Intraoperative electromyography for predicting facial function in vestibular schwannoma surgery

Impact of Latency Variations on the Predictive Value of Facial Nerve Proximal-to-Distal Amplitude Ratio during Vestibular Schwannoma Surgery

Introduction  This study highlights the relation between compound muscle action potential (CMAP) latency variations and the predictive value of facial nerve (FN) proximal-to-distal (P/D) amplitude ratio measured at the end of vestibular schwannoma resection. Methods  Forty-eight patients underwent FN stimulation at the brainstem (proximal) and internal acoustic meatus (distal) using a current intensity of 2 mA. The proximal latency and the P/D amplitude ratio were assessed. House-Brackmann grades I & II indicated good FN function, and grades III to VI were considered fair/poor function. A P/D amplitude ratio > 0.6 was used as a cutoff to indicate a good FN function, while a ratio of ≤ 0.6 indicated a fair/poor FN function. Results  The P/D amplitude ratio was measured for all patients, and the calculated sensitivity (SE), specificity (SP), positive predictive value (PPV), and negative predictive value (NPV) were 85.2, 85.7, 88.5, and 81.8%, respectively. The CMAPs from the mentalis muscle were then classified based on their proximal latency into group I (< 6 ms), group II (6-8 ms), and group III (> 8 ms). The SE, SP, PPV, and NPV became 90.5, 90.9, 95, and 83.3%, respectively, in group II. In group I, SE and NPV increased, whereas SP and PPV decreased. While in group III, SP and PPV increased, whereas SE and NPV decreased. Conclusion  At a latency between 6 and 8 ms, the P/D amplitude ratio was predictive of outcomes with high SE and SP. When latency was < 6 ms or > 8 ms, the same predictive ability was not observed. Knowing the strengths and limitations is important for understanding the predictive value of the P/D amplitude ratio.

A multi-institutional machine learning algorithm for prognosticating facial nerve injury following microsurgical resection of vestibular schwannoma

Vestibular schwannomas (VS) are the most common tumor of the skull base with available treatment options that carry a risk of iatrogenic injury to the facial nerve, which can significantly impact patients' quality of life. As facial nerve outcomes remain challenging to prognosticate, we endeavored to utilize machine learning to decipher predictive factors relevant to facial nerve outcomes following microsurgical resection of VS. A database of patient-, tumor- and surgery-specific features was constructed via retrospective chart review of 242 consecutive patients who underwent microsurgical resection of VS over a 7-year study period. This database was then used to train non-linear supervised machine learning classifiers to predict facial nerve preservation, defined as House-Brackmann (HB) I vs. facial nerve injury, defined as HB II-VI, as determined at 6-month outpatient follow-up. A random forest algorithm demonstrated 90.5% accuracy, 90% sensitivity and 90% specificity in facial nerve injury prognostication. A random variable (rv) was generated by randomly sampling a Gaussian distribution and used as a benchmark to compare the predictiveness of other features. This analysis revealed age, body mass index (BMI), case length and the tumor dimension representing tumor growth towards the brainstem as prognosticators of facial nerve injury. When validated via prospective assessment of facial nerve injury risk, this model demonstrated 84% accuracy. Here, we describe the development of a machine learning algorithm to predict the likelihood of facial nerve injury following microsurgical resection of VS. In addition to serving as a clinically applicable tool, this highlights the potential of machine learning to reveal non-linear relationships between variables which may have clinical value in prognostication of outcomes for high-risk surgical procedures.

Brazilian Society of Otology task force - Vestibular Schwannoma ‒ evaluation and treatment

OBJECTIVE

To review the literature on the diagnosis and treatment of vestibular schwannoma.

METHODS

Task force members were educated on knowledge synthesis methods, including electronic database search, review and selection of relevant citations, and critical appraisal of selected studies. Articles written in English or Portuguese on vestibular schwannoma were eligible for inclusion. The American College of Physicians' guideline grading system and the American Thyroid Association's guideline criteria were used for critical appraisal of evidence and recommendations for therapeutic interventions.

