Antenatal ultrasound selected images showing severe ventriculomegaly and increased head size (HC/BPD) for gestational age. The third ventricle is dilated.
Hand views show the thumb in an adducted state (see last stack images and cine loop). In addition, the repeated "snapping" movement of the thumb across the palm is abnormal and indicative of spasticity that is characteristic of this condition which involves abnormal underdevelopment of the corticospinal tracts and absence of the medullary pyramids, demonstrable on postnatal imaging and pathology but not on fetal US or MRI.