Facial Motor Evoked Potential Research Articles

Predictive value of facial motor–evoked potential and electromyography for facial motor function in vestibular schwannoma surgery

PurposeIntraoperative neuromonitoring (IONM) aims to preserve facial nerve (FN) function during vestibular schwannoma (VS) surgery. However, current techniques such as facial nerve motor evoked potentials (FNMEP) or electromyography (fEMG) alone are limited in predicting postoperative facial palsy (FP). The objective of this study was to analyze a compound fEMG/FNMEP approach.MethodsIntraoperative FNMEP amplitude and the occurrence of fEMG-based A-trains were prospectively determined for the orbicularis oris (ORI) and oculi (OCU) muscle in 322 VS patients. Sensitivity and specificity of techniques to predict postoperative FN function were calculated. Confounding factors as tumor size, volume of intracranial air, or IONM duration were analyzed.ResultsA relevant immediate postoperative FP was captured in 105/322 patients with a significant higher risk in large VS. While fEMG demonstrated a high sensitivity (77% and 86% immediately and 15 month postoperative, respectively) for identifying relevant FP, specificity was low. In contrast, FNMEP have a significantly higher specificity of 80.8% for predicting postoperative FP, whereas the sensitivity is low. A retrospective combination of techniques demonstrated still an incorrect prediction of FP in ~ 1/3 of patients.ConclusionsFNMEP and fEMG differ in sensitivity and specificity to predict postoperative FP. Although a combination of IONM techniques during VS surgery may improve prediction of FN function, current techniques are still inaccurate. Further development is necessary to improve IONM approaches for FP prediction.

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.

Comparison Between Cz-C3/C4 and C3-C4 Montages to Protect Against Peripheral Stimulation in Transcranial Facial Motor-Evoked Potential Monitoring.

In facial motor-evoked potential monitoring, efforts to reduce peripheral stimulation are necessary because it can cause false-negatives. The effects of peripheral stimulation on Cz-C3/C4 and C3-C4 montages were compared. Facial motor-evoked potentials were recorded from bilateral orbicularis oculi (Oculi) and oris (Oris) muscles. The double-train approach combining single-pulse and five-train pulse stimulation was used to determine the effect of peripheral stimulation. If the five-train pulse produced a significant waveform, it was defined as "total success." In total success cases, "true success" was defined as a case in which no waveform appeared after the single pulse at the threshold level of the five-train pulse. The total and true success rates and the threshold value of Oculi and Oris were compared between Cz-C3/C4 and C3-C4 montages. Thirty-six muscles each of Oculi and Oris of 18 patients were used for the analysis. True success was more likely to be obtained by the Cz-C3/C4 montage than the C3-C4 montage in Oculi (42% vs. 22%, p = 0.039). Both Oculi and Oris had higher thresholds to elicit facial motor-evoked potentials with the Cz-C3/C4 montage (Oculi: 101.7 vs. 71.4 mA, p = 0.038; Oris: 94.8 vs. 73.1 mA, p = 0.016). Cz-C3/4 montage is more effective at reducing peripheral stimulation compared with the C3-4 montage. This effect was primarily seen in the orbicularis oculi muscle. It should be noted that the Cz-C3/C4 montage has a higher threshold than the C3-C4 montage in facial muscles. In facial motor-evoked potential monitoring, the Cz-C3/C4 montage may be more suitable to eliminate peripheral stimulation.

Application of two kinds of electrophysiological monitoring techniques for the prediction of facial nerve outcomes after vestibular Schwannoma surgery

