Original ArticlePharyngeal Motor Evoked Potential Monitoring During Skull Base Surgery Predicts Postoperative Recovery from Swallowing Dysfunction
Introduction
Intraoperative monitoring of swallowing function is important in patients undergoing skull base surgery when the glossopharyngeal and vagus nerves are involved in the tumor. Motor function of these nerves can be 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 1, 7, 8, 11, 12. However, these devices are usually used for recording compound muscle action potentials obtained from direct electrical stimulation of the glossopharyngeal and vagus nerves during intraoperative neurophysiologic monitoring.
Recently, we have demonstrated that monitoring pharyngeal motor evoked potential (PhMEP) using a modified endotracheal tube placed on the posterior pharyngeal muscles can be useful in predicting postoperative swallowing function during skull base surgery 3, 4. Patients with reduced PhMEP amplitude after tumor resection often experience deteriorated swallowing function immediately after surgery compared with those with preserved PhMEP amplitude. However, the correlation between intraoperative PhMEP findings and the postoperative course of swallowing function is not clear. The aim of this study was to determine whether PhMEP monitoring predicts outcomes of swallowing function not only immediately after surgery but also in the period of recovery from swallowing dysfunction.
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Patients
We assessed data from 38 consecutive patients with skull base tumors treated surgically at the University of Niigata from February to October 2013, in whom PhMEP monitoring was performed. Two patients had severe preoperative swallowing dysfunction and were excluded. Therefore, the study included 36 patients (15 males and 21 females). Twenty-one of the 36 patients described here were included in a previous study (3) and 15 new patients were added. The cranial base tumors were as follows: jugular
Swallowing Function Immediately After Surgery
Seven of the 36 patients had mild preoperative dysfunction (1 point); all of them reported mild swallowing dysfunction but had no objective palsy of the glossopharyngeal or vagus nerve. Five of the 7 patients had jugular foramen schwannomas, 1 had a foramen magnum meningioma, and 1 had a petroclival meningioma. Magnetic resonance imaging revealed that all 7 patients had tumors affecting the lower cranial nerves. In 3 of the patients, their immediate postoperative swallowing function
Discussion
In the present study, we demonstrated that PhMEP amplitude ratios negatively and weakly correlated with the time to the end of drip or tube feeding and the beginning of oral intake in patients who underwent skull base surgery. If the PhMEP ratios were >50%, patients were able to start oral intake within 4 days after surgery. In contrast, it took approximately 2 weeks postsurgery to start oral intake in patients with PhMEP ratios ≤50%. For recovery from swallowing dysfunction, considered to be
Conclusions
PhMEP amplitude after removal of a skull base tumor was significantly correlated to earlier recovery from swallowing dysfunction by both univariate and multivariate analysis. Patients with preserved PhMEP ratios >50% during surgery had faster recovery than those with PhMEP ratios <50%. PhMEP monitoring is useful for predicting swallowing function outcomes not only immediately after surgery but also the period of recovery from swallowing dysfunction.
Acknowledgments
The authors thank Motohiro Soma and Kiyoe Nonaka for their technical support.
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