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Predictive value of Blink reflex and facial corticobulbar motor evoked potential in cerebellopontine angle tumor surgery
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Using diagnostic testing to determine the presence or absence of a disease is essential in clinical practice. In many cases, test results are obtained as continuous values and require a process of conversion and interpretation and into a dichotomous form to determine the presence of a disease. The primary method used for this process is the receiver operating characteristic (ROC) curve. The ROC curve is used to assess the overall diagnostic performance of a test and to compare the performance of two or more diagnostic tests. It is also used to select an optimal cut-off value for determining the presence or absence of a disease. Although clinicians who do not have expertise in statistics do not need to understand both the complex mathematical equation and the analytic process of ROC curves, understanding the core concepts of the ROC curve analysis is a prerequisite for the proper use and interpretation of the ROC curve. This review describes the basic concepts for the correct use and interpretation of the ROC curve, including parametric/nonparametric ROC curves, the meaning of the area under the ROC curve (AUC), the partial AUC, methods for selecting the best cut-off value, and the statistical software to use for ROC curve analyses.
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.
ROC curve analysis is often applied to measure the diagnostic accuracy of a biomarker. The analysis results in two gains: diagnostic accuracy of the biomarker and the optimal cut-point value. There are many methods proposed in the literature to obtain the optimal cut-point value. In this study, a new approach, alternative to these methods, is proposed. The proposed approach is based on the value of the area under the ROC curve. This method defines the optimal cut-point value as the value whose sensitivity and specificity are the closest to the value of the area under the ROC curve and the absolute value of the difference between the sensitivity and specificity values is minimum. This approach is very practical. In this study, the results of the proposed method are compared with those of the standard approaches, by using simulated data with different distribution and homogeneity conditions as well as a real data. According to the simulation results, the use of the proposed method is advised for finding the true cut-point.
Continuous diagnostic tests are often used for discriminating between healthy and diseased populations. For the clinical application of such tests, it is useful to select a cutpoint or discrimination value c that defines positive and negative test results. In general, individuals with a diagnostic test value of c or higher are classified as diseased. Several search strategies have been proposed for choosing optimal cutpoints in diagnostic tests, depending on the underlying reason for this choice. This paper introduces an R package, known as OptimalCutpoints, for selecting optimal cutpoints in diagnostic tests. It incorporates criteria that take the costs of the different diagnostic decisions into account, as well as the prevalence of the target disease and several methods based on measures of diagnostic test accuracy. Moreover, it enables optimal levels to be calculated according to levels of given (categorical) covariates. While the numerical output includes the optimal cutpoint values and associated accuracy measures with their confidence intervals, the graphical output includes the receiver operating characteristic (ROC) and predictive ROC curves. An illustration of the use of OptimalCutpoints is provided, using a real biomedical dataset.
Although various monitoring techniques have been used routinely in the treatment of the lesions in the skull base, iatrogenic facial paresis or paralysis remains a significant clinical problem. The aim of this study was to investigate the effect of intraoperative facial motor evoked potentials monitoring with transcranial electrical stimulation on preservation of facial nerve function.
From January to November 2005, 19 patients with large acoustic neuroma were treated using intraoperative facial motor evoked potentials monitoring with transcranial electrical stimulation (TCEMEP) for preservation of facial nerve function. The relationship between the decrease of MEP amplitude after tumor removal and the postoperative function of the facial nerve was analyzed.
MEP amplitude decreased more than 75% in 11 patients, of which 6 presented significant facial paralysis (H-B grade 3), and 5 had mild facial paralysis (H-B grade 2). In the other 8 patients, whose MEP amplitude decreased less than 75%, 1 experienced significant facial paralysis, 5 had mild facial paralysis, and 2 were normal.
Intraoperative TCEMEP can be used to predict postoperative function of the facial nerve. The decreased MEP amplitude above 75 % is an alarm point for possible severe facial paralysis.
The authors evaluated the clinical manifestations and surgical results in patients with cystic vestibular schwannoma (VS), and investigated the matrix metalloproteinase (MMP) expression of the cyst fluid and wall in an attempt to elucidate the pathogenesis and characteristics of this disease.
