THE DEVELOPMENT OF THE CORPUS-CALLOSUM IN SEMILOBAR AND LOBAR HOLOPROSENCEPHALY

Objective. The objective of this study was to determine whether and ho w a true corpus callosum develops in milder cases of holoprosencephaly . Materials and methods. The MR scans of seven patients with holoprose ncephaly and a callosum-like structure were reviewed. The anatomy of t he callosum-like structure and the pericallosal anatomy were evaluated . Results. Six of the seven cases had a posterior corpus callosum. The seventh case was indeterminate because lack of myelination prevented confirmation that the callosum-like structure consisted only of white matter. In each case the posterior corpus callosum formed posterior to white matter which spanned the interhemispheric fissure beneath a lay er of cortical gray matter. Conclusion. A posterior corpus callosum ca n develop in holoprosencephaly because the first callosal axons use th e white matter of the undivided hemispheres as a bridge to cross the i nterhemispheric fissure.