RESULTS

The topics were divided into 2 parts: (1) Diagnosis - audiologic, electrophysiologic tests, and imaging; (2) Treatment - wait and scan protocols, surgery, radiosurgery/radiotherapy, and systemic therapy.

CONCLUSIONS

Decision making in VS treatment has become more challenging. MRI can diagnose increasingly smaller tumors, which has disastrous consequences for the patients and their families. It is important to develop an individualized approach for each case, which highly depends on the experience of each surgical team.

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.

Pre- and intra-operative prognostic factors of facial nerve function in cerebellopontine angle surgery

PURPOSE

The study assesses whether pre- and intraoperative factors linked to electromyography and direct electrical stimulation (DES) of facial nerve can predict facial nerve function in the short- (12 days) and long-term (1 year) after cerebellopontine angle (CPA) tumor resection.

METHODS

157 patients who underwent surgical resection of CPA tumors with facial nerve monitoring. Pre-operative factors (age, tumor size, pure tone average), surgical time and intra-operative parameters regarding facial function, minimum stimulation threshold (MST), compound muscle action potential (CMAP) and the difference between proximal and distal CMAP (DPDC) were evaluated.

RESULTS

A correlation between tumor size, MST, CMAP and facial function in both short and long term was found. A higher grade of immediate facial paralysis corresponded to a higher risk of poor outcome after one year. A postoperative House-Brackmann (HB) score of V or VI was correlated with poor outcome in 88.8% and 93.8% of cases. A risk of HB 3 or more, in the long term, was correlated with a tumor size of 20.2 mm. Using an MST of 0.1 mA, for long-term predictions, sensitivity and specificity were 0.62 (95% CI 0.46-0.75) and 0.73 (95% CI 0.61-0.82), respectively. With a CMAP cut-off < 200 µV, for long-term prediction, sensitivity was 0.73 (95% CI 0.53-0.87) and specificity 0.73 (95% CI 0.55-0.85).

CONCLUSION

The assessment based on the cut-offs described increases the ability to predict facial function. Improving predictive accuracy enables surgeons to address patients' expectations and to establish an intervention timeline for planning facial reanimation.

Predictive Ability of Direct Electrical Stimulation on Facial Nerve Function Following Vestibular Schwannoma Surgery: A Systematic Review and Meta-analysis

OBJECTIVE

Facial nerve preservation is critical in vestibular schwannoma (VS) surgery. Direct electrical stimulation (DES) is a widely used method for intraoperative localization of the facial nerve and assessment of nerve integrity. We sought to assess the predictive ability of DES parameters on facial nerve function post-VS surgery.

DATABASES REVIEWED

A systematic literature search of English-language studies published from 1946 to 2019 was undertaken using EMBASE, MedLine/PubMed, and the Cochrane Central Register of Controlled Trials.

METHODS

Included studies involved patients undergoing VS surgery and assessed predictive ability of any DES parameter on postoperative facial function. Two authors independently reviewed studies and extracted data. Meta-analysis of diagnostic accuracy of DES parameters was used to calculate pooled sensitivities and specificities of common cutoffs. For DES parameters reported by less than four studies, outcomes were reported descriptively.

RESULTS

A MST cutoff of 0.10 mA had sensitivity of 0.76 (95% CI 0.53-0.90) and specificity 0.68 (95% CI 0.42-0.87) for facial function in the long term, and MST 0.05 mA had sensitivity 0.73 (95% CI 0.58-0.84) and specificity 0.74 (95% CI 0.59-0.85). CMAP amplitude < 500 μV had sensitivity of 0.87 (95% CI 0.78-0.93) for poor short-term facial function.