Objective: To investigate the application of transcranial facial nerve motor evoked potential (FNMEP) and direct nerve electrical stimulation (DNES) for the prediction of facial nerve function after vestibular schwannoma surgery. Methods: The clinical data of 106 patients who underwent vestibular schwannoma surgery under electrophysiological monitoring of facial nerve between 2017 and 2021 were retrospectively examined, and there were 57 males and 49 females, with a mean age of (51±11) years. Neuroelectrophysiological monitoring was performed in all patients during the operation. After the tumor was removed, FNMEP and DNES were used for electrophysiological evaluation of facial nerve function. The amplitude ratios of FNMEP to baseline (M1) and the brainstem segment to the internal auditory canal segment of DNES (M2) were recorded after the tumor was removed, respectively. The correlation between these two ratios and facial nerve function at 1 day, 1 month and 3 months after the operation were compared. According to the House-Brackmann (HB) scale, Grade Ⅰ-Ⅱ refers to good facial nerve function, and grade Ⅲ-Ⅵ refers to moderate and severe facial nerve dysfunction. Non-parameter Spearman correlation coefficient was used to evaluate the correlation between M1 and M2 and facial nerve function at 1 day, 1 month and 3 months after operation, and the receiver operating characteristic (ROC) curves were plotted to verify the diagnostic efficacy of M1 and M2 for predicting the prognosis of postoperative facial nerve function. Results: Among 106 patients, 102 cases (96.3%) underwent total tumor resection, 4 patients (3.7%) underwent subtotal resection, 104 patients (98.1%) had anatomical preservation of facial nerves, and there were no deaths reported. All patients could evoke reliable FNMEP and 2 patients could not evoke DNES in the brainstem segment of the facial nerve. There were 81 (76.4%), 99 (93.4%) and 103 patients (97.2%) with satisfactory function of facial nerve at 1 day, 1 month and 3 months after surgery, respectively. M1 had large absolute values of Spearman correlation coefficient at 1 day (ρ=|-0.648|) and 1 month (ρ=|-0.552|) after surgery (both P<0.001), while M2 showed a greater absolute value of Spearman correlation coefficient at 3 months (ρ=|-0.395|) than that of M1 (ρ=|-0.378|) (P<0.001). Cut-off value of M1 was 0.58 (sensitivity=0.92, specificity=0.64), and that of M2 was 0.36 (sensitivity=0.64, specificity=1.00). Meanwhile, M1<0.58 or M2<0.36 suggested moderate and severe impairment of facial nerve function. Conclusions: Both FNMEP and DNES during vestibular schwannoma surgery can effectively evaluate the postoperative facial nerve function. FNMEP is better than DNES in predicting the early postoperative facial nerve function, but DNES is better for predicting the long-term postoperative facial nerve function.

A Study on the Role of Intraoperative Corticobulbar Motor Evoked Potentials for Improving Safety of Cerebellopontine Angle Surgery in Elderly Patients

Preservation of facial nerve function (FNF) during neurosurgery for cerebellopontine angle (CPA) tumors is paramount in elderly patients. Corticobulbar facial motor evoked potentials (FMEPs) allow assessment intraoperatively of the functional integrity of facial motor pathways, thus improving safety. We aimed to evaluate the significance of intraoperative FMEPs in patients 65 years and older. A retrospective cohort of 35 patients undergoing CPA tumors resection was reported; outcomes of patients aged 65-69 years vs. ≥70 years were compared. FMEPs were registered both from upper and lower face muscles, and amplitude ratios (minimum-to-baseline, MBR; final-to-baseline, FBR; and recovery value, FBR minus MBR) were calculated. Overall, 78.8% of patients had a good late (at 1 year) FNF, with no differences between age groups. In patients aged ≥70 years, MBR significantly correlated with late FNF. At receiver operating characteristics (ROC) analysis, in patients aged 65-69 years, FBR (with 50% cut-off value) could reliably predict late FNF. By contrast, in patients aged ≥70 years, the most accurate predictor of late FNF was MBR, with 12.5% cut-off. Thus, FMEPs are a valuable tool for improving safety in CPA surgery in elderly patients as well. Considering literature data, we noticed higher cut-off values for FBR and a role for MBR, which suggests an increased vulnerability of facial nerves in elderly patients compared to younger ones.

SURG-34. INTRAOPERATIVE CORTICOBULBAR MOTOR EVOKED POTENTIALS RELIABLY PREDICT FACIAL NERVE FUNCTION IN ELDERLY PATIENTS WITH CEREBELLOPONTINE ANGLE TUMORS. A CLINICAL AND NEUROPHYSIOLOGY STUDY

