Prediction of postoperative facial nerve function in acoustic neuroma surgery

[Utility of the intraoperative neurophysiological monitoring as a prognostic value of postoperative facial paresis in vestibular schwannomas]

BACKGROUND AND OBJECTIVE

Intraoperative neurophysiological monitoring allows us to predict the functional status of the facial nerve after vestibular schwannoma surgery. Due to the great variability of the neurophysiological protocols used for it, the goal of this study is to determine the prognostic ability of our neurophysiological protocol.

MATERIAL AND METHODS

We have performed a statistical analysis of the neurophysiological monitoring data collected from patients operated between March 2009 and July 2021 at the Neurosurgery Service of Salamanca according to their functional status, both in the immediate post-surgical period and one year after surgery.

RESULTS

A number of 51 patients between 46 and 63 years old (median: 54) were analyzed. We have found significant differences studying the threshold value of the stimulation intensity of the facial nerve and the variation of the Cortico-bulbar Evoked Motor Potentials (P=0.043 and P=0.011, respectively) between the patients with good and bad clinical situation after surgery. The most discriminating intensity threshold value was 0.35mA (Sensitivity: 85%; Specificity: 48%). No statistical relationship was found in the study group one year after surgery.

CONCLUSIONS

Our intraoperative monitoring protocol allows us to predict the clinical situation of patients in the immediate postoperative period and improve information for the patient and her relatives after surgery. We cannot, however, use these parameters to predict the functional situation one year after surgery and make clinical decisions in this regard.

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.

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 Neurophysiologic Assessment in Vestibular Schwannoma Removal with Transcanal Approach: A Pilot Clinical Study

BACKGROUND

The transcanal transpromontorial approach has been introduced to remove vestibular schwannomas. As with other techniques, preservation of the facial nerve (FN) is challenging. This pilot study described FN outcomes of patients preoperatively and postoperatively assessed with electromyography (EMG) and blink reflex (BR).

METHODS

Between September 2017 and December 2018, 10 patients (5 men; 5 women; mean age, 59.8 years; age range, 25-77 years) underwent removal of vestibular schwannoma via the transcanal transpromontorial approach. FN assessment using EMG/BR and clinical evaluation with the House-Brackmann (HB) grading scale was performed preoperatively and 2 months postoperatively. If facial impairment was present postoperatively, further analysis was performed 6 months after surgery.

RESULTS

All 10 patients had normal FN function on preoperative EMG/BR. After 2 months, 4 patients had normal FN function on EMG/BR, 4 patients showed a slight delay of FN responses, 1 patient had moderate dysfunction, and 1 patient had consistent damage. After 6 months, among the 6 patients with a pathologic neurophysiologic study, consistent EMG/BR improvement was shown, with complete recovery in 3 cases. At the last follow-up, 8 patients had HB grade I, 1 patient had HB grade II, and 1 patient had HB grade III in 1, showing progression toward healing in 9 of 10 cases.

CONCLUSIONS

The transcanal transpromontorial approach is an effective procedure for vestibular schwannoma removal. EMG/BR represents an objective evaluation method to verify FN recovery after surgery and confirms the low impact of this surgical procedure on the FN.

Neurophysiological Characteristics of Cranial Nerves V- and VII-Triggered EMG in Endoscopic Endonasal Approach Skull Base Surgery

Objective  This study proposes to present reference parameters for trigeminal (V) and facial (VII) cranial nerves (CNs)-triggered electromyography (tEMG) during endoscopic endonasal approach (EEA) skull base surgeries to allow more precise and accurate mapping of these CNs. Study Design  We retrospectively reviewed EEA procedures performed at the University of Pittsburgh Medical Center between 2009 and 2015. tEMG recorded in response to stimulation of CN V and VII was analyzed. Analysis of tEMG waveforms included latencies and amplitudes. Medical records were reviewed to determine the presence of perioperative neurologic deficits. Results  A total of 28 patients were included. tEMG from 34 CNs (22 V and 12 VII) were analyzed. For CN V, the average onset latency was 2.9 ± 1.1 ms and peak-to-peak amplitude was 525 ± 436.94 μV ( n  = 22). For CN VII, the average onset latency and peak-to-peak amplitude were 5.1 ± 1.43 ms and 315 ± 352.58 μV for the orbicularis oculi distribution ( n  = 09), 5.9 ± 0.67 ms and 517 ± 489.07 μV on orbicularis oris ( n  = 08), and 5.3 ± 0.98 ms 303.1 ± 215.3 μV on mentalis ( n  = 07), respectively. Conclusion  Our data support the notion that onset latency may be a feasible parameter in the differentiation between the CN V and VII during the crosstalk phenomenon in EEA surgeries but the particularities of this type of procedure should be taken into consideration. A prospective analysis with a larger data set is necessary.