CONCLUSIONS

A CMAP amplitude response < 500 μV is sensitive for poor short-term facial function, whereas MST values of 0.05 mA and 0.10 mA are both sensitive and specific in the long term. Other DES parameters may be able to accurately predict both short- and long-term postoperative facial function, but have been less studied.

Facial nerve function and hearing after microsurgical removal of sporadic vestibular schwannomas in a population-based cohort

BACKGROUND

Vestibular schwannoma (VS) is a benign tumor originating from the vestibulocochlear nerve. The optimal treatment strategy is debated, since surgery may result in iatrogenic facial nerve injury. We report the results of VS surgery in a population-based unselected cohort in a center with access to Cyber Knife (CK) radiosurgery.

METHODS

We reviewed 117 consecutive operations and found 95 patients who had their primary operation due to vestibular schwannoma between 2001 and 2017. Facial nerve function was evaluated with the House-Brackmann (HB) scale and hearing with the EU classification.

RESULTS

The population consisted of 37 males and 58 females with a median age of 54 years (range 19-79). One year after surgery 67% of patients had a good outcome (HB 1-2). The rate of good outcome was 90% if no facial nerve damage was observed during intraoperative monitoring, the size of the tumor was under 30 mm and no hydrocephalus was present. During the study period, the treatment strategy changed from total to near-total resection after the introduction of CK radiosurgery, which could be used as a second-line treatment in case of residual tumor regrowth. This resulted in an improvement of outcomes (0% HB 5-6) despite the larger tumor sizes (25 ± 14 mm vs. 31 ± 9 mm, p < 0.05). Hearing preservation rates did not increase.

CONCLUSIONS

Near-total resection and subsequent CK radiosurgery in case of residual tumor regrowth during follow-up seems to provide a good outcome of facial nerve function even in large VSs.

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

OBJECTIVE

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.

DESIGN

Prospective consecutive non-comparative observational case series.

SETTING

Tertiary referral center.

MAIN OUTCOME MEASURES

Facial function, immediate post operation and at 1 year using House-Brackmann (HB) grading scale.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Total Facial Paralysis after Vestibular Schwannoma Surgery: Probability of Regaining Normal Function

The aim of the present study was to ascertain the precise fraction of vestibular schwannoma cases that recover to normal function after postoperative total facial nerve paralysis and to compare our results with those presented in the literature. This was a retrospective case review of 631 cases. Among the 132 cases with immediate postoperative facial nerve palsy (House Brackmann [HB] grade VI), only 2 (1.5%) recovered to normal function (HB grade I). In an attempt to compare our results with those of other series in the literature, we found a large variation in the incidence of recovery of this group of patients to grade I, ranging from 0% to 50%. Our analysis of the reported data revealed widely varying methods of data collection and presentation, making a scientifically valid comparison particularly difficult. According to our data, complete (HB grade I) or near-complete (HB grade II) facial nerve function recovery from an immediate postoperative grade VI palsy is extremely rare.

Early Nerve Grafting for Facial Paralysis After Cerebellopontine Angle Tumor Resection With Preserved Facial Nerve Continuity

IMPORTANCE

Preserving facial nerve function is a primary goal and a key decision factor in the comprehensive management of vestibular schwannoma and other cerebellopontine angle (CPA) tumors.

OBJECTIVE

To evaluate the use of the pattern of facial paralysis recovery in the early postoperative months as a sole predictor in selecting patients for facial nerve grafting after CPA tumor resection when cranial nerve VII is uninterrupted.

DESIGN, SETTING, AND PARTICIPANTS

Sixty-two patients with facial paralysis and uninterrupted cranial nerve VII who developed facial paralysis after CPA tumor resection at The Johns Hopkins Hospital were followed up prospectively to assess for spontaneous recovery and to determine candidacy for facial reanimation surgery. The study dates and dates of analysis were January 1, 2009, to March 31, 2015.

