A comparison of facial nerve monitoring systems in cerebellopontine angle surgery.

The use of peripheral nerve monitoring during skull base surgery is becoming a more common procedure. One widely used method (Jako) detects surface muscle contraction, which can be transduced into an audible signal. A 200 microsecond square wave current can be delivered periodically, in order to identify the nerve and verify its integrity. Another monitoring method has been developed, which provides a continuous audible needle electromyographic (EMG) feedback signal from computer averaging of a monopolar low impedance constant voltage stimulus. This study compares facial nerve preservation and postoperative facial nerve function results of three groups of cerebellopontine angle surgical cases: 38 cases performed with no monitoring; 29 cases done with Jako motion detection monitoring; and 41 performed with evoked needle EMG audible feedback monitoring. Postoperative facial nerve function is evaluated using the House-Brackmann grading system. Each of the three study groups are matched for a time at which postoperative evaluation was made. Analysis of results reveals that in addition to the expected increase in facial nerve preservation rates when monitoring is in use, the near real-time feedback provided by audible evoked EMG results in a significant reduction in permanent postoperative facial nerve dysfunction. Using evoked monitoring, a greater proportion of the cases had a final outcome of class I or II results, compared to those cases performed using Jako motion detection monitoring.