TcMEP threshold change is superior to A-train detection when predicting facial nerve outcome in CPA tumour surgery

After the Knife: A Detailed Roadmap for Vestibular Schwannoma Resection in the Semi-Sitting Position - How I do it

BACKGROUND

Vestibular schwannoma surgery remains a neurosurgical challenge, with known risks, dependent on a number of factors, from patient selection to surgical experience of the team. The semi-sitting position has gained popularity as an alternative to the traditional supine position for vestibular schwannoma resection due to potential advantages such as improved surgical exposure due to clearer surgical field and anatomical orientation. However, there is a lack of standardized protocols for performing the procedure in the semi-sitting position, leading to variations in surgical techniques and outcomes.

METHODS

In this study, we aimed to establish a standardized approach for vestibular schwannoma resection using the semi-sitting position. Initiating after final position for semi-sitting, the authors have divided the surgical steps into five major parts for improved understanding and replication. Surgical techniques were analyzed through one hundred steps to identify commonalities, determining the optimal procedural steps for the semi-sitting position using surgical video for visual conceptualization.

RESULTS

The analysis described one hundred steps for vestibular schwannoma resection in the semi-sitting position, with visual demonstration of the various parts of the procedure through surgical videos. Specific recommendations for each step were outlined, including appropriate approach, monitoring strategies, and tumor and posterior fossa structures manipulation. Five major parts of the procedure were identified, leading to a reproducible standardization of the surgical procedure of vestibular schwannoma resection in the semi-sitting position.

CONCLUSIONS

This study provides a comprehensive standardized protocol for the semi-sitting procedure in vestibular schwannoma resection. By establishing a consistent approach, surgeons can minimize variations in surgical techniques and improve patient outcomes. The identified steps and recommendations can serve as a valuable resource for surgical teams involved in vestibular schwannoma resection and facilitate the dissemination and reproducibility of best practices.

Facial nerve outcome score: a new score to predict long-term facial nerve function after vestibular schwannoma surgery

Introduction

Patients' quality of life (QoL), facial nerve (FN), and cochlear nerve (CN) (if conserved) functions should be pursued as final outcomes of vestibular schwannoma (VS) surgery. In regard to FN function, different morphologic and neurophysiological factors have been related to postoperative outcomes. The aim of the current retrospective study was to investigate the impact of these factors on the short- and long-term FN function after VS resection. The combination of preoperative and intraoperative factors resulted in designing and validating a multiparametric score to predict short- and long-term FN function.

Methods

A single-center retrospective analysis was performed for patients harboring non-syndromic VS who underwent surgical resection in the period 2015-2020. A minimum follow-up period of 12 months was considered among the inclusion criteria. Morphological tumor characteristics, intraoperative neurophysiological parameters, and postoperative clinical factors, namely, House-Brackmann (HB) scale, were retrieved in the study. A statistical analysis was conducted to investigate any relationships with FN outcome and to assess the reliability of the score.

Results

Seventy-two patients with solitary primary VS were treated in the period of the study. A total of 59.8% of patients showed an HB value < 3 in the immediate postoperative period (T1), reaching to 76.4% at the last follow-up evaluation. A multiparametric score, Facial Nerve Outcome Score (FNOS), was built. The totality of patients with FNOS grade A showed an HB value < 3 at 12 months, decreasing to 70% for those with FNOS grade B, whereas 100% of patients with FNOS grade C showed an HB value ≥ 3. The ordinal logistic regression showed three times increasing probability to see an HB value ≥ 3 at 3-month follow-up for each worsening point in FNOS score [Exp(B), 2,999; p < 0.001] that was even more probable [Exp(B), 5.486; p < 0.001] at 12 months.

Conclusion

The FNOS score resulted to be a reliable score, showing high associations with FN function both at short- and long-term follow-up. Although multicenter studies would be able to increase its reproducibility, it could be used to predict the FN damage after surgery and the potential of restoring its function on the long-term period.

Utility of Dual Monitoring of the Lower Cranial Nerve Motor-Evoked Potentials Threshold Level Criterion to Predict Swallowing Function in Skull Base and Brainstem Surgery

PURPOSE

Evaluate the value of bilateral final/baseline threshold level changes of lower cranial nerve MEPs in postoperative swallowing function deterioration prediction.

METHODS

Bilateral lower cranial nerve motor-evoked potentials (MEPs) were recorded in 51 patients who underwent treatment for skull base and brainstem tumors. Corkscrew-like electrodes were positione 2 cm below C3/C4 and Cz. The MEPs were recorded from different muscle groups, including the posterior pharyngeal wall muscle, tongue muscle, genioglossus muscle, and cricothyroid muscle through paired needle electrodes. Swallowing function was assessed clinically using the Mann Assessment of Swallowing Ability score before and after the procedure at 7 days, 1 month, and 3 months.

RESULTS

Bilateral final/baseline threshold level increases in lower cranial nerve MEPs under the dual monitoring were significantly correlated with postoperative swallowing function deterioration ( r = 0.660 at 7 days, r = 0.735 at 1 month, and r = 0.717 at 3 months; p < 0.05). Bilateral final/baseline threshold level changes of more than 20% were recorded in 23 of the 51 patients, with 21 patients experiencing swallowing function deterioration postoperatively. The other 28 patients had bilateral threshold level changes of less than 20%, with 26 patients maintaining or improving their swallowing function, and 12 of those patients presented transient deterioration of swallowing function in the early postoperative period.

