Intraoperative facial nerve monitoring.

Facial nerve monitoring is one of the most exciting innovations in otologic surgery in the past decade. Intraoperative monitoring has been shown to reduce the probability of iatrogenic injury to the facial nerve during surgery. It saves surgical time and reduces the anxiety level of both patients and surgeons. There are several reasons to use facial nerve monitoring: The surgeon nerve knows when it will be needed in a particular case, the operating room personnel become familiar with the equipment, and the surgeon learns how to interpret the sounds produced by the monitor and how to correlate them with surgical manipulations around the facial nerve. Facial nerve monitoring has added another dimension of safety to otologic and neurotologic surgery and has reduced the incidence of facial weakness or paralysis in the authors' surgical practice.     

Cost-effectiveness of intraoperative facial nerve monitoring in middle ear or mastoid surgery

OBJECTIVES: Despite the utility of intraoperative facial nerve monitoring in reducing the risk of iatrogenic facial nerve injury during neurotologic surgery, its routine use during primary or revision surgery remains controversial. One of the major barriers to its acceptance is cost. This study evaluates the cost-effectiveness of intraoperative facial nerve monitoring during middle ear or mastoid surgery. RESEARCH DESIGN/METHODS: A simple decision analytic cost-effectiveness model and a societal approach were used to evaluate three cohorts of individuals who received (1) intraoperative facial nerve monitoring for both primary and revision middle ear or mastoid surgeries, or (2) facial nerve monitoring for revision surgeries only, or (3) no monitoring for any middle ear or mastoid surgeries. RESULTS: Our results strongly favored the use of intraoperative facial nerve monitoring in all patients undergoing middle ear or mastoid surgery, adding about $222.73 to $528.00 US dollars to the total cost. The strategy to monitor primary and revision surgeries had the greatest effectiveness and lowest cost, with an average quality-adjusted life-year (QALY) of 45.68 at an average cost of $238 US dollars. Facial nerve monitoring in revision patients only had similar QALYs (45.67) and higher costs ($292.1). Finally, the strategy not to monitor had the lowest QALY (45.65) and highest cost ($449.8). The analysis was robust across a wide range of changes in both costs and probabilities. CONCLUSIONS: Facial nerve monitoring is cost-effective, and its routine use should be adopted to reduce the risk of iatrogenic facial nerve injury during otologic surgery.     

Iatrogenic facial nerve injury during otologic surgery

Perhaps the most devastating complication in otologic surgery is that of inadvertent injury to the facial nerve. A review of 22 patients who had sustained an iatrogenic facial nerve injury was conducted. Although the most common procedure being performed during the injury was mastoidectomy (55%), a surprising number of patients had injury during tympanoplasty (14%) or during removal of exostoses (14%). The most common area of injury to the facial nerve in this series was in the tympanic segment. In 79% of the patients, the facial nerve injury was not detected at the time of surgery. All patients underwent surgical exploration of the facial nerve. Otologic surgeons are cautioned to be familiar with the normal course of the facial nerve and to be aware of the potential for facial nerve injury when performing transcanal surgery.     

Routine identification of the facial nerve using electrical stimulation during otological and neurotological surgery

We routinely identify the facial nerve to avoid facial nerve injury during most otologic surgery. Since 1985, we have used a facial nerve stimulator/monitor as an added safety feature in 383 consecutive otologic and neurotologic cases. In our last 30 middle-ear, 8 retrolabyrinthine vestibular neurectomy, and 14 acoustic neuroma cases we used the monopolar stimulator probe-tip to determine threshold currents needed to produce facial twitch. Stimulation thresholds varied according to the amount of soft tissue or bone overlying the facial nerve. The stimulator was useful for predicting dehiscences in the bony facial canal during middle-ear and mastoid surgery. The exposed facial nerve usually stimulated at a level less than 0.1 mA (mean 0.05 mA), and the horizontal facial nerve covered by bone stimulated at 0.25 mA or greater (mean 0.6 mA). The stimulator was also used to predict the amount of bone overlying the vertical facial nerve at the annulus. An approximate relationship of 1.0 mA of threshold current to 1.0 mm of bony covering was found. After acoustic neuroma surgery, the stimulation threshold of the facial nerve at the brain stem helped predict postoperative facial function. Cases with current thresholds of 0.3 mA or less resulted in normal facial function. During ear surgery, routine identification of the facial nerve with the aid of a facial nerve stimulator will help avoid facial nerve injury.     