INTERVENTIONS

After a minimum of 6 months of clinical follow-up and no signs of clinical recovery, patients underwent facial nerve exploration and a masseteric or hypoglossal nerve transfer. Intraoperative direct nerve stimulation was performed to assess for the presence of subclinical reinnervation. Patients were followed up for a minimum of 18 months after surgery to evaluate outcomes.

MAIN OUTCOMES AND MEASURES

Facial function and recovery were studied objectively with a Smile Recovery Scale, Facial Asymmetry Index, and House-Brackmann (HB) grading system. Other outcome measures included the duration of paralysis, time to recovery, and evidence of synkinesis.

RESULTS

Sixty-two patients (33 men, 29 women; mean age 51.8 years) with uninterrupted facial nerves after CPA tumor resection developed HB grade IV, V, or VI facial paralysis. Ten patients underwent nerve grafting by 12 months, 9 patients received grafting after 12 months, and 8 patients had no intervention. Thirty-five patients spontaneously recovered. In all patients who underwent nerve grafting, there were no detectable facial muscle movements or electromyographic response to direct facial nerve stimulation suggestive of occult reinnervation. Overall, early facial reanimation surgery resulted in a shorter total duration of paralysis. Masseteric nerve grafting resulted in earlier recovery compared with hypoglossal nerve grafting (5.6 vs 10.8 months, P = .005). Patients who showed no signs of recovery by 6 months after CPA surgery but declined facial reanimation surgery demonstrated at best HB grade V recovery after 18 months of observation.

CONCLUSIONS AND RELEVANCE

The recovery pattern in the early postoperative period among patients who develop facial paralysis after CPA tumor resection is a useful clinical tool in selecting patients for facial reanimation surgery. Patients can be counseled for facial reanimation surgery as early as 6 months after surgery because satisfactory facial functional recovery is unlikely to occur when there is no clinical evidence of spontaneous nerve regeneration in the first 6 months.

LEVEL OF EVIDENCE

3.

Evolution of Patients With Immediate Complete Facial Paralysis Secondary to Acoustic Neuroma Surgery

OBJECTIVE

To study the evolution of patients with immediate complete facial paralysis after acoustic neuroma surgery in different scenarios and assess different facial reanimations techniques.

METHODS

This study included 50 patients with complete facial paralysis immediately after acoustic neuroma surgery. Data were analyzed into 4 groups according to the need and type of reconstruction of the facial nerve, either none, immediate, or on a deferred basis. All patients had intraoperative facial nerve monitoring, and facial nerve function was evaluated according the House-Brackmann (HB) scale.

RESULTS

Of all patients with immediate total paralysis, no patients achieved totally normal facial function (grade I), and only 5 (10%) recovered to a grade II. For all groups included, the majority of patients (82%) achieved an acceptable final facial function (grade III HB). In this series, only 2 patients remained with a grade VI facial function.

CONCLUSIONS

The possibility of recovering near normal facial function after a grade VI facial paralysis is very low. Procedures like the immediate repair of the facial nerve with an interposed donor graft may provide better facial function in patients with partially injured facial nerve. Even in cases of total section, there are other procedures that can improve the results.

Predictive value of intraoperative neurophysiologic monitoring in assessing long-term facial function in grade IV vestibular schwannoma removal

BACKGROUND

Despite routine use of intraoperative neuromonitoring in acoustic neuroma removal, its application in predicting long-term facial function is limited.

METHODS

Prospective recording of facial nerve function and subsequent review of intraoperative neurophysiologic data. Stimulation of the facial nerve was performed proximal and distal to the tumor locus after tumor removal with measurement of amplitude and latency responses in the orbicularis oculi and oris muscles. Prospective review of current facial nerve function was performed using the House-Brackmann (HB) scoring system. Good facial function was determined as HB I/II and HB III-VI was considered poor facial function. Minimum follow-up time was 15 months, and averaged 40 months.

