Intraoperative monitoring of facial nerve antidromic potentials during acoustic neuroma surgery

The present paper presents monopolar recording of facial nerve antidromic potentials as an alternative technique to facial electromyography for the continuous monitoring of the facial nerve during acoustic neuroma surgery. The investigation involved 22 patients undergoing acoustic neuroma surgery via a retrosigmoid approach (tumour sizes ranging from 5 to 28 mm). Bipolar electrical stimulation of the marginalis mandibulae was performed to elicit facial nerve antidromic potentials. Stimulus intensity ranged from 2 to 6 mA with a delivery rate of 7/sec. A silver wire monopolar electrode positioned intracranially on the proximal portion of the acoustic facial bundle was used to record antidromic potentials. To define the specific origin of the action potentials and acquire normative data, monopolar and bipolar recordings of facial nerve antidromic potentials were performed in 15 subjects undergoing retrosigmoid vestibular neurectomy for Meniere's disease. The average facial nerve antidromic potential latency was 4.2 (+/- 0.6) msec in subjects with acoustic neuroma and 3.3 (+/- 0.2) msec in subjects with Meniere's disease. Facial nerve antidromic potentials furnished near real-time information about intraoperative facial nerve damage and postoperative facial nerve function during acoustic neuroma surgery. Facial nerve antidromic potentials may provide additional information to conventional EMG. They allow the use of endplate blockers, yield quantitative estimation of facial nerve conduction properties in terms of amplitude and latency, and allow actual continuous monitoring of the facial nerve.     

Unusual metastasis of hypernephroma in the maxillary sinus

OBJECTIVES: To determine the predictive value of intraoperative threshold stimulus for facial nerve outcome and the prevalence and prognostic value of persistent trains of activity and frequent spontaneous or mechanically induced contractions during acoustic neuroma surgery. STUDY DESIGN: Prospective recording and subsequent review of facial nerve activity. SETTING: Tertiary referral centre. PATIENTS AND METHODS: Consecutive patients undergoing acoustic neuroma surgery. Intraoperative facial nerve activity was digitised and stored on a personal computer for future analysis. Operative events were flagged. Recordings were available in 27 patients. MAIN OUTCOME MEASURES: Frequent mechanically induced contractions (< 20), prolonged trains of facial nerve activity (total time > 199 seconds), and facial nerve brainstem stimulus threshold were correlated with facial nerve outcome. RESULTS: A brainstem stimulus threshold > 0.1 mA was significantly associated with intermediate or poor facial nerve function (House-Brackmann grade > 2) on the sixth postoperative day, at 1 month and 6 months. Patients with normal or near-normal facial function on the first day and a threshold of > 0.1 mA were significantly more likely to develop a delayed facial nerve palsy. Frequent contractions were noted in 74% of patients and persistent train activity in 59%. Neither was predictive of facial nerve outcome. CONCLUSIONS: An elevated brainstem threshold is helpful in predicting delayed facial nerve palsy and suboptimal facial nerve outcome. Persistent train activity and frequent contractions, do not have major prognostic significance.     

Rehabilitation of the paralysed face: results of facial nerve surgery

The case notes of 34 patients undergoing rehabilitative facial nerve surgery between 1978 and 1994 were retrospectively examined. Thirteen patients underwent facio-hypoglossal transposition with six achieving a facial nerve grade of IV (House-Brackmann scale) at 24 months post-surgery. Twelve patients underwent cable grafting of the facial nerve defect. Of these, 10 achieved a grade III result at 24 months. Nine patients underwent end to end anastomosis of the facial nerve, seven achieving a grade III result at 24 months after the repair. Re-routing of the facial nerve and the use of tissue glue to effect the anastomosis did not have an adverse effect on the outcome. Comparison of rerouted end to end anastomosis with non-re-routed cable grafting showed no difference. Patients presenting pre-operatively with facial weakness and those in whom nerve repair surgery was delayed for more than six months were less likely to have a good result.     