The clinical and neuroimaging features, perioperative findings, and surgical outcomes in 24 cases of cystic VS and 82 cases of solid VS, all of which were treated using the suboccipital approach, were retrospectively compared. To evaluate the role of MMP in cystic VS, gelatin zymography and immunohistochemical studies of the cyst fluid, wall, and solid portion were performed in nine cases of this disease. The mean duration of symptoms was shorter (14.0 months compared with 26.1 months; p = 0.04) and the mean size of the tumor was larger (43.8 mm compared with 34.2 mm; p = 0.048) in the cystic than the solid VS group. Although gross-total resection was easier to accomplish in this group (100% compared with 84.1%), adhesion to the facial nerve was more frequent (62.5% compared with 48.8%; p = 0.042). On gelatin zymography studies, MMP-2 expression was ubiquitously observed in all cyst fluids. Immunohistochemical analysis of the cyst wall showed that MMP-2 was apparently localized to the tumor cells on the luminal inner surface, adjacent to the cyst cavity.
Resection of cystic VS is complicated by severe adhesion of the tumor capsule to the facial nerve and the large size of the lesion. The authors believe that MMP-2 may be involved in the pathogenesis of cyst formation or in its enlargement and may aggravate adhesion to the facial nerve, either by promoting the enlargement of the tumor or engendering the degradation of the tumor-nerve barrier proteolytically.
Objective
We propose a novel method that predicts facial nerve function (FNF) calculated from the drop and recovery of facial motor evoked potential (FMEP) amplitude ratio during the surgery of cerebellopontine angle tumors.
Methods
We enrolled 73 patients with cerebellopontine angle tumor, and used a biphasic, suprathreshold, and constant current stimulation (BCS) protocol to record FMEP of the orbicularis oris. We measured the intraoperative minimum-to-baseline amplitude ratio (MBR), the final-to-baseline amplitude ratio (FBR), and the recovery value (RV). RV was measured by subtracting MBR from FBR. Using those values, we evaluated FNF both at early postoperative (EP) and late postoperative (LP) periods.
Results
We successfully obtained 62 FMEP readings. Facial palsies occurred in 22 patients during the EP period, and 14 patients recovered during the LP period. Both MBR and FBR showed a significant correlation with FNF in the EP period. RV showed a good predictive power of FNF recovery during the LP period for the first time.
Conclusions
RV is a new and useful predictor of FNF recovery. MBR can be an intraoperative predictor of FNF in the EP period.
Significance
FNF outcome in the early and late postoperative periods can be predicted by FMEP.
Objective
The goal of this study was to retrospectively analyze clinical and surgical data of a consecutive series of twenty-six patients with unilateral cystic vestibular schwannomas.
Methods
Tumors were classified as type A (central cyst) and type B (peripheral cyst), and as small (tumor diameter < 3cm) and large (tumor diameter >3cm). All patients underwent microsurgical removal via retrosigmoid approach. The course of facial nerve (FN) was classified into anterior, anterior-inferior, anterior-superior and dorsal to the tumor’s surface.
Results
Mean age was 53.5 years. Mean tumor size was 3.2 cm. Twenty-two cases were classified as type A and only 4 as type B. Total or near total resection (>95%) was achieved in 16 cases (61.5%), subtotal removal (90-95%) in 9 cases (34.6%), and partial removal (<90%) in 1 case (3.9%). Position pattern of FN was anterior-inferior in 10 cases (38.4%), anterior-superior in 10 cases (38.4%), anterior in 23.2% of cases. At hospital discharge, 9 (36%), 10 (38%), 3 (12%), 3 (12%) and 1 (4%) patients had a FN function of HB I-V, respectively; at final follow-up HB I, II, III and IV accounted respectively for 18 (72%), 6 (24%), 1 and 1 cases. At a follow-up ranging from 6 months to 10 years, a reoperation for growing of residue was never necessary.
Conclusions
According to the literature and to the results of our series, microneurosurgery of cystic vestibular schwannomas is associated with good outcomes in terms of extent of resection and FN function. In particular, long-term FN result is much more satisfactory than short-term function. In majority of cases microsurgery represents the treatment of choice of cystic vestibular schwannomas.
Objective:
To determine the role of neurophysiological preoperative and intraoperative parameters in providing prognostic information regarding facial nerve (FN) function at 1 year after translabyrinthine acoustic neuroma (AN) resection surgery.
Study design:
Prospective observational study in a tertiary referral center. Patients treated via translabyrinthine surgical approach for sporadic AN microresection between December 2015 and 2018.
