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1. Severe ventriculomegaly involving lateral ventricles; third ventricle also dilated.
2. Septum pellucidum is absent. This is most likely secondary to perforation due to aqueduct obstruction, rather than primary malformation, as there is dip between the frontal horns (as opposed to the flat roof characteristic of primary failure of septal formation).
3. Abnormally thin corpus callosum and almost completely absent splenium, consistent with hypoplasia. The degree of VM is not sufficient to account for this purely on the basis of stretching by dilated ventricles, as is seen in simple aqueduct stenosis.
4. Failure of appropriate progression of sulcal development. Primary sulcal development is currently about 4 weeks delayed with only slight concavity seen at the expected locaton of the Sylvian fissure. While underdeveloped opercularisation may be seen in association with aqueduct stenosis alone, and is due to severe VM in that situation, association with enlarged ganglionic eminences is indicative of a malformative cause, and in particular the lissencephalies. The parietooccipital and calcarine sulci are also absent but may be delayed or effaced by simple obstructive ventricular enlargement.
5. Severely reduced cerebellar biometry consistent with cerebellar hypoplasia.
6. No brainstem kink in this case.