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.

Estimation of Intraoperative Stimulation Threshold of the Facial Nerve in Patients Undergoing Microvascular Decompression

Introduction  Facial weakness can result from surgical manipulation of the facial nerve. Intraoperative neuromonitoring reduces functional impairment but no clear guidelines exist regarding interpretation of intraoperative electrophysiological results. Most studies describe subjects with facial nerves encumbered by tumors or those with various grades of facial nerve weakness. We sought to obtain the neurophysiological parameters and stimulation threshold following intraoperative facial nerve triggered electromyography (t-EMG) stimulation during microvascular decompression for trigeminal neuralgia to characterize the response of normal facial nerves via t-EMG. Methods  Facial nerve t-EMG stimulation was performed in seven patients undergoing microvascular decompression for trigeminal neuralgia. Using constant current stimulation, single stimulation pulses of 0.025 to 0.2 mA intensity were applied to the proximal facial nerve. Compound muscle action potentials, duration to onset, and termination of t-EMG responses were recorded for the orbicularis oculi and mentalis muscles. Patients were evaluated for facial weakness following the surgical procedure. Results  Quantifiable t-EMG responses were generated in response to all tested stimulation currents of 0.025, 0.05, 0.1, and 0.2 mA in both muscles, indicating effective nerve conduction. No patients developed facial weakness postoperatively. Conclusions  The presence of t-EMG amplitudes in response to 0.025 mA suggests that facial nerve conduction can take place at lower stimulation intensities than previously reported in patients with tumor burden. Proximal facial nerve stimulation that yields responses with thresholds less than 0.05 mA may be a preferred reference baseline for surgical procedures within the cerebellopontine angle to prevent iatrogenic injury.

Decision Making in the Wait-and-Scan Approach for Vestibular Schwannomas: Is There a Price to Pay in Terms of Hearing, Facial Nerve, and Overall Outcomes?

BACKGROUND

The wait-and-scan modality has emerged as an important strategy in the management of vestibular schwannoma (VS) as it has been demonstrated that many tumors grow slowly or do not show any growth over long periods.

OBJECTIVE

To analyze long-term outcomes of wait-and-scan in the treatment of patients with VS, discuss the factors contributing to the decision making, determine the inherent risks of the policy, and compare our results with literature.

METHODS

In total, 576 patients with sporadic unilateral VS who were managed with wait-and-scan were reviewed retrospectively. Of these, a subset of 154 patients with 5-yr follow-up was separately analyzed. The tumor characteristics including patterns of growth, rate of growth, hearing outcomes, and likely factors affecting the above parameters were analyzed.

RESULTS

The mean period of follow-up was 36.9 ± 30.2 mo. The mean age was 59.2 ± 11.6 yr. Thirteen different patterns of tumor growth were observed. Eighty-four (54.5%) of 154 tumors with 5-yr follow-up showed no growth throughout 5 yr. Fifty-six (36.4%) tumors showed mixed growth rates. Only 57 (37%) patients had serviceable hearing at the start of follow-up, but 32 (56.1%) maintained it at the end of follow-up. One hundred fifty (26%) of the 576 patients who failed wait-and-scan had to be taken up for surgery.

CONCLUSION

While there may be no price to pay in wait-and-scan as far as hearing is concerned, this may not be the case for facial nerve outcomes, wherein the results may be better if the patients are taken earlier for surgery.

Ophthalmic Complications Following Acoustic Neuroma Resection

BACKGROUND

Past studies have shown high rates of ocular complications with the need for ophthalmic surgery following acoustic neuroma resection (ANR).

OBJECTIVE

To determine the rates of ophthalmic complications, referrals, and surgery following ANR, and the factors associated with poor outcomes.

