authors to the use of intraoperative BAEP monitoring, which allows the surgeon to alter the operation in response to degradations in the wave patterns. Based on our experience and that of others, we believe that intraoperative BAEP monitoring is of value in reducing the auditory morbidity of posterior fossa microvascular decompression surgery.

The efficacy of brainstem auditory evoked potentials in acoustic tumor surgery

As the identification of patients with small acoustic neuromas and salvageable hearing increases, intraoperative auditory nerve monitoring has been used increasingly in an attempt to improve the hearing preservation rate. Far-field recordings obtained by brainstem auditory evoked potentials (BAEP), at times enhanced by electrocochleography, have become a standard method of intraoperative auditory nerve assessment. To evaluate the usefulness of this monitoring technique, the hearing preservation results of a series of unmonitored acoustic tumor removals were compared to a series of patients monitored via the standard brainstem auditory evoked potentials. With comparable average tumor sizes, 4 of 7 unmonitored patients had hearing preserved at preoperative levels compared to 4 of 9 monitored patients. Neither preoperative BAEP assessments nor absolute tumor size were predictive of hearing preservation. This report brings into question the effectiveness of far-field intraoperative BAEP monitoring during acoustic tumor resection and suggests that direct auditory nerve monitoring may be more appropriate.

Intraoperative Monitoring of Brainstem Auditory Evoked Potentials

Brainstem auditory evoked potentials (BAEPs) were monitored intraoperatively during 44 posterior fossa operations. Technically satisfactory recordings were obtained from 42 patients (95%) and, in 41 of these cases (98%), the intraoperative changes in BAEPs were correlated with the postoperative neurological findings. The functional integrity of the brainstem was assessed by intraoperative BAEP monitoring in 33 patients. Transient, reversible changes were observed in six (18%), and none had postoperative brainstem dysfunction. The functional integrity of the auditory pathway was monitored in 11 cases, and nine of these patients (82%) exhibited alterations of BAEP waveforms. Transient, reversible dysfunction occurred in three, and permanent changes in six (obliteration in five). Seven patients experienced postoperative hearing loss, six of whom had intraoperative changes in BAEPs that became permanent. The seventh had only transient derangement during surgery. BAEP monitoring appeared to be a much more sensitive indicator of auditory than of brainstem function.The study suggests that the maximum delay in wave V latency in reversible dysfunction is about 1.0 msec. Therefore, surgery should be interrupted before the wave V latency is delayed by 1.0 msec, in order to avert postoperative neurological deficits. However, when BAEP changes are rapid, it is extremely difficult to halt the surgical procedure before such alterations become irreversible. The authors conclude that a more timely indicator of reversible trauma must be developed.

The use of brainstem auditory evoked potentials during posterior fossa surgery as a monitor of brainstem function.

Nine patients with unilateral ponto-cerebellar tumour, one with epidermoid, eight with acoustic neuroma had intraoperative monitoring of the brainstem auditory evoked potentials (BAEP) using bilateral scalp recording (Cz-A1 and Cz-A2) and binaural stimulation in order to monitor brainstem function during the surgery. Results were correlated with preoperative and postoperative BAEP findings. There was some intraoperative BAEP change in all the patients. Halothane anaesthesia caused bilateral wave V. prolongation in six patients. Lumbar drainage produced ipsilateral or bilateral wave V. prolongation in three of four patients in whom lumbar drainage was established. Opening the dura produced ipsilateral or bilateral wave V. depression or bilateral prolongation in four patients. Tumour dissection caused BAEP changes in all the patients: bilateral prolongation or depression in five patients, and ipsilateral prolongation and/or depression in six patients, three of them together with bilateral changes. The only patient who had no changes in wave I-IV. but in whom a big wave VI. appeared at the tumour side during removal, had epidermoid tumour. At the end of surgery there was some improvement in all patients, but in two the improvement was not striking: in one BAEP remained flat ipsilaterally, and in other, latency did not improve. All the patients had a good clinical recovery a few days later, but the control BAEP performed from the 3rd-7th postoperative day was not yet completely recovered in four patients. Intraoperative BAEP monitoring can be a useful technique to monitor brainstem function.(ABSTRACT TRUNCATED AT 250 WORDS)