FIG 2. 19-year-old woman with incidentally found arachnoid cysts in the cerebellopontine angle.

A, Transverse T2-weighted SE image (2000/80/1) shows high signal intensity within the enlarged cerebellopontine angles (arrows) and in the prepontine cistern. The shape of the enlarged CSF space suggests arachnoid cysts.

B, On the corresponding SSFP image (20/25/1), signal attenuation due to CSF flow is found in the prepontine cistern and fourth ventricle (curved arrows). Persistently high signal intensity is found in the cerebellopontine cysts (straight arrows) due to stationary CSF, confirming the diagnosis of arachnoid cysts.

C, Sagittal T1-weighted SE image (500/12/2) with suspected thin membrane (long arrow) between the isointense subpeduncular space (curved arrow) and the left cerebellopontine mass (short straight arrow).

D, Corresponding sagittal SSFP image (500/12/2) shows functional separation of the hypointense pulsating CSF between the temporal bone and the cerebellar peduncles (curved arrow) and the hyperintense stationary CSF within the cyst (straight arrow).