Evoked Facial Nerve EMG and Brainstem Auditory Evoked Potential Monitoring in Cerebellopontine Angle Tumor Resection

Background: The preservation of normal nerve function or identification of nerve route is critical in some surgeries of cerebellopontine angle tumors. Over the last 5 years, intraoperative facial nerve electromyogram (EMG) and brainstem auditory evoked potential (BAEP) were applied for evaluation of facial nerve integrity and brainstem function in patients while undergoing resection of cerebellopontine angle (CPA) tumor. This report represents the retrospective analysis of our results. Methods: The inhalational anesthesia with 1-1.5 % isoflurane in pure O_2 was used. Muscle relaxation was maintained with continuous infusion of atracurium, The degree of muscle relaxation was aimed at a T_4/T_1 ratio of train-of-four response more than 20% of the adductus pollicis upon ulnar nerve stimulation at the wrist, In 236 patients suffering from CPA tumor without facial palsy, the EMG of the mentalis muscle ipisilateral to the tumor was obtained through stimulation of the facial nerve. The stimulation was applied with a nerve finder, which delivered an electrical stimulation at a single 2 mamp direct current. The EMG finding was compared with the clinical result. In 198 patients, BAEP was used to monitor the brainstem function during tumor resection. In case of intact hearing the BAEP was taken ipsilateral to the operation side and in case with total hearing loss contralateral BAEP to operation side was used. For BAEP stimulation, 90 db click sound stimulation with frequency of 11.26 Hz was applied to both ears. BAEP signals were obtained and recorded at the mastoid region of either side in reference to the vertex. The EMG and BAEP signals were recorded and saved to an evoked potential monitor. Results: In facial nerve EMG monitoring, there were two false positive and no false negative tests. Except for the two false positive tests, the postoperative clinical results in the other cases were compatible with the intra-operative facial nerve EMG findings. In BAEP monitoring, there were twenty-eight positive tests. Conclusions: The low incidence of false negative test suggests that facial nerve EMG is valuable in detection of facial nerve function in CPA tumor resection. Intraoperative BAEP abnormality is possibly useful in identifying postoperative brainstem dysfunction.

關鍵字

Brain neoplasms, cerebellopontine angle ； Electromyography ； Evoked potentials, auditory, brain stem

並列摘要

背景：正常神經功能與神經傳導徑路之保護是手術中重要之一環。在過去五年中，顏面神經肌電圖圈及腦幹聽覺誘發電位被應用於小腦橋腦角腫瘤切除手術。方法：手術中病患以吸入性麻醉劑，並以周邊神經刺激器監測肌肉鬆弛劑之使用。在236例無顏面神經麻痺病例中，顏面神經功能經由腫瘤同側之下頜肌測定。在腫瘤切除中及切除後，顏面神經經由一神經探測器刺激，而引起下頜肌收縮，其收縮產生之肌電圖予以記錄。於腫瘤切除手術進行中，198例應用同側或對側腦幹聽覺誘發電位監測腦幹功能。結果：在顏面神經肌電圖監測，除2例假陽性外，其餘病患手術後之顏面神經肌電圖結果相符合，於腦幹聽覺誘發電位監測，28例有明顯之腦幹聽誘發電位變化。結論：在本研究顯示，顏面神經肌電圖及腦幹聽覺誘發電位可協助在小腦橋腦角腫瘤切除術中監測顏面神經及腦幹功能。

並列關鍵字

腦腫瘤：小腦橋腦角；肌電圖；誘發電位：聽覺，腦幹

國際替代計量

Evoked Facial Nerve EMG and Brainstem Auditory Evoked Potential Monitoring in Cerebellopontine Angle Tumor Resection

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