[Depiction of the trigeminal nerve deviated by a tumor lesion, using probabilistic diffusion tensor tractography].

We attempted presurgical visualization of the trigeminal nerve deviated by tumor compression using the probabilistic diffusion tractography (PDT) technique, which is used to analyze diffusion tensor imaging (DTI) data. We acquired DTI data of 3 patients with a tumor lesion around the trigeminal nerve (2 patients with trigeminal neurinomas and 1 with epidermoid) using the 3T magnetic resonance imaging system. The DTI data was analyzed by PDT using the Diffusion Toolbox, and the software of FMRIB (FDT; www.fmrib.ox.ac.uk/fsl). In all 3 patients, PDT allowed successful visualization of the trigeminal nerve which is further distal to the trigeminal ganglion, even when heavy T2-weighted imaging and conventional fiber-tracking analysis of the DTI data revealed only the cisternal segment of the nerves. Especially in 2 cases with the tumor mainly located in the Meckel's cave, the location of the nerve was determined only by PDT. All these findings obtained by PDT were concordant with the intraoperative observation of the actual nerves. In conclusion, PDT is a useful technique for visualization of the trigeminal nerve even when it is severely deviated by tumor compression, and this technique could have potential for evaluating other cranial nerves in surgical cases with a tumor in the skull base.