Pharyngeal motor evoked potentials elicited by transcranial electrical stimulation for intraoperative monitoring during skull base surgery

Object. The purpose of this study was to determine whether monitoring of pharyngeal motor evoked potentials (PhMEPs) elicited by transcranial electrical stimulation during skull base tumor surgery might be useful for predicting postoperative swallowing deterioration. Methods. The authors analyzed PhMEPs in 21 patients during 22 surgical procedures for the treatment of skull base tumors. Corkscrew electrodes positioned at C3 or C4 and Cz were used to deliver supramaximal stimuli (220-550 V). Pharyngeal MEPs were recorded from the posterior wall of the pharynx through a modified endotracheal tube. The correlation between the final/baseline PhMEP ratio and postoperative swallowing function was examined. Results. Postoperative-swallowing function was significantly (p < 0.05), although not strongly (r = -0.47), correlated with the final/baseline PhMEP ratio. A PhMEP ratio < 50% was recorded during 4 of 22 procedures; in all 4 of these cases, the patients experienced postoperative deterioration of swallowing function. After 18 procedures, the PhMEP ratios remained > 50%; nevertheless, after 4 (22.2%) of these 18 procedures, patients showed deterioration of swallowing function. Conclusions. Intraoperative PhMEP monitoring can be useful for predicting swallowing deterioration following skull base surgery, especially in patients with swallowing disturbances that are mainly due to reduction in the motor functions of the pharyngeal muscles. (DOI: 10.3171/2011.10.JNS111343)