Methods:
Patients underwent preoperative (electroneurography-ENG, electromyography-EMG, and Blink Reflex-BR) and intraoperative (FN motor action potential-MAP and continuous EMG traces) neurophysiological studies. FN function was graded postoperatively at 1 year using House-Brackmann Scoring System.
Results:
Sixty-two patients were included in the analysis. Mean age was 53±10 years and average tumor diameter was 23 ± 9 mm. At 1 year a normal facial function was observed in 68% of patients. In the univariate analysis a pathologic BR, low FN MAP values and ratios, and the presence of pathological neurotonic tracing (A-trains) on continuous EMG were associated with a poor facial nerve function outcome at 1 year postoperatively. Pathological preoperative BR testing and intraoperative A-trains showed a statistical significance also in the multivariable analysis, regardless of tumor size.
Conclusions:
Preoperative pathological BR testing and A-train activity on intraoperative EMG are correlated with poor FN outcomes at 1 year postoperative. This may provide important prognostic information to both patients and treating neuro-otologists. In the future this may guide preoperative and postoperative patient counselling and possibly optimize timing of facial nerve reanimation in selected patients.
Objective:
To investigate the variation in the position and course of facial nerve (FN) in patients undergoing vestibular schwannoma (VS) microsurgery by key-hole retrosigmoid aTonellipproach and the relationship between its position and postoperative facial results.
Methods:
The series consists of 100 patients who underwent VS microsurgery during a 5-year period, in whom the position and course of the FN could be confirmed by direct stimulation. In relation to the position of FN, patients were classified into four groups: anterior (ventral) surface of the tumor (A), anterior-superior (AS), anterior-inferior (AI), and dorsal (D).
Results:
The FN position and course was AS in 48 cases, A in 31, AI in 21 and D in zero. For tumors <1.5 cm, AS position was most common (68,4%). For tumors ≥1.5 cm, the proportion of A and AI increased (31,4% and 25,5%) respectively). Significant differences were observed between position and course patterns of the FN and postoperative nerve results: AS and AI had better House-Brackmann (HB) FN function in comparison to A group (p<0.05). Moreover, in tumors >3.0 cm, the FN had the tendency to adhere strongly to the tumor capsule, and postoperative facial deficit were more frequent (p<0.05).
Conclusions:
The AS pattern was most common for smaller VS. The A position and course and adhesion of the nerve to the tumor capsule were the two factors most strongly associated with worst postoperative FN result.
Objective To investigate the variation in the course of the facial nerve (FN) in patients undergoing acoustic neuroma (AN) surgery, its adhesion to tumors, and the relationship between such adhesions and postoperative facial palsy.
Methods The subjects were 356 patients who underwent AN surgery in whom the course of the FN could be confirmed. Patients were classified into six groups: ventro-central surface of the tumor (VCe), ventro-rostral (VR), ventro-caudal (VCa), rostral (R), caudal (C), and dorsal (D).
Results The FN course was VCe in 185 cases, VR in 137, VCa in 19, R in 10, C in 4, and D in one. For tumors < 1.5 cm, VCe was most common. For tumors ≥ 1.5 cm, the proportion of VR increased. No significant difference was observed between the course patterns of the FN in terms of postoperative FN function, but for tumors > 3.0 cm, there was an increasing tendency for the FN to adhere strongly to the tumor capsule, and postoperative facial palsy was more severe in patients with stronger adhesions.
Conclusions The VCe pattern was most common for small tumors. Strong or less strong adhesion to the tumor capsule was most strongly associated with postoperative FN palsy.
Object:
During surgeries that put the facial nerve at risk for injury, its function can be continuously monitored by transcranial facial nerve motor evoked potentials (FNMEPs) in facial nerve target muscles. Despite their advantages, FNMEPs are not yet widely used. While most authors use a 50% reduction in FNMEP response amplitudes as a warning criterion, in this paper the authors' approach was to keep the response amplitude constant by increasing the stimulation intensity and to establish a warning criterion based on the "threshold-level" method.
Methods:
The authors included 34 consecutive procedures involving 33 adult patients (median age 47 years) in whom FNMEPs were monitored. A threshold increase greater than 20 mA for eliciting FNMEPs in the most reliable facial nerve target muscle was considered a prediction of reduced postoperative facial nerve function, and subsequently a warning was issued to the surgeon. Preoperative and early postoperative function was documented using the House-Brackmann grading system.