METHODS

A retrospective study of ophthalmic outcomes in patients who underwent ANR was conducted, following institutional review board approval. Surgical approach, tumor size, tumor characteristics, completeness of resection, postoperative House-Brackmann grades, ocular complications, referrals to ophthalmology, and ophthalmic treatments were recorded.

RESULTS

Between 2007 and 2012, 174 patients underwent ANR. There were 3 surgical groups: retrosigmoid (n = 97), translabyrinthine (n = 59), and combined retrosigmoid and translabyrinthine (n = 18). Median tumor size was 2.2 cm. Postoperatively, 30% of patients had facial nerve dysfunction (House-Brackmann ≥3), which recovered to 19% by 1 mo and 8.6% by 1 yr following ANR. Fifty-six (32.9%) patients experienced ocular complications postoperatively, with lagophthalmos, dry eye, and blurry vision as the most common complications. Thirty-six (67.9%) of the patients who required ophthalmic treatment were managed nonsurgically, with just 13 (7.6%) patients requiring referral to an ophthalmologist. In total, only 9 (5.3%) patients received an ophthalmic procedure. Patients with tumors &gt;2 cm, those undergoing combined retrosigmoid and translabyrinthine resection, and those with severe facial nerve dysfunction which did not improve in the first month following surgery were more likely to have poor ophthalmic outcomes.

CONCLUSION

We present lower rates of ophthalmic complications following ANR than previously reported. Improved surgical technique, better postoperative eye care, and facial nerve monitoring most likely accounted for the improved ocular outcomes.

How Deleterious Is Facial Nerve Dissection for the Facial Nerve in Parotid Surgery: An Electrophysiological Evaluation

OBJECTIVE

This study was conducted to investigate subclinical electrophysiological deleterious effect due to microtrauma to the nerve in response to the dissection of a tumor and parotid tissue from the facial nerve and its branches and surgical traction experienced during the operation.

METHODS

The study included 34 adult patients who underwent parotidectomy operations under intraoperative facial nerve monitoring. Three measurements were taken from each patient to evaluate facial nerve functions, with 3 stimuli of different intensities applied with different timing. An initial stimulus of 1 mA was applied to confirm the identification of the main trunk of the facial nerve (Group 1: Initial-Normal). Then, a threshold value was found by stimulating the main trunk until muscle fasciculations were observed on facial muscles (Group 2: Basal-Minimal). The same procedure was repeated after the tumor was resected (Group 3: Final-Minimal).

RESULTS

There was no significant difference between the stimulus thresholds of Group 2 (0.31 mA) and Group 3 (0.30 mA). The highest amplitude in all 3 groups was observed at the mental branch, and the lowest at the frontal. The highest latency value was measured at the frontal branch and the lowest at the mental branch. Five (14.7%) of the patients developed postoperative pareses that was completely resolved by the seventh postoperative day visit in these patients.

CONCLUSION

This study demonstrated that the surgical trauma of a meticulously conducted dissection and surgical traction did not cause any deleterious electrophysiological alteration on the facial nerve.

Hypoglossal-facial nerve “side”-to-side neurorrhaphy for persistent incomplete facial palsy

Object

Hypoglossal-facial nerve neurorrhaphy is a widely used method for treating complete facial palsy. However, the classic surgical procedure using a “side”-to-end neurorrhaphy is not suitable for incomplete facial palsy (IFP), because sectioning of the facial nerve for neurorrhaphy compromises remnant axons and potential spontaneous reinnervation. For the treatment of persistent IFP, the authors investigated in rats a modified method using hypoglossal-facial nerve “side”-to-side neurorrhaphy.

Methods

An IFP model was created by crushing the facial nerve and then ligating the injury site to limit axonal regeneration. After 9 weeks, rats with IFP were submitted to hypoglossal-facial nerve “side”-to-side neurorrhaphy: The gap between the 2 nerves was bridged with a predegenerated peroneal nerve graft, which was sutured to only one-half of the hypoglossal nerve and to the remnant facial nerve through a small window created by removing the epineurium, thus preserving regenerating facial axons.