Abstract BACKGROUND Cerebellopontine angle (CPA) surgery for extra-axial lesions in elderly patients could be hampered by concerns regarding functional outcomes. However, an overall ageing society warrants an improved approach. Intraoperative neuromonitoring is crucial for facial nerve (FN) preservation: intraoperative cortico-bulbar facial motor evoked potentials (FMEPs) can be effectively coupled to standard techniques. In a previous work, we validated the use of FMEPs as preditors of early and late post-operative FN function (FNF). Aim of this study was to re-evaluate FMEP role in patients beyond 65 years of age. METHODS An institutional series of 83 patients was reported. A pair of needle electrodes was used to record FMEP from orbicularis oculi (OOc) and orbicularis oris (OOr) muscles; baseline, final and minimum values were recorded. From FMEP amplitudes, minimum-to-baseline (MBR) and final-to-baseline (FBR) amplitude ratios, and recovery value (RV=FBR-MBR), were calculated. These indices were correlated to early (at discharge) and late (at 1-year) post-operative FNF. RESULTS 23 (27.7%) patients were older than 65 years. Among these, 52.2% and 81% had a good early and late FNF, respectively. Early and late FNF were not associated to age (p &amp;gt; 0.99 and p=0.72, respectively). In elderly patients, higher FBR (from OOc and OOr) and MBR (from OOc) were associated to a good early FN recovery (p=0.01, p=0.009, and p=0.03, respectively). Conversely, MBR from OOr was the only parameter significantly associated with late FN function (p=0.049). ROC analysis confirmed that, in elderly patients, the most accurate index for predicting late FN function was MBR as measured from OOr (AUC=0.869, cut-off value 12.5%). The most accurate index for predicting early FN function was FBR from OOc (AUC=0.865). CONCLUSION Cortico-bulbar FMEPs are reliable predictors of early and late post-operative FNF in elderly patients and allow a safe and feasible surgery in this important cohort.

Intraoperative Corticobulbar Motor Evoked Potential in Cerebellopontine Angle Surgery: A Clinically Meaningful Tool to Predict Early and Late Facial Nerve Recovery.

Intraoperative neuromonitoring is crucial for facial nerve preservation in cerebellopontine angle (CPA) surgery. Among the available techniques, the role of intraoperative corticobulbar facial motor evoked potentials (FMEPs) is unclear. To evaluate the significance of intraoperative FMEPs as indicators for early and late postoperative facial nerve function (FNF) in CPA tumor resection and the feasibility of their integration with standard monitoring techniques. An institutional series of 83 patients who underwent surgery under intraoperative monitoring for CPA extra-axial tumor resection was reported. A pair of needle electrodes was used to record FMEP from orbicularis oculi (OOc) and orbicularis oris (OOr) muscles at baseline, at the end of surgery and minimum values recorded. From FMEP amplitudes, minimum-to-baseline amplitude ratio (MBR), final-to-baseline amplitude ratio (FBR), and recovery value, intended as FBR minus MBR, were calculated. These indices were correlated with early and late postoperative FNF. Our analysis demonstrated that higher FBR (both from OOc and OOr) and MBR (from OOr only) were associated with a good early and late FNF; a higher MBR from OOc was significantly associated with a good late FNF. The most accurate index in predicting early FNF was FBR measured from OOr with a cutoff of 35.56%, whereas the most accurate index in predicting late FNF was FBR as measured from OOc with a cutoff of 14.29%. Our study confirmed that FMEPs are reliable predictors of early and late postoperative FNF in CPA surgery and could be easily integrated with standard intraoperative neuromonitoring techniques.

Intraoperative transcranial facial motor evoked potential monitoring in surgery of cerebellopontine angle tumors predicts early and late postoperative facial nerve function

ObjectiveWe propose a novel method that predicts facial nerve function (FNF) calculated from the drop and recovery of facial motor evoked potential (FMEP) amplitude ratio during the surgery of cerebellopontine angle tumors. MethodsWe enrolled 73 patients with cerebellopontine angle tumor, and used a biphasic, constant current, and suprathreshold stimulation (BCS) protocol to record FMEP of the orbicularis oris. We measured the intraoperative minimum-to-baseline amplitude ratio (MBR), the final-to-baseline amplitude ratio (FBR), and the recovery value (RV). RV was measured by subtracting MBR from FBR. Using those values, we evaluated FNF both at early postoperative (EP) and late postoperative (LP) periods. ResultsWe successfully obtained 62 FMEP readings. Facial palsies occurred in 22 patients during the EP period, and 14 patients recovered during the LP period. Both MBR and FBR showed a significant correlation with FNF in the EP period. RV showed a good predictive power of FNF recovery during the LP period for the first time. ConclusionsRV is a new and useful predictor of FNF recovery. MBR can be an intraoperative predictor of FNF in the EP period. SignificanceFNF outcome in the early and late postoperative periods can be predicted by FMEP.