Results:
Monitoring of FNMEPs was feasible in all 34 surgeries in at least one facial nerve target muscle. The mentalis muscle yielded the best results. The House-Brackmann grade deteriorated in 17 (50%) of 34 cases. The warning criterion was reached in 18 (53%) of 34 cases, which predicted an 83% risk of House-Brackmann grade deterioration. Sensitivity amounted to 88% (CI 64%-99%) and specificity to 82% (CI 57%-96%). Deterioration of FNMEPs and a worse House-Brackmann grade showed a high degree of association (p < 0.001). The impact of FNMEP monitoring on surgical strategy is exemplified in an illustrative case.
Conclusions:
In surgeries that put the facial nerve at risk, the intraoperative increase in FNMEP stimulation threshold was closely correlated to postoperative facial nerve dysfunction. Monitoring of FNMEPs is a valid indicator of facial nerve function in skull base surgery. It should be used as an adjunct to direct electrical facial nerve stimulation and continuous electromyographic monitoring of facial nerve target muscles.
There is evidence that primary hemifacial spasm (HFS) in the majority of patients is related to a vascular compression of the facial nerve at its root exit zone (REZ). As a consequence, the hyperexcitability of facial nerve generates spasms of the facial muscles. Microvascular decompression (MVD) of the facial nerve near its REZ has been established as an effective treatment of HFS. Intra-operative disappearance of abnormal muscle responses (lateral spread) elicited by stimulating one of the facial nerve branches has been used as a method to predict MVD effectiveness. Other neurophysiologic techniques, such as facial F-wave, blink reflex and facial corticobulbar motor evoked potentials (FCoMEP), are feasible to intra-operatively study changes in excitability of the facial nerve and its nucleus during MVDs. Intra-operative neuromonitoring with the mentioned techniques allows a better understanding of HFS pathophysiology and helps to optimise the MVD.
This study was conducted to investigate the success rate of using the facial motor evoked potential (FMEP) of orbicularis oculi and oris muscles for facial nerve function monitoring with use of a stepwise protocol, and its usefulness in predicting facial nerve outcome during cerebellopontine angle (CPA) surgeries.
FMEPs were recorded intraoperatively from 60 patients undergoing CPA surgeries. Transcranial electrocortical stimulation (TES) was performed using corkscrew electrodes positioned at hemispheric montage (C3/C4 and CZ). The contralateral abductor pollicis brevis muscle was used as the control response. Stimulation was always applied contralaterally to the affected side using 1, 3, or 5 rectangular pulses ranging from 200 to 600 V with 50 micros of pulse duration and an interstimulus interval of 2 ms. Facial potentials were recorded from needles placed in the orbicularis oculi and oris muscles.
FMEP from the orbicularis oris and oculi muscles could be reliably monitored in 86.7% and 85% of the patients, respectively. The immediate postoperative facial function correlated significantly with the FMEP ratio in the orbicularis oculi muscle at 80% amplitude ratio (P = .037) and orbicularis oris muscle at 35% ratio (P = .000). FMEP loss was always related to postoperative facial paresis, although in different degrees.
FMEPs can be obtained reliably by using TES with 3 to 5 train pulses. Stable intraoperative FMEPs can predict a good postoperative outcome of facial function. However, further refinements of this technique are necessary to minimize artifacts and to make this method more reliable.
Until now, there have been no reports on eliciting the blink reflex (BR) during anesthesia at a depth compatible with surgery. We introduce a novel method for eliciting the R1 component of the BR under inhalation or total intravenous anesthesia by using a short train of four to seven stimuli applied over the supraorbital nerve. Recording is done from the ipsilateral orbicularis oculi muscle. We set out to record the BR in 27 patients (age 1-78 years) without involvement of the facial nerve, trigeminal nerve, or brainstem. The BR could not be recorded in only 4 patients (recordability: 86.2%). All patients received at least one bolus of propofol while in surgery. Using this method, the BR was recorded on 4 awake healthy subjects. Boluses of propofol and muscle relaxants should be avoided in order to successfully record the responses. BR recording is feasible in patients under general anesthesia by using this novel technique. Muscle Nerve 39: 642-646, 2009.
To assess the nerve facial displacement by a vestibular schwannoma and nerve adhesion to tumor as predictive factors of facial function outcome.
