Aberrant Course of the Corticospinal Tracts in the Brain Stem Revealed by Diffusion Tensor Imaging/Tractography

Abstract

ABSTRACT AberrantCSTsrefertocollateralpathwaysseparatingfromtheoriginalCSTatthemidbrain,descending through the pontine ML, and re-entering the original CST at the upper medulla.We report conventional MR imaging, DTI, and FT of a child with a completely aberrant rightCST.OnlyFTrevealedthecompletelyaberrantcourseoftheCST,whereasconventionalMRimagingandcolor-codedFA-mapssuggestedtheabsenceoftherightCST.Thiscaseshowsthe ability of FT to study the abnormal course of white matter tracts. INTRODUCTION The CST is the principal motor white mat-ter pathway. Its fibers originate from thepyramidal cells in layer V of the cerebralcortex, run down through the capsula in-terna and the brain stem, and end withinthe spinal cord. 1 Although the CSTs al-ready reach the level of the pyramidal de-cussation at the eighth gestational week,their complete development ends only atthe age of about 2 years with their com-plete myelination. Because of the long de-velopmental period, the CSTs are vulnera-ble to injuries and may be affected inseveral brain malformations that may in-fluence their final course.