RESULTS

Twenty-four grade IV acoustic neuromas (54 % larger than 4 cm) were completely removed from October 2008 to November 2013. Nine patients (37.5 %) had HB I/II and 15 (62.5 %) had HB III-VI. The poor prognosis group had a higher latency than the good prognosis group (p = 0.045). Lower proximal amplitude was detected in the poor prognosis group (p = 0.046). Lower proximal-to-distal amplitude ratio was also detected in the poor prognosis group (p = 0.052). Amplitude ratio cut-offs of 0.44 and 0.25 were able to predict poor prognosis with sensitivity of 0.73 and 0.4 and specificity of 0.78 and 1, respectively (p = 0.046).

CONCLUSIONS

Lower proximal amplitude and proximal-distal amplitude ratio were previously reported as predictors of poor facial function in different sizes of vestibular schwannomas. We observed that the same applies specifically for large-sized, completely removed, grade IV tumors. Additionally, we describe a difference in proximal latency time between the good and poor prognosis groups, which was not previously reported.

The anatomically intact but electrically unresponsive facial nerve in vestibular schwannoma surgery

BACKGROUND

Permanent facial nerve (FN) paresis after vestibular schwannoma surgery is distressing to both the patient and surgeon. Intraoperative electrophysiological testing has proven invaluable in reducing the incidence of FN injury and may assist in prognosticating long-term function.

OBJECTIVE

To report definitive FN outcomes among a cohort of patients with an unevokable but anatomically intact seventh nerve after microsurgical vestibular schwannoma resection.

METHODS

All patients undergoing vestibular schwannoma surgery between 2000 and 2010 at a single tertiary academic referral center were identified. Intraoperative FN monitoring data and definitive FN outcomes were reviewed, and all patients with an anatomically intact but electrically unresponsive FN were included.

RESULTS

Eleven patients met the inclusion criteria. The median preoperative and definitive postoperative FN scores were House-Brackmann grades 1 and 3, respectively. The median time to definitive FN recovery was 9.4 months.

CONCLUSION

These data demonstrate that even among this extreme subset, modern electroprognostic testing strategies are incapable of reliably predicting poor outcomes. Therefore, if FN continuity is maintained, attempts at same-surgery FN repair should not be pursued.

Use of supramaximal stimulation to predict facial nerve outcomes following vestibular schwannoma microsurgery: results from a decade of experience

Object

The goal of vestibular schwannoma surgery is tumor removal and preservation of neural function. Intraoperative facial nerve (FN) monitoring has emerged as the standard of care, but its role in predicting long-term facial function remains a matter of debate. The present report seeks to describe and critically assess the value of applying current at supramaximal levels in an effort to identify patients destined for permanent facial paralysis.

Methods

Over more than a decade, the protocol for stimulating and assessing the FN during vestibular schwannoma surgery at the authors' institution has consisted of applying pulsed constant-current stimulation at supramaximal levels proximally and distally following tumor resection to generate an amplitude ratio, which subtracted from 100% yields the degree to which the functional integrity of the FN “dropped off” intraoperatively. These data were prospectively collected and additional variables that might impact postoperative FN function were retrospectively reviewed from the medical record. Only patients with anatomically intact FNs and > 12 months of follow-up data were analyzed.

Results

There were 267 patients available for review. The average posterior fossa tumor diameter was 24 mm and the rate of long-term good (House-Brackmann Grade I–II) FN function was 84%. Univariate logistic regression analysis revealed that prior treatment, neurofibromatosis Type 2 status, tumor size, cerebellopontine angle extension, subjectively thinned FN at the time of operation, minimal stimulation threshold, percent dropoff by supramaximal stimulation (SMS), and postoperative FN function all correlated statistically (p < 0.05) with long-term FN function. When evaluating patients with significant FN weakness at the time of hospital discharge, only the percent dropoff by SMS remained a significant predictor of long-term FN function. However, the positive predictive value of SMS for long-term weakness is low, at 46%.

