Dysgenesis of the corpus callosum and associated telencephalic anomalies: MRI.

We analysed the MRI findings in 23 patients with callosal dysgenesis in relation to their associated telencephalic anomalies to investigate the morphological significance of the development of Probst's bundles and the anterior commissure in congenital callosal dysgenesis. We classified callosal dysgenesis into three types: total defect (9 patients), partial defect (7) and hypoplasia (7). Associated anomalies were observed in 15 patients, including migration disorder (8 patients), micrencephaly (5), and lipoma (2). The remaining 8 patients had no associated anomalies. Probst's bundles were not identified in 4 patients with a severe migration disorder. An absent or hypoplastic anterior commissure was observed in 9 of the 16 patients with callosal defect and all 7 of those with callosal hypoplasia. Colpocephaly and keyhole dilatation of the temporal horns were seen in 16 and 21 patients, respectively. Callosal dysgenesis may occur not only through a defect in the callosal anlage, but also from impaired growth of axonal fibres projecting from the cerebral isocortex. Therefore, associated telencephalic anomalies may be responsible for additional features in callosal dysgenesis. Consequently, identification of Probst's bundles and the anterior commissure may be important when assessing cortical development in patients with callosal dysgenesis.