Usefulness Of Intraoperative Electromyography And Brainstem Auditory Evoked Potential During Skull Base Surgery

Objectives: to investigate the technique of intraoperative electromyographic monitoring of oculomotor and abducens nerves and its usefulness during skull base surgery Methods: From March 2016 to November 2016,patients with skull base tumors,who have been operated on at the Department of Neurosurgery,Xuanwu Hospital,Capital Medical University,China,were included on the basis of a request from the operating surgeon for the oculomotor nerve(CN III)and abducense nerve(CN VI)monitoring.We recorded electromyography(EMG)of muscles innervated by CN III and CN VI: levator palpebrae superioris(LPS)muscle and/or inferior rectus(IR)muscle for CN III monitoring,and lateral rectus(LR)muscle for CN VI monitoring.We correlate the intraoperative spontaneous muscle activity(SMA)and compound muscle action potential(CMAP)with the postoperative function of the oculomotor and abducense nerves.Results:1.There were 23 patients with CN III and/or CN VI monitoring during skull base surgery.A total of 19 patients had 19 oculomotor nerves monitored during surgery.Bipolar paired recording electrodes were applied to the IR and the LPS muscles in 19 and 15 out of the 19 patients,respectively.There were 14 IR muscles(73.7%)and 7 LPS muscles(43.8%)that displayed the trains responses,however,only 7 and 3 patients exhibited postoperative oculomotor function deficits respectively.2.A total of 22 patients had 22 abducens nerves monitored through recording muscle responses from the LR muscle during surgery.There were 6 nerves(27.3%)that displayed the trains responses,however,only one exhibited transient abducens paresis.3.Electrical stimulation of CN III was attempted in 11 patients,however,the CMAP could be only recorded from the IR muscle with 0.5 mA in 8 patients(72.7%)and the LPS muscle never displayed the CMAP.Two out of these 8 patients exhibited postoperative oculomotor function deficits and the latencies of them were much longer than the others.In the remaining 3 patients who had no CMAP with 0.5 mA,2 patients developed permanent oculomotor paresis4.CN VI electrical stimulation was attempted in 4 patients.Reproducible CMAPs following stimulation of the cisternal segment with 0.1 mA after tumor removal were successfully obtained from the LR muscle in all patients.One out of these 4 patients had transient CN VI deficits,whose amplitude of the evoked CMAP was much lower than the others.Conclusions: The feasibility of the intraoperative EMG monitoring of the extaocular mcuslce has been confirmed by our study.The SMA activity can reflect the proximity of the extraocular cranial nerve(EOCN)and the CMAP can help identification of EOCN during surgery,hence providing value in the operating field and potentially reducing the incidence of iatrogenic injury.However,both of them have no significant predictive value in postoperative function assessment.Objective: to investigate the value of intraoperative facial muscles abnormal muscle responses(AMR)and brainstem auditory evoked potential(BAEP)in the microvascular decompression(MVD)for hemifacial spasm(HFS).Methods: From September 2015 to September 2016,patients diagnosed with HFS,who have been operated on at the Department of Neurosurgery,Xuanwu Hospital,Capital Medical University,China,were included.They were divided into two groups,monitoring group and nonmonitoring group,according to the application of AMR and BAEP intraoperatively.Counting and analyzing the effects of two groups cases,the rate of hearing changes,as well as the relationships between AMR and postoperative effects and BAEP and postoperative hearing changes.Results: 1.There were 52 patients totally.The monitoring group and nonmonitoring group had 28 and 24 patients,respectively.There was no significance of outcome and hearing changes between these two groups.However,the long-term outcome of monitoring group was better than that of nonmonitoring group.The hearing loss rate of monitoring group was lower than that of nonmonitoring group.2.AMR waveform was recorded in all of the 28 patients intraoperatively.AMR disappeared in 16 patients and sustained in 11 patients.AMR was never triggered in one patient.There was no significance of outcome between these two groups.However,the clinical outcomes of 1st postoperative day and long-term follow-up of AMR-free group were better than that of AMR-sustained group.3.BAEP waveform was recorded in all of the 28 patients intraoperatively.There was significance of latency of III and V between the hearing loss group and non-hearing loss group.Conclusions:1.AMR can be used as a prognosis evaluation index.2.AMR was still sustained in some patients after MVD.The application of AMR can improve early and long-term efficacy.3.The application of BAEP can reduce hearing damage in MVD.Wave III could be used as a predictive value for hearing assessment,especially for the high frequency hearing level.