The role of facial nerve motor evoked potentials in predicting facial nerve function in vestibular schwannoma surgery

Objective: To analyze the role of facial nerve motor evoked potentials in predicting facial nerve function in vestibular schwannoma surgery. Methods: In a retrospective clinical study of 226 patients with acoustic neuroma, admitted to our hospital from January 2016 to May 2019, were investigated by facial nerve motor evoked potentials (FNMEP) elicited by multi-pulse transcranial electrical motor cortex stimulation from. For recording the same electrode set-up was used as for continuous EMG monitoring of the orbicularis oculi,oris muscles and mentalis. Pre-surgical (opening dural), intraoperative and post-surgical (closing dural) FNMEP amplitudes and latencies were recorded. End (closing dura) to start (opening dura) amplitude ratios were compared to early-term(3 day after surgery) facial nerve function by House-Brackmann(HB) Grading. Results: 201 patients(88.9%) get a total tumor resection, 15 patients (6.6%) were a subtotal resection, 10 patients(4.4%) were a partial resection. 100 percent of patients had a integrated anatomical preservation of facial nerves, there were four (1.8%) death cases in this group. Reliable FNMEPs were obtained in all patients. The ratio of end-operative to start-operative FNMEP-amplitude showed a negative correlation with early facial nerve function. Correlation was especially close with early function: an amplitude preservation rate of 85.3% led to HB Ⅰ or Ⅱ in 190(84.1%) patients, of 45.6% to HB Ⅲ in 17(7.5%) patients, of 23.1% to HB Ⅳ in 13(5.8%) patients and of 6.7% to HB Ⅴor Ⅵ in 6(2.7%) patients. There was a negative correlation between FNMEP amplitude ratio and post-surgical early HB grading(r=-0.895, P=0.000). Conclusion: FNMEP was highly reliable in predicting early postoperative facial function of the resection of vestibular schwannoma, was a valid protection technique of facial nerve.

Differential Recovery in Early- and Late-Onset Delayed Facial Palsy Following Vestibular Schwannoma Resection.

Delayed facial palsy (DFP) after resection of vestibular schwannomas (VS) is worsening of facial nerve function after an initially normal postoperative result. To characterize different types of DFP, compare recovery rates, and review of series of outcomes in patients following resection of VS. Between 2001 and 2017, 434 patients (51% female) with VS underwent resection. We categorized the patients who developed facial palsy into groups based on timing of onset after surgery, immediate facial palsy (IFP), early-onset DFP (within 48 h), and late-onset DFP (after 48 h). Introduction of facial nerve motor-evoked potentials (fMEP) in 2002 and a change of practice utilizing perioperative minocycline in 2005 allowed for historical analysis of these interventions. Mean age of study cohort was 49.1 yr (range 13-81 yr), with 19.8% developing facial palsy. The late-onset DFP group demonstrated a significantly faster recovery than the early-onset DFP group (2.8±0.5 vs 47±8 wk, P<.0001), had prolonged latency to palsy onset after initiating perioperative minocycline (7.3 vs 12.5 d, P=.001), and had a nonsignificant trend towards faster recovery from facial palsy with use of minocycline (2.6 vs 3.4 wk, P=.11). Given the timings, it is likely axonal degeneration is responsible for early-onset DFP, while demyelination and remyelination lead to faster facial nerve recovery in late-onset DFP. Reported anti-apoptotic properties of minocycline could account for the further delay in onset of DFP, and possibly reduce the rate and duration of DFP in the surgical cohort.

Facial motor evoked potential with paired transcranial magnetic stimulation: prognostic value following microvascular decompression for hemifacial spasm.

