Subcortical topography and proportions of the pyramidal tract

The pyramidal tract (PT) was dissected in 30 normal human hemispheres according to the method of Klingler. The various dimensions as well as the cerebral landmarks were studied. The pyramidal tract is built up like a fan in the white matter by a thin layer of fibers of 2.8-3.5 mm in thickness. The fibers converge toward the internal capsule to a solid fiber tract with a lateral and apdiameter of 7.8 +/- 1.6 mm and 17.5 +/- 2.1 mm, respectively. This configuration of the PT presents different possibilities of damage during surgery. The evaluation of the three-dimensional course of the PT is possible by using three cerebral landmarks, the precentral gyrus, the entrance into the internal capsule and the posterior limb of the internal capsule. Their topography is described. Additionally the pyramidal tract can be defined medially by the sulcus cinguli and the roof of the lateral ventricle and laterally by the superior sulcus circularis Insulae. The possible displacement of the PT by space occupying lesions and the intra-operative orientation is discussed.