Conclusions

In a large cohort of patients, the authors found that interrogating intraoperative FN function with SMS is safe and technically simple. It is useful for predicting which patients will ultimately have good facial function, but is very limited in identifying patients destined for long-term facial weakness. This test may prove helpful in the future in tailoring less than gross-total tumor removal to limit postoperative facial weakness.

A Real-Time Monitoring System for the Facial Nerve

OBJECTIVE

Damage to the facial nerve during surgery in the cerebellopontine angle is indicated by A-trains, a specific electromyogram pattern. These A-trains can be quantified by the parameter “traintime,” which is reliably correlated with postoperative functional outcome. The system presented was designed to monitor traintime in real-time.

METHODS

A dedicated hardware and software platform for automated continuous analysis of the intraoperative facial nerve electromyogram was specifically designed. The automatic detection of A-trains is performed by a software algorithm for real-time analysis of nonstationary biosignals. The system was evaluated in a series of 30 patients operated on for vestibular schwannoma.

RESULTS

A-trains can be detected and measured automatically by the described method for real-time analysis. Traintime is monitored continuously via a graphic display and is shown as an absolute numeric value during the operation. It is an expression of overall, cumulated length of A-trains in a given channel; a high correlation between traintime as measured by real-time analysis and functional outcome immediately after the operation (Spearman correlation coefficient [ρ] = 0.664, P &lt; .001) and in long-term outcome (ρ = 0.631, P &lt; .001) was observed.

CONCLUSION

Automated real-time analysis of the intraoperative facial nerve electromyogram is the first technique capable of reliable continuous real-time monitoring. It can critically contribute to the estimation of functional outcome during the course of the operative procedure.

Comparison between intraoperative observations and electromyographic monitoring data for facial nerve outcome after vestibular schwannoma surgery

A four-channel device may enhance the sensitivity of electromyography (EMG). Determination of stimulation thresholds (STs) below 0.05 mA improves facial prognostic information after vestibular schwannoma (VS) surgery. To compare intraoperative observations with electromyographic data for predicting the immediate facial function outcome after VS surgery.A total of 111 VS patients operated on and intraoperatively monitored using four-channel facial EMG between October 2002 and September 2003 were included in this multicentre, prospective study. Mascular activity detection was performed in the frontal, orbicularis oculi, orbicularis oris and platysma muscles. Intraoperative observations were made concerning adhesion and nerve stretch, and facial function was graded (House-Brackmann classification) at postoperative Days 1 and 8.Facial function at postoperative Days 1 and 8 was related to the intraoperative nerve STs at the brainstem and in the adhesion zone (range 0.01-3 mA for a response > 100 microV). At postoperative Day 8, good facial function (Grades 1 or 2) was observed in 93% of cases for STs in the adhesion zone of 0.01-0.04 mA, 85% for STs of 0.05-0.3 mA and 79% for STs > 0.3 mA. These STs were related to the degree of tumor adhesion and not to the nerve stretch. The maximal EMG response was detected in the frontal or platysma muscles in 26% of cases, and in the orbicularis oris and orbicularis oculi muscles in 74%.

Prediction of Long-Term Facial Nerve Outcomes with Intraoperative Nerve Monitoring

OBJECTIVE

Evaluate the utility of a statistical equation using two independent intraoperative monitoring parameters in predicting long-term facial nerve function.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary care hospital.

PATIENTS

Sixty patients undergoing resection of vestibular schwannomas with intraoperative facial nerve monitoring at a single institution.

INTERVENTION

All patients underwent microsurgical resection of vestibular schwannomas with the use of intraoperative cranial nerve monitoring.

MAIN OUTCOME MEASURE

Final facial nerve outcome measured using the House-Brackmann scale at least 6 months after microsurgical resection.