Results

Four months after repair surgery, double innervation of the target whisker pad by hypoglossal and facial motor neurons was supported by the recording of muscle action potentials and their retrograde labeling. Regenerated hypoglossal and facial motor neurons effectively participated in the reinnervation of the whisker pad, significantly improving facial symmetry without evident synkinesis, compared with rats that underwent IFP without hypoglossal-facial nerve neurorrhaphy.

Conclusions

This study demonstrates that hypoglossal-facial nerve “side”-to-side neurorrhaphy with a predegenerated nerve graft can lead to rapid functional benefits for persistent IFP without compromising the remnants of facial axons, thus providing a proof-of-feasibility for further studies in humans.

Combination of hypoglossal-facial nerve surgical reconstruction and neurotrophin-3 gene therapy for facial palsy

Object

Facial nerve injury results in facial palsy that has great impact on the psychosocial conditions of affected patients. Reconstruction of the facial nerve to restore facial symmetry and expression is still a significant surgical challenge. In this study, the authors assessed a hypoglossal-facial nerve anastomosis method combined with neurotrophic factor gene therapy to treat facial palsy in adult rats after facial nerve injury.

Methods

Surgery consisted of the interposition of a predegenerated nerve graft (PNG) that was anastomosed with the hypoglossal and facial nerves at each of its extremities. The hypoglossal nerve was cut approximately 50% for this anastomosis to conserve partial hypoglossal function. Before their transplantation, the PNGs were genetically engineered using lentiviral vectors to induce overexpression of the neurotrophic factor neurotrophin-3 (NT-3) to improve axonal regrowth in the reconstructed nerve pathway. Reconstruction was performed after facial nerve injury, either immediately or after a delay of 9 weeks. The rats were followed up for 4 months postoperatively, and treatment outcomes were then assessed.

Results

Compared with the functional innervation in control rats that underwent facial nerve injury without subsequent treatment, functional innervation of the paralyzed whisker pad by hypoglossal motoneurons in rats treated 4 months after nerve reconstruction was evidenced by the retrograde transport of neuronal tracers, the recording of muscle action potentials conducted by the PNG, and the recovery of facial symmetry. Although a better outcome was observed when reconstruction was performed immediately after facial nerve injury, reconstruction with NT3-treated PNGs significantly improved functional reinnervation of the paralyzed whisker pad even when implantation occurred 9 weeks posttrauma.

Conclusions

Results demonstrated that hypoglossal-facial nerve anastomosis facilitates innervation of paralyzed facial muscle via hypoglossal motoneurons without sacrificing ipsilateral hemitongue function. Neurotrophin-3 treatment through gene therapy could effectively improve such innervation, even after delayed reconstruction. These findings suggest that the combination of surgical reconstruction and NT-3 gene therapy is promising for its potential application in treating facial palsy in humans.

Intraoperative neuromonitoring techniques in the surgical management of acoustic neuromas

Unfavorable outcomes such as facial paralysis and deafness were once unfortunate probable complications following resection of acoustic neuromas. However, the implementation of intraoperative neuromonitoring during acoustic neuroma surgery has demonstrated placing more emphasis on quality of life and preserving neurological function. A modern review demonstrates a great degree of recent success in this regard. In facial nerve monitoring, the use of modern electromyography along with improvements in microneurosurgery has significantly improved preservation. Recent studies have evaluated the use of video monitoring as an adjunctive tool to further improve outcomes for patients undergoing surgery. Vestibulocochlear nerve monitoring has also been extensively studied, with the most popular techniques including brainstem auditory evoked potential monitoring, electrocochleography, and direct compound nerve action potential monitoring. Among them, direct recording remains the most promising and preferred monitoring method for functional acoustic preservation. However, when compared with postoperative facial nerve function, the hearing preservation is only maintained at a lower rate. Here, the authors analyze the major intraoperative neuromonitoring techniques available for acoustic neuroma resection.

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.

Prognostic factors for the incidence and recovery of delayed facial nerve palsy after vestibular schwannoma resection

Object

Preservation of facial nerve function in vestibular schwannoma (VS) resections remains a significant operative challenge. Delayed facial palsy (DFP) is one specific challenge yet to be fully elucidated. The aim of this study was to evaluate DFP among VS resection cases to identify significant prognostic factors associated with its incidence and clinical recovery.