Microvascular decompression (MVD) is widely considered the treatment of choice for hemifacial spasm (HFS), but not all patients immediately benefit from it. Numerous electrophysiological tests have been employed to monitor the integrity of the facial nerve prior to, during, and after MVD treatment. The authors sought to verify if facial motor evoked potential (FMEP) with paired transcranial magnetic stimulation (pTMS) can be utilized as a tool to predict prognosis following MVD for HFS. FMEP using pTMS was performed preoperatively and postoperatively for 527 HFS patients who underwent an MVD treatment. Various interstimuli intervals (ISIs), which included 2, 10, 20, 25, 30, 75, and 100 msec, were applied for each paired stimulation and pTMS(%) was obtained. A graph of pTMS(%) versus each ISI was drawn for every patient and its pattern was analyzed in accordance with patients' clinical outcomes. With ISIs of 75 and 100 msec, pTMS(%) was physiologically further inhibited, whereas it was relatively facilitated under ISIs of 20, 25, and 30 msec; loss of this specific pattern, that is, further inhibition-relative facilitation, indicated impaired integrity of the facial nerve. Those patients who immediately benefited from an MVD and experienced no relapse tended to show proper restoration of this further inhibition-relative facilitation pattern (p = 0.01). Greater resemblance between the physiological pattern of pTMS(%) and postoperative pTMS(%) was correlated to better outcome (p = 0.019). A simple linear graph of pTMS(%) versus each ISI may be a helpful tool to predict prognosis for HFS following an MVD.

Blink synkinesis monitoring during microvascular decompression for hemifacial spasm.

In the present study, we investigated whether blink synkinesis monitoring during microvascular decompression (MVD) is effective for predicting long-term outcomes in patients with hemifacial spasm (HFS). This retrospective study included 69 patients who had undergone MVD for HFS at a tertiary hospital. All patients underwent intraoperative monitoring of blink synkinesis, lateral spread responses (LSRs), and facial nerve motor-evoked potentials (FNMEPs). Baseline signals were compared to those obtained following decompression with Teflon, and postoperative outcomes were recorded. A total of 65 patients were observed with complete relief of symptoms after 1 year after MVD, while 61 patients were observed with initial disappearance of blink synkinesis, 57 patients were observed with initial elimination of the LSR, and 45 patients with initial decreases in FNMEP amplitude (>50%). The highest sensitivity and accuracy values were observed for blink synkinesis. Chi-square tests comparing the sensitivity of the three methods revealed that FNMEP monitoring was associated with significantly lower sensitivity values than the remaining methods. Combined use of blink synkinesis and LSRs did not significantly increase sensitivity (61/65 vs 62/65) or accuracy (62/69 vs 63/69). Our results demonstrate that blink synkinesis monitoring is safe during MVD for HFS. Furthermore, blink synkinesis was associated with the highest sensitivity and predictive values among the three methods evaluated. These findings suggest that blink synkinesis can be regarded as the first choice for intraoperative monitoring during MVD. Concurrent use of blink synkinesis and LSR monitoring may maximize the ability to predict patient prognosis and determine the extent of decompression.

Impact of Motor-Evoked Potential Monitoring on Facial Nerve Outcomes after Vestibular Schwannoma Resection

Assess the utility of intraoperative transcranial facial motor-evoked potential (FMEP) monitoring in predicting and improving facial function after vestibular schwannoma (VS) resection. Retrospective chart review. Data were obtained from 82 consecutive VS resections meeting inclusion criteria. Sixty-two cases were performed without FMEP and 20 with FMEP. Degradation of FMEP response was defined as a final-to-baseline amplitude ratio of 0.5 or less. House-Brackmann (HB) grade was assessed preoperatively, postoperatively, at follow-up assessments, and it was compared between pre- and post-FMEP cohorts. Positive predictive value (PPV) and negative predictive value (NPV), sensitivity, and specificity of FMEP degradation in predicting facial weakness were calculated. In the pre-FMEP group, at length of follow-up (LOF) ⩾9 months, 83.9% (52/62) of patients exhibited HB 1-2 outcome. In the post-FMEP cohort, 75.0% (15/20) exhibited HB 1-2 function at LOF ⩾9 months. There was no difference in rates of HB 1-2 outcomes between groups in the immediate postoperative period ( P = .35) or at long-term follow-up ( P = 1.0). With respect to predicting immediate postoperative facial function, FMEP demonstrated high specificity (88.9%) and moderate sensitivity (54.5%). The PPV and NPV for immediate postoperative facial function were 85.7% and 61.5%, respectively. With respect to long-term (⩾9 months LOF) facial function, intraoperative FMEP was moderately sensitive (71.4%) and highly specific (84.6%); PPV was moderate (71.4%), and NPV was high (84.6%). Intraoperative FMEP is highly specific and moderately sensitive in predicting postoperative facial function for patients undergoing VS resection, but its use may not be associated with improved facial nerve outcomes. 4.