CONCLUSIONS

Dual monitoring of lower cranial nerves and their different muscle groups MEPs was a safe and effective way to predict postoperative swallowing function. An increase in bilateral final/baseline threshold level change of more than 20% was predictive of permanent swallowing deterioration, especially in patients with poor swallowing function preoperatively.

Facial Nerve Function After Microsurgical Resection in Vestibular Schwannoma Under Neurophysiological Monitoring

Background

The use of intraoperative neurophysiological monitoring, including direct nerve stimulation (especially the facial nerve), acoustic evoked potentials (AEP) and somatosensory evoked potentials (SSEP), is a helpful tool in the microsurgery of vestibular schwannoma to prevent nerve injury. Patient characteristics and intraoperative and postoperative variables might also influence the postoperative facial nerve function. The study was performed to investigate these variables and the intraoperative neurophysiological monitoring values.

Methods

Seventy-nine patients with vestibular schwannoma were included consecutively into this study. Intraoperative neurophysiological monitoring, including SSEP, AEP, and direct nerve stimulation for facial and trigeminal nerve electromyography, was performed utilizing digital data storage in all cases. The intensity (in volts) of the direct stimulation and the latency (in ms) for the orbicularis oculi and the orbicularis oris muscle and the amplitude (in mV) was measured. Univariate and multivariate statistical analyses concerning the different parameters was performed directly after the operation and in the subsequent follow-ups 3 and 6 months after the operation.

Results

The mean intensity was 0.79 V (SD.29). The latency and amplitude for the oris muscle was 5.2 ms (SD 2.07) and 0.68 mV (SD.57), respectively. The mean latency for the occuli muscle was 5.58 ms (SD 2.2) and the amplitude was 0.58 mV (SD 1.04). The univariate and multivariate statistical analyses showed significance concerning the postoperative facial nerve function and the amplitude of the direct stimulation of the facial nerve in the orbicularis oris muscle (p = 0.03), so repeated direct nerve stimulation might show FN function deterioration. The mean diameter of the tumors was 24 mm (range 10–57 mm). Cross total resection and near total was achieved in 76 patients (96%) and subtotal in three patients (4%). The preoperative House–Brakeman score (HBS) 1 was constant in 65 (82%) cases. The mortality in our series was 0%; the overall morbidity was 10%. The HBS was not influenced concerning the extent of resection. The mean follow-up was 28 months (range 6 to 60 months). The limitations of the study might be a low number of patients and the retrospective character of the study.

Conclusion

Intraoperative neurophysiological monitoring is crucial in vestibular schwannoma surgery. Repeated direct nerve stimulation and a detected decreased amplitude might show facial nerve function deterioration.

Bilateral and Optimistic Warning Paradigms Improve the Predictive Power of Intraoperative Facial Motor Evoked Potentials during Vestibular Schwannoma Surgery

Simple Summary

During surgery for vestibular schwannomas, the facial nerve is monitored via motor evoked potentials (facial nerve MEP). The established warning criteria for facial nerve MEP signal changes mostly refer to the ipsilateral side and disregard the contralateral side. Furthermore, the surgeon is warned as soon as the signal of a single facial muscle deteriorates. We examined how the predictive power of the facial nerve MEP would change if we used the percent change in ipsilateral versus contralateral MEP stimulation intensity over time as warning criterion; additionally, if we warned in a novel optimistic manner, a manner in which the surgeon would be warned only if all derived facial muscles deteriorate significantly, as opposed to the traditional method, in which the surgeon is warned as soon as a single muscle deteriorates. We retrospectively compared this approach to actual intraoperative warnings (based on unilateral threshold change, A-trains, and MEP loss) and show that with our method, the facial nerve MEP was significantly more specific and triggered fewer unnecessary warnings.

Abstract

Facial muscle corticobulbar motor evoked potentials (FMcoMEPs) are used to monitor facial nerve integrity during vestibular schwannoma resections to increase maximal safe tumor resection. Established warning criteria, based on ipsilateral amplitude reduction, have the limitation that the rate of false positive alarms is high, in part because FMcoMEP changes occur on both sides, e.g., due to brain shift or pneumocephalus. We retrospectively compared the predictive value of ipsilateral-only warning criteria and actual intraoperative warnings with a novel candidate warning criterion, based on “ipsilateral versus contralateral difference in relative stimulation threshold increase, from baseline to end of resection” (BilatMT ≥ 20%), combined with an optimistic approach in which a warning would be triggered only if all facial muscles on the affected side deteriorated. We included 60 patients who underwent resection of vestibular schwannoma. The outcome variable was postoperative facial muscle function. Retrospectively applying BilatMT, with the optimistic approach, was found to have a significantly better false positive rate, which was much lower (9% at day 90) than the traditionally used ipsilateral warning criteria (>20%) and was also lower than actual intraoperative warnings. This is the first report combining the threshold method with an optimistic approach in a bilateral multi-facial muscle setup. This method could substantially reduce the rate of false positive alarms in FMcoMEP monitoring.