Displacement of the facial nerve course by vestibular schwannoma: Preoperative visualization using diffusion tensor tractography

Purpose: To preoperatively visualize the course of the facial nerve, which is displaced by vestibular schwannoma, using diffusion tensor (DT) tractography, and to evaluate the agreement with surgical findings. Material and Methods : The subjects were eight patients with vestibular schwannoma who had undergone removal surgery. DT MR images were obtained and tracts that were considered to represent the facia nerve were constructed. We assess the success rate for tract construction and evaluated the agreement between tractography findings and surgery. Results: We obtained a tract that connected the internal auditory meatus and brainstem, and was considered to represent the facial nerve in seven of the eight cases. The course of the constructed tract agreed with surgical findings in five of these seven cases. One exception was a case in which the tumor was too large to enable intraoperative observation of the facial nerve; however, the facial nerve appeared to be displaced anteriorly at intracapsular resection, in agreement with tractography. In the other case, the schwannoma was mostly cystic. Conclusion: Tractographs constructed using MR tensor images enabled to to identify tracts considered to represent facial nerves. We consider DT tractography to be a useful tool for preoperatively predicting facial nerve displacement in vestibular schwannoma.