Prognostic value of transcranial facial nerve motor-evoked potentials in predicting facial nerve function following cerebellopontine angle tumorectomy.

Facial nerve paralysis is a common complication following cerebellopontine angle (CPA) surgery. This study investigated the prognostic value of facial nerve motor-evoked potentials (FNMEPs) elicited by transcranial electrical stimulation for facial nerve outcome after CPA tumorectomy.A total of 95 patients were enrolled in this study between January 2014 and January 2016. All these patients underwent CPA tumorectomy (unilateral, n = 95; bilateral, n = 1). Intraoperative FNMEP elicited by transcranial electrical stimulation was recorded. The short- and long-term postoperative facial nerve functions were evaluated according to the House–Brackmann (HB) scale. The correlation between perioperative changes in the FNMEP stimulus threshold (delta FNMEP = postoperative stimulus threshold level–preoperative stimulus threshold level) and postoperative facial nerve functions were analyzed.On the first day postoperatively, the facial nerve function was HB grade I in 67, grade II in 17, grade III in 7, and grade IV in 5 facial nerves. One year postoperatively, the facial nerve function was grade I in 80, grade II in 11, grade III in 3, and grade IV in 2 facial nerves. The delta FNMEP was significantly correlated with the short- and long-term facial nerve function; receiver operating characteristic (ROC) curves yielded a cut-off delta FNMEP value of 30 V (sensitivity, 91.3%; specificity, 98.6%) and 75 V (sensitivity, 100%; specificity, 98.8%) for predicting short- and long-term facial nerve function damage, respectively.FNMEP elicited by transcranial electrical stimulation is an effective and safe approach for predicting facial nerve function in CPA tumorectomy. A high delta FNMEP is a potential indicator for the prediction of postoperative facial nerve damage.

Predictive value of neurophysiological monitoring in facial nerve function after cerebellopontine angle tumor surgery

Objective To investigate the predictive value of preoperative and intraoperative electrophysiological parameters in facial nerve (FN) function after cerebellopontine angel (CPA) tumor surgery. Methods A total of 58 patients with CPA tumor underwent operations from August 2016 to March 2017 at Department of Neurosurgery, Beijing Tiantan Hospital, Capital Medical University and were enrolled into this retrospective study. Preoperative blink reflex (BR) and FN F wave response were tested in all patients. The R1 component latency and mean F wave latency were determined. Intraoperative facial motor evoked potentials (FMEP) was applied to monitor the FN function and the amplitude ratio of FMEP was documented. According to the House-Brackmann (H-B) grading system, the functional classification of FN was determined preoperatively, at 1 week, 3 months and 6 months postoperatively. Multiple logistic regression analysis was applied to explore the predictor of postoperative FN function. Results A total of 58 cases of CPA tumor underwent microsurgical excisions by retrosigmoid approach. Total and subtotal resections were performed in 55 (94.8%) and 3 cases, respectively. Single factor Logistic regression analysis showed that the results of blink reflex in patients with good FN outcome were better than those in the group with poor outcome at 3 follow-up time points (P<0.05). The results of F wave response in patients with good FN outcome were better than those in poor outcome group at 6 months post operation (P<0.05). At 3 and 6 months post surgery, the maximal tumor diameters in the good outcome group were (31.9±10.2) mm and (31.9±9.3) mm, respectively, which were smaller than those in the poor outcome group [(37.8±9.7) mm and (40.0±10.0) mm, respectively] (both P<0.05). At 1 week, 3 and 6 months post surgery, the FMEP amplitude ratios in the good outcome group were (84.6±21.3)%, (83.0±19.0)% and (81.0±19.1)%, respectively, which were higher than those in the poor outcome group [(66.2±27.0)%, (63.4±29.0)% and (59.6±31, 2)%] (all P<0.05). Multivariate Logistic regression analysis showed that FMEP amplitude ratio was the independent predictor of FN outcome at 1 week, 3 and 6 months post operation (P<0.05). The maximal tumor diameter was the independent predictor of FN outcome at 3 and 6 months post operation (P<0.05). BR classification was the independent predictor of FN outcome at 6 months after operation (P<0.05). ROC (receiver operating characteristic) curve analysis showed that the FMEP amplitude ratio cut-off values of 89.2% [AUC (area under the curve)=0.709], 58.2% (AUC=0.706) and 58.2% (AUC=0.713) predicted good FN function at 1 week, 3 and 6 months after surgery, respectively. Conclusions BR and maximal tumor diameter have certain predictive values for postoperative FN function. The FMEP amplitude ratio is a valuable predictor for postoperative FN function and its value of at least 60% is predictive of favorable long-term postoperative FN function. Key words: Cerebellopontine angle; Brain neoplasms; Facial nerve; Electrophysiology; Forecasting