Intraoperative facial nerve monitoring: a comparison between electromyography and mechanical-pressure monitoring techniques

OBJECTIVES: To examine the hypothesis that for intraoperative facial nerve monitoring, an EMG monitor is more sensitive than a mechanical-pressure monitor. To compare the threshold sensitivity of the two facial nerve monitoring methods-mechanical-pressure versus EMG--by using them simultaneously during surgery. To assess and compare their true- and false-positive responses in otologic and neurotologic procedures. SETTING: A tertiary referral private otology/neurotology practice. STUDY DESIGN: Prospective case-controlled study. PATIENTS AND METHODS: The facial nerve of 46 consecutive patients undergoing various otologic and neurotologic procedures was stimulated intraoperatively using a pulsed constant-current. Facial responses were monitored using the Silverstein WR-S8 Monitor/Stimulator and the Brackmann EMG System simultaneously. The threshold (i.e., minimal) current level required to elicit a response from each monitor was recorded. Monitor responses to facial nerve manipulation (including false-positive responses) were assessed by continuous recording of all responses, using the Wiegand Monitoring System, and noting the causative event for each response. RESULTS: The EMG monitor responded to lower current threshold (p < 0.001) in every surgical procedure and for every nerve segment studied. However, the average threshold difference was <0.05 mAmps and in clinical practice, when using above threshold stimulation, becomes negligible. In posterior fossa surgery, the EMG monitor showed higher sensitivity by responding earlier to various manipulations of the bare facial nerve. The EMG had more false-positive responses than the mechanical-pressure monitor. CONCLUSIONS: In otologic surgery, if monitoring is required, the mechanical-pressure monitor is used. In neurotologic surgery, both monitors are used simultaneously.     

Intraoperative neurophysiologic monitoring: indications and techniques for common procedures in otolaryngology-head and neck surgery

Intraoperative cranial nerve monitoring can be an effective adjunct in otolaryngology-head and neck surgery. Monitoring is not considered standard of care, despite indications of cost effectiveness and improved functional outcomes. Lessons learned performing facial nerve monitoring are applicable to upper and lower cranial motor nerves. Auditory nerve monitoring can be modified accord-ing to need for selected otologic and neurotologic surgery. Process standardization and effective communication can lead to improved patient outcomes.     

Use of laser, otoendoscopy and facial nerve monitoring in otological surgery: United Kingdom survey

Newer surgical tools, which have been widely accepted as important adjuncts in otological surgery, include the laser, otoendoscopy and facial nerve monitoring. A confidential postal questionnaire survey was carried out to evaluate the usage of these newer techniques among the Consultant members of the British Association of Otorhinolaryngology-Head and Neck Surgery. Our study revealed that the usage of otoendoscopy, laser and/or facial nerve monitoring is not as widespread as might be thought among otological surgeons in the United Kingdom.     

Minimally invasive, image-guided, facial-recess approach to the middle ear: demonstration of the concept of percutaneous cochlear access in vitro.

HYPOTHESIS: Image-guided surgery will permit accurate access to the middle ear via the facial recess using a single drill hole from the lateral aspect of the mastoid cortex. BACKGROUND: The widespread use of image-guided methods in otologic surgery has been limited by the need for a system that achieves the necessary level of accuracy with an easy-to-use, noninvasive fiducial marker system. We have developed and recently reported such a system (accuracy within the temporal bone = 0.76 +/- 0.23 mm; n = 234 measurements). With this system, image-guided otologic surgery is feasible. METHODS: Skulls (n = 2) were fitted with a dental bite-block affixed fiducial frame and scanned by computed tomography using standard temporal-bone algorithms. The frame was removed and replaced with an infrared emitter used to track the skull during dissection. Tracking was accomplished using an infrared tracker and commercially available software. Using this system in conjunction with a tracked otologic drill, the middle ear was approached via the facial recess using a single drill hole from the lateral aspect of the mastoid cortex. The path of the drill was verified by subsequently performing a traditional temporal bone dissection, preserving the tunnel of bone through which the drill pass had been made. RESULTS: An accurate approach to the middle ear via the facial recess was achieved without violating the canal of the facial nerve, the horizontal semicircular canal, or the external auditory canal. CONCLUSIONS: Image-guided otologic surgery provides access to the cochlea via the facial recess in a minimally invasive, percutaneous fashion. While the present study was confined to in vitro demonstration, these exciting results warrant in vivo testing, which may lead to clinically applicable access.     

Delayed facial nerve palsy after otologic surgery

Delayed facial nerve palsy (DFP) is rarely experienced after otologic surgeries that do not directly touch the facial nerves, such as tympano-mastoidectomy, cochlear implants, and stapes surgery, and is troublesome to both surgeons and patients if it happens. Here, we report 7 cases of DFP, including one case that developed DFP after endolymphatic sac surgery. The ratios of occurrence were as follows: 0.7% (2/305) for tympano-mastoidectomy, 0.8% (3/354) for cochlear implant, 0.4% (1/260) for stapes surgery and 1.0% (1/98) for endolymphatic sac surgery. All otologic surgeries, except for endolymphatic sac surgery, exposed the chorda tympani, and all surgeries, except for stapes surgery, underwent drilling for a mastoidectomy. Furthermore, DFP was always observed ipsilaterally to the operated ear after otologic surgeries and was never seen after benign parotid tumor surgery or total laryngectomy. Therefore, there may be a strong relationship between DFP and the procedures, used during otologic surgeries.     