Methods

This investigation involves a retrospective review of 104 cases of VS resection that occurred between December 2005 and May 2007. Patients who developed DFP were compared with patients exhibiting no facial palsy postoperatively with regard to surgical approach, severity and day of palsy onset, tumor size, intraoperative facial nerve monitoring, and postoperative recovery and treatment. Patients who demonstrated immediate facial palsy (IFP) following VS resection were also analyzed. Furthermore, specific analyses were performed in 2 distinct DFP patient groups: those who developed DFP after postoperative Day 3 (“late onset DFP”), and those whose palsy worsened after initial DFP identification (“deteriorators”).

Results

Of the 104 patients who underwent VS resection, 25.0% developed DFP and 8.6% demonstrated IFP postoperatively. The DFP group did not differ significantly in any measure when compared with patients with no postoperative facial palsy. However, patients with DFP presented with significantly smaller tumor sizes than patients with IFP. This IFP group averaged significantly smaller intraoperative facial nerve responses than patients without facial palsy, and larger tumor sizes than both the DFP and no facial palsy groups. Within the DFP group, patients with late onset DFP showed diminished intraoperative facial nerve responses when compared with the total DFP patient population. In total, 25 (96.2%) of 26 patients with DFP and 7 (77.8%) of 9 patients with IFP recovered to normal or near-normal facial function (House-Brackmann Grade I or II) at longest clinical follow-up.

Conclusions

Although patients with DFP did not exhibit any distinguishable characteristics when compared with patients without postoperative facial palsy, our analysis identified significant differences in patients with palsy presenting immediately postoperatively. Further study of patients with DFP should be undertaken to predict its incidence following VS resection.

Cyclin D1 expression and facial function outcome after vestibular schwannoma surgery

HYPOTHESIS

The proto-oncogen cyclin D1 has been implicated in the development and behavior of vestibular schwannoma. This study evaluates the association between cyclin D1 expression and other known prognostic factors in facial function outcome 1 year after vestibular schwannoma surgery.

METHODS

Sixty-four patients undergoing surgery for vestibular schwannoma were studied. Immunohistochemistry analysis was performed with anticyclin D1 in all cases. Cyclin D1 expression, as well as other demographic, clinical, radiologic, and intraoperative data, was correlated with 1-year postoperative facial function.

RESULTS

Good 1-year facial function (Grades 1-2) was achieved in 73% of cases. Cyclin D1 expression was found in 67% of the tumors. Positive cyclin D1 staining was more frequent in patients with Grades 1 to 2 (75%) than in those with Grades 3 to 6 (25%). Other significant variables were tumor volume and facial nerve stimulation after tumor resection. The area under the receiver operating characteristics curve increased when adding cyclin D1 expression to the multivariate model.

CONCLUSION

Cyclin D1 expression is associated to facial outcome after vestibular schwannoma surgery. The prognostic value of cyclin D1 expression is independent of tumor size and facial nerve stimulation at the end of surgery.

Prognostic clinical and radiological parameters for immediate facial nerve function following vestibular schwannoma surgery

OBJECTIVE

The paper aims to define the parameters available before surgery which could predict immediate facial nerve function after excision of a vestibular schwannoma (VS).

METHODS

Ninety-nine patients with VS operated consecutively by a single surgeon using an identical surgical technique have been evaluated retrospectively. Data were collected regarding patients' sex, age at onset of symptoms and at surgery, initial symptoms, neurological status at presentation, early post-operative neurological status and complications. The main radiological parameters included in the study were tumour extension pattern, diameters, shape, and volume, as well as extent of bony changes of the internal auditory canal.

RESULTS

As the tumour stage and volume increase, facial nerve function is worse after surgery (p < 0.001 and p < 0.05, respectively). Concomitantly, larger extra-meatal tumour diameters in three dimensions (sagittal, coronal and axial) led to worse function (p < 0.01). Anterior and/or caudal tumour extension (p = 0.001 and p = 0.004, respectively) had more significant correlation than posterior and/or cranial extension (p = 0.022 and p = 0.353, respectively). Polycyclic VS had the worst prognosis, followed by the tumours with oval shape. The extent of intra-meatal tumour growth does not correlate with immediate facial nerve outcome. The different angles, lengths and diameters of the internal auditory channel showed no significant correlation with facial nerve outcome. Patients with headache as an initial symptom and those with gait instability and/or pre-operative poor facial nerve function had significantly worse immediate facial nerve outcome.

