The corpus callosum is the major commissure of the forebrain, connecting homologous cortical regions of the two cerebral hemispheres. The corpus callosum is divided into anterior and posterior parts, known as the genu and splenium, respectively. The genu includes fibers of the frontal forceps (forceps minor) interconnecting frontal areas. Posteriorly, the splenium includes the occipital forceps (forceps major), interconnecting the parietal, occipital, and temporal lobes. A corpus callosotomy, a surgical lesioning of the corpus callosum, has been performed in patients with medication-refractory epilepsy. The goal of this surgery is to prevent seizure spread from one hemisphere to another. Agenesis of the corpus callosum (ACC) is a congenital birth defect characterized by an absence of a corpus callosum. This condition can occur in isolation (with little to no impact on cognitive performance) or can occur as part of abnormalities such as Dandy-Walker syndrome, Arnold-Chiari malformation, schizencephaly, holoprosencephaly, Andermann syndrome, or Aicardi syndrome (a syndrome more commonly seen in females). Midline facial defects often accompany ACC.
COLOR IMAGING OF THE CORPUS CALLOSUM BY DIFFUSION TENSOR IMAGING
A-C diffusion weighted imaging (DWI) measures the rate of water diffusion in brain tissue, measured using an apparent diffusion constant (ADC). Diffusion tensor imaging (DTI) is used to measure the “anisotropy” or randomness of water diffusion. The degree of anisotropy is called fractional anisotropy (FA), and is measured from 0 to 1, where 0 is unrestricted and 1 is fully restricted and diffuses along only one axis. Due to the properties of white matter, parallel bundles of axons and the myelin sheaths allow for a certain orientation of water diffusion. Water diffuses more rapidly along the direction of aligned direction, and more slowly perpendicular to this direction. This enables “visualization” of white matter tracts based on the calculated FA values. To discriminate the direction of different fiber bundles, a color scheme is adopted in which green represents an anterior-posterior direction, red a left-right direction, and blue a superior-inferior direction. In these images of the corpus callosum, components of this major commissural bundle are represented in red.