Intraoperative facial nerve monitoring in acoustic neuroma surgery

Intraoperative facial nerve monitoring simultaneously using electromyography and mechanical pressure sensors is being used in retrosigmoid and translabyrinthine approaches for acoustic neuroma resection. Insulated electrified microsurgical instruments and air drills are used to stimulate the facial nerve with a pulsed, constant current through bone and tumor, before the facial nerve is visually encountered. Electrical stimulation is used to help locate the facial nerve, map the course of the facial nerve within tumor, warn the surgeon of unexpected facial nerve locations, and help predict facial nerve function postoperatively. In 57 unmonitored cases a House-Brackmann (H-B) grade I or II result was obtained in 77 percent of small, 81 percent of medium, and 60 percent of large tumors. In 64 monitored cases H-B grade I or II was obtained in 88 percent of small, 79 percent of medium, and 90 percent of large tumors. Overall, facial nerve outcomes were better after monitored procedures (p < 0.02). A modified H-B classification for acute facial nerve injury is introduced to grade facial weakness immediately postoperatively and until function is stable at 1 year. In the unmonitored group there were five (9%) cases with a complete facial paralysis, facial nerve intact (i.e., acute H-B grade VIA) and seven (13%) cases with the facial nerve transected (i.e., acute H-B grade VIB). In the monitored group there were five (8%) acute H-B grade VIA and two (3%) acute H-B grade VIB results. In the unmonitored group of large tumors, there were statistically more patients with an acute H-B grade VIB result (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Idiopathic facial paralysis

Although acute idiopathic facial paresis is often labelled "Bell's palsy", historical studies show that Nicolaus Anton Friedreich (1761-1836) from Würzburg was the first physician to describe the typical symptoms of the disorder in 1797, approximately 24 years prior to the paper published by Sir Charles Bell. Diagnostics has now improved to the extent that acute idiopathic facial palsy can more frequently be assigned to etiologies caused by inflammatory disorders. Herpes simplex virus type I and Borrelia burgdorferi are particularly relevant. Underestimation of the degree of paresis is, particularly in children, a drawback of the clinical examination. "Incomplete eyelid closure" is not a reliable indicator of remaining nerve function. For this reason complete electromyography (EMG) is recommended in all cases of severe facial paresis. Since electroneurography does not reliably reflect the degree of denervation present, needle EMG is preferred. The therapy of the facial palsy of unclear etiology is still not well defined. Nevertheless, we recommend that a combined treatment should be used early, at least in patients with disfiguring pareses. Combinations may consist of cortisone, virostatic agents and hemorrheologic substances and possibly antibiotics. Surgical decompression of the facial nerve remains controversial, since positive surgical results lack statistical support. Individual instructions for facial exercises, massage and muscle relaxation can support rehabilitation and possibly reduce the production of pathological synkinesia. Electrical stimulation should not be used. There are a number of possibilities available to reduce the effects of misdirected reinnervation, especially the use of botulinum-A-toxin. However, intensive diagnosis and therapy in the early phase of paresis are decisive in obtaining a favorable outcome. Further refinements in rehabilitation and comparative multicenter controlled studies are still required for future improvements in affected patients.     

Intraoperative monitoring of the function of the peroneal nerve in knee joint operations

Operations on the knee are known to be associated with postoperative neurological complications. There is no consensus opinion on the causes of these complications. The aim of the present study was to develop a method for the intraoperative monitoring of the function of the common peroneal nerve. This was done as to identify intraoperative factors that might be responsible for reversible and irreversible neurological deficits. Computer-aided neuromonitoring is based on online digitizing of the surface EMG of the anterior tibial muscle. An algorithm continuously modifies the amplitude to determine the motor threshold. The method described has been used in 18 patients undergoing high tibial osteotomy. In 10 of the 18 patients, the nerve is rendered completely non-excitable after an average tourniquet application time of 59 min. This non-excitability was reversed on release of the tourniquet. In the remaining 8 patients, excitability was maintained throughout the ischaemic period, which did not exceed 60 minutes in any of the cases. Our method enables accurate quantification of the neural function throughout the entire operation, and convincingly documents the influence of ischaemia on peripheral nerve block.     

