Perivascular spaces, also called Virchow-Robin spaces (VRS), are pial-lined extensions that sorround the walls of vessels as they course from the subarachnoid space through the brain parenchyma.
Dilated Virchow-Robin spaces typically occur in three characteristics locations. Type I VRS appear along the lenticulostriate arteries entering the basal ganglia through the anterior perforated substance. Type II VRS 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 VRS appear in the midbrain.
There is evidence from tracer studies and from pathologic analysis of the human brain that Virchow-Robin spaces carry solutes from the brain and are, in effect, the lymphatic drainage pathways of the brain.
Small VRS (<2mm) are found in patients of all ages and are a normal anatomic variant. Perivascular spaces increase in size (>2mm) and frequency with advancing age.
Some authors found a correlation between dilated VRS and neuropsychiatric disorders, recent-onset multiple sclerosis, mild traumatic brain injury, and diseases associated with microvascular abnormalities.
Various conditions may be included in the differential diagnoses of dilated VRS: 1.Lacunar infarction tend to be larger than VRS and often exceed 5mm. Lacunar infarction are usually localized in the upper two-thirds of the anterior perforated substance and basal ganglia. Large VRS are found in the inferior third of the anterior perforated substance and basal ganglia;
2.Neurocisticercosis in the inital vesicular stage may simulate VRS. The presence of a discrete eccentric scolex within the cyst helps in the correct diagnoses of cysticercosis;
3.Neuroepithelial cysts are rare benign lesions spherical or ovoid and measure up to several centimeters in size. They are lined with thin epithelium and have CSF-like content. Differentiation between neuroepithelial cysts and enlarged VRS can be made with certainty only by pathological studies.
On CT or MR Virchow-Robin spaces are mostly seen as well-defined oval, rounded or tubular structures, with smooth margins, usually measure 5mm or less. They have identical attenuation and signal intensity of CSF.