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The Hannover classification of vestibular schwannomas is designed to stratify tumors based on extrameatal extension and compression of the brainstem. We have previously reported the reliability of the Koos system, but to date, no study has assessed the reliability of the similar Hannover classification. We present an assessment of the intrarater and interrater reliability of the Hannover classification system. After institutional review board approval was obtained, a cross-sectional group of the magnetic resonance imaging of 40 patients with vestibular schwannomas varying in size comprised the study sample. Four raters were selected to assign a Hannover grade to 50 total scans. Interrater and intrarater reliability was calculated and reported using Fleiss's kappa, Kendall's W, and intraclass correlation coefficient (ICC). Interrater observer reliability was found to be moderate when measured using Fleiss' kappa (0.49), extremely strong using Kendall's W (0.93), and excellent as calculated by ICC (0.88). The results were all statistically significant (P < 0.05). Intrarater reliability for Hannover grade ranged from 0.77 to 1.00 (substantial to perfect). By Kendall's W and ICC, all raters had near perfect or excellent agreement. The results were all statistically significant (P < 0.05). The Hannover classification is a reliable system for grading the size of vestibular schwannomas. This supports its continued use and previously published results of the literature in studies relying on this classification. Further studies are needed to evaluate its validity and determine its role in preoperative counseling and determining microsurgery and radiosurgery outcomes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]