A comparison of electroneuronography with facial nerve latency testing for prognostic accuracy in patients with Bell's palsy

The purpose of this study was to evaluate the ability of electroneuronography (ENOG), also called evoked electromyography (EEMG), and facial nerve latency testing (FNLT) to assess the prognosis of facial nerve palsy, using the House-Brackmann facial nerve grading system as criterion. From 1988 to 1994 these tests were employed at the ORL Clinic of the University of Ioannina in 250 patients with idiopathic facial nerve palsy. The ENOG test results indicated that when the amplitude of the compound muscle action potentials ranged from 51% to 95% of the normal value, 97% of the patients achieved complete functional recovery (grade I) within at least 2 months. When the muscle action potential decreased to a value below 51% of normal values, prognosis for recovery was considerably worse. FNLT test results indicated that as the latency time extended, the recovery grade of the facial nerve worsened. When latency time was within the normal range (group A patients), about 92% of patients had complete functional recovery. In contrast all patients having either a very extended latency time or unable to be monitored (groups C and D) demonstrated incomplete functional recoveries that ranged from grade II to grade VI. Comparing each test with the House-Brackmann facial nerve grading system, we ascertained that the percent accuracy for ENOG was 97.6%, and that for FNLT was 94.4%.     

Intensity of MR contrast enhancement does not correspond to clinical and electroneurographic findings in acute inflammatory facial nerve palsy

PURPOSE: To determine the value of MR contrast enhancement in predicting the course of acute inflammatory facial nerve palsy and in selecting patients for surgical decompression. METHODS: Six patients with an acute inflammatory incomplete or complete peripheral facial nerve palsy (five idiopathic and one herpetic in origin) had repeated MR imaging studies with and without contrast enhancement, electroneurography, and clinical examinations to establish a connection between the intensity of contrast enhancement on MR images, the clinical condition, and the electrophysiological data. The examinations were performed every second day starting on the first day of admission until clinical recovery was proved by clinical deblockage (spontaneous clinical improvement). The last examination was performed 3 months after the onset of the facial nerve palsy. RESULTS: An abnormal, very intense contrast enhancement of the facial nerve was always present in the distal intrameatal and proximal tympanic segments and in the geniculate ganglion. The labyrinthine segment exhibited a mild to moderate enhancement, and the distal tympanic and mastoid segments showed a moderate to intense enhancement. The intensity of contrast enhancement did not correspond to the severity, duration, or course of the facial nerve palsy, and the electroneurographic data had no predictive value in indicating the severity of the inflammatory process. Three months after clinical recovery, a persistent and more or less unchanged or even slightly more intense contrast enhancement was observed. CONCLUSION: The long-lasting intense contrast enhancement seen in the facial nerve segments of patients who have acute peripheral inflammatory facial nerve palsy is explained by a two-phase breakdown of the blood-nerve barrier.     

Quantitative analyses for facial nerve MR imaging

It is clear, from our clinical experience, that the facial nerve in patients with facial palsy is enhanced on magnetic resonance (MR) imaging after intravenous administration of gadolinium diethylenetriamine. However, some problems with clinical reliability persist. There have been reports that normal facial nerves often show enhancement on MR imaging. We also question whether there are any differences in the degree of enhancement between Bell's palsy and Ramsay Hunt syndrome. To solve these problems, analyses were conducted using a personal computer by means of digital image-processing to measure the gray scale levels of enhanced facial nerves on MR imaging films. Seventeen cases of Bell's palsy, eight cases of Ramsay Hunt syndrome and fourteen normal subjects whose facial nerves showed enhancement on MR imaging were selected for the analyses. The concept of a facial nerve/whole image ratio (F/W ratio), analyzing the degree of enhancement of the facial nerve quantitatively, is introduced in this paper. The F/W ratio is the ratio of the gray scale level of the facial nerve region to the highest gray scale level in the skull at the MR imaging film. When the F/W ratios of these subjects were analyzed, no significant differences were found between Bell's Palsy and Ramsay Hunt syndrome in the degree of enhancement; facial palsy cases showed quantitatively larger F/W ratios than normal subjects.     

