Preoperative Vestibular Testing to Identify the Vestibular Nerve Branch of Vestibular Schwannoma Origin: Is It Possible to Predict the Course of the Facial Nerve, Optimize the Surgical Strategy, and Improve the Facial Nerve Results?

Objective: Vestibular schwannoma is a benign tumor originating from one of the two vestibular nerves (VN), which constitute the dorsal portion of the vestibulo-facial bundle in its cisternal course. Surgical removal remains the gold standard in case of progressive increase in tumor size or clinical symptoms secondary to compressive effects within the cerebellopontine angle. The purpose of surgery is radical extirpation, though judiciously balanced with the attempt to preserve the facial nerve (FN) and, when possible, the auditory function. Preoperative anticipation of the nerve of origin can be a useful indicator of the position of FN relative to the tumor, allowing for better surgical planning.

Methods: A retrospective review of 84 patients was performed, comparing clinical data, surgical videos and preoperative functional tests, consisting of: cervical vestibular myogenic evoked potential (cVEMPs), audiometric test and caloric stimulation. The processing of cVEMPs allowed us to predict the nerve of origin of the tumor. Association (chi-square) tests were performed as well as ROC curves of cVEMPs as predictors of nerve of origin and FN peritumoral course.

Results: The results of preoperative cVEMPs were compared with intraoperative anatomical inspection: in 78 cases (92.9%), the data agreed with a contingency coefficient 0.86 (p < 0.0001, 95% CI: 0.75–0.97), indicating high predictivity. ROC curve of cVEMPs as nerve-of-origin predictors showed high accuracy (AUC: 0.94). A statistically significant association emerged between the VN of origin and the peritumoral course of FN: ventral course was more frequent in case of origin from superior VN (OR: 11.76, p < 0.0001, 95% CI: 3.99–34.59), while origin from inferior VN was associated with a polar course pattern (anterosuperior or anteroinferior). After stratification and pairwise analysis, anterosuperior course was significantly associated with smaller tumor size (p = 0.046), better preoperative hearing (AAO-HNS B, p = 0.0136) and better early postoperative facial outcome (HB 1-2, p = 0.022) when compared to anteroinferior course. In comparison to ventral course, antero-superior course was significantly associated with better early and late facial outcome (p = 0.024).

Conclusion: Preoperative vestibular tests are simple, rapid and noninvasive procedures that can effectively anticipate the nerve of origin and, indirectly, the position of FN around the schwannoma capsule—something feasible, but at a considerably higher cost, by 3T MRI diffusion tensor tractography. Our preoperative protocol allowed us a better operative strategy with an outlook to the anatomical–functional preservation of FN.

No conflict of interest has been declared by the author(s).

Publication History

Article published online:
05 February 2024