CONCLUSION

Our data suggests that the analysis of the radiological and neurological patient data prior to surgery could give reliable clues regarding the immediate post-operative facial nerve function.

Long-term facial nerve clinical evaluation following vestibular schwannoma surgery

BACKGROUND: Facial function is important in accompaniment of patients operated on vestibular schwannoma (VS). OBJETIVE: To evaluate long term facial nerve function in patients undergoing VS resection and to correlate tumor size and facial function in a long-term follow-up. METHOD: Transversal study of 20 patients with VS operated by the retrosigmoid approach. House-Brackmann Scale was used preoperatively, immediately after surgery and in a long-term follow-up. Student t test was applied for statistic analysis. RESULTS: In the immediate postoperative evaluation, 65% of patients presented FP of different grades. Improvement of facial nerve function (at least of one grade) occurred in 53% in the long-term follow-up. There was statistically significant difference in facial nerve outcome in long-term follow-up when tumor size was considered (p<0.05). Conclusion: The majority of patients had improvement of FP in a long-term follow-up and tumor size was detected to be a factor associated with the postoperative prognostic.

A Novel Method in Predicting Immediate Postoperative Facial Nerve Function Post Acoustic Neuroma Excision

To determine whether the percentage calculated by dividing the amplitude of postexcision direct facial nerve stimulus responses (at pontomedullary junction) by the amplitude of distal ipsilateral transcutaneous (stylomastoid region) maximal stimulus responses and response amplitude progression by increasing stimulus intensities have predictive value for determining normal or near-normal (House-Brackmann Grade 1 or 2) immediate postoperative facial nerve function.

STUDY DESIGN

Intraoperative recordings of three muscle groups: 1) frontalis, 2) orbicularis oculi, and 3) orbicularis oris. Postexcision direct facial nerve stimulation at the pontomedullary junction and transcutaneous maximal facial nerve stimulation at the ipsilateral stylomastoid region and their associated response amplitudes were recorded.

SETTING

Tertiary referral center.

PATIENTS AND METHODS

Patients who underwent acoustic neuroma surgery from January 2004 to March 2006 with intraoperative facial nerve monitoring and an intact facial nerve after tumor excision were included. Recordings were available for 38 patients.

RESULTS

With a stimulus intensity of 0.3 mA at the root exit zone, there was an 81% positive predictive value in patients that exhibited a compound action potential of greater than 20% of maximum (sensitivity, 81%). This increased to 93% when the compound action potential was greater than 50% of maximum. When the amplitude increase was greater than 5 microV, there was a 77% positive predictive value (sensitivity, 87%).

CONCLUSION

The percentage of the response amplitude of direct facial nerve stimulation at the pontomedullary junction when compared with the maximum response amplitude of ipsilateral transcutaneous stimulation at the stylomastoid foramen is a good predictor of normal to near-normal immediate postoperative facial nerve function. Progression of amplitude response also seems to be a good predictor of normal to near-normal immediate postoperative facial nerve function.

Optimal extent of resection in vestibular schwannoma surgery: relationship to recurrence and facial nerve preservation

Surgical treatment of vestibular schwannoma is targeted at complete removal with preserved neurological function. Complete removal may cause significant deficits, whereas subtotal tumor removal is associated with a high recurrence rate. The present study assessed the risk of tumor recurrence and postoperative facial nerve function in relation to the extent of surgical resection by reviewing the clinical records and radiological findings of 116 patients with vestibular schwannoma treated between 1990 and 1999. The extent of resection was classified as follows: gross total resection (GTR), near total resection (NTR), and subtotal resection (STR). Facial nerve function was graded using the modified House-Brackmann grade, and patients grouped into good (grades 1-2) and intermediate or poor (grades 3-6). Of the 116 patients, 26 (22%) underwent GTR, 32 (28%) NTR, and 58 (50%) STR. The recurrence rates were 3.8% (1/26 cases), 9.4% (3/32), and 27.6% (16/58) for GTR, NTR, and STR, respectively. GTR and NTR showed no statistically significant difference in terms of recurrence rate (p=0.620). However, recurrence was significantly less after NTR than STR (p=0.043). Immediately postoperative facial nerve function was good in 15.4% of patients after GTR, 40.6% after NTR, and 46.6% after STR. The STR and NTR carried a lower risk of facial nerve palsy than GTR in the immediately postoperative stage (p=0.006 and 0.036, respectively). Nevertheless, no statistical significance was observed in extent of resection and postoperative facial nerve outcome between the groups at last follow up (p=0.227). GTR is the ideal surgical treatment for vestibular schwannoma, but NTR is a good option, with better facial nerve function preservation than GTR without significantly increasing the risk of recurrence.

