An Investigation Of Facial Nerve Monitoring In Vestibular Schwannoma Surgery

Objectives In order to improve the surgical facial nerve function of vestibular schwannoma,to investigate the prognostic factors of postoperative nerve function,and to evaluate the value of facial nerve monitoring in opposite nerve protection and prediction of postoperative nerve function in vestibular schwannoma surgery.Methods Clinical data of 72 patients with vestibular schwannoma hospitalized in the department of neurosurgery,general hospital of Tianjin medical university from September 2016 to September 2018 were retrospectively collected,and after screening by inclusion and exclusion criteria,a total of 60 patients were included in the study.The clinical data of 60 patients were collected,including preoperative MR、CT scanning,and the tumor was divided into 1-4 levels according to the Koos standard,and the facial nerve function and the posterior group cranial nerve function were examined emphatically by physical examination.Using electrophysiological monitor during operation,60 patients with vestibular schwannoma(postoperative pathological confirmation)were monitored by free-EMG and trigger-EMG.During the operation,spontaneous EMG(A trains)was observed and recorded.At the end of the operation,the brain stem and inner auditory canal were stimulated with different intensity current,and the threshold of evoked action potential stimulation was recorded.Postoperative surgical videos were reviewed to record the surgical approach,tumor resection degree and cranial nerve retention of the patients.Follow-up of patients with postoperative 1day,1 week and 6 months of facial nerve function,according to the House-Brackmann(H-B)classification system,the I-III grade of H-B was defined as facial nerve function retention,and the IV-VI grade as facial nerve dysfunction,then we compared the possible influencing factors of facial nerve function in the two groups and their possible correlation with facial nerve monitoring results.The results were analyzed by Chi-square test,Chi-square test of continuity correction or spearman correlation test,and P<0.05 was identified as the standard of statistically significant difference.Results 1.60 patients underwent retrosigmoid sinus approach.The total resection rate of intraoperative tumor was 91.7%(55/60)and the anatomical retention rate of facial nerve was 93.3%(56/60).2.By analyzing the results of facial nerve monitoring in 56patients with vestibular schwannoma preserved by facial nerve anatomy,there were23 cases of facial nerve dysfunction 1 week after operation,of which 19 were A trains,and the correction~2=5.357,P=0.021,the difference was statistically significant.3.By Spearman correlation analyzing,there was a correlation between facial nerve function and the stimulation threshold of direct electrical stimulation at the brain stem end of the facial nerve at the end of the operation,~2=0.781,P<0.05.4.The age,gender,tumor profile,tumor texture and postoperative facial nerve function of the patients were not statistically significant by single factor analysis,and there was a correlation between tumor grade and postoperative facial nerve function(r=0.656,P<0.05).5.There was no significant difference between the occurrence of delayed facial paralysis and A trains during free electromyography,~2=0.083,P=0.773>0.05.By spearman correlation analysis,there was no correlation between the incidence of delayed facial paralysis and the stimulation threshold of direct electrical stimulation at the end of the operation,r=0.224,P>0.05.Conclusions 1.The combination of free-EMG and trigger-EMG can accurately locate facial nerve,reduce the probability of facial nerve injury during operation of vestibular schwannoma,and play an important role in the preservation of anatomy and function of posterior nerve.2.Early postoperative facial nerve function injury probability is higher in patients with intraoperative monitoring A trains.3.The lower the nerve stimulation intensity at the end of operation,the better the prognosis of nerve function after operation.4.Preoperative tumor size is an important factor affecting the postoperative nerve function of patients.the higher the tumor grade,the worse the prognosis of postoperative nerve function.5.For those with large tumor,unclear membrane interface and difficulty in facial nerve separation,direct electrical stimulation at the end of brain stem did not lead to action potential,not all of them developed severe facial paralysis(above grade H-B V)immediately after operation.6.Intraoperative facial nerve monitoring such as the occurrence of A trains,the intensity of stimulation at the end of the brain stem is not statistically significant for the occurrence of delayed facial paralysis,and it is difficult to predict the occurrence of delayed facial paralysis after operation.7.Facial nerve monitoring has reached a consensus as an important auxiliary tool for the protection of nerve function in vestibular schwannoma and skull base and brain stem surgery,but the primary factor affecting postoperative nerve function is the skilled surgical skills of the operator.