Specific Imaging Findings

Perivascular spaces (PVS) show a well-defined oval, rounded, or tubular configuration with smooth margins and are commonly seen bilaterally in the supratentorial white matter with a radial orientation and in the basal nuclei (around the anterior commissure and in the midbrain). PVS appear on CT as hypodense areas, with similar attenuation as CSF. Calcifications or other associated abnormalities are not present. On MRI, their signal intensity also follows the CSF, being hypointense on FLAIR images, typically without any bright rim. Contrast enhancement is absent and there is water-like diffusivity on ADC maps. MR spectroscopy around dilated PVS shows normal spectra. In rare cases PVS may continuously enlarge to over 2 cm in size, frequently containing internal septations. The surrounding brain parenchyma generally has normal signal intensity; however, adjacent to dilated and enlarging PVS, hyperintense signal on FLAIR images may be present, likely representing reactive gliosis or spongiosis.

Pertinent Clinical Information

Small PVS (≤ 5 mm) are seen on high-resolution MRI in all age groups. Dilatation of PVS has been associated with aging. In healthy children, they are present in 25–30% of cases and must be considered a benign normal variant. They are usually asymptomatic and discovered incidentally. However, in the pediatric age group, prominent PVS are also well-known findings of mucopolysaccharidoses (types I and II). In those cases, PVS dilation specifically involves the corpus callosum, in addition to the periventricular white matter.