Intraoperative Funktionsüberwachung des N. facialis: Operationen an Vestibularisschwannomen

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

PURPOSE

Intraoperative 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.

METHODS

Intraoperative 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.

RESULTS

A 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.

CONCLUSIONS

FNMEP 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.

Neural networks for estimation of facial palsy after vestibular schwannoma surgery

PURPOSE

Facial nerve damage in vestibular schwannoma surgery is associated with A-train patterns in free-running EMG, correlating with the degree of postoperative facial palsy. However, anatomy, preoperative functional status, tumor size and occurrence of A-trains clusters, i.e., sudden A-trains in most channels may further contribute. In the presented study, we examine neural networks to estimate postoperative facial function based on such features.

METHODS

Data from 200 consecutive patients were used to train neural feed-forward networks (NN). Estimated and clinical postoperative House and Brackmann (HB) grades were compared. Different input sets were evaluated.

RESULTS

Networks based on traintime, preoperative HB grade and tumor size achieved good estimation of postoperative HB grades (chi2 = 54.8), compared to using tumor size or mean traintime alone (chi2 = 30.6 and 31.9). Separate intermediate nerve or detection of A-train clusters did not improve performance. Removal of A-train cluster traintime improved results (chi2 = 54.8 vs. 51.3) in patients without separate intermediate nerve.

CONCLUSION

NN based on preoperative HB, traintime and tumor size provide good estimations of postoperative HB. The method is amenable to real-time implementation and supports integration of information from different sources. NN could enable multimodal facial nerve monitoring and improve postoperative outcomes.

Facial nerve in skullbase tumors: imaging and clinical relevance

Facial nerve, the 7th cranial nerve, is a mixed nerve composed of sensory and motor fibers, and its main branch is situated in the cerebellopontine angle. Facial nerve dysfunction is a debilitating phenomenon that can occur in skullbase tumors and Bell's pals. Recovery of the facial nerve dysfunction after surgery for skullbase tumors can be disappointing, but is usually favorable in Bell's palsy. Advances in magnetic resonance imaging (MRI) allow to visualize the facial nerve and its course in the cerebellopontine angle, also when a large tumor is present and compresses the nerve. Here, we describe the anatomical, neurochemical and clinical aspects of the facial nerve and highlight the recent progress in visualizing the facial nerve with MRI.

Application of intentional facial nerve stimulation during cochlear implantation as an electrophysiological tool to estimate the intracochlear electrode position

This proof of concept describes the use of evoked electromyographic (EMG) activation of the facial nerve for intraoperative monitoring of the electrode insertion during cochlear implantation (CI). Intraoperative EMG measurements from the facial nerve were conducted in nine patients undergoing CI implantation. Electric current pulses were emitted from contacts on the CI array during and immediately after electrode insertion. For control, the results of EMG measurements were compared to postoperative flat panel volume computed tomography scans with secondary reconstruction (fpVCT_SECO). During insertion, the EMG response evoked by the electrical stimulation from the CI was growing with the stimulating contact approaching the facial nerve and declined with increasing distance. After full insertion, contacts on the apical half of the CI array stimulated higher EMG responses compared with those on the basal half. Comparison with postoperative imaging demonstrated that electrode contacts stimulating high EMG responses had the shortest distances to the facial nerve. It could be demonstrated that electrically evoked EMG activation of the facial nerve can be used to monitor the progress during CI electrode insertion and to control the intracochlear electrode position after full insertion.

Applicability of contemporary quality indicators in vestibular surgery-do they accurately measure tumor inherent postoperative complications of vestibular schwannomas?

Background

Due to rising costs in health care delivery, reimbursement decisions have progressively been based on quality measures. Such quality indicators have been developed for neurosurgical procedures, collectively. We aimed to evaluate their applicability in patients that underwent surgery for vestibular schwannoma and to identify potential new disease-specific quality indicators.

Methods

One hundred and three patients operated due to vestibular schwannoma were subject to analysis. The primary outcomes of interest were 30-day and 90-day reoperation, readmission, mortality, nosocomial infection and surgical site infection (SSI) rates, postoperative cerebral spinal fluid (CSF) leak, facial, and hearing function. The secondary aim was the identification of prognostic factors for the mentioned primary outcomes.

