Facial Nerve Adherence in Vestibular Schwannomas: Classification and Radiological Predictors

Background  Facial nerve palsy is one of the most frequent complications after resection of vestibular schwannomas (VS). Several mechanisms have been implicated in the poor postoperative facial nerve outcome. Adherence between the facial nerve and tumor capsule is one of the most relevant factors. There is no clear preoperative parameter permitting identification of these adhesions. Objective  The aim of this study was to identify the correlation between the grade of adherence of the facial nerve to the tumor capsule and its functional outcome after VS resection. Methods  A total of 26 patients with sporadic VS (tumor sized T3, T4A, and T4B according to Hannover classification) were evaluated. Grade of adherence of the facial nerve to the tumor capsule was checked during surgery and graduated according to a proposed scale into 1 to 3 different grades. Facial nerve function was assessed postoperatively and after 1-year follow-up. Size of tumor according to Hannover classification, presence of cystic components, "cerebrospinal fluid (CSF) cleft sign," and the contour of tumor capsule were tested as radiological predictors of grade of adherence to the facial nerve. Results and Conclusion  Only Grade 2 (11 cases) and 3 (15 cases) of adherence were seen in large VS. Lower grade of adherence was associated with good facial nerve outcome after 1-year follow-up ( p  = 0.029). Presence of the "CSF cleft sign" and regular contour of tumor capsule were independent predictors of adherence. When both factors were associated, sensitivity and specificity of this method were 83 and 80%, respectively.