Cisterna magna is a normal retro cerebellar Csf density space, when unusually prominent termed as Giant Cisterna magna.
A subarachnoid septa / dural fold is usually seen within the cistern.
A normal anatomical variation of no clinical significance as there are no associated Vermian or cerebellar anomalies.
Normal Vermis. Normal fourth ventricle or communication with fourth ventricle differentiate it from Dandy Walker malformation spectrum.
No mass effect. No associated Ventriculomegaly.
Sometimes may be so large that it extends laterally and superiorly far beyond the normal anatomic limits of the cisterna magna with an associated cerebellar hypoplasia.
The tentorium cerebelli are normally located.
An associated scalloping of occipital bone, postulated to be due to Csf pulsations.
On MRI, iso intense to Csf on all pulse sequences. No restricted diffusion on Dw images.