Results

Thirty-day (90-days) outcomes in terms of reoperation were 10.7% (14.6%), readmission 9.7% (13.6%), mortality 1% (1%), nosocomial infection 5.8%, and SSI 1% (1%). A 30- versus 90-day outcome in terms of CSF leak were 6.8% vs. 10.7%, new facial nerve palsy 16.5% vs. 6.1%. Hearing impairment from serviceable to non-serviceable hearing was 6.8% at both 30- and 90-day outcome. The degree of tumor extension has a significant impact on reoperation (p < 0.001), infection (p = 0.015), postoperative hemorrhage (p < 0.001), and postoperative hearing loss (p = 0.026).

Conclusions

Our data demonstrate the importance of entity-specific quality measurements being applied even after 30 days. We identified the occurrence of a CSF leak within 90 days postoperatively, new persistent facial nerve palsy still present 90 days postoperatively, and persisting postoperative hearing impairment to non-serviceable hearing as potential new quality measurement variables for patients undergoing surgery for vestibular schwannoma.

Intraoperative Neuromonitoring of Blink Reflex During Posterior Fossa Surgeries and its Correlation With Clinical Outcome

PURPOSE

Blink reflex (BR) under general anesthesia as an intraoperative neuromonitoring method was used to monitor facial nerves in few studies. This study aimed to test the utility of intraoperative BR during cerebellopontine angle and skull base surgeries, assess its prognostic value for facial nerve functions, and compare it with facial corticobulbar motor evoked potentials (CoMEPs).

METHODS

Blink reflex and facial CoMEPs were recorded from 40 patients undergoing skull base surgeries. Subdermal needles were placed in the supraorbital notch for stimulation and in the orbicularis oculi muscle for recording the BR. A double train of 20 to 40 V intensity with an intertrain interval of 40 to 60 milliseconds, an interstimulus interval of 2.5 milliseconds, and a stimulus duration of 0.5 milliseconds were applied. Facial nerve functions were assessed with the House-Brackmann grading system in the postoperative day 1 and third-month period and correlated with intraoperative BR and CoMEPs measurements.

RESULTS

Of 40 patients, BR was recordable on the affected side in 32 (80%) and contralateral side in 35 (87.5%) patients. According to our statistical results, BR had a slightly better sensitivity than facial CoMEPs in predicting impairment of facial nerve functions for both postoperative and third-month time points. Blink reflex showed better accuracy for predicting postoperative nerve functions, whereas CoMEPs correlated better in predicting third-month outcome.

CONCLUSIONS

We suggest that BR is a valuable intraoperative neuromonitoring method that can be used in addition to facial CoMEPs during skull base surgeries to assess real-time facial nerve integrity and predict prognosis.

Facial Nerve Outcomes Following Total Excision of Vestibular Schwannoma by the Enlarged Translabyrinthine Approach

OBJECTIVE

To study the early and late facial nerve (FN) outcomes in different tumor classes in addition to determining the predictive factors for the same.

STUDY DESIGN

A retrospective clinical study.

SETTING

A quaternary referral otology and skull base center.

PATIENTS AND METHODS

A retrospective study of 1983 cases of vestibular schwannomas (VSs) with preoperative normal FN function, undergoing total excision with anatomical preservation of the nerve by enlarged translabyrinthine approach (ETLA) were included. FN status was recorded postoperatively at day 1, at discharge, and at 1-year follow-up and were analyzed in different tumor sizes.

RESULTS

At 1 year, 988 patients with House-Brackmann (H-B) grade I and II FN at day 1 after surgery, 958 (96.9%) maintained their status up-to 1 year. Of the 216 patients with H-B grade III at day 1 after surgery, 113 (52.3%) improved to H-B grade I and II. Similarly, of the 779 patients with H-B grade IV and VI FN function at day 1 after surgery, improvement to H-B III and H-B I and II were noted in 442 (56.7%) and 80 (10.3%) of patients, respectively. Intrameatal and extrameatal tumors upto 2 cm showed better recovery from H-B grade III to H-B I and II and from H-B grade IV and VI to H-B I and III when compared with extrameatal tumors >2 cm (p = 0.001).

CONCLUSION

Tumors of smaller sizes have good immediate postoperative FN results and recover well at the end of 1 year while more than 3 cm have poor outcomes and recover poorly at the end of 1 year. When the VSs reaches more than 1 cm, the HB I and II outcomes drop significantly.

Face-to-face four hand technique in vestibular schwannoma surgery: results from 256 Danish patients with larger tumors

BACKGROUND

The objective of this study was to investigate the clinical outcome after microsurgical treatment of vestibular schwannomas using face-to-face four hand technique in 256 Danish patients treated in the Department of Neurosurgery at the Copenhagen University Hospital from 2009 to 2018.

METHODS

Data were retrospectively collected from patient records.

