Prediction of Facial Nerve Function After Surgery for Cerebellopontine Angle Tumors: Use of a Facial Nerve Stimulator and Monitor

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Abstract
A series of 18 patients undergoing surgery for cerebellopontine angle tumors is reported. Patients were grouped according to size of tumor (0 to 2.5 cm, 11 cases; more than 2.5 cm, 7 cases). In all, the facial nerve was identified and conductance assessed by monitoring the facial electromyographic response to facial nerve stimulation. Postoperative facial nerve function was graded clinically after 3 months according to the House scale. Tumor removal was complete in all cases. In patients with tumors up to 2.5 cm the facial nerve was intact to visual inspection at the end of the procedure in all but one, where partial division was evident. In this group intraoperative facial nerve stimulation indicated electrical integrity in 8 of the 11 cases, all of which regained good facial nerve function postoperatively (House grades I and II). Nerve conduction was lost during the operation in the remaining three patients with small tumors; two subsequently developed a moderately severe (grade IV) dysfunction and the third, a total paralysis (grade VI). In the large (more than 2.5 cm) tumor group the facial nerve was anatomically intact in five of the seven cases, partially divided in one, and completely sectioned in the remaining case. Facial nerve stimulation indicated functional integrity in three patients, two of whom developed moderate (grade III) and the third a severe (grade V) dysfunction. In the other four cases nerve function could not be detected at operation; three of these developed a moderate facial nerve dysfunction (grade III/IV) and the final case a complete paralysis (grade VI). Intraoperative facial nerve monitoring appeared to predict eventual facial function accurately in the small tumor group, but did not predict facial nerve recovery reliably following surgery for larger tumors.