The corpus callosum is the largest of the commissural fibers, linking the cerebral cortex of the left and right cerebral hemispheres. It is divided into four parts (from anterior to posterior): rostrum, genu, body, and splenium.

Corpus callosum Isthmus is a focal thinning at the body-splenium junction. It is a normal variant incidentally seen in about 22% of populations. The radiologists should be aware of to avoid misinterpretation as dysgenesis or focal hypoplasia ^1_.