[4] Perivascular spaces are gaps containing interstitial fluid that span between blood vessels and their host organ, such as the brain, which they penetrate and serve as extravascular channels through which solutes can pass.

[8] Perivascular spaces, especially around fenestrated capillaries, are found in many organs, such as the thymus, liver, kidneys, spleen, bones, and pineal gland.

[17] While the BBB is often described as the tight junctions between the endothelial cells, this is an oversimplification that neglects the intricate role that perivascular spaces take in separating the venous blood from the parenchyma of the brain.

This holds true for many T and B cells, as well as monocytes, giving this small fluid filled space an important immunological role.

[17] Perivascular spaces also play an important role in immunoregulation; they not only contain interstitial and cerebrospinal fluid, but they also have a constant flux of macrophages, which is regulated by blood-borne mononuclear cells, but do not pass the basement membrane of the glia limitans.

[5] Upon the clinical application of MRI, it was shown in several studies that perivascular space dilation and lacunar strokes are the most commonly observed histological correlates of signaling abnormalities.

Dilation of perivascular spaces has been shown to correlate best with age, even when accompanying factors including hypertension, dementia, and white matter lesions are considered.

[20] In the elderly, such dilation has been correlated with many symptoms and conditions that often affect the arterial walls, including vascular hypertension, arteriosclerosis, reduced cognitive capacity, dementia, and low post-mortem brain weight.

In cases of severe dilation in only one hemisphere, symptoms reported include a non-specific fainting attack, hypertension, positional vertigo, headache, early recall disturbances, and hemifacial tics.

Symptoms associated with severe bilateral dilation include ear pain (which was reported to have resolved on its own), dementia, and seizures.

[13] Other general symptoms associated with VRS dilation include headaches, dizziness, memory impairment, poor concentration, dementia, visual changes, oculomotor abnormality, tremors, seizures, limb weakness, and ataxia.

There is a fourth miscellaneous group of disorders typically associated with dilation that includes autism in children, megalencephalopathy, secondary Parkinson's disease, recent-onset multiple sclerosis, and chronic alcoholism.

[13] In addition, insufficient fluid draining and injury to ischemic perivascular tissue resulting in an ex vacuo effect have been suggested as possible causes for dilated VRS.

At one point in time, dilated Virchow–Robin spaces were so commonly noted in autopsies of persons with dementia, they were believed to cause the disease.

However, additional research is currently being performed in order to confirm or refute a direct connection between dilation of VRS and dementia.

[24] Cerebral amyloid angiopathy (CAA), a blood vessel failure often associated with Alzheimer's disease, utilizes dilated VRS to spread inflammation to the parenchyma.

In support of this hypothesis, studies have noted the greater frequency of β-amyloid plaques in the cerebral cortex than in the basal ganglia of Alzheimer's disease patients.

[8] Because dilated perivascular spaces are so closely correlated with cerebrovascular disease, there is much current research on their use as a diagnostic tool.

Studies have noted that in comparison to family members lacking the affected haplotype that leads to the condition, an increased number of dilated spaces is observed in individuals with CADASIL.

These perivascular spaces are localized primarily in the putamen and temporal subcortical white matter and they appear to correlate with age of the individual with the condition rather than severity of the disease itself.

[13] Similar to the research concerning a potential connection between perivascular spaces and Alzheimer's, MRI scans of people recently diagnosed with multiple sclerosis (MS) have been studied.

The immunological significance was discovered by Wilhelm His, Sr. in 1865 based on his observations of the flow of interstitial fluid over the spaces to the lymphatic system.

Upon the application of MRI, measurements of the differences of signal intensity between the perivascular spaces and cerebrospinal fluid supported these findings.