Imaging the pyramidal tract in patients with brain tumors.

The clinical usefulness of diffusion-weighted magnetic resonance imaging (DWI) of the pyramidal tract was evaluated in patients with brain tumors. Five normal volunteers and seven patients with glioma (n = 4) or meningioma (n = 3) near the pyramidal tract underwent coronal echo planar DWI. Greyscale DWIs in each of the three orthogonal diffusion gradients were transformed into graduations, color-coded as red, green or blue, respectively, and then composited to form a combined color image. The entire pyramidal tract was visualized on a single fiber mapping image by combining the upper half of the image slice including the primary motor cortex, the corona radiata and the internal capsule with the lower half of the image slice including the internal capsule, the cerebral peduncle and the ventral brain stem. Fiber mapping images demonstrated the pyramidal tract as a distinct band indicating nerve fiber integrity in all volunteers. The entire pyramidal tract from the primary motor subcortex to the ventral brain stem could be traced. Fiber mapping images showed the ipsilateral pyramidal tract as either discontinuous due to impaired anisotropy or compressed due to mass effect in patients with brain tumors. These findings corresponded well with the pre- and postoperative motor functions. Fiber mapping images are useful for evaluating the white matter neuronal tracts and can provide indications for determining surgical strategy.