Clinical Analysis Of F Wave Assisted Electrophysiological Monitoring During The Operation For Acoustic Neuromas

Objectives:To evaluate the long-term facial function of patients following microsurgical removal of acoustic neuroma and identify factors that influence these outcomes and investigate the relations between intraoperative F wave monitoring results and postoperative facial nerve function.Methods:A retrospective review was performed that included 192 consecutive patients who underwent suboccipital retrosigmoid craniotomy for removal of acoustic neuroma at the Neurosurgical Department, Xiangya hospital by the senior surgeon (Professor Yuan Xianrui, MD&PhD) between January 2002 to November 2009. Patient and tumor characteristics as well as perioperative complications and long-term symptoms are described. House-Brackmann Scale was used preoperatively and in a long-term follow-up i.e. one week,6 months,12 months and more than one year after surgery. Correlating intraoperative monitoring index of F wave with the follow-up results of facial nerve function 1 day and 6 months after their operations.Results:These 192 patients were all operated through the suboccipital retrosigmoid approach. Complete resection was achieved in 183(95.3%) of these 192 patients and near-total resection in 7 cases, partial in 1 case, subtotal in 1 case with a mortality of 1.6%. Anatomic preservation of the facial nerve was attained in 96.4% of patients (n=185 of 192). Amone the 106 patient who had at least 1-year follow-up(mean 3.0 years), for all tumor sizes, HB gradeⅠ/Ⅱfunction was attained in 83%, HB gradeⅢin 9.4%, and HB gradeⅣ/Ⅴin 7.5%.Facial function at 1 year after removal of VS was significantly impacted by the Preoperative symptom duration≥36 months.In patients with duration≤36 months,HB gradeⅠ/Ⅱfunction was attained in 88.9%(n=64 of 72). For duration≥36 months, HB gradeⅠ/Ⅱfunction was attained in 70.6%(n=24 of 34). There was statistically significant difference in facial nerve outcome in long-term follow-up when preoperative symptom duration was considered (P<0.05).Facial function at 1 year after removal of VS was significantly impacted by the size of the tumor. In patients with tumors <30mm, HB grade 1/2 function was attained in 90%(n=9of 10). For tumors≥30mm, HB grade 1/2 function was attained in 82.3%(n=79 of 96). There was statistically significant difference in facial nerve outcome in long-term follow-up when tumor size was considered (P<0.05). The non-parameter analysis and test for linear trend show that tumor size and preoperative symptom duration correlate with the facial nerve function at 1 year or more postoperatively.Patient age,cystic change,and expansion of internal auditory canal do not influence facial nerve function.The intraoperative monitoring indexes in nasal muscle F wave recording are correlate well with the facial nerve function in the 1 day after operation (κ=0.426, P＜0.001).and the intraoperative monitoring indexes in nasal muscle F wave recording are also correlate well with the facial nerve function in the 6th month's follow-up (κ=0.514, P＜0.001).Conclusions:Resetion of large and giant acoustic neuroma via retrosigmoid approach using electromyography monitoring is a safe and effctive method,and could abained well long-term facial nerve function after operation.Large tumor size and duration of symptoms≥36 months are the unfavorable factors of long-term facial nerve function after operation.F wave recording intraoperatively correlates well with the postoperative facial nerve function in 1st day and 6th month.Introperative electrophysiological monitoring helps to explore and position facial nerve, protect facial nerve and peripheral tissue, and forecast prognosis of the facial nerve function.