What posterior fossa abnormality is present?
Dandy-Walker spectrum malformation - hypoplastic upwardly rodated vermis, with expanded 'cyst' continuous with the fourth ventricle.
What supratentorial complication is present?
Obstructive hydrocephalus due to aqueduct stenosis.
What third ventricular recesses can you identify?
Supra-optic, infundibular and pineal recesses. These are all 'ballooned' out due to obstructive hydrocephalus.
A flow void is now seen through the floor of the third ventricle with reduced dilatation of the third and lateral ventricles (implied by reduction in upward bowing of the corpus callosum).