Facial nerve function following cerebellopontine angle surgery: prognostic value of intraoperative thresholds

Intraoperative stimulation of the facial nerve during surgery of the cerebellopontine angle greatly aids the surgeon in identification of the nerve. The preservation of the ability to stimulate the facial nerve, at the brain stem following tumor removal, has been shown to correlate with good postoperative facial outcome. Thresholds of facial nerve stimulation recorded in our series, using constant voltage stimulation, showed statistically significant relevance to facial nerve outcome. When the difference between thresholds before and after tumor removal was 0.2 V or less or when the threshold after tumor removal was less than or equal to 0.2 V, a good postoperative facial outcome could be expected. This paper discusses the relevance of stimulation threshold prior to tumor removal to the size of tumor.