The posterior cranial fossa is obscured by susceptibility artefact from previous posterior craniocervical fusion. Abnormal flattening of the skull base (platybasia). Note the massively enlarged subcutaneous venous collaterals overlying the posterior fossa.
Both the lateral ventricles and third ventricle are dilated. The fourth ventricle is not dilated.
There are bilateral arachnoid cysts of the middle cranial fossa with mass effect on the inferior temporal lobe and significant widening of the Sylvian fissure. There is high signal on T2-weighted FLAIR sequence at the bilateral frontal periventricular white matter region. There is no extra-axial fluid collection and no restricted diffusion.
Conclusion:
Enlarged lateral ventricles and third ventricle as well as the arachnoid cysts of the bilateral middle cranial fossa. Bilateral frontal periventricular white matter region demonstrates a high signal on T2-weighted FLAIR sequence.