Application of small current perioperative stimulation threshold in evaluation of facial nerve function post acoustic neuroma surgery(report of 96 cases)

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