FIG 1. Coronal anatomic diagram depicts multiple bilateral giant perivascular spaces (PVSs) in the mesencephalothalamic region. There are fenestrations of the giant PVSs, which may allow accumulation of interstitial fluid between the vessel and pia or within the interpial space causing enlargement of the PVSs. Note the mass effect upon the third ventricle with associated obstructive hydrocephalus. Graphic courtesy of James Cooper, MD and AMIRSYS, Inc (35).