Figure 1 Axial (A) images of a head CT without IV contrast demonstrate hypodense foci at the left medulla suggestive of PVS. These structures are prominent and appear to be extending into the fourth ventricle, exerting a mass effect upon adjacent structures causing consequent ventricular enlargement, consistent with obstructive hydrocephalus. Axial (B, D–F) and (C) coronal images of a brain MRI with and without IV contrast. T2 WI (B, C), T2 FLAIR (D), contrast-enhanced T1 WI (E), and DWI (F) show a cluster of well-defined T2 hyperintense and T1 hypointense oval-shaped cystic-like lesions, isointense to CSF in all sequences, and demonstrating no associated contrast enhancement. Non-enhancement on post-contrast T1 WI (E) and lack of restricted diffusion on DWI (F) help to rule out abscess or other acute infectious/inflammatory causes. These findings are consistent with enlarged perivascular (Virchow-Robin) spaces (red arrows). There were subsequent obstruction of the cerebral aqueduct with supratentorial obstructive hydrocephalus and transependymal CSF accumulation (yellow arrows). WI – weighted image.