Diffusion tensor MR imaging visualizes the altered hemispheric fiber connection in callosal dysgenesis

Abstract

We report three cases of callosal dysgenesis that were evaluated by diffusion tensor imaging and fiber tractography. In partial agenesis of corpus callosum, fiber tracts from all regions of brain converged to a partially developed small genu portion and connected to the contralateral side. In complete callosal agenesis, fibers from the hemispheres failed to cross the midline and formed thick bundles running anteroposteriorly (eg, Probst bundle). The thickness of the anterior commissure was enlarged or smaller than normal brain, and other white matter tracts were not markedly different from normal brain tissue.

Fig 1.

Anatomic T2-weighted images, diffusion tensor-based color maps, FA maps, and FT of callosal dysgenesis. Upper row depicts normal findings of corpus callosum; i.e., clear red fibers and high FA bundles crossing midline at diffusion tensor MR imaging. Tractography shows interhemispheric fiber connections through corpus callosum; i.e., red-colored fibers in the midline. Middle row shows partially developed corpus callosum in genu portion (white arrow). Tractography demonstrates fibers from parieto-occipital regions converging into small red-colored genu as well as fibers from frontal lobes. Fibers from the posterior part run anteriorly and form longitudinal green-colored fibers, the Probst bundle. In complete agenesis of corpus callosum, the Probst bundle is more apparent as thick, green, high-FA fibers medial to lateral ventricle (double arrows). Tractography shows thick bundles of green color consist of various fibers from ipsilateral hemisphere, Probst bundle, and thick red-colored AC (black arrows).

Fig 2.

T2-weighted and diffusion tensor-based color images at the level of the AC. Right-to-left running red fibers are identified in control subject and one patient with callosal agenesis, whereas other patients did not show these transverse fascicles on diffusion tensor maps (white arrows).