Perivascular spaces, also known as Virchow-Robin spaces, are naturally occurring, fluid-filled channels that surround blood vessels as they travel through the brain tissue. These microscopic areas are a normal part of the brain’s complex network, playing a role in its overall fluid dynamics. They contain interstitial fluid and are considered extensions of the subarachnoid space, which encases the brain and spinal cord in cerebrospinal fluid.
Where Perivascular Spaces Are Found
Perivascular spaces are microscopic channels that accompany small blood vessels, including arteries, arterioles, capillaries, and venules, as they penetrate the brain’s surface and extend into the deeper brain tissue. These spaces essentially form a sheath around the vessels, separating them from the surrounding brain cells. They are a normal anatomical feature of every brain.
These spaces are found throughout the brain, with some areas showing a higher prevalence or larger size. They are commonly observed surrounding perforating arteries in the basal ganglia, a deep brain structure involved in movement control, and within the white matter of the cerebrum, particularly in the centrum semiovale. The outer boundary of these spaces is formed by the glia limitans, a layer of glial cells called astrocytes, while the inner boundary is the basement membrane of the blood vessel itself.
How Perivascular Spaces Maintain Brain Health
Perivascular spaces are a component of the brain’s waste clearance system, often referred to as the glymphatic system. This system functions like a specialized plumbing network for the brain, helping to remove metabolic waste products, toxins, and excess proteins that accumulate during normal brain activity. Cerebrospinal fluid (CSF) flows from the subarachnoid space into these perivascular channels, propelled by arterial pulsations.
As CSF moves through the perivascular spaces, it mixes with interstitial fluid, which is the fluid surrounding brain cells. This fluid exchange helps to flush out waste molecules, including amyloid-beta and tau proteins, which are implicated in neurodegenerative diseases like Alzheimer’s. The fluid then drains along perivenous spaces, eventually exiting the brain and reaching the lymphatic system in the neck. This clearance process is significantly more active during sleep.
Beyond waste removal, perivascular spaces also play roles in nutrient transport and immune surveillance. They facilitate the delivery of glucose, lipids, and signaling molecules throughout the brain. These spaces also contain immune cells, such as macrophages, which contribute to the brain’s defense against pathogens.
Understanding Enlarged Perivascular Spaces
Enlarged perivascular spaces (EPVS) are a common finding on brain imaging, particularly magnetic resonance imaging (MRI), and are frequently observed as individuals age. They appear as small, fluid-filled areas, typically less than 5 millimeters in diameter, that follow the path of blood vessels. While a few enlarged spaces are considered normal at any age, their number generally increases with advancing age.
Several factors can contribute to the enlargement of these spaces. Age-related changes, such as arterial stiffening and brain atrophy, contribute. High blood pressure (hypertension) is also associated with an increased number and faster enlargement of perivascular spaces. Additionally, certain conditions like cerebral small vessel disease, which affects the small blood vessels in the brain, can be linked to EPVS.
While EPVS can be associated with some neurological conditions, such as certain forms of dementia or stroke, their presence does not automatically indicate a serious problem. They are often seen in healthy individuals without any cognitive impairment or other symptoms. Research continues to explore the exact relationship between EPVS and various brain disorders, balancing their commonality with potential clinical significance.