Prediction of facial nerve position in large vestibular schwannomas using diffusion tensor imaging tractography and its intraoperative correlation.

Abstract

Resection of large Vestibular Schwannomas (VSs) can be associated with postoperative facial nerve injury. Diffusion-based tractography has emerged as a powerful tool for three-dimensional imaging and reconstruction of white matter fibers; however, tractography of the cranial nerves has not been well studied. In this prospective study, we aim to predict the position of facial nerve in large VSs (>3 cm) using Diffusion Tensor Imaging (DTI) tractography and correlate it with the intraoperative finding of the position of facial nerve. Twenty patients with a large VS (>3 cm) undergoing surgery were subjected to preoperative DTI to predict the position of the facial nerve in relation to the tumor. The surgeon was blinded to the results of the preoperative DTI tractography. A comparative analysis was then made during operation. The location of the facial nerve in relation to the tumor was recorded during surgery using facial nerve stimulator. Of the 20 patients who underwent DTI tractography, it was not possible to preoperatively identify facial nerve in one patient. In another patient, although DTI tractography predicted the position of facial nerve, it was not identified intraoperatively. In the remaining 18 patients, DTI tractography accurately predicted the facial nerve position. The predicted position was in synchronization with the intraoperative facial nerve position in 16 patients (89% concordance). It was discordant in two patients (11%), but this was not found to be statistically significant (P = -0.3679). This study validates the reliability of facial nerve DTI-based fiber tracking for prediction of the facial nerve position in patients with large VSs. The reliable preoperative visualization of facial nerve location in relation to the VS will allow surgeons to plan tumor removal accordingly and may increase the safety of surgery.