Monitoring Of Facial Function Research Articles

Introduction: Cranial nerve surgery

In this issue of Neurosurgical Focus, we have compiled a group of interesting papers related to anatomy, physiology, pathology, and surgery of the cranial nerves. We were very pleased to receive many more submissions of excellent papers on this topic from which we had the difficult task of having to select, because of limitations in space, only 8 papers. Rodgers and colleagues give an excellent review of the syndrome of short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing. In the authors’ case, the syndrome was caused by an epidermoid tumor of the cerebellopontine angle that was clearly compressing the trigeminal nerve. We found this case report interesting because the etiology of this syndrome has not been clear, and this paper suggests that compression of the trigeminal nerve may be one of the causes. We thought that the excellent review of this topic the authors provide to us is important because neurosurgeons are so frequently called upon to treat trigeminal neuralgia, and we must be able to differentiate that condition from this interesting syndrome. Ross and colleagues report on 4 patients with rare facial nerve tumors and use the opportunity to present us with a nice review of the literature on the clinical syndrome, imaging characteristics, and surgical treatment of these tumors. Wang and colleagues from the University of Pittsburgh review their extensive experience with microvascular decompression for hemifacial spasm and conclude that botulinum toxin injections, which many of these patients underwent for treatment of their spasms before microvascular decompression, had no impact on the results of this operation. This finding is important because nowadays most patients have already had this type of palliative treatment before undergoing microvascular decompression. The second paper by this group of authors (Thirumala et al.) is a careful study of neurophysiological monitoring during microvascular decompression for hemifacial spasm; essentially, the authors conclude that changes in interpeak latency of brainstem auditory evoked potentials during surgery do not increase the odds of postoperative hearing loss and should not be used as an “alarm criteria” during microvascular decompression. Kshettry and colleagues present a nice historical review of the early studies of the anatomy of the petroclival region and the contributions of Primo Dorello, an Italian anatomist, after whom the Dorello canal is named. Interestingly, it turns out that the canal now widely known by Dorello’s name had been previously described 50 years earlier by W. Gruber. This paper also contains a nice review of anatomical studies of this region followed by a brief review of clinical implications. Schmidt et al. present a case of a malignant peripheral nerve sheath tumor of the trigeminal nerve, which they used as an opportunity to review the literature and summarize very nicely a total of 36 cases of malignant peripheral nerve sheath tumors of the trigeminal nerve. As expected, these tumors usually present with altered facial sensation and/or facial pain, and it appears that aggressive resection followed by radiation therapy offers the best chance for survival. Sarnthein and colleagues present another interesting paper concerning neurophysiological monitoring of facial nerve function during skull base surgery. In this careful study, the authors find that an intraoperative increase in the threshold for transcranial stimulation necessary to elicit a facial nerve motor evoked response is very specifically correlated with postoperative facial nerve dysfunction, and they suggest that such monitoring should be used in these operations in addition to the widely used direct electrical stimulation of the facial nerve. This issue also contains a very nice review of the neurosurgical options for management of glossopharyngeal neuralgia by Rey-Dios and Cohen-Gadol. The authors conclude that microvascular decompression is an excellent option but that when a convincing neurovascular conflict is not found, section of the glossopharyngeal nerve and the upper rootlets of the vagus nerve is a satisfactory alternative. (http://thejns.org/doi/abs/10.3171/2013.1.FOCUS1322)

How Many Electromyography Channels Do We Need for Facial Nerve Monitoring?

Continuous electromyography (EMG) monitoring is a standard method for intraoperative monitoring of facial nerve function. Typically, only two or three bipolar channels are recorded from needle electrodes to detect pathologic activity, which may provide an incomplete sample. Therefore, we evaluated the influence of channel number on monitoring quality. The EMG data of 30 patients undergoing surgery for vestibular schwannoma were recorded using 9 bipolar channels from subdermal needle electrodes located in the orbicular oculi, oris, and nasal muscle. Pathologic A-train activity was evaluated in regard to correlation to postoperative nerve function. Channel combinations with different channel numbers were compared. A-train quantity showed high correlations to postoperative nerve function: Spearman rank correlation of 0.58 for 2, 0.61 for 3 channels. It increased further with every additional channel to 0.69 for all 9 channels (48% of variance accounted for). Single channels with more than one-third of total A-train activity ("hot spots") were observed in 17 patients, which did not show consistent spatial patterns and could only be completely detected with a high number of channels. Few channels as used in conventional monitoring setups yield acceptable results. However, correlation between train time and postoperative functional results improves with every additional EMG channel.