Chronic electrical stimulation of the facial nerve causes signs of facial nucleus hyperactivity

The proximal segment of the facial nerve in rats was stimulated electrically daily for a duration of 2-10 min. After 4-8 weeks of such stimulation, 12 of 18 rats developed abnormal muscle responses that could be demonstrated by recording the electromyographic response from lower face muscles (the mentalis muscle) while the temporal branch of the facial nerve was being stimulated electrically. This abnormal electromyographic response consists of activity that appears in the latency range 6.5-15 ms. In addition, these chronically stimulated rats developed signs of facial synkinesis on the side that had been chronically stimulated. This could be demonstrated by recording electromyographic activity when the blink reflex was being elicited by electrical stimulation of the ophthalmic nerve. Rats in which electrodes had been implanted but which had not been stimulated did not develop any abnormal electromyographic activity. The abnormal electromyographic activity that could be recorded in rats that had been stimulated chronically could not be recorded 4-8 weeks after the stimulation had been terminated. We interpret these results to indicate that chronic electrical stimulation of the facial nerve can render the facial motonucleus hyperactive, and that the signs of this hyperactivity (abnormal muscle response and synkinesis) are similar to those typically seen in patients with hemifacial spasm. We thus presume that these results support the hypothesis that it is the irritation of the facial nerve from a compressing blood vessel that causes the facial nucleus to become hyperactive in patients with hemifacial spasm.     

Submandibular secretion of immunoglobulins IgA and IgG in peripheral paralysis of the facial nerve

INTRODUCTION: In all lesions of the facial nerve suprachoroidally localized, and due to disturbance of parasympathetic and sympathetic component, there comes to qualitative and quantitative disorders of the secretion of submandibular salivary gland. Glandular immunoglobulins IgA and IgG are the secretion of the specific plasma cells in the interstice of this gland. The mechanism of the secretion of immunoglobulins is not sufficiently clear, but it is certainly under the direct neurogenic control, since the disorders of the secretion emerge after the denervation of the submandibular salivary gland. The aim of the study was to prove the direct relation between the degree of submandibular immunoglobulin secretion IgA and IgG, and the degree of the lesion of the facial nerve U which is vitally important in the clinical estimation of the peripheral paralysis of this nerve. MATERIAL AND METHODS: In 35 patients with peripheral idiopathic facial nerve paralysis, the quantity of the secreted immunoglobulins IgA and IgG was examined by laser nephelometar BLN, Module 3. The quantity of the secreted immunoglobulins IgA and IgG (mg lit) in the saliva of the paralysed side was indirectly compared to the secreted immunoglobulins of the healthy, i.e. control side. The examination was performed three times: a) after the appearance of the disease, in the first 30 days; b) two to three months later; c) after six to twelve months. RESULTS: The quantity of the secreted immunoglobulins is significantly higher in the saliva samples taken from the paralysed side (9.50U204.77 mg lit), in comparison with the samples taken from the healthy side (9.50U70.36 mg lit). In the group of patients with favourable results and significantly higher secretion (p 0.01) normalization occurred in the final period of observation. In patients with unfavourable results the difference in secretion was continuously present (p 0.05) (table 1). DISCUSSION: In the lesions of the facial nerve suprachoroidally localized, there comes to disorder concerning the secretion of immunoglobulins IgA and IgG by submandibular salivary gland, which can be applied in the estimation of the degree of paralysis and the prognosis of the final result. CONCLUSION: The results of the research show that in the peripheral idiopathic facial nerve paralysis, there comes to increased secretion of immunoglobulins IgA and IgG in submandibular gland, at the paralysed side. In the patients who, during the paralysis, show quicker fall and normalization of the previously increased quantities of immunoglobulins, the recovery of the motor function of the facial nerve comes more successfully and more certainly. The degree of the secretion of immunoglobulins IgA and IgG can be used for the estimation of the severely of the pathological process in the suprachoroidal part of the nerve, and it can be used as a reliable parameter for the prognosis of the paralysis outcome.     

