Intra-operative facial nerve monitoring. Its predictive value after skull base surgery

Purpose: Facial nerve monitoring can be used to predict post-operative facial function after skull base surgery. In this study three methods of prediction of facial function were compared. These methods utilize various parameters of the evoked electromyographic monitoring. Material and methods: Twenty-three patients who underwent surgery for skull base diseases were retrospectively reviewed. Amplitude of ongoing electromyographic activity, stimulation current thresholds and amplitude of evoked response were analysed. The predictive value of the three methods was correlated with post-operative facial nerve function. Results: The method that used only the stimulation thresholds predicted the final post-operative facial function in 86.9 per cent of the patients. The second employed a mathematical ratio which combined the amplitude of evoked response and the stimulation current thresholds and confirmed the prediction of the facial function in 91.3 per cent of the patients. The last method does not consider the stimulation thresholds greater than 0.05 mA and failed to predict the final VIIth nerve function in patients in whom the stimulation was greater than 0.05 mA. Conclusion: Analysis of prognostic value demonstrates that the first two methods had the smaller degree of variation showing the better sensitivity.