The value of microsurgery for acoustic neuromas

Objective To evaluate the value of microsurgery for acoustic neuromas. Methods The author performed a retrospective study of 63 consecutive patients after vestibular schwannomas (VSs) microsurgery with the retrosigoid approaches. The tumor was debulked firstly and dissected from surrounding neural and vascular structures by gripping the tumor capsule, and then drilled of the IAC. Intraoperative electrophysiological monitoring of facial nerve function during operation.Results Total tumor resection was achieved in 52 cases, subtotal resection was achieved in 11 cases. The anatomic preservation of facial nerve was achieved in 58 cases, the acoustic nerve was preserved anatomically in 29 cases. Fifty-eight cases received a follow-up, the mean follow-up time was 7.2 years. Two recurrent patients were found and there were no operative deaths. A long term facial nerve status:twenty-three cases were in grade Ⅰ, twenty-nine cases in grade Ⅱ ,five cases in grade Ⅲ , one cases in grade Ⅳ. Hearing level had an improvement in 9 cases and remained unchanged in 8 cases. Conclusion Microsurgery treatment is the main choice of the treatment of VSs, could achieve better result in control of tumor and facial and acoustic nerve function restoration. Key words: Acoustic neuroma; Acoustic nerve; Facial nerve ; Microsurgery

Does Electrode Placement Influence Quality of Intraoperative Monitoring in Vestibular Schwannoma Surgery?

Continuous recording of electromyographic signals (EMG) is a standard method for intraoperative monitoring of facial nerve function in cerebello-pontine angle surgery. Subcutaneous needle electrodes in the facial muscles are used in different setups. The goal of this study was to compare two commonly used electrode setups concering sensitivity for pathological EMG activity. A group of 10 patients undergoing vestibular schwannoma surgery were examined. Continuous EMG from facial muscles was recorded using needle electrodes in setups according to Kartush or Møller, with narrow or wide interelectrode distances, respectively. Quantity of pathological A-train activity and signal-to-noise ratios were compared between setups. A-train activity was seen in all patients. On average, 37% of A-train activity was seen in the Kartush setup alone, 4% in Møller setups alone and 59% in both setups synchronously (p<0.05; ratio of median train time--Kartush:Møller 3:2). The wide interelectrode distance of the Møller setup was found to be significantly more susceptible to artefacts, especially to low frequency and power line noise. Artefacts were the main reason for the Møller setup to fail detecting A-train activity. For continuous intraoperative monitoring of facial nerve function, narrow interelectrode distance should be used.

Intraoperative Monitoring of Motor Evoked Potential for the Facial Nerve Using a Cranial Peg-Screw Electrode and a “Threshold-level” Stimulation Method

Transcranial motor evoked potential (MEP) for the facial nerve (facial MEP) has been recognized as a good method for quantitative monitoring of facial nerve function in skull base surgery. To improve the feasibility and safety of facial MEP monitoring, a peg-screw electrode and a "threshold-level" method were investigated. From 2007 to 2009, intraoperative facial MEP monitoring with the peg-screw electrode and threshold-level method was successfully achieved in 26 of 29 patients who underwent surgery for the posterior fossa extra-axial tumor. The relationship between the change in the facial MEP threshold level and the postoperative function of the facial nerve was analyzed in 23 patients who had no facial palsy preoperatively. There were no complications associated with facial MEP monitoring. Nine patients who had stable facial MEP threshold had no facial palsy. Fourteen patients who had worsened but measurable facial MEP threshold had mild palsy at discharge. Two of three patients who had severely worsened and unmeasurable facial MEP threshold had severe facial palsy. The change in the facial MEP was well correlated with the postoperative facial function. The peg-screw electrode and threshold-level method are good options for facial MEP monitoring.