Predictive Value of Intraoperative Facial Motor Evoked Potentials in Vestibular Schwannoma Surgery Under 2 Anesthesia Protocols.

We sought to validate the feasibility of facial motor evoked potential (FMEP) in facial nerve (FN) monitoring during vestibular schwannoma (VS) surgery under 2 anesthesia protocols and to examine its value for postoperative prognosis. This prospective study included 106 patients with VS who underwent microsurgical excision between May 2014 and November 2016 at the Beijing Tiantan Hospital, Capital Medical University, China. All patients were investigated for FMEP elicited by transcranial electrical stimulation in the contralateral facial motor cortex. The patients randomly received total intravenous anesthesia or combined intravenous-inhalation anesthesia. Postoperative FN function was evaluated 7-10 days after surgery (short-term) and at the last follow-up (long-term) using the House-Brackmann (HB) grading system. HB grades 1 and 2 were deemed satisfactory, whereas HB grades 3-6 were deemed unsatisfactory. The value of the final-to-start FMEP ratio for predicting short-term and long-term postoperative FN functions was examined. Valid FMEPs were obtained in 97 patients, which were recorded from the mentalis muscle. The FMEP amplitude ratio was significantly correlated with short-term and long-term postoperative FN functions. Receiver operating characteristic curve analysis showed that the FMEP ratio cut-off values of 77.4% (area under the curve= 0.797) and 56.9% (area under the curve= 0.900) predicted satisfactory FN function 7-10 days after surgery and at the last follow-up, respectively. No statistically significant difference was found in FMEP quantitative parameters between the 2 anesthesia protocols. The FMEP amplitude ratio is a valuable predictor for postoperative FN function. FMEP ratio ≥57% is predictive of satisfactory long-term FN function.

O3-6-21. Time-dependent changes in intraoperative monitoring findings during microvascular decompression for hemifacial spasm

We analyzed time-dependent changes in the intraoperative monitoring of abnormal muscle responses (AMRs) and facial motor evoked potentials (FMEPs) elicited by transcranial electrical stimulation during microvascular decompression (MVD) in 26 patients with hemifacial spasm. In the orbicularis oculi muscle, the AMRs disappeared in 11 patients before MVD, in six after MVD, and in three during dural closure. The AMRs persisted in six patients. FMEP amplitudes decreased to less than 50% in two patients before MVD, in four after MVD, and in six during dural closure. FMEP amplitudes did not decrease in 14 patients ( p p

Role of Facial Nerve Motor-Evoked Potential Ratio in Predicting Facial Nerve Function in Vestibular Schwannoma Surgery Both Immediate and at 1 Year.

To determine whether transcranial electrical stimulation-induced facial motor-evoked potential (FMEP) monitoring of the facial nerve (FN) during vestibular schwannoma (VS) tumor resection can predict both immediate and 1 year postoperative FN functional outcome. Prospective consecutive non-comparative observational case series. Tertiary referral center. Facial function, immediate post operation and at 1 year using House-Brackmann (HB) grading scale. The study included 367 consecutive patients (men 178; women 189; age 13-81 years) monitored during primary sporadic VS microsurgery between November 2002 and April 2015. Neurofibromatosis type II, revision surgery, previous radiotherapy treatment, preoperative facial nerve weakness, and non-VS cases were excluded retrospectively during analysis of data. Data of facial function were missing from eight patients at 1 year and were excluded. The correlation between the final-to-baseline FMEP ratio and immediate and 1 year facial nerve function was examined. Using logistic regression model, the cut-off points of FMEP ratio were 0.62 (PPV 0.96) and 0.59 (PPV 0.98) which predicted satisfactory FN function (HB grades 1 or 2) immediately postoperative and at 1 year after surgery, respectively. Transcranial electrical stimulation FMEP is a valuable tool for monitoring facial nerve function during resection of vestibular schwannoma. Maintaining a FMEP event-to-baseline ratio of 60% or greater is predictive of satisfactory long-term FN function.

