Perivascular space

Perivascular space
A perivascular space as seen on CT
Anatomical terms of neuroanatomy []

A perivascular space, also known as a Virchow–Robin space, is an immunological space between an artery and a vein (not capillaries) and the pia mater that can be expanded by leukocytes. The spaces are formed when large vessels take the pia mater with them when they dive deep into the brain. The pia mater is reflected from the surface of the brain onto the surface of blood vessels in the subarachnoid space. Perivascular cuffs are regions of leukocyte aggregation in the spaces, usually found in patients with viral encephalitis.

Perivascular spaces are extremely small and can usually only be seen on MRI images when dilated. While many normal brains will show a few dilated spaces, an increase in these has been shown to correlate with the incidence of several neurodegenerative diseases, making the spaces a popular topic of research.

Perivascular spaces are gaps containing interstitial fluid that span between blood vessels and the brain matter which they penetrate. Like the blood vessels around which they form, perivascular spaces are found in both the subarachnoid space and the subpial space.Perivascular spaces surrounding arteries in the cerebral cortex and the basal ganglia are separated from the subpial space by one or two layers of leptomeninges, respectively, as well as the pia mater. By virtue of the leptomeningeal cell layer, the perivascular spaces belonging to the subarachnoid space are continuous with those of the subpial space. The direct communication between the perivascular spaces of the subarachnoid space and the subpial space is unique to the brain’s arteries, as no leptomeningeal layers surround the brain’s veins. Use of the scanning electron microscope has determined that the spaces surrounding blood vessels in the subarachnoid space are not continuous with the subarachnoid space because of the presence of pia mater cells joined by desmosomes.