A prospective cohort study.
Tertiary referral center.
Ninety-six patients undergoing a solitary vestibular schwannoma surgery during 2005 were included. Data concerning tumor size (Stage 1, intracanalicular; Stage 2, < or =15 mm in the cerebellopontine angle [CPA]; Stage 3, 15-30 mm in the CPA; and Stage 4, >30 mm in the CPA), intraoperative facial nerve displacement (Type 1, anterior to the tumor; Type 2, anterior and superior to the tumor and separated from the cochlear nerve; Type 3, superior to the tumor; and Type 4, posterior to the tumor), degree of tumor adhesion (weak, intermediate, and strong) and postoperative facial function according to the House and Brackmann classification at days 10, 30, 90 and 180 were collected.
A good facial function (Grade 1 or 2) was reported in 73% at postoperative Day 180. Univariate analysis showed that facial outcome was better in small tumors, in displacement Types 1 and 2 (Type 1, 46%; Type 2, 34%; and Type 3, 20%), and in tumors with weak and intermediate adhesion (weak, 10%; intermediate, 38%; and strong, 52%). Facial nerve displacement and adhesion were related to tumor stage. The combination of tumor stage, adhesion, and nerve displacement in a logistic regression model was highly predictive of postoperative facial function.
Facial nerve displacement and nerve adhesion to tumor are significant predictive factors of facial function outcome after vestibular schwannoma surgery in addition to tumor size.
Brainstem auditory evoked potentials (BAEP) and blink reflexes (BR) were obtained from 13 patients with pontocerebellar angle (PCA) tumors whose pathological diagnosis was as follows: 7 acoustic neurinoma, 3 meningioma, 1 neurinoma, 1 brain stem epidermoid tumor, 1 arteriovenous malformation. The most prominent abnormality was noted in BAEP generated by stimulating the ear ipsilateral to the lesion and ipsilateral R1 reflexes obtained from ipsilateral stimulation of the supraorbital nerve.
Facial nerve injury associated with acoustic neuroma surgery has declined in incidence but remains a clinical concern. A retrospective analysis of 611 patients surgically treated for acoustic neuroma between 1973 and 1994 was undertaken to understand patterns of facial nerve injury more clearly and to identify factors that influence facial nerve outcome.
Anatomical preservation of the facial nerve was achieved in 596 patients (97.5%). In the immediate postoperative period, 62.1% of patients displayed normal or near-normal facial nerve function (House—Brackmann Grade 1 or 2). This number rose to 85.3% of patients at 6 months after surgery and by 1 year, 89.7% of patients who had undergone acoustic neuroma surgery demonstrated normal or near-normal facial nerve function.
The surgical approach appeared to have no effect on the incidence of facial nerve injury. Poor facial nerve outcome (House—Brackmann Grade 5 or 6) was seen in 1.58% of patients treated via the suboccipital approach and in 2.6% of patients treated via the translabyrinthine approach. When facial nerve outcome was examined with respect to tumor size, there clearly was an increased incidence of facial nerve palsy seen in the immediate postoperative period in cases of larger tumors: 60.8% of patients with tumors smaller than 2.5 cm had normal facial nerve function, whereas only 37.5% of patients with tumors larger than 4 cm had normal function. This difference was less pronounced, however, 6 months after surgery, when 92.1% of patients with tumors smaller than 2.5 cm had normal or near normal facial function, versus 75% of patients with tumors larger than 4 cm.
The etiology of facial nerve injury is discussed with emphasis on the pathophysiology of facial nerve palsy. In addition, on the basis of the authors' experience with these complex tumors, techniques of preventing facial nerve injury are discussed.
Facial nerve monitoring is an established method that is routinely used during cerebellopontine angle tumor surgery. The aim of this study was to determine quantitative electromyographic (EMG) parameters that were predictive of facial nerve outcomes.
In 137 patients with intra-/extrameatal vestibular schwannomas, the most proximal (the exit from the brainstem) and distal (the fundus of the internal auditory canal) parts of the facial nerve were stimulated after total tumor removal. A quantitative analysis of absolute values and ratios (proximal/distal) of evoked EMG parameters (amplitude, latency, and duration) was performed, and parameters were correlated with postoperative (1 and 6 wk and 6 mo) facial nerve function (FNF).
