Female, 18 years old, 30 weeks and 5 days GA, with nonvisualization of the cavum septum pellucidum on fetal ultrasound, concern for absent corpus callosum. The corpus callosum is absent in its entirety with an expected colpocephalic pattern of ventricular dilatation. The caliber of the ventricles at the level of the atria is approximately 13 mm bilaterally.Asymmetry is also evident involving the frontal lobes and insula. The left frontal lobe is smaller than the right and the left insula may be smaller as well, or perhaps it simply appears this way due to a greater degree of closure of the left sylvian fissure.The brainstem and cerebellum are within normal limits. No evidence of any mass lesion is seen. No abnormal extra-axial collections or evidence of intracranial hemorrhage is seen.
1.Agenesis of the corpus callosum.2.Asymmetry of the frontal lobes and insular regions is seen with structures on the left being somewhat smaller than those on the right. The precise nature and etiology for this asymmetry is not clear on the present examination. Findings can be better assessed on postnatal imaging.