Rerouting of the intratemporal facial nerve: an analysis of the literature

Anterior rerouting of the intratemporal facial nerve in the infratemporal fossa approach is employed to access to the jugular bulb, hypotympanum, and lateral skull base, whereas posterior rerouting of the facial nerve, as employed in the transcochlear craniotomy, is most frequently used for surgery of the posterior fossa, cerebellopontine angle, prepontine region, and petrous apex. Facial nerve rerouting may lead to facial paresis or paralysis. This review of the literature is intended to define the physiologic "cost" of these procedures, so that the neurotologic surgeon can determine if the morbidity incurred in these techniques is worth the resultant exposure. Inconsistencies in reporting facial function places into question the validity of some of the cumulative data reported. Postoperatively, grades I-II facial nerve function was seen in 91% of patients undergoing short anterior rerouting, 74% of patients undergoing long anterior rerouting, and 26% of patients undergoing posterior complete rerouting. Although facial nerve rerouting allows unhindered exposure to previously inaccessible regions, it is achieved at the cost of facial nerve function. Facial nerve dysfunction increases with the length of facial nerve rerouted.     

Differential diagnosis in facial nerve palsy: a clinical review

BACKGROUND: The facial nerve possesses five functional components and manifests a complex course from its origin in the motor cortex to its peripheral distribution. Pathologies that impact the facial nerve in various locations along its route result in characteristic clinical manifestations that often involve other neurologic entities. CASE REPORTS: Case reports of three patients who manifested lesions of the facial nerve are presented. Each case represents a specific facial nerve pathology occurring within the supranuclear, nuclear, and infranuclear location. An anatomic, regional, and etiologic approach to the spectrum of facial nerve disorders is provided. Additionally, hyperkinetic facial disorders is discussed, and the management of facial nerve palsy is emphasized. CONCLUSION: The clinician must understand the fundamental anatomy and distribution of the facial nerve in order to localize lesions and institute the appropriate management. Abnormalities of lid position and insufficient corneal wetting are problematic. All efforts should be directed toward the maintenance of corneal integrity by appropriate wetting strategies.     

Intraoperative computer-assisted measurement of stimulation threshold of the common peroneal nerve in osteotomy of the head of the tibia

Using a computer-assisted threshold hunting paradigm the motoric threshold of the common peroneal nerve was monitored in 18 patients during a high tibial osteotomy (HTO). The exposed nerve (lateral approach) was stimulated proximal to the osteotomy area and the surface EMG of the M. tibialis anterior was used to guide a threshold hunting device. Motoric threshold as a sensitive indicator of nerve function was found to be almost unaffected by several surgical steps of HTO. Only forceful rotation of a subperiostal Hohmann device during high peroneal osteotomy evoked a slight threshold shift that was fully reversible with device repositioning. The tourniquet, however, affected the threshold significantly. In 10 of the 18 patients the nerve became completely inexcitable after an average time of 59 min. The inexcitability was reversible after opening of the tourniquet. On the other hand, the eight patients maintaining an excitability throughout the entire ischemic period had tourniquet times that did not exceed 60 min. There are several factors that may be responsible for the observed inexcitability after long ischemic periods and we conclude that tourniquet time minimization appears appropriate to avoid neurological deficits during a high tibial osteotomy.     

The use of the rat facial nerve model to assess the effect of differing nerve anastomotic agents on the facial nerve

There are relatively few papers which prove that one nerve anastomotic agent for the facial nerve is superior to any other. Previous experiments on the division and anastomosis of the facial nerve have failed to consider the indeterminate variables involved, i.e. operator variability, controls and the reaction of the materials on normal nerve tissue. In this experiment, a variety of anastomotic agents were tested to see if the anastomotic agents themselves affected the extra-temporal facial nerve function. The absorbable suture, non-absorbable suture, glue and tube wrap used had no effect on normal nerve tissue or on the anastomosis of the sectioned facial nerve of the rat compared with simple laying together of the divided ends of the divided nerve.     

