Chu Pan MD, Presenter: Nothing to Disclose

Kyung K. Peck PhD, Abstract Co-Author: Nothing to Disclose

Robert J. Young MD, Abstract Co-Author: Nothing to Disclose

Andrei I. Holodny MD, Abstract Co-Author: Nothing to Disclose

To map the controversial location of the motor pathways of tongue, face, hand and foot in the posterior limb of the internal capsule (PLIC) using probabilistic diffusion tractography.

Twenty subjects (mean age =39.7 years, range 17-54 years) with normal neuro exams and MRIs were retrospectively studied. DTI was acquired on a GE 3T scanner using SE EPI (TR/TE=13000/89ms; directions=15; b-value=1000). Probabilistic diffusion tractography was performed using DTI&Fiber Tools implemented in MATLAB. Tracts were separately calculated between regions-of-interest (ROI) drawn in the pons and in the tongue, face, hand and foot motor homunculi in the precentral gyrus. Parameters were: Number of random walks=100,000; maximum fiber length=150 voxels; trace<0.002; fractional anisotropy>0.15. The voxel with the highest probability was designated as the position of the motor pathway. The posterior index (PI) and lateral index (LI) were defined as the relative anteroposterior and mediolateral locations of the motor pathways. Paired t-tests compared the mean difference of the PI and LI for each ROI.

Probabilistic tracking successfully mapped all 40 motor tracks traversing the PLIC. Tongue pathways were located anteromedial to face in 16 tracts (40%) with p<.05 for PI and LI. Face pathways were located anteromedial to hand in 25 tracts (62.5%) with p<.05 for PI and LI. Hand pathways were anteromedial to foot in 14 tracts (35%) and anterior in 11 tracts (27.5%) with p<.05 for PI but p>.13 for LI. Group analysis showed that the bilateral hemisphere somatotopic arrangement was identical.

We describe the anteroposterior alignment of the motor pathways along the long axis of the PLIC. The tongue pathways were located anteromedial to the face, the face anteromedial to the hand, and the hand variably anterior to the foot. Probabilistic tractography successfully tracks the motor pathways of the tongue, face and hand from the precentral gyrus through their intersection with the larger superior longitudinal fasciculus to the PLIC, overcoming limitations of standard (non-probabilistic) tractography methods.

Identifying the accurate location of the motor pathways is clinically importance to precisely determine whether a lesion (such as a brain tumor, infarct or multiple sclerosis) correlates to a certainT

Pan, C, Peck, K, Young, R, Holodny, A, Somatotopic Organization of Motor Pathways in the Internal Capsule: Probabilistic Diffusion Tractography Study.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11000338.html