RESULTS

The mean tumor size was 30.6 mm and approximately 46% of the patients had tumors >30 mm. In around 1/3 of the patients a retrosigmoid approach was used and in 2/3 a translabyrinthine. In 50% of the patients, the tumor was completely removed, and in 38%, only smaller remnants were left to preserve facial function. The median operative time was approximately 2.5 h for retrosigmoid approach, and for translabyrinthine approach, it was around 3.5 h. One year after surgery, 84% of the patients had a good facial nerve function (House-Brackmann grade 1-2). In tumors ≤ 30 mm approximately 89% preserved good facial function, whereas this was only the case for around 78% of the patients with tumors > 30 mm. In 60% of the patients who had poor facial nerve function at hospital discharge, the function improved to good facial function within the 1 year follow-up period. Four patients died within 30 days after surgery, and 6% underwent reoperation for cerebrospinal fluid leakage.

CONCLUSION

Surgery for vestibular schwannomas using face-to-face four hand technique may reduce operative time and can be performed with lower risk and excellent facial nerve outcome. The risk of surgery increases with increasing tumor size.

Bifid Facial Nerve with Dual Origin Identified During Resection of Vestibular Schwannoma

Facial nerve identification and preservation is a critical step in the resection of vestibular schwannoma. The use of intraoperative neurostimulation to positively identify the facial nerve along its entire course is essential to prevent injury. To our knowledge, this is the first reported case of a bifid facial nerve with a dual origin at the brainstem, which we observed during resection of vestibular schwannoma via the translabyrinthine approach. Both roots were visualized to join as one facial nerve trunk outside the brainstem in the cisternal segment of the facial nerve, and both trunks demonstrated positive signal with neurostimulation. This case highlights an important anatomic variation and also the importance of correct identification of facial nerve anatomy during resection of vestibular schwannoma and other pathologies within the cerebellopontine angle.

[Neuroprotective medication in vestibular schwannoma surgery]

BACKGROUND

Except for glucocorticoids there is a lack of neuroprotective medication in neurosurgical interventions.

OBJECTIVE

An overview of clinical trials investigating administration of the calcium antagonist nimodipine and hydroxyethyl starch (HES) in vestibular schwannoma (VS) surgery is given. Basic research is addressed and potential neuroprotective effect mechanisms are discussed, as are perspectives for application of the concept to other types of surgery with a risk postoperative impairment of nerve function.

MATERIALS AND METHODS

A selective PubMed search was performed and all 10 clinical trials corresponding to the search criteria were included.

RESULTS

Four trials with an intraoperative start of the medication showed a positive effect for the preservation of facial nerve function and hearing preservation. A pilot study showed superiority of prophylactic treatment over intraoperative application. There were no significant results in a prospective multicenter phase III trial. After 1 year, postoperative facial nerve preservation rates were excellent in both groups. However, the risk of hearing loss was twice as high in the control group. A combined analysis of the phase III trial with its pilot study showed significant results for better hearing preservation rates in the treatment group (probably by increasing the case load).

CONCLUSION

Prophylactic nimodipine can be recommended in VS surgery in patients with good preoperative hearing. The effect mechanisms of nimodipine and modifications to prophylaxis should be clarified in basic research.

[Surgical techniques for treatment of vestibular schwannoma]

BACKGROUND

Microsurgical resection of vestibular schwannomas is demanding, even if not all of these tumors represent a challenge for experienced surgeons. In order to make the right decisions when it comes to balancing the extent of tumor resection with preservation of function, the surgeon must possess detailed knowledge of the surgical techniques and also have mastered these.

OBJECTIVE

The current article describes the state-of-the-art of the three major microsurgical techniques for resection of vestibular schwannomas, their pearls and their perils.

MATERIALS AND METHODS

The literature-based review of the three surgical techniques is complemented by a discussion of operative nuances and weighting of advantages and possible complications based on the authors' own experience.

RESULTS

The translabyrinthine, retrosigmoidal, and subtemporal microsurgical approaches are well documented in the literature regarding their modifications and the achievable surgical results. Hearing preservation is possible with the latter two approaches. The choice of approach and the preservation of neural function depend primarily on the size of the tumor and pre-existing neurologic deficits. Preoperative diagnostics and preparation differ only for semi-sitting patient positioning, where transesophageal echocardiography is required. The classic surgical techniques have been supplemented by fine-tuned electrophysiologic monitoring, endoscopic views, special microinstruments, and intraoperative image guidance.

CONCLUSION

The choice of surgical approach often depends on the personal preference and experience of the surgeon. Preoperative hearing and tumor extension are the main objective selection criteria.