Correlation between Electrophysiological Change and Facial Function in Parotid Surgery Patients

This observational study investigated intraoperative electrophysiological changes and their correlation with postoperative facial expressions in parotidectomy patients with visual confirmation of facial nerve (FN) continuity. Maximal electromyography(EMG) amplitudes of the facial muscles corresponding to temporal, zygomatic, buccal and mandibular branches were compared before/after FN dissection, and facial function at four facial regions were evaluated before/after parotidectomy in 112 patients. Comparisons of 448 pairs of EMG signals revealed at least one signal decrease after FN dissection in 75 (67%) patients. Regional facial weakness was only found in 13 of 16 signals with >50% amplitude decreases. All facial dysfunctions completely recovered within 6 months. EMG amplitude decreases often occur after FN dissection. An amplitude decrease >50% in an FN branch is associated with a high incidence of dysfunction in the corresponding facial region. This study tries to establish a standard facial nerve monitoring (FNM) procedure and a proper facial function grading system for parotid surgery that will be useful for the future study of FNM in parotid surgery.

1578 Advances in Facial Nerve Monitoring Parameters During Vestibular Schwannoma Surgery

Aim To evaluate the effectiveness of multi-channel electromyographic monitoring of the facial nerve in improving the detection of mechanically elicited EMG activity and providing new predictive criteria for post-operative facial nerve function. Method The Study was conducted on 20 patients undergoing vestibular schwannoma resection in a tertiary referral cerntre. All patients were subjected to facial nerve monitoring during the surgery by a 5-channel setup monitoring the frontalis, O.oculi, nasalis, O.oris, and mentalis muscle. Mechanically elicited EMG activities of the monitored facial muscles were recorded for analysis. After tumour removal, the facial nerve was stimulated proximal to the tumour site using two different types of probes: Prass and flush-tip. Post-operative facial nerve function was assessed using House-Brackmann scale immediately post-operatively and after six months and correlated to the study tested parameters. Results The use of 5-channel montage led to significantly higher sensitivity in detecting mechanically elicited EMG activity than would have been possible with the ordinary 2-channel one. Mentalis muscle showed significantly higher number and amplitude of spontaneous EMG activities than other facial muscles. Positive correlation was found between the proximal threshold and the post-operative facial nerve outcome. The Prass stimulator showed significantly lower threshold than the ball-tip probe. Conclusions The use of multi-channel facial nerve monitoring allowed earlier and more efficient monitoring of the facial nerve. The use of the Prass stimulator is more accurate and correlates more with the real threshold needed for post-resection stimulation of the facial nerve than the ball-tip.

Sequential Bilateral Cochlear Implantation in a Child with Severe External, Middle, and Inner Ear Malformations: Surgical Considerations and Practical Aspects

Cochlear implantation (CI) is a safe and beneficial surgery for children with congenital inner ear malformations, with the exception of cochlear nerve aplasia. The combination of microtia with middle and inner ear abnormalities is extremely uncommon and sufficiently severe to make a surgical approach to the cochlea difficult. We report herein the case of a 2-year-old girl who presented with profound bilateral sensorineural hearing loss, congenital aural atresia, microtia, and inner ear malformations. High-resolution computed tomography revealed poor development of the bilateral middle ear spaces, absence of the incus and stapes, aberrant courses of facial nerves, aplastic lateral semicircular canals, and covered round windows. With intraoperative imaging assistance, sequential bilateral CI was performed using a transmastoid approach with no complication. We propose that CI is feasible in patients with severe external and middle ear malformations. However, major malformations increase the risk of complications. As the facial nerve and cochlea are difficult to locate due to the lack of important anatomical landmarks, detailed planning and adequate preparation, including review of the preoperative imaging data, and the use of facial nerve monitoring and intraoperative imaging are very important. In addition, experienced surgeons should perform CI to ensure the success of the operation.

