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  • Title: Comparison of response amplitude versus stimulation threshold in predicting early postoperative facial nerve function after acoustic neuroma resection.
    Author: Mandpe AH, Mikulec A, Jackler RK, Pitts LH, Yingling CD.
    Journal: Am J Otol; 1998 Jan; 19(1):112-7. PubMed ID: 9455959.
    Abstract:
    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.
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