- Department of Neurosurgery, Brain Research Institute, University of Niigata, 1-757 Asahimachi-dori, Chuo ku, Niigata-City, Japan
Department of Neurosurgery, Brain Research Institute, University of Niigata, 1-757 Asahimachi-dori, Chuo ku, Niigata-City, Japan
DOI:10.4103/2152-7806.115650Copyright: © 2013 Fukuda M This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Fukuda M, Takao T, Hiraishi T, Yajima N, Saito A, Fujii Y. Novel devices for intraoperative monitoring of glossopharyngeal and vagus nerves during skull base surgery. Surg Neurol Int 25-Jul-2013;04:97
How to cite this URL: Fukuda M, Takao T, Hiraishi T, Yajima N, Saito A, Fujii Y. Novel devices for intraoperative monitoring of glossopharyngeal and vagus nerves during skull base surgery. Surg Neurol Int 25-Jul-2013;04:97. Available from: http://sni.wpengine.com/surgicalint_articles/novel-devices-for-intraoperative-monitoring-of-glossopharyngeal-and-vagus-nerves-during-skull-base-surgery/
Background:Swallowing disturbance is among the most burdensome complications suffered by patients with glossopharyngeal and vagus nerve involvement in lesions adjacent the jugular foramen. For monitoring these nerves, we have developed new devices that comprised four contacts adhering to the surface of the cuff of an endotracheal tube, with attachment the posterior pharyngeal wall. To determine whether these devices are useful for monitoring the glossopharyngeal and vagus nerves and predicting postoperative swallowing dysfunction in patients undergoing removal of skull base tumors involving these nerves.
Methods:We studied 10 patients. Compound muscle action potentials (CMAPs) were recorded from the posterior pharyngeal wall by stimulating the glossopharyngeal or vagus nerve in order to identify the nerve course, especially in patients showing severe nerve distortion due to the tumor. Pharyngeal motor evoked potential (PhMEP) elicited by transcranial electrical stimulation were recorded in all patients. The correlation between the final to baseline PhMEP ratio and postoperative swallowing function was examined.
Results:Responses were obtained in six of the seven patients in whom CMAP monitoring was performed. Deterioration of swallowing function postoperatively was demonstrated in six of seven (86%) patients with intraoperative PhMEP ratios 50% showed deterioration of swallowing function after surgery, although the one patient already had severe swallowing dysfunction requiring preoperative tracheostomy.
Conclusions:Our novel devices were useful for monitoring the glossopharyngeal and vagus nerves in patients undergoing removal of skull base tumors involving these nerves.
Keywords: Compound muscle action potential, glossopharyngeal nerve, pharyngeal motor evoked potential, transcranial electrical stimulation, vagus nerve
Intraoperative monitoring of swallowing function is important for skull base surgery in patients in whom the glossopharyngeal and vagus nerves are involved in the tumor. Motor function of these nerves have been monitored using needle electrodes placed in the vocal cords or pharyngeal wall, as well as surface electrodes on an endotracheal tube adhering to the vocal cords. [
We previously applied pharyngeal motor evoked potential (PhMEP) monitoring employing a modified endotracheal tube placed on the posterior pharyngeal muscles to predict postoperative swallowing function during skull base surgery. [
We studied 10 patients (7 men and 3 women) with skull base tumors treated surgically at the University of Niigata from May 2011 to December 2012, in whom our new devices were used for monitoring the glossopharyngeal and vagus nerves [
We monitored the glossopharyngeal and vagus nerves by recording both compound muscle action potentials (CMAPs) and PhMEP from the posterior pharyngeal wall. These novel monitoring devices were comprised of four contacts adhering to the surface of the cuff of the endotracheal tube [
Our methods of intraoperative PhMEP monitoring have already been described elsewhere in detail. [
Bipolar stimulators for CMAP monitoring were utilized. Current was delivered using a 0.2-ms pulse duration and a pulse frequency of one per second. Stimulus intensity was 1.0 mA. If reliable CMAPs were not obtained at this intensity, the current was increased in 1.0 mA increments until 3.0 mA was reached. The CMAPs from the posterior pharyngeal wall were recorded at the paired contacts with the largest amplitude in PhMEPs employing transcranial electrical stimulation. We used exclusively CMAP monitoring to identify the courses of the nerves with severely distorted anatomy.
Pre-and postoperative swallowing function
Four of the ten patients had swallowing dysfunction (1 point in 2 patients and 2 in 2) prior to surgery [
Intraoperative PhMEP and CMAP recordings
In all patients including two who underwent tracheostomy preoperatively, valid PhMEPs were obtained from the paired contacts adherent to the cuff of the endotracheal tube [
Intraoperative CMAP monitoring in a patient with a cerebellopontine angle meningioma (Patient 9,
PhMEPs and postoperative swallowing function
Swallowing function deteriorated postoperatively in six of seven (86%) patients with an intraoperative PhMEP ratio <50% [
Intraoperative PhMEP monitoring in a patient with a cerebellar hemangioblastoma (Patient 8,
In the present study, we obtained both CMAP and PhMEP recordings from the posterior pharyngeal wall using our newly modified endotracheal tube during skull base tumor surgery. The CMAP recordings facilitated identifying the course of the glossopharyngeal and vagus nerves, especially in patients with nerves severely distorted by the tumor. The final amplitude ratios in PhMEPs, using a cut-off point of 50%, appear to predict swallowing function deterioration after surgery.
Needle electrodes have been inserted into the pharyngeal wall and soft palate for CMAP monitoring of the glossopharyngeal and vagus nerves. [
We recently reported a redesigned endotracheal tube attached to the posterior pharyngeal wall to be useful for PhMEP monitoring to predict postoperative swallowing dysfunction. [
In this study, the PhMEP amplitude ratio after tumor resection tended to correlate with postoperative deterioration of swallowing function, although the number of patients was small. In all three patients with PhMEP amplitude ratios >50%, preoperative states of swallowing function were unaffected by surgery, although one patient already had severe dysfunction prior to the operation. Six of seven patients with PhMEP amplitudes <50% experienced deterioration of swallowing function after tumor removal. The one remaining patient already had severe swallowing dysfunction (points 2). It may be difficult to evaluate postoperative deterioration of swallowing function, as reflected by reduced PhMEP amplitude ratios at the final examinations. Exclusion of such patients from this study, would have assured that there were no false positive or negative data assuming that patients with PhMEP amplitude ratios <50% after tumor removal had deterioration of swallowing function postoperatively. Previously, we analyzed the PhMEPs obtained with the prototype devices in 21 patients during 22 surgical procedures for the treatment of skull base tumors. [
The CMAPs obtained with our newly modified endotracheal tube attached to the posterior pharyngeal wall allow the course of the glossopharyngeal and vagus nerves distorted by the skull base tumor to be identified. The final amplitude of PhMEP ratios apparently predicts postoperative deterioration of swallowing function. These new devices were useful for monitoring the glossopharyngeal and vagus nerves in patients undergoing removal of skull base tumors involving these nerves.
The authors thank Motohiro Soma and Kiyoe Nonaka for their technical support.
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