Diagnosis and therapy of vestibular schwannoma

MRI studies are of paramount importance for diagnosis and follow-up measurements during conservative and postinterventional management of vestibular schwannomas (VS). MRI findings that convey important information for hearing-preservation VS surgery are: length of tumor–cochlear nerve contact, involvement of the internal auditory canal, incomplete filling of internal auditory canal, tumor size less than 15 mm and the intralabyrinthine signal intensity on 3DFT-CISS gradient-echo images. Functional neuro-otologic studies of facial nerve function, hearing and vestibular/balance function provide a valuable means of assessment of the actual impairment of the functional status of the VS patient. Intraoperative monitoring of facial nerve function and hearing has been refined, resulting in improved final postoperative facial nerve and hearing outcomes in VS patients treated with microsurgery. Long-term results reported by teams practicing stereotactic radiosurgery or fractionated stereotactic radiotherapy have been very encouraging. On the other hand, conservative management appears to be a viable option for a select group of VS patients. The refinement of surgical technique has rendered surgery safer and less invasive, resulting in better functional outcomes. Steroid use is currently used postinterventionally to improve final hearing outcome, although with questionable effectiveness. Physical rehabilitation programs are applied to accelerate vestibular functional recovery postoperatively and there is weak evidence that early physical rehabilitation may improve the final facial nerve outcome. Quality-of-life measures have emerged as important determinants of final therapeutic decision-making. More studies with high levels of evidence are needed to support clinical decisions.

Train time as a quantitative electromyographic parameter for facial nerve function in patients undergoing surgery for vestibular schwannoma

The authors describe a quantitative electromyographic (EMG) parameter for intraoperative monitoring of facial nerve function during vestibular schwannoma removal. This parameter is based on the automated detection of A trains, an EMG pattern that is known to be associated with postoperative facial nerve paresis. For this study, 40 patients were examined. During the entire operative procedure, free-running EMG signals were recorded in muscles targeted by the facial nerve. A software program specifically designed for this purpose was used to analyze these continuous recordings offline. By automatically adding up time intervals during which A trains occurred, a quantitative parameter was calculated, which was named "train time." A strong correlation between the length of train time (measured in seconds) and deterioration of postoperative facial nerve function was demonstrated. Certain consecutive safety thresholds at 0.5 and 10 seconds were defined. Their transgression reliably indicated postoperative facial nerve paresis. At less than a 10-second train time, discrete worsening, and at more than 10 seconds, profound deterioration of facial nerve function can be anticipated. Train time as a quantitative parameter was shown to be a reliable indicator of facial nerve paresis after surgery for vestibular schwannoma.

Influence of electrode setup on detection of pathological EMG activity during intraoperative continuous monitoring of facial nerve function

Influence of electrode setup on detection of pathological EMG activity during intraoperative continuous monitoring of facial nerve function

Influence of electrode setup on detection of pathological EMG activity during intraoperative continuous monitoring of facial nerve function

Influence of electrode setup on detection of pathological EMG activity during intraoperative continuous monitoring of facial nerve function

