Abstract
Objective To explore the predictive value of small current stimulation threshold for the facial nerve outcome after acoustic neuroma surgery. Methods Ninety-six acoustic neuroma patients underwent tumor resection by a single team at Department of Neurosurgery, Huashan Hospital, Fudan University from January 2013 to April 2015 and were enrolled into a prospective cohort study. We defined the minimal stimulation intensity of facial nerve proximal to the brainstem to induce action potential after tumor total resection as stimulation threshold (ST) and a ST of ≤ 0.05 mA as small current. Facial nerve function was evaluated using House-Brackmann (H-B) scale preoperatively and postoperatively (1, 3, 6, 12 months). By means of binary, ordinal and linear regression analysis, the facial nerve function outcomes in the small current and control (> 0.05 mA) groups were compared.The sensitivity and specificity of the small current prediction facial nerve function were calculated by the four-grid method. Results The ST in all 96 cases was 0.01-0.35 mA with an average of 0.06±0.02 mA. Seventy-four patients were included in the small current group and 22 in the control group. While adjusting for the following covariates: ages, tumor size, tumor location, tumor texture, Samii scale and preoperative H-B scale, binary logistic regression analysis showed that the rate of good facial nerve outcome (H-B score of Ⅰ-Ⅱ) in small current group was significantly better than that in control group [43.2%(32/74) vs. 4.5%(1/22) at 1 month; 62.2%(46/74) vs. 31.8%(7/22) at 3 months; 70.3%(52/74) vs. 40.9%(9/22) at 6 months; 81.1%(60/74)vs. 45.5%(10/22) at 12 months; all P<0.05]. Ordinal regression analysis revealed that compared with the control group the facial nerve outcome in small current group shifted toward a better condition at 1, 3, 6, and 12 months postoperatively. A faster recovery rate was found in small current group among patients with H-B score of Ⅳ at 1 month postoperatively (slope: -0.163 vs. -0.057, P=0.004). The sensitivity and specificity of small current for predicting facial nerve function 1 year after surgery were 85.7% and 46.2%, respectively. Conclusions Small current seems to be a better short-term and long-term predictor of postoperative facial nerve function. For patients with H-B Ⅳ at 1 month post operation, small current could predict faster recovery rate of facial nerve function. Key words: Neuroma, acoustic; Facial nerve; Small current; Prognosis
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