Agenesis of the corpus callosum
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MRI images showing the absence of the corpus callosum with the medial surfaces of the brain having radial gyri due and cingulate gyrus. The lateral ventricles run parallel rather than the normal "bow-tie" configuration giving a racing car appearance on axial imaging, there is also colpocephaly (dilatation of the trigones and occipital horns) giving a characteristic "longhorn"/moose head/viking helmet appearance on coronal imaging. Remainder brain is unremarkable.
This case demonstrates a primary agenesis of the corpus callosum, which means that it was never formed. It is a result of an insult occurring at approximately 8-12 weeks gestation and resulting in failure to form the corpus callosum. The white matter tracts which usually cross the midline, instead are oriented vertically, separating the lateral ventricles widely, in a racing car sign configuration.