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Atypical callosal dysgenesis

Dr Frank Gaillard et al.

Atypical callosal dysgenesis is a term used to denote an unusual pattern of dysgenesis of the corpus callosum.

The development of the corpus callosum occurs between the 12^th and 16 - 20^th weeks of gestation ^2-3. It begins with the genu and then continues posteriorly along the body to the splenium. The rostrum is the last part to be formed. In primary agenesis parts of the corpus callosum to form before the insult will be present whereas later parts will be absent. Presence of the rostrum essentially excludes primary agenesis.

In holoprosencephaly however the posterior parts of the corpus callosum are often preserved, whereas the anterior parts are absent.

It is thought that this pattern results secondary to absence of the interhemispheric fissure whose presence seems to be required for callosal formation ¹.