Identification of the corticospinal tracts achieved using blood-oxygen-level-dependent and diffusion functional MR imaging in patients with brain tumors

Abstract

Diffusion-weighted MR imaging was used to delineate the corticospinal tract (CST) successfully and to depict its relationship to adjacent brain tumors. The CST was defined by a method by which it seems possible to delimit the distance from the CST to the main tumor mass and to show displacement and infiltration of the tract by the neoplasia. This information cannot be gathered from routine anatomic MR imaging.

fig 1. Images from the case of a 44-year-old woman with a grade III/IV left frontal glioma. A, Routine axial T1-weighted image. The location of the CST is difficult to determine. B, Diffusion trace image of the CST co-registered to an axial T1-weighed image. Visualization of the CST of the foot (blue) and the hand (red) shows its proximity to the main tumor mass. The space between the blue area and the red area probably represents the location of the CST that controls the leg and torso.

fig 2.

Images from the case of a 30-year-old man with a right frontal grade III/IV glioma. A, Routine axial T1-weighted image. The location of the CST is difficult to determine. B, Diffusion trace image coregistered to an axial T1-weighted image shows the relationship of the tumor to CST (red) on the right. The CST on the side with the tumor (red) is not only displaced posteriorly but appears to be infiltrated by the tumor (see Discussion). The contralateral CST is shown in blue.

fig 3.

Representation of the method used to identify the CST. Two regions of interest that contained the CST were selected: the motor homunculus of the precentral gyrus (yellow) and the posterior limb of the internal capsule (orange). A, Using a lower FA, diffusion trace images of the precentral gyrus (yellow) would show all the white matter tracts emanating from the motor cortex. These would include tracts to the posterior limb of the internal capsule, the corpus callosum, and multiple other areas in the frontal and parietal lobes (red lines). B, Similarly, diffusion trace images of the posterior limb of the internal capsule (orange) would show the CST and multiple other white matter tracts to the frontal and parietal lobes (red lines). To eliminate the white matter tracts that were depicted in each tracing but were not part of the CST, we mathematically intersected the two maps, eliminating those tracings that were not present on both maps. C, Resultant map showed only the CST that was common to maps A and B.

fig 4.

Diffusion trace image of the CST coregistered to an axial echo-planar (b = 0) image shows that the CST is located in the third quarter of the posterior limb of the internal capsule