Absolute values of EMG amplitudes were statistically correlated with FNF (P < 0.05). Amplitude ratios (proximal/distal) demonstrated an even greater predictive power. The risk of exhibiting facial palsy 6 months after surgery increased from 1.6% (amplitude ratio of >0.8) to 75% (ratio of <0.1). For EMG latencies, only the ratios revealed a significant correlation with FNF. The latency ratio-dependent risk of facial palsy after 6 months increased from 2.9% (ratio of <1.05) to 33% (ratio of >1.35). The durations of the muscle responses were not significantly correlated with clinical outcomes.
The predictive power of the amplitudes and latencies of electrically evoked muscle responses could be improved by calculating proximal/distal ratios. The proximal/distal amplitude ratio proved to be the most powerful parameter for intraoperative assessment of postoperative FNF.
The study goal was to demonstrate that blink reflex analysis can predict postoperative facial nerve outcome in cerebellopontine angle tumor surgery. STUDY DESIGN, SETTING, AND PATIENTS: In an open and prospective study conducted at a single tertiary care center over 3 years, 91 subjects with a vestibular schwannoma filling the internal auditory meatus were enrolled and operated on via a translabyrinthine approach. The difference in latency of the early response (DeltaR1) of the blink reflex between the pathologic side and the healthy side was calculated in every patient during a complete electrophysiologic examination of the facial nerve performed on the day before surgery. MIN OUTCOME MEASURES: DeltaR1 was compared with the other preoperative data (tumor volume, facial function), with the perioperative observations (difficulties with the dissection of the facial nerve), and especially with the postoperative status after 1 year. The statistical study was conducted using polynomial regression.
Patients with a negative or zero DeltaR1 have normal facial function at 1 year. For those with a positive DeltaR1 the outcome is not favorable unless the tumor is small. For patients presenting with an immediate complete facial paralysis, the value of DeltaR1 is also indicative of facial function outcome.
Statistical analysis shows that the blink reflex, through DeltaR1, has an excellent prognostic value in anticipating the difficulties with facial nerve dissection and postoperative facial function after 1 year.
The aim of this study was to determine if factors such as postoperative hearing, facial function, headaches, or other factors have an impact on self-assessed quality of life (QOL) after acoustic neuroma surgery.
The SF-36 and seven additional questions on the impact of surgery on the QOL were sent to 135 consecutive patients who had undergone acoustic neuroma surgery. The Spearman rho correlations were calculated for each of the eight categories of the SF-36 (general health, physical functioning, physical role limitations, emotional role limitations, mental health, energy/vitality, pain, social functioning). The results were correlated with patients' sex, age, persistent headache, years since surgery, postoperative hearing level, and facial function. The response rate was 74.8%. The transformed scores of the eight categories of the SF-36 were lower than age-matched healthy controls in approximately half of the categories. The strongest trend toward lower scores with statistical significance in two categories was persistent headaches. Some categories demonstrated trends toward lower scores with females or age older than 55 years. Postoperative hearing and facial functioning, and time since surgery showed no statistically significant impact on QOL measured by the SF-36. Responses to the additional questions indicate that hearing, facial function, and headache influenced people's feelings about surgery and had an impact on their return to work.
The QOL scores are not consistently lower than population normative values compared with different normative studies. The strongest correlation was between the presence of persistent headache and QOL. Other correlations were not consistent in all categories, and few were statistically significant. These trends in some categories do not explain the difference seen between patients after acoustic neuroma surgery in this study and normal populations in other studies.
To address the limitations of standard electromyography (EMG) facial nerve monitoring techniques by exploring the novel application of multi-pulse transcranial electrical stimulation (mpTES) to myogenic facial motor evoked potential (MEP) monitoring.
In 76 patients undergoing skull base surgery, mpTES was delivered through electrodes 1cm anterior to C1 and C2 (M1-M2), C3 and C4 (M3-M4) or C3 or C4 and Cz (M3/M4-Mz), with the anode contralateral to the operative side. Facial MEPs were monitored from the orbicularis oris muscle on the operative side. Distal facial nerve excitation was excluded by the absence of single pulse responses and by onset latency consistent with a central origin.