Neurophysiologic intraoperative monitoring: II. Facial nerve function

Intraoperative facial nerve monitoring provides a potentially useful adjunct to recent surgical advances in neurotology and neurosurgery. These measures further aid the surgeon in preserving facial nerve function by enhancing visual identification with electrical monitoring of mechanically evoked facial muscle activation. Facial nerve monitoring in neurotologic surgery may achieve the following goals: (1) early recognition of surgical trauma to the facial nerve, with immediate feedback made available to the surgeon through monitoring of mechanical activation; (2) assistance in distinguishing the facial nerve from regional cranial nerves and from adjacent soft tissue and tumor with selective electrical stimulation; (3) facilitation of tumor excision by electrical mapping of portions of tumor that are remote from the facial nerve; (4) confirmation of nerve stimulability at the completion of surgery; and (5) identification of the site and degree of neural dysfunction in patients undergoing nerve exploration for suspected facial nerve neoplasm or undergoing decompression in acute facial palsy. This paper provides an overview of intraoperative facial nerve monitoring principles and methodology and reports a recent clinical investigation that demonstrates the utility of facial nerve monitoring in translabyrinthine acoustic neuroma surgery.     

Use of a novel ultrasonic surgical system for decompression of the facial nerve

OBJECTIVE: The middle cranial fossa approach has been used to explore and decompress the facial nerve in patients with Bell's palsy and facial nerve tumors. Unfortunately, this approach is technically challenging and has a significant risk of injury to the facial nerve and to the cochleovestibular organs. One way to minimize the risk may be with the use of the Sonopet Omni ultrasonic aspirator (Synergetics Inc., St Charles, MO) instead of an otologic drill. METHODS: In this prospective study using cadaveric temporal bones, a total of 17 temporal bone specimens were used. Seven cadaveric temporal bones were used (4-left, 3-right) for the initial feasibility study. At a second session, an additional 10 temporal bones (5-left, 5-right) underwent decompression of the facial nerve from the fundus of the internal auditory canal (IAC) to the geniculate ganglion (ie, labyrinthine segment). The average time to decompress the labyrinthine segment was measured. The temporal bones were then examined for evidence of any injury. RESULTS: None of the 17 temporal bones showed any sign of injury to the superior semicircular canal or the cochlea. However, one specimen did have penetration of the IAC dura; another specimen did have penetration of the epineurium of the facial nerve. However, in neither case was there any evidence of injury to the facial nerve itself. At the first session, the average time for decompression of the labyrinthine segment was 10 minutes and 12 seconds. At the second session, the average time for decompression was 5 minutes and 0 seconds. CONCLUSION: The ultrasonic surgical system may be used as an alternative to the surgical drill for decompression of the facial nerve. Although a learning curve does exist, as with any new surgical tool or device, our results indicate that the device can be used safely and in a reasonable amount of time. However, before proceeding with intraoperative use of this device for otologic and neurotologic procedures, familiarization is first recommended on cadaveric temporal bone specimens.     

Delayed facial nerve paresis after using the KTP laser in the treatment of cholesteatoma despite inter-operative facial nerve monitoring

To describe an unforeseen complication that occurred in three patients following the use of the KTP laser. We present a case series including three consecutive patients (two boys and one girl, mean age 11.7 years) who underwent tympanomastoidectomy using a KTP laser and standard intra-operative facial nerve monitoring, and in whom a post-operative facial nerve injury was identified. Intra-operatively, the facial nerve was not encountered or exposed, and the KTP laser was not used directly on the nerve. The facial nerve monitor did not alarm. The three patients began experiencing a paresis from POD #7-9, with House-Brackmann facial nerve score of II-III at maximum severity. This resolved fully between 4 and 7 weeks after the onset of the paralysis. The KTP laser during cholesteatoma surgery has been shown to decrease residual disease but may however also cause a temporary, delayed, mild facial nerve paresis. We discuss the mechanisms for injury and the role of intra-operative facial nerve monitoring in the context of this uncommon and unforeseen complication.     

