Dorsal displacement of the facial nerve in acoustic neuroma surgery: clinical features and surgical outcomes of 21 consecutive dorsal pattern cases

In acoustic neuroma surgery, the facial nerve (FN) course varies among patients, but a dorsal pattern is rarely observed. We retrospectively reviewed and classified 556 acoustic neuromas operated on via a lateral suboccipital retrosigmoid (LSO) approach into two groups: dorsal (group D) and non-dorsal (group ND). The clinical features and outcomes including functional preservation of the FN, the extent of tumor resection, and the retreatment rate were compared. Among 556 cases, 21 (3.8%) patients with dorsal patterns were identified. No significant differences in clinical features or preoperative status were noted between groups D and ND. No significant differences in functional FN preservation were found between groups D and ND in the immediate postoperative period (90.5 and 83.0%, respectively) or 1-year postoperatively (95.2 and 97.0%, respectively). Compared with group ND, the extent of tumor resection was significantly less (p < 0.0001) and the retreatment rate was significantly higher in group D (hazard ratio, 33.6; 95% confidence interval [CI], 11.7-96.1; p < 0.0001). In one dorsal pattern case, surgical resection was abandoned based on the intraoperative findings. Dorsal displacement of the FN was accurately predicted with preoperative imaging evaluations in just two cases. Functional preservation of the FN during acoustic neuroma surgery is achievable if the FN runs along the dorsal side of the tumor. However, a dorsal pattern, especially when the FN is broadened, is clearly associated with less complete tumor removal and a higher rate of retreatment than typical pattern cases.