Facial Nerve Monitoring Parameters As a Predictor of Postoperative Facial Nerve Outcomes after Vestibular Schwannoma Resection

OBJECTIVE

To evaluate whether the intraoperative stimulus threshold and response amplitude measurements from facial electromyography can predict facial nerve function at 1 year after vestibular schwannoma resection.

STUDY DESIGN

Prospective study.

SETTING

Tertiary academic center.

PATIENTS

Seventy-four consecutive vestibular schwannoma patients.

INTERVENTION

The minimal stimulus intensity (in milliamperes) and electromyographic response amplitude (in microvolts) were recorded during stimulation applied to the proximal facial nerve after vestibular schwannoma removal.

MAIN OUTCOME MEASURE

Facial nerve outcomes at 1 year were evaluated using the House-Brackmann scale. Analysis was then performed to evaluate whether these electrophysiologic recordings and tumor size could predict facial nerve functional outcomes.

RESULTS

Of the 74 patients, 66 of 74 (89%) had House-Brackmann Grade I or II facial nerve function and 8 of 74 (11%) had House-Brackmann Grade III-VI function at 1 year after surgery. If standards were set for intraoperative minimal stimulus intensity of 0.05 mA or less and response amplitude of 240 microV or greater, the authors were able to predict a House-Brackmann Grade I or II outcome in 56 of 66 (85%) patients at 1 year after surgery. With these same electrophysiologic parameters, only 1 of 8 (12%) House-Brackmann Grade III-VI patients also met this standard and thus gave a false-positive result. Logistic regression analysis of the data showed that both a stimulus threshold of 0.05 mA or less and a response amplitude of 240 microV or greater predicted a House-Brackmann Grade I or II outcome with a 98% probability. However, stimulus threshold or response amplitude alone had a much lower probability of the same result. In addition, although tumor size was found to independently predict facial nerve outcomes at 1 year, it did not improve the ability to predict facial nerve function over a model using stimulus intensity and amplitude alone.

CONCLUSION

Individually, minimal stimulus intensity or response amplitude was less successful in predicting long-term postoperative facial nerve function. However, if both parameters are considered together, the study demonstrates that they are good prognostic indicators for facial nerve function at 1 year after surgery.

Staged Stereotactic Irradiation for Acoustic Neuroma

OBJECTIVE:

Stereotactic radiosurgery has proven effective in the treatment of acoustic neuromas. Prior reports using single-stage radiosurgery consistently have shown excellent tumor control, but only up to a 50 to 73% likelihood of maintaining hearing at pretreatment levels. Staged, frame-based radiosurgery using 12-hour interfraction intervals previously has been shown by our group to achieve excellent tumor control while increasing the rate of hearing preservation at 2 years to 77%. The arrival of CyberKnife (Accuray, Inc., Sunnyvale, CA) image-guided radiosurgery now makes it more practical to treat acoustic neuroma with a staged approach. We hypothesize that such factors may further minimize injury of adjacent cranial nerves. In this retrospective study, we report our experience with staged radiosurgery for managing acoustic neuromas.

METHODS:

Since 1999, the CyberKnife has been used to treat more than 270 patients with acoustic neuroma at Stanford University. Sixty-one of these patients have now been followed up for a minimum of 36 months and form the basis for the present clinical investigation. Among the treated patients, the mean transverse tumor diameter was 18.5 mm, whereas the total marginal dose was either 18 or 21 Gy using three 6- or 7-Gy fractions. Audiograms and magnetic resonance imaging were obtained at 6-months intervals after treatment for the first 2 years and then annually thereafter.

