The development of the corpus callosum in semilobar and lobar holoprosencephaly.

OBJECTIVE

The objective of this study was to determine whether and how a true corpus callosum develops in milder cases of holoprosencephaly.

MATERIALS AND METHODS

The MR scans of seven patients with holoprosencephaly and a callosum-like structure were reviewed. The anatomy of the 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 layer of cortical gray matter.

CONCLUSION

A posterior corpus callosum can develop in holoprosencephaly because the first callosal axons use the white matter of the undivided hemispheres as a bridge to cross the interhemispheric fissure.