Anterior callosal agenesis in mild, lobar holoprosencephaly.

The corpus callosum normally grows in a ventral to dorsal direction with the genu appearing first followed by posterior growth to form the body and splenium. In holoprosencephaly there usually is a malformation of the lamina terminalis which results in lack of formation of the corpus callosum. This paper presents a patient with mild, lobar holoprosencephaly in whom a different type of callosal dysgenesis was detected: the callosal body and splenium were apparently formed but the anterior parts were absent. The existence of this type of callosal dysgenesis appears to be in contrast to current theories on callosal development.