Delayed facial nerve palsy after endolymphatic sac surgery

Data on delayed facial nerve palsy (DFNP) following endolymphatic sac enhancement surgery are limited. We conducted a retrospective chart review to determine the incidence, possible predisposing factors, treatment, and prognosis of DFNP in such cases. We reviewed the records of 779 patients who had undergone endolymphatic sac surgery for intractable Ménière disease from January 1997 through December 2007 at a tertiary care otologic referral center. We found 5 cases (0.64%) of postoperative DFNP. The length of time between surgery and the onset of DFNP ranged from 7 to 20 days (mean: 11). Paralysis was incomplete in all 5 patients. Four of these patients had an abnormal mastoid bone anatomy, as the sigmoid sinus was either anteriorly or anteromedially displaced. The 5 patients had been treated with a steroid, either with or without an antiviral, and all 5 experienced a complete recovery of facial nerve function within 8 weeks of the onset of their paralysis. It is difficult to delineate the exact etiology of DFNP following endolymphatic sac surgery, but we speculate that factors such as physical injury to the nerve and/or a viral reactivation might have played a role. Also, the unusual mastoid bone anatomy seen in 4 of these patients might have been responsible, as well.     

Use of dilute epinephrine as an aid in facial nerve monitoring.

Facial nerve monitoring during otologic and neurotologic procedures has been previously described, and its use is becoming routine. Although these procedures are done under general anesthesia, lidocaine is often used as a vehicle for epinephrine to aid hemostasis during the procedure. The routine use of lidocaine in these preparations presents the theoretical and sometimes real problem of anesthetizing the facial nerve at the start of the procedure, thereby invalidating subsequent attempts at monitoring and stimulation. We present the data from our experience with 74 patients using an epinephrine solution 1:100,000 for infiltration without any local anesthetic. We have found this procedure to be effective in maintaining hemostasis, quite safe and well tolerated, and without adverse effects on the desired monitoring of the facial nerve.     

Iatrogenic facial nerve exposure in cochlear implant surgery: incidence and clinical significance in the absence of intra-operative nerve monitoring

Objectives: Iatrogenic facial nerve injury is one of the most feared complications of cochlear implantation. Intraoperative facial nerve monitoring is used as an adjunctive modality in a variety of neurotologic surgeries including cochlear implantation. With the lack of nerve monitoring, there is a theoretically higher risk of iatrogenic fallopian canal dehiscence with facial nerve exposure, particularly the mastoid portion, during cochlear implant surgery. The purpose of this study is to determine the incidence of iatrogenic exposure of the facial nerve and its relation to the incidence of post-operative facial paralysis in the absence of facial nerve monitoring.

Methods: This was a retrospective study. Medical charts of 307 patients who underwent cochlear implantation without facial nerve monitoring, from 2012 to 2017 were reviewed to identify cases with a reported iatrogenic defect over the mastoid facial nerve. The incidence of post-operative facial palsy was determined and compared to the incidence with the use of intra-operative monitoring which has been reported in the literature.

Results: The incidence of iatrogenic dehiscence with facial nerve exposure was 46.58%. However, the incidence of post-operative facial palsy was only 2.1% which decreased to 0.72% in cases without injury of the facial neural sheath. This was not significantly different from the 0.73% rate reported in the literature with the use of intra-operative facial monitoring (P?=?0.99).

Conclusion: The incidence of iatrogenic facial nerve exposure during cochlear implantation may be relatively high. However, no additional risk of post-operative facial nerve paralysis was found, provided that the integrity of the neural sheath was preserved, even with the lack of intra-operative monitoring.     

Facial nerve monitoring in middle ear and mastoid surgery

HYPOTHESIS: Intraoperative electromyographic facial nerve monitoring, long accepted as the standard of care in surgery for acoustic neuroma and other cerebellopontine angle tumors, may be of aid in middle ear and mastoid surgery. STUDY DESIGN: Retrospective series of 262 cases of middle ear/mastoid surgery in which monitoring was performed by a neurophysiologist. METHODS: Neurophysiological monitoring events were classified as mechanical or electrical. The voltages producing facial nerve stimulation were compiled and compared with observed facial nerve dehiscence. RESULTS: The most common use of monitoring was localization of the facial nerve by electrical stimulation (60%) or identification of mechanically evoked activity (39%). In 57 cases (36%), the first electrical stimulation event evoked a facial nerve response at less than 1 V threshold, indicating little or no bony covering. The minimum stimulation threshold throughout each of these cases was less than 1 V in 88 of the 159 cases (55%) in which stimulation was attempted. In contrast, the facial nerve was visibly dehiscent in only 35 cases (13%). Neurophysiological monitoring confirmed aberrant facial nerve course through the temporal bone in four cases resulting in cancellation of surgical treatment in two cases. Postoperative facial nerve function was preserved in all cases when present preoperatively. CONCLUSIONS: An electrical stimulation threshold of less than 1 V is a more useful criterion of dehiscence than observation under the operating microscope. The absence of monitoring events allows safe dissection. Monitoring can help locate the facial nerve, guide the dissection and drilling, and confirm its integrity, thereby allowing more definitive surgical treatment while preserving neural function.