Diffusion Tensor Imaging and Tractography for Cranial Nerves. Interest in Skull Base Surgery and Anatomy

Introduction: The skull base tumors surgery remains a challenge since numerous cranial nerves or vessels closely surround them. Recently, diffusion tensor imaging has developed with the tractography following white fibers and visualizing functional tracts. Cranial nerves tractography could allow predicting their displacement by skull base tumors that may help the surgeon to spare them along the surgery.

Methods: Preoperative cerebral MRI was performed on patients who presented with skull base tumors. A 3 tesla MRI machine was used to acquire DTI sequence with specific parameters: 32 directions, slice thickness 2 mm, echo time 86 ms, repetition time 12000 ms, matrix 128x128, b-value 1000 s.mm-1. An anatomic sequence hyperT2 was overlaid as reference. Distortion was corrected by topup and eddy functions from FSL. Cranial nerves fibers were probabilistically tracked with Mrtrix3. Cranial nerves were selected according to their location around the tumor. The "radiological" expected position of the cranial nerve was compared to its "operative" real position.