Virchow-Robin spaces at MR imaging.

Virchow-Robin (VR) spaces surround the walls of vessels as they course from the subarachnoid space through the brain parenchyma. Small VR spaces appear in all age groups. With advancing age, VR spaces are found with increasing frequency and larger apparent sizes. At visual analysis, the signal intensity of VR spaces is identical to that of cerebrospinal fluid with all magnetic resonance imaging sequences. Dilated VR spaces typically occur in three characteristic locations: Type I VR spaces appear along the lenticulostriate arteries entering the basal ganglia through the anterior perforated substance. Type II VR spaces are found along the paths of the perforating medullary arteries as they enter the cortical gray matter over the high convexities and extend into the white matter. Type III VR spaces appear in the midbrain. Occasionally, VR spaces have an atypical appearance. They may become very large, predominantly involve one hemisphere, assume bizarre configurations, and even cause mass effect. Knowledge of the signal intensity characteristics and locations of VR spaces helps differentiate them from various pathologic conditions, including lacunar infarctions, cystic periventricular leukomalacia, multiple sclerosis, cryptococcosis, mucopolysaccharidoses, cystic neoplasms, neurocysticercosis, arachnoid cysts, and neuroepithelial cysts.