Intraoperative facial nerve monitoring in the surgery of cerebellopontine angle tumors: improved preservation of nerve function.

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The surgery of cerebellopontine angle tumors has shown remarkable progress over the last 20 years due to improved microsurgical techniques. However, the dissection of the facial nerve may lead to postoperative paresis as the result of the surgical trauma and the disruption of blood supply over a large distance. The functional status of the nerve can be intraoperatively monitored by means of intramuscular electromyography of facial muscles and direct electrical stimulation. In this study, the impact of monitoring techniques on the preservation of facial function was evaluated by comparing monitored (n = 30) and unmonitored (n = 34) patients. Both groups were comparable with regard to the size of the tumor, the surgical approach and the duration of operation. All patients were operated by the same surgeon (T.L.) either via the middle fossa or the translabyrinthine approach. The EMG was recorded with needle electrodes from the orbicularis oris and oculi muscles. For electrical stimulation, bipolar forcep electrodes were used delivering rectangular, constant current pulses of 100 microseconds duration and a current strength between 0.05 and 0.8 mA. The mechanically or thermally elicited activity by drilling, direct manipulation or coagulation consisted of bursts and trains which are signs of minor nerve impairment. Their occurrence can lead to a modified surgical technique with a more precise preparation around and at the facial nerve. The immediate postoperative nerve function was normal or showed only a minor impairment (classes I and II according to House and Brackmann) in 87% of the monitored as compared with 74% of the unmonitored patients.(ABSTRACT TRUNCATED AT 250 WORDS)