FIG 5. Right temporal arachnoid cyst. The cyst's content (arrow) is isointense to CSF (see controlateral cortical cysterns, fourth ventricle, lateral ventricles) in all of the sequences. This appearance is attributable to the similarity of CSF and cystic content.

A, T1-weighted sequence.

B, T2-weighted sequence.

C, PD-weighted sequence.

D, FLAIR sequence. On the FLAIR image, the hyperintensity seen in the fourth ventricle is owing to flow artifact.