Delayed facial palsy after resection of vestibular schwannoma

In this study the authors investigate delayed facial palsy (DFP), which is an underreported phenomenon after surgery for vestibular schwannoma (VS). The authors identified 15 (4.8%) patients from a consecutive series of 314 who underwent surgery for VS between 1988 and 2000, and in whom DFP developed. Delayed facial palsy was defined as a deterioration of facial nerve function from House-Brackmann Grades 1 or 2 more than 3 days postoperatively. All patients underwent intraoperative neurophysiological monitoring of facial nerve function. The average latency of DFP was 10.9 days (range 4-30 days). In six patients (40%) minor deterioration (< or = two House-Brackmann grades) had occurred at a mean of 10.2 days postsurgery, whereas in nine patients (60%) moderate deterioration (> or = three House-Brackmann grades) had occurred at a mean of 11.8 days postoperatively. Five (33%) of 15 patients recovered to Grade 1 of 2 function within 6 weeks of DFP onset. Of the 15 patients with DFP, 14 had completed 1 year of follow up at the time of this study. Twelve (80%) of these 15 patients recovered to Grade 1 or 2 function within 3 months, and 13 (93%) of 14 patients recovered within 1 year. In all cases, stimulation of the seventh cranial nerve on completion of tumor resection revealed the nerve to be intact, both anatomically and functionally, to proximal and distal stimulation at 0.1 mA. A smaller tumor diameter correlated with greater recovery of facial nerve function. There was no correlation between the latency or severity of or recovery from DFP, and the patient's age or sex, the surgical approach, frequency of neurotonic seventh nerve discharges, anatomical relationship of the facial nerve to the tumor, patient's history of tobacco use, or cardiovascular disease. It appears that DFP is an uncommon consequence of surgery for VS. Although excellent recovery of facial nerve function to its original postoperative status nearly always occurs after DFP, the magnitude and time course of the disorder were not predictors for subsequent recovery of facial nerve function.

Poster 65 Monitoring of Facial Nerve Function Through Pulsed Magnetic, Transcranial Stimulation

Poster 65 Monitoring of Facial Nerve Function Through Pulsed Magnetic, Transcranial Stimulation

Intraoperative Electrophysiological Monitoring of the Facial Nerve in the Presence of Damage to the Pre-Parotid Segment

Abstract A method is described for obtaining intraoperative monitoring of facial nerve function in patients who have previously lost facial nerve function distal to the pes anserinus or who have absent function because of trauma to the facial nerve in the pre-parotid segment during operative exposure.

Intraoperative monitoring of facial nerve function in cerebellopontine angle surgery

Facial nerve paralysis associated with cerebellopontine angle surgery has been reported to range up to 26% in a recent series. Various methods of intraoperatively monitoring the facial nerve have been developed to reduce the incidence of facial paralysis. We report our experience with an intraoperative monitoring technique using intramuscular EMG electrodes to detect subclinical electrical responses that were amplified and made audible to the operating surgeon after gating stimulus artifacts. A 3.6% incidence of facial paralysis in 111 consecutive cases with this intraoperative monitoring method compared with 14.5% in 207 previously unmonitored cases indicates significant reduction of this complication in cerebellopontine angle surgery (p less than 0.001). Along with this reduction in facial paralysis, an increase in the percentage of partial facial paresis was observed in the monitored group (p less than 0.05). The percentage of those with intact facial function was similar in the monitored (82.0%) and unmonitored groups (78.3%).

Adaptor for Continuous Stimulation (SACS) with the WR‐S8 Monitor‐Stimulator

An adaptor for continuous stimulation of the facial nerve (SACS) to be used with the WR-S8 Monitor/Stimulator during otologic surgery has been developed. This device allows the surgeon to use the electrified air drill and microsurgical instruments instead of a probe-tip during dissection. The SACS saves surgical time, is easy and convenient to use, and is safe. Routine monitoring of facial nerve function using SACS has helped prevent iatrogenic facial nerve injuries and has improved our ability to save the facial nerve during otologic and neurotologic surgery.

Neurography for intraoperative monitoring of facial nerve function

Neurography for intraoperative monitoring of facial nerve function

Orthodromic (Intra/Extracranial) Neurography to Monitor Facial Nerve Function Intraoperatively

This report introduces the technique of orthodromic neurography for monitoring of facial nerve function during operation in the cerebellopontine angle. By stimulation of the intracisternal segment of the facial nerve, a compound nerve action potential with amplitudes of 15 to 480 microV can be recorded extracranially from the nerve near the stylomastoid foramen after 0.95 to 2.27 ms. Usually there is no need for signal averaging, and the method is independent of the effect of muscle relaxants. With the use of the same electrophysiological equipment as for evoked potential neuromonitoring, immediate and repeated localization of the facial nerve and its discrimination from the trigeminal and the lower cranial nerves during nerve preparation within the tumor capsule is possible.