Evaluation of the Somatotopic Organization of Corticospinal Tracts in the Internal Capsule and Cerebral Peduncle: Results of Diffusion-Tensor MR Tractography

Abstract

ObjectiveWe have used diffusion tensor tractography (DTT) for the evaluation of the somatotopic organization of corticospinal tracts (CSTs) in the posterior limb of the internal capsule (PLIC) and cerebral peduncle (CP).Materials and MethodsWe imaged the brains of nine healthy right-handed subjects. We used a spin-echo echo-planar imaging (EPI) sequence with 12 diffusion-sensitized directions. DTT was calculated with an angular threshold of 35 degrees and a fractional anistropy (FA) threshold of 0.25. We determined the location of the CSTs by using two regions of interest (ROI) at expected areas of the pons and expected areas of the lateral half of the PLIC, in the left hemisphere of the brain. Fiber tracts crossing these two ROIs and the precentral gyrus (PCG) were defined as CSTs. Four new ROIs were then defined for the PCG, from the medial to lateral direction, as ROI 1 (medial) to ROI 4 (lateral). Finally, we defined each fiber tract of the CSTs between the pons and each ROI in the PCG by using two ROIs methods.ResultsIn all subjects, the CSTs were organized along the long axis of the PLIC, and the hand fibers were located anterior to the foot fibers. The CSTs showed transverse orientation in the CP, and the hand fibers were located usually medial to the foot fibers.ConclusionCorticospinal tracts are organized along the long axis of the PLIC and the horizontal direction of the CP.

Anatomic Location and Somatotopic Arrangement of the Corticospinal Tract at the Cerebral Peduncle in the Human Brain

“…2,3,[7][8][9][10][11][12]15 A few DTT studies have reported the location of CST in the CP. 1,13,14 In 2002, Mori and van Zijl 13 provided data suggesting that the CST was located in the mid-to-lateral portion of the CP. Subsequently, by using functional MR imaging and DTI, Newton et al (2006) 1 demonstrated the pathway of corticofugal fibers from multiple cortical motor areas to the CP.…”

“…Moreover, studies elucidating detailed anatomic information have been limited. 14,15 Studies reporting that the CST was located in the middle portion of the CP have been a general trend [7][8][9][10]12 ; however, some textbooks or studies have suggested more specific data: the middle three-fifths, 3 middle half, 11 or middle two-thirds. 2 As for the somatotopic arrangement of the CST, by direct brain stimulation study during stereotactic surgery in more than 700 cases, Martinez et al (1967) 15 found unique data demonstrating an anteroposterior somatotopic arrangement from the face to the upper to the lower limbs rather than a mediolateral arrangement at the upper CP.…”

“…2,3 However, studies elucidating detailed somatotopic anatomy have been limited and somewhat controversial. 14,15 Therefore, the exact anatomic location and somatotopic arrangement of the CST at the CP have not been clearly elucidated for easy application in the clinical field.…”

“…2,3,[7][8][9][10][11][12] However, some studies have provided slightly different data, suggesting that the CST was located in the mid-to-lateral portion of the CP. 1,13,14 As for the somatotopic arrangement of the CST at the CP, many neuroanatomy textbooks have shown mediolateral arrangement of somatotopies for the arm and leg. 2,3 However, studies elucidating detailed somatotopic anatomy have been limited and somewhat controversial.…”

“…[17][18][19][20][21][22][23][24] However, little is known about the detailed anatomic location and somatotopic arrangement of the CP. 14 In the current study, by using DTT, we attempted to investigate the detailed anatomic location and somatotopic arrangement of the CST at the CP in the healthy human brain.…”