Anatomical variability of the corticospinal decussation: a diffusion tensor imaging study.

purposeThe corticospinal tract (CST) is a well-known white matter tract of the motor projection described by Hippocrates. The morphological anatomical decussation has not been specifically studied using tractography. We aim to investigate the anatomy and variability of the CST decussation in healthy patients using high-resolution tractography technique.

methodsMRI data from the Human Connectome Project were acquired on a modified 3T scanner with 64-channel coil. Image data from 35 subjects were processed using Freesurfer and FSL. A 2 ROI approach was used to identify each CST in each diffusion MRI. CST deccusation types, variations and localization were analyzed.

resultsPyramidal decussation was visible in 32 patients. There was no difference between right and left CST characteristics. Three patterns of pyramidal decussation were identified. In 56,2% of patients the CST decussation was a crossing (i.e. with fibers entanglement) of left and right CSTs fibers. In 40,6% of patients the CSTs did not cross but rotated around each other without entanglement. In one case, the CST did not cross the midline. In one case, the right CST completely crossed the midline.

conclusionCST decussation is variable in its organization: complete versus partial crossing, rotation vs. crossing. It may have some significance in rare clinical conditions. Clinical and embryological implications are discussed.