Callosotopy: leg motor connections illustrated by fiber dissection

Precise anatomical knowledge of the structure of the corpus callosum is important in split-brain research and during neurosurgical procedures sectioning the callosum. According to the classic literature, commissural fibers connecting the motor cortex are situated in the anterior part of the corpus callosum. On the other hand, more recent imaging studies using diffusion tensor imaging indicate a more posterior topography of callosal fibers connecting motor areas. Topographical knowledge is especially critical when performing disconnective callosotomies in epilepsy patients who experience sudden loss of leg motor control, so-called epileptic drop attacks. In the current study, we aim to precisely delineate the topography of the leg motor connections of the corpus callosum. Of 20 hemispheres obtained at autopsy, 16 were dissected according to Klingler’s fiber dissection technique to study the course and topography of callosal fibers connecting the most medial part of the precentral gyrus. Fibers originating from the anterior bank of the central sulcus were invariably found to be located in the isthmus of the corpus callosum, and no leg motor fibers were found in the anterior part of the callosum. The current results suggest that the disconnection of the pre-splenial fibers, located in the posterior one-third of the corpus callosum, is paramount in obtaining a good outcome after callosotomy.