Comparison of response amplitude versus stimulation threshold in predicting early postoperative facial nerve function after acoustic neuroma resection.

OBJECTIVE

This study aimed to better predict the early postoperative facial nerve (FN) function after acoustic neuroma (AN) resection.

STUDY

DESIGN

This study was a prospective series.

SETTING

The surgery was conducted in a tertiary referral center.

PATIENTS: A total of 44 patients undergoing AN resection with cranial nerve monitoring were observed for at least 1 year after surgery.

MAIN OUTCOME MEASURES: The predictive value of amplitude of the FN stimulus response on the early postoperative FN function was measured.

RESULTS

Cranial nerve monitoring in AN surgery was used to obtain the stimulation threshold and facial electromyograph response amplitudes to FN stimulation proximal and distal to the tumor at 0.2 V above threshold. Thirty-eight of forty-four patients studied had a low postresection threshold (< or = 0.1 V). Of these (10), 26% sustained a postoperative FN dysfunction of House-Brackmann (HB) grades 3-6. In an effort to improve the predictive value from cranial nerve monitoring, the response amplitude to suprathreshold stimulation was compared with the threshold and FN function. Eighty-nine percent of patients with an amplitude of > or =200 microV had a grade 1-2 early postoperative FN function, whereas only 41% of patients with < 200 microV had a grade 1-2 early postoperative FN function (p = 0.00035). Eighty-eight percent of patients with both a low threshold and high amplitude had a grade 1-2 early postoperative FN function, whereas the remaining 12% of patients had a grade 3-6 FN function (p = 0.0032). The false-positive rate of threshold alone in predicting a grade 1-2 FN function was 26% compared to 12% for low threshold and high amplitude combined.

CONCLUSIONS

The use of FN threshold and amplitude together is superior to threshold alone as a predictor of early postoperative FN function.