Correlation of skin phototype with facial wrinkle formation

We previously described the augmentation of sensory nerve action potential amplitudes after near and remote isometric muscle contraction. In this study, we wished to determine if the sensory cortex was involved in this process. In this prospective, intrinsically controlled study, we studied threshold somatosensory evoked potentials in 12 normal subjects with stimulation of the median nerve at 5.1 Hz. The subjects were tested during the following conditions: baseline, 25%, and 75% maximum isometric abductor digiti minimi contraction for 4 min. Each of these conditions was recorded before, during, and 4 min and 8 min after contraction. Results showed that at 25% contraction, there was a significant temporal increase in N9 amplitude (2.1-2.6 microV; P = 0.05, analysis of variance, repeated measures) and a decrease in N20 amplitude with 75% contraction (1.9-1.6 microV; P = 0.03, analysis of variance, repeated measure). No significant changes were noted in the spinal cord or brainstem recordings. In conclusion, it appears that augmentation of the brachial plexus peripheral nervous system recording occurs concurrently with central inhibitory gating. The possibility of peripheral nervous system adaptability will be discussed.     

Botulinum toxin injection effective for post-peripheral facial nerve palsy synkinesis]

Facial synkinesis is an involuntary activation of muscles innervated by the zygomatic or mandibular branch of the facial nerve in conjunction with voluntary activation of the other branch. It appears frequently after recovery from peripheral facial nerve paralysis. We report 10 patients with facial synkinesis following Bell's palsy with a mean duration of synkinesis of 7 +/- 4 years before treatment with periorbital injections of Botulinum toxin type A. 9 had marked subjective and objective improvement starting a few days after injection and lasting 4-9 months. The results suggest a useful treatment option for post-Bell's palsy facial synkinesis with Botulinum toxin type A.     

Management and rehabilitation of the facial nerve in parotid surgery

The facial nerve is the single most important consideration in the surgical management of most parotid disorders. Its surgical anatomy should be well known by the head and neck surgeon. Very few conditions of the parotid gland necessitate the sacrifice of the facial nerve. When this decision is made, the benefits to be derived should be very thoughtfully measured against the tremendous cosmetic and functional sequelae that follow, and the patient should understand preoperatively to the fullest the magnitude of this decision and all its consequences. Most facial nerve deficits resulting from injury or sacrifice of the nerve can be and are best repaired by either direct anastomosis or autografting using a donor sensory nerve. Such restorations of the neuromuscular mechanism yield a physiologic result that is as close to the preinjury state as possible, and this is reflected in cosmetic and functional recoveries that are generally superior to any other of a variety of rehabilitative techniques. In all patients with a paralyzed face, extremely close attention must be given the involved eye to minimize the hazards of corneal injury.     

Trans-petrous surgery in acoustic neuroma. Value of preoperative audiovestibular and facial investigation in the risk evaluation of facial nerve function

Between 1987 and february 1994, 162 consecutive patients with acoustic neuroma were operated on by an otoneurosurgery team, using transpetrous approaches (89% translabyrinthine, 8% middle fossa and 3% retrosigmoid). The relationship between the clinical, audiometric and vestibulographic characteristics and the post-operative facial nerve function were evaluated. In acoustic neuromas with cerebello-pontine component inferior to 3 cm without central neurologic signs (ic: central controlateral auditory and/or ipsilateral vestibular pathway alteration), good post-operative facial nerve function was achieved in 80% of cases. In acoustic neuromas superior to 3 cm with alteration of the central vestibular and auditory pathways, a good result was obtained in only 30% of cases which correlated negatively with preoperative facial dysfunction. These results underline the value of preoperative facial and audiovestibular examinations in predicting the postoperative facial nerve function following surgery for acoustic neuroma.     

A quantitative study of nerve fibers in the human facial nerve

The facial and intermediate nerves were quantitatively evaluated in seven patients who died from systemic malignancies not involving the facial nerve. In addition, five of the specimens were also qualitatively evaluated by measuring the total and axon diameters of the facial and intermediate nerve fibers. In two cases the facial nerve fibers were counted at five different levels. The total number of myelinated nerve fibers in the facial nerve varied from 7500 to 9370. The total number of myelinated nerve fibers in the intermediate nerve varied between 3120 and 5360. The peak diameter of the facial nerve axon was between 4 and 6 microns, and was between 2 and 3 microns in the intermediate nerve. When comparing nerve segments at different anatomical levels, the largest amount of nerve fibers was found at the level of the middle mastoid portion. However, this number did not reach the amount of nerve fibers counted in the internal acoustic meatus.