Facial Nerve Monitoring under Different Levels of Neuromuscular Blockade with Cisatracurium Besilate in Parotid Tumour Surgery

Background. Anaesthesia can alter neuronal excitability and vascular reactivity and ultimately lead to neurovascular coupling. Precise control of the skeletal muscle relaxant doses is the key in reducing anaesthetic damage. Methods. A total of 102 patients with the normal functioning preoperative facial nerve who required parotid tumour resection were included in this study. Facial nerve monitoring was conducted intraoperatively. The surgeon stimulated the facial nerve at different myorelaxation intervals at TOF% (T4/T1) and T1% (T1/T0) and recorded the responses and the amplitude of electromyogram (EMG). Body movements (BM) or patient-ventilator asynchrony (PVA) was recorded intraoperatively. Results. In parotid tumour resection, T1% should be maintained at a range of 30 to 60% while TOF% should be maintained at a range of 20 to 30%. Analysis of the decision tree model for facial nerve monitoring suggests a partial muscle relaxation level of 30 % < T 1 % ≤ 50 % and TOF ≤ 60 % . A nomogram prediction model, while incorporating factors such as sex, age, BMI, TOF%, and T1%, was constructed to predict the risk of BM/PVA during surgery, showing good predictive performance. Conclusions. This study revealed an adequate level of neuromuscular blockade in intraoperative parotid tumour resection while conducting facial nerve monitoring. A visual nomogram prediction model was constructed to guide anaesthetists in improving the anaesthetic plan.

Prospective Study on Effectiveness of Facial Nerve Monitoring in Improving the Surgical Outcomes for Parotidectomy of Benign Parotid Tumours in a Tertiary Hospital in South India

BACKGROUND Salivary gland diseases are rare but an important group of disorders. Following surgeries involving the parotid gland, facial nerve paresis is a common postoperative complication. The reported worldwide incidence of facial nerve paresis following parotidectomy is approximately 20 - 60 %. We need to determine the incidence of facial nerve paresis in the post-operative period following superficial, adequate, or extra-capsular parotidectomy of benign parotid tumours with the use of intraoperative facial nerve monitoring. METHODS A non-randomised interventional trial was initiated once cleared by the institutional review board. With the calculated sample size of 44, the patients underwent nervemonitoring for the identification of the branches of the facial nerve. Clinical grading of the nerve function was done using the House-Brackmann score on the postoperative days 2, 7, and 60. The findings were compared with the historical controls (HC) of 53 patients who underwent similar procedures but with no intraoperative facial nerve monitoring. All patients were recruited in continuity for over two years. RESULTS The incidence of facial nerve paresis was 30 - 40 % and 10 - 20 % in the historical control and nerve monitoring group, respectively (P = 0.07). The duration of surgery in the nerve monitoring group was 83 ± 30 minutes and 95 ± 15 minutes in the HC group. The incidence of nerve paresis was similar among the trainees and consultants suggestive of adequate training. CONCLUSIONS Intraoperative facial nerve monitoring is a useful adjunct to reduce the incidence of early postoperative facial nerve paresis. The technique would not prolong the duration of the procedure. The technique may be utilized safely on a routine basis even during surgical training. KEYWORDS Facial Nerve Monitoring, Parotidectomy, Benign Parotid Tumour, HouseBrackmann Score

Value of Intraoperative Monitoring of the Trigeminal Nerve in Detection of a Superiorly Displaced Facial Nerve During Surgery for Large Vestibular Schwannomas

ObjectiveTo investigate the role of trigeminal and facial nerve monitoring in the early identification of a superiorly displaced facial nerve.Patients and MethodsThis prospective study included 24 patients operated for removal of large vestibular schwannomas (VS). Electromyographic (EMG) events recorded after mapping the superior surface of the tumor were evaluated by analyzing the latencies of the responses from the masseter and facial nerve innervated muscles.ResultsThe latency of the recorded compound muscle action potential (CMAP) from the masseter muscle was 3.6 ±0.5 msec, and of the simultaneously recorded volume conducted responses from the frontalis, o.oculi, nasalis, o.oris and mentalis muscles were 4.6 ±0.9, 4.1 ±0.7, 3.9 ±0.4, 4.3 ±0.8 and 4.5 ±0.6 msec respectively after trigeminal nerve stimulation in 24 (100%) patients. In 6 (25%) patients, the mean latency of CMAP on the masseter was 3.6 ±0.5 msec, and the latencies of the CMAP from the frontalis, nasalis, o.oris and mentalis muscles were longer than those of the volume conduced responses (p=0.002; p=0.001; p< 0.001; and p=0.015 respectively) indicating stimulation of both nerves (trigemino-facial EMG response). All patients with this response were later confirmed anatomically to have an AS displaced facial nerve. ConclusionUnderstanding the trigemino-facial EMG response is of value in identifying an AS displaced facial nerve; in preventing electrophysiological confusion between the trigeminal and the facial nerves; and in detecting the presence of volume conducted contributions in the measured facial nerve CMAP at the end of surgery.