M3/M4-Mz mpTES (n=50) reliably produced facial MEPs while M1-M2 (n=18) or M3-M4 (n=8) stimulation produced 6 technical failures. Facial MEPs could be successfully monitored in 21 of 22 patients whose proximal facial nerves were inaccessible to direct stimulation. Using 50, 35 and 0% of baseline amplitude criteria, significant facial deficits were predicted with a sensitivity/specificity of 1.00/0.88, 0.91/0.97 and 0.64/1.00, respectively.
Facial MEPs can provide an ongoing surgeon-independent assessment of facial nerve function and predict facial nerve outcome with sufficiently useful accuracy.
This method substantially improves facial nerve monitoring during skull base surgery.
The facial nerve in vestibular schwannomas (VSs) is located on the ventral tumor surface in more than 90% of cases; other courses are rare. A split facial nerve course with two distinct bundles has thus far been described exclusively for medial extrameatal tumors.
Between 1996 and 2005, 16 consecutive cases of 241 surgically treated VSs were observed to have distinct splitting of the facial nerve. The mean tumor size measured 27 mm. In one third of the cases, intrameatal tumor extension with obliteration of the fundus was documented. All patients underwent extensive intraoperative neurophysiological monitoring using multichannel electromyography recordings. Patients were reevaluated 12 months after surgery. In all 16 patients, distinct splitting of the facial nerve was demonstrated. The major portion of the facial nerve followed a typical course on the ventral tumor surface. The smaller nerve portion in all cases ran parallel to the brainstem up to the level of the trigeminal root exit zone and crossed on the cranial tumor pole to the internal auditory canal. The two nerve portions rejoined at the level of the porus acusticus. The smaller portion carried fibers exclusively to the orbicularis oris muscle, whereas the major portion supplied all three branches of the facial nerve.
In VSs, an aberrant course with distinct splitting of the facial nerve adds considerably to the surgical challenge. Long-term facial nerve results are excellent with extensive neurophysiological monitoring, which allows the differentiation and identification of aberrant facial nerve fibers and avoids additional risks to facial nerve preservation.
The aim of this study was to assess the consequences of total removal of a large vestibular schwannoma on the patient's symptoms and quality of life (QOL).
A questionnaire regarding preoperative and postoperative symptoms with measures of both daily and global QOL and a modified 36-Item Short Form Health Survey (SF-36) QOL instrument were sent to 103 patients who had undergone surgery via a retrosigmoid approach for total removal of a Grade III or IV vestibular schwannoma. In addition, 48 patients underwent follow-up clinical examinations to assess their conditions. Seventy-two of the 103 patients completed and returned the questionnaire. Forty-six (64%) of the schwannomas were Grade IV and 26 (36%) were Grade III. The patients' pre- and postoperative symptoms were similar to those reported in other studies. The patients' perceptions of facial movement were likely to be worse than the clinicians' estimation based on the House-Brackmann classification. All scores in the QOL categories were significantly reduced when compared with normative data. Patients with large vestibular schwannomas had lower scores in all SF-36 categories except pain compared with data from other studies. Psychological problems were the preponderant symptoms, and their presence was the most powerful predictive variable for global and daily QOL.
Surgery for a large vestibular schwannoma has a significant impact on the patient's QOL. To improve QOL postoperatively, the patient should be prepared and well informed of the consequences of such a surgery on QOL. Clinicians must be aware that early involvement of a clinical psychologist may be very helpful.
To determine whether monitoring facial nerve motor-evoked potentials (FNMEPs) elicited by transcranial electrical stimulation during skull base tumour surgery is useful for predicting facial nerve outcome.
This study analysed FNMEP findings in 26 patients with skull base tumours. Corkscrew electrodes positioned at C3 or C4 and Cz were used to deliver supramaximal stimuli (180-550 V). FNMEPs were recorded from the orbicularis oculi and oris muscles. The correlation between the final-to-baseline FNMEP ratio and postoperative facial nerve function was examined.
Postoperative facial nerve function correlated significantly with the FNMEP ratios in the orbicularis oculi (p = 0.004) and orbicularis oris (p<0.001) muscles. An FNMEP ratio of <50% consistently predicted immediate postoperative facial palsy, although the degree of palsy differed among patients. All patients had satisfactory facial nerve function (House and Brackmann grades I and II) postoperatively if the FNMEP ratio remained at >50%.
Intraoperative FNMEP monitoring can be useful for predicting facial nerve function after skull base surgery. This new method is a valuable adjunct to conventional facial nerve monitoring.