RESULTS:

Of the 61 patients with a minimum of 36 months of follow-up (mean, 48 mo), 74% of patients with serviceable hearing (Gardner-Robinson Class 1–2) maintained serviceable hearing at the last follow-up, and no patient with at least some hearing before treatment lost all hearing on the treated side. Only one treated tumor (2%) progressed after radiosurgery; 29 (48%) of 61 decreased in size and 31 (50%) of the 61 tumors were stable. In no patients did new trigeminal dysfunction develop, nor did any patient experience permanent injury to their facial nerve; two patients experienced transient facial twitching that resolved in 3 to 5 months.

CONCLUSION:

Although still preliminary, these results indicate that improved tumor dose homogeneity and a staged treatment regimen may improve hearing preservation in acoustic neuroma patients undergoing stereotactic radiosurgery.

Fractionated stereotactic radiotherapy for acoustic neuromas

PURPOSE

When compared with radiosurgery, fractionated stereotactic radiotherapy for acoustic neuroma (AN) offers escalation of the tumor dose and potential sparing of auditory and facial nerve functions.

METHODS AND MATERIALS

Between 1996 and 2001, 249 consecutive patients have received fractionated stereotactic radiotherapy for AN. One hundred twenty-five patients had follow-up >1 year and were the subject of this report. A noninvasive, repeat-fixation mask allowed simulation by way of spiral CT. Two distinct schedules for total dose and fractionation were used. For an AN <3.0 cm in diameter (volume 1.4 +/- 0.2 cm(3)), patients received 25 Gy given in 5 consecutive daily fractions of 5 Gy (111 patients), and for ANs >or=3.0 cm (volume 8.1 +/- 1.2 cm(3)), patients received 30 Gy given in 10 fractions of 3 Gy (14 patients).

RESULTS

The percentage of decrease in tumor size was 12% +/- 2% (range 0-100%) vs. 13% +/- 3% (range 0-38%) for the 25 Gy vs. 30 Gy regimens, respectively. No patient had growth of the AN or developed facial weakness. Two patients developed transient decreases in facial sensation. The rates of hearing preservation were similar for the larger and smaller tumors.

CONCLUSION

Fractionated stereotactic radiotherapy may preserve normal function and control both small and large ANs.

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.

[Is hearing preservation feasible with the retrosigmoid approach?]

The main advantages of the retrosigmoid approach are fast and good visualization of the brainstem structures and the possibility to remove tumors of all sizes. Hearing preservation, although possible, is not always achieved. The aim of this study is to present our experience with the retrosigmoid approach for acoustic neuroma resection, emphasizing our hearing results. The notes of 56 cases of acoustic neuroma removed through a the retrosigmoid approach were reviewed. Tumor size ranged from 8 to 50 mm (mean 24 mm). Considering patients with preoperative serviceable hearing, postoperative serviceable and measurable hearing was achieved in 13.3% and 26.7% of cases respectively. No tumor recurrence occurred in our series. The retrosigmoid approach is a reliable surgical procedure for most vestibular schwannoma. However, hearing preservation results may be unsatisfactory and show wide differences depending on selection criteria and the hearing terminology used. Concerns about hearing preservation should not be the deciding factor for using this approach.

Reanimation of the paralyzed face by indirect hypoglossal-facial nerve anastomosis

BACKGROUND

The results of indirect hypoglossal facial nerve anastomosis with interposition of a free nerve graft, end-to-end to the periferal facial nerve stump, and end-to-side to the hypoglossal nerve are prospectively evaluated. This technique is supposed to overcome loss of hypoglossal function.

METHODS

Tongue function in 39 consecutive patients and facial reanimation in 29 patients who completed 24 months follow-up were assessed. Facial nerve function was judged using the House-Brackmann (HB) grading system.

RESULTS

Tongue movements were normal in all operated on patients. Initial facial movements occurred on average 7.5 months postoperatively. The results were graded HB II in 6 (20.9%), HB III in 13 (44.6%), HB IV in 7 (24.1%), HB V in 2 (6.8%) patients, and HB VI in 1 (3.4%) patient. The results were significantly better in young patients and when a short time interval between paralysis and surgery existed.

CONCLUSIONS

Indirect hypoglossal-facial anastomosis is the preferred technique in most patients for whom the classical direct hypoglossofacial anastomosis is indicated.