Intraventricular Arachnoid cyst MRI

A 30 years old female with history of progressive headache, giddiness and vomiting.

Here is Non contrast CT Brain, MRI Brain with axial T2, T2*GRE, Diffusion and post contrast T1w images. 

Findings:

Non contrast CT Brain : Marked dilatation of fourth ventricle iso dense to Csf. Mild non communicating hydrocephalus. Dilated outlet foramen of fourth ventricle. 

Diffuse cerebral edema.

MRI Brain : Fourth ventricular lesion is iso intense to Csf, non enhancing on post contrast T1.l
No restricted diffusion on Dw images.
No low signal intensity hemosiderin staining or calcification on GRE.

Posterior fossa craniotomy done.
Intra operative finding is Intra ventricular Arachnoid cyst.