Objective: To determine whether monitoring facial nerve motor evoked potentials (FNMEPs) elicited by transcranial electrical stimulation during skull base tumour surgery is useful for predicting facial nerve outcome.
Methods: We analysed FNMEP findings in 26 patients with skull base tumour. Corkscrew electrodes positioned at C3 or C4 and Cz were used to deliver supramaximal stimuli (180-550 V). FNMEPs were recorded from the orbicularis oculi and oris muscles. Correlation between the final-to-baseline FNMEP ratio and postoperative facial nerve function was examined.
Results: Postoperative facial nerve function correlated significantly with the FNMEP ratios in the orbicularis oculi (p = 0.004) and orbicularis oris (p < 0.001) muscles. An FNMEP ratio of < 50% consistently predicted immediate postoperative facial palsy, although the degree of palsy differed among patients. All patients had satisfactory facial nerve function (House & Brackmann grades I and II) postoperatively if the FNMEP ratio remained at > 50%.
Conclusions: Intraoperative FNMEP monitoring can be useful for predicting facial nerve function after skull base surgery. This new method is a valuable adjunct to conventional facial nerve monitoring.
- Facial nerve
- Motor evoked potentials
- Skull base tumour
- Transcranial electrical stimulation
- Vestibular schwannoma