Knowledge of electrophysiologic features of nervus intermedius stimulation can help protect the facial nerve during cerebellopontine angle surgery. The surgeon must recognize that stimulation of the nervus intermedius can cause electromyographic activity in the facial nerve monitoring channels, but the main trunk of the facial nerve may lie in entirely different location in the cerebellopontine angle.
First branchial cleft (FBC) anomalies are uncommon. The aim of this retrospective clinical study is to describe our experience in dealing with these sporadically reported lesions. Eighteen cases presenting with various FBC anomalies managed surgically during an 8-year period at a tertiary referral medical institution were included. Ten were males (56 %) and eight females (44 %) with age range 3-18 years. Anomaly was right-sided in 12 cases (67 %). None were bilateral. Nine patients (50 %) had prior abscess incision and drainage procedures ranging from 1 to 9 times. Two also had previous unsuccessful surgical excisions. Clinical presentations included discharging tract openings in external auditory canal/conchal bowl (n = 9), periauricular (n = 6), or upper neck (n = 4); cystic postauricular, parotid or upper neck swellings (n = 5); and eczematous scars (n = 9). Three distinct anatomical types were encountered: sinuses (n = 7), fistulas (n = 6), and cysts (n = 5). Complete surgical excision required superficial parotidectomy in 11 patients (61 %). Anomaly was deep to facial nerve (FN) in three cases (17 %), in-between its branches in two (11 %) and superficial (but sometimes adherent to the nerve) in remaining cases (72 %). Continuous intraoperative electrophysiological FN monitoring was used in all cases. Two cases had postoperative temporary lower FN paresis that recovered within 2 months. No further anomaly manifestation was observed after 49.8 months' mean postoperative follow-up (range 10-107 months). This study has shown that awareness of different presentations and readiness to identify and protect FN during surgery is essential for successful management of FBC anomalies. Intraoperative electrophysiological FN monitoring can help in that respect.
ObjectiveTo investigate the role of trigeminal and facial nerve monitoring in the early identi cation 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 con rmed 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.
Introduction This study highlights the relation between compound muscle action potential (CMAP) latency variations and the predictive value of facial nerve (FN) proximal-to-distal (P/D) amplitude ratio measured at the end of vestibular schwannoma resection. Methods Forty-eight patients underwent FN stimulation at the brainstem (proximal) and internal acoustic meatus (distal) using a current intensity of 2 mA. The proximal latency and the P/D amplitude ratio were assessed. House–Brackmann grades I & II indicated good FN function, and grades III to VI were considered fair/poor function. A P/D amplitude ratio > 0.6 was used as a cutoff to indicate a good FN function, while a ratio of ≤ 0.6 indicated a fair/poor FN function. Results The P/D amplitude ratio was measured for all patients, and the calculated sensitivity (SE), specificity (SP), positive predictive value (PPV), and negative predictive value (NPV) were 85.2, 85.7, 88.5, and 81.8%, respectively. The CMAPs from the mentalis muscle were then classified based on their proximal latency into group I (< 6 ms), group II (6–8 ms), and group III (> 8 ms). The SE, SP, PPV, and NPV became 90.5, 90.9, 95, and 83.3%, respectively, in group II. In group I, SE and NPV increased, whereas SP and PPV decreased. While in group III, SP and PPV increased, whereas SE and NPV decreased. Conclusion At a latency between 6 and 8 ms, the P/D amplitude ratio was predictive of outcomes with high SE and SP. When latency was < 6 ms or > 8 ms, the same predictive ability was not observed. Knowing the strengths and limitations is important for understanding the predictive value of the P/D amplitude ratio.
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