Analysis of facial motor evoked potentials for assessing a central mechanism in hemifacial spasm.

OBJECTIVE Hemifacial spasm (HFS) is a cranial nerve hyperactivity disorder characterized by unique neurophysiological features, although the underlying pathophysiology remains disputed. In this study, the authors compared the effects of desflurane on facial motor evoked potentials (MEPs) from the spasm and nonspasm sides of patients who were undergoing microvascular decompression (MVD) surgery to test the hypothesis that HFS is associated with a central elevation of facial motor neuron excitability. METHODS Facial MEPs were elicited in 31 patients who were undergoing MVD for HFS and were administered total intravenous anesthesia (TIVA) with or without additional desflurane, an inhaled anesthetic known to centrally suppress MEPs. All measurements were completed before dural opening while a consistent mean arterial blood pressure was maintained and electroencephalography was performed. The activation threshold voltage and mean amplitudes of the MEPs from both sides of the face were compared. RESULTS There was a significantly lower mean activation threshold of facial MEPs on the spasm side than on the nonspasm side (mean ± SD 162.9 ± 10.1 vs 198.3 ± 10.1 V, respectively; p = 0.01). In addition, MEPs were also elicited more readily when single-pulse transcranial electrical stimulation was used on the spasm side (74% vs 31%, respectively; p = 0.03). Although desflurane (1 minimum alveolar concentration) suppressed facial MEPs on both sides, the suppressive effects of desflurane were less on the spasm side than on the nonspasm side (59% vs 79%, respectively; p = 0.03), and M waves recorded from the mentalis muscle remained unchanged, which indicates that desflurane did not affect the peripheral facial nerve or neuromuscular junction. CONCLUSIONS Centrally acting inhaled anesthetic agents can suppress facial MEPs and therefore might interfere with intraoperative monitoring. The elevated motor neuron excitability and differential effects of desflurane between the spasm and nonspasm sides support a mechanism of central pathophysiology in HFS. Clinical trial registration no.: B2012:099 ( clinicaltrials.gov ).

Microvascular decompression for glossopharyngeal neuralgia using intraoperative neurophysiological monitoring: Technical case report.

Background:Glossopharyngeal neuralgia (GN) is a rare functional disorder representing around 1% of cases of trigeminal neuralgia. Lancinating throat and ear pain while swallowing are the typical manifestations, and are initially treated using anticonvulsants such as carbamazepine. Medically refractory GN is treated surgically. Microvascular decompression (MVD) is reportedly effective against GN, superseding rhizotomy and tractotomy.Methods:We encountered three patients with medically refractory GN who underwent MVD using intraoperative neurophysiological monitoring (IONM). The offending vessels were the posterior inferior cerebellar arteries, which were confirmed intraoperatively via a transcondylar fossa approach to be affecting the root exit zones of the glossopharyngeal and vagus nerves. As IONM, facial motor-evoked potentials (MEPs) and brainstem auditory-evoked potentials were monitored during microsurgery in all three patients. Pharyngeal and vagal MEPs were added for two patients to avoid postoperative dysphagia.Results:GN disappeared immediately after surgery with complete preservation of hearing acuity and facial nerve function. Transient mild swallowing disturbance was observed in 1 patient without pharyngeal or vagal MEPs, whereas the remaining two patients with pharyngeal and vagal MEPs demonstrated no postoperative dysphagia.Conclusion:Although control of severe pain is expected in surgical intervention for GN, lower cranial nerves are easily damaged because of their fragility, even in MVD. IONM including pharyngeal and vagal MEPs appears very useful for avoiding postoperative sequelae during MVD for GN.