Intraoperative facial nerve motor evoked potential monitoring during skull base surgery predicts long-term facial nerve function outcomes.

OBJECTIVES

This study was designed to clarify whether facial nerve motor evoked potentials (FNMEPs) elicited by transcranial electrical stimulation during skull base surgery are useful for predicting long-term facial nerve function.

METHODS

We analyzed FNMEP findings in 35 patients with skull base tumors. Mean follow-up was 24.4 months. Corkscrew electrodes positioned at C3 or C4 and Cz were used to deliver supramaximal stimuli. FNMEPs were recorded from the orbicularis oculi and oris muscles.

RESULTS

The correlation between the final-to-baseline FNMEP ratio and initial or long-term facial nerve function was examined. Initial post-operative facial nerve function correlated significantly with the FNMEP ratios in the orbicularis oculi (r = -0.53, P < 0.005) and orbicularis oris (r = -0.80, P < 0.001) muscles. The correlations between FNMEP ratios and facial nerve function remained significant during long-term follow-up (orbicularis oculi muscle: r = -0.43, P < 0.05; orbicularis oris muscle: r = -0.71, P < 0.001). All patients in whom the FNMEP ratio in the orbicularis oculi muscles remained above 50% were assigned to the satisfactory facial nerve function (House-Brackmann Grades i and ii) group at the final examination.

DISCUSSION

FNMEP monitoring can predict facial nerve function not only immediately after surgery but also long-term.