RESULTS

Five out of 60 (8.3%) patients demonstrated significant long-term weakness (i.e., House-Brackmann grade III or worse). Intraoperative monitoring parameters (proximal stimulation threshold, proximal-to-distal response amplitude ratio) were accurate in predicting increased risk of long-term facial nerve dysfunction when used in a logistic regression model. A Student's t test confirmed the equation result was statistically significant in differentiating long-term facial nerve outcomes.

CONCLUSION

Patients with immediate weakness are at higher risk of having long-term poor facial nerve function. The use of intraoperative monitoring parameters was reliable in predicting facial nerve outcomes. Patients with permanent facial nerve dysfunction often require rehabilitative procedures. The ability to predict facial nerve outcomes with intraoperative monitoring may allow early rehabilitative procedures to improve quality of life and prevent ocular complications.

Intraoperative Monitoring and Facial Nerve Outcomes after Vestibular Schwannoma Resection

OBJECTIVE

To determine the predictive value of proximal facial nerve electrical threshold and proximal-to-distal facial muscle compound action potential amplitude ratio on facial nerve outcomes after resection of vestibular schwannomas.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary care hospital.

PATIENTS

Two hundred twenty-nine patients undergoing resection of vestibular schwannomas with intraoperative facial nerve monitoring at a single institution.

INTERVENTION

All patients underwent resection of vestibular schwannomas with the use of intraoperative monitoring.

MAIN OUTCOME MEASURE

Facial nerve function was classified according to the House-Brackmann scale at the patient's last office follow-up. Last follow-up was at least 6 months after surgery.

RESULTS

Good facial nerve function (House-Brackmann Grade I or II) was observed in 87% of the patients at their last office follow-up. Proximal-to-distal amplitude ratio and proximal electric threshold were statistically significant in predicting facial nerve outcome. A mathematical model predicting the probability of good outcome on the basis of the intraoperative parameters is presented.

CONCLUSION

Intraoperative monitoring has significantly decreased facial nerve morbidity in vestibular schwannoma surgery. Despite the advances in surgery and monitoring, a group of patients still have poor facial nerve outcomes. The use of intraoperative nerve monitoring may be able to predict poor long-term facial nerve outcomes and thus modify the timing of rehabilitation.

Predictive factors of long-term facial nerve function after vestibular schwannoma surgery

OBJECTIVE

To assess predictive factors of long-term facial nerve function in a series of patients undergoing vestibular schwannoma surgery and to evaluate the reproducibility of the relevant parameters.

STUDY DESIGN

Prospective.

SETTING

Three tertiary referral neurotology units in two separate countries.

PATIENTS

A total of 67 patients, with normal preoperative facial function and an anatomically intact facial nerve postoperatively, undergoing vestibular schwannoma surgery during a sequential 18-month period.

INTERVENTIONS

Recording of intraoperative stimulus amplitudes (minimum intensity medial to the tumor after excision) and postoperative facial nerve function up to 2 years after surgery.

MAIN OUTCOME MEASURES

Long-term facial nerve function related to tumor size, early postoperative facial nerve function, and intraoperative electrophysiologic intensities.

RESULTS

Multivariate logistic regression model identified tumor size and the minimum intensity required to provoke a stimulus threshold event medial to the tumor after excision as independent predictors of a favorable initial outcome. Immediate facial nerve function was the only independent predictor of long-term normal function. The sensitivity of this predictor was 95% (95% confidence interval [CI], 89-100%); specificity, 83% (95% CI, 62-100%); positive predictive accuracy, 96% (95% CI, 91-100%); and negative predictive accuracy, 77% (95% CI, 54-100%).

CONCLUSION

The combination of electrophysiologic intensities and tumor size are reproducible and better predictors of initial facial nerve function than any individual parameter, but long-term facial nerve function is more likely to have a better outcome if the nerve is left intact and a per-operative graft repair is not performed. The study suggests that although the best available predictor of overall long-term facial nerve outcome is the level of early postoperative function, this factor is not useful in surgical rehabilitation decision making.