Perivascular spaces

Last revised by Rohit Sharma on 23 Mar 2024

Perivascular spaces, also known as Virchow-Robin spaces are fluid-filled spaces that surround small arterioles, capillaries and venules in the brain. Those that surround perforating vessels are frequently seen on routine MRI imaging. 

Despite having been described well over a century ago and seen routinely in the majority of MRI studies, significant uncertainty and controversy continue to exist surrounding their anatomy and function. 

Their importance can be broadly divided into:

  1. perivascular cysts: larger rounded perivascular spaces mimicking lacunae or cystic lesions

  2. perivascular spaces: smaller linear fluid-intensity structures relevant to neurodegenerative disease (e.g. Alzheimer disease

When perivascular spaces are very numerous the brain can have a colander-like appearance, referred to as état criblé (as opposed to numerous lacunar infarcts, sometimes referred to as état lacunaire).

When perivascular spaces are very large, they are referred to as tumefactive perivascular spaces

When located in the anterior temporal lobe and related to a vascular loop, they are known as anterior temporal lobe perivascular spaces; however, these likely represent a different entity compared to typical scattered perivascular spaces.

Perivascular spaces are very common, and increasingly seen with better MRI image resolution. Depending on defining criteria, they are seen in 50-100% of patients 2,3.

Previously, enlarged perivascular spaces were believed to be entirely incidental findings, mostly significant so as not to be mistaken for a more sinister pathology. 

More recently, studies have suggested an association between extensive basal ganglia perivascular spaces (état criblé) and changes of chronic microvascular ischemic disease 12-14,20. This is related to the observation that, although a few scattered perivascular spaces are a nearly ubiquitous imaging finding, the number and prominence of these spaces increases with aging, along with other findings of microvascular disease, e.g. periventricular white matter lesions and lacunar infarcts. The association remains controversial 14.

Similarly, the association of enlarged perivascular spaces with subsequent development of dementia has been reported but variably so 20

Enlarged perivascular spaces have also been reported with greater frequency in a variety of settings, albeit generally in smaller size cohorts 1,4,11,20:

Perivascular spaces are normal anatomical structures. Even when enlarged they are almost invariably asymptomatic, even when quite large. Rarely, they can cause mass-effect and can result in obstructive hydrocephalus.

More recently it has been postulated that an increased number of perivascular spaces may be a marker of evolving neurodegenerative diseases, including Alzheimer disease and Parkinson disease 18. The relationship between prominent perivascular spaces and disease remains poorly understood 18

Perivascular spaces are normal, usually microscopic structures, that consist of a single or double layer of invaginated pia and basement membrane - depending on location -  surrounding small cerebral blood vessels 8,14,20

Perivascular spaces that surround perforating arteries at the base of the skull, extending into the basal ganglia and internal capsule appear to communicate directly with the subarachnoid space, and thus are presumably filled with CSF, whereas those that surround perforating vessels in the subcortical white matter appear to remain subpial and are thus presumably filled with interstitial fluid 20,21

Perivascular spaces which are visible on imaging take on two forms, either thin linear regions, most commonly seen in the centrum semiovale or more oval or cystic appearing spaces, typically less than 5 mm in diameter, most often seen at the base of the brain. These cystic perivascular spaces can reach much larger sizes, so-called "giant" perivascular space or tumefactive perivascular space, and can exert enough mass effect to be symptomatic 1

Perivascular spaces and cysts are filled with fluid similar to CSF in an appearance on all imaging modalities and sequences. There is no clear cutoff between a visible perivascular space and a cystic perivascular space as they appear to exist along a continuum. 

Perivascular spaces are seen as linear regions of high T2 signal, most frequently seen in the basal ganglia long perforating arteries and in the subcortical white matter. 

Perivascular cysts are rounded, sometimes seen surrounding a vessel with smooth margins. They are divided into three main types, although a type 4 has been recently suggested 4,19:

  • type 1: located in the area supplied by the lenticulostriate arteries entering the basal ganglia

  • type 2: located in the area supplied by the perforating medullary arteries as they enter the cortical grey matter

  • type 3: located in the midbrain

  • type 4: temporal pole, insular - see anterior temporal lobe perivascular spaces 9,10,19

  • well-circumscribed fluid-density spaces

  • no enhancement

  • no calcification

  • CT angiography occasionally demonstrates a traversing vessel

They follow CSF signal on all pulse sequences 7. When small, the adjacent white matter is normal, thus helping to distinguish perivascular spaces from lacunar infarcts, which have surrounding gliosis (best seen on T2 FLAIR sequence). 

In a minority of cases, especially when they are large, a thin increased T2-signal halo may be seen. Usually, they will have a positive mass effect. On T2 sequences, a traversing vessel is sometimes seen.

The exception to the 'no surrounding high T2 signal' rule is anterior temporal lobe perivascular spaces 9,10

Perivascular spaces were first described by Durand-Fardel (1842) - who described état criblé  - and Pestalozzi (1849) 20.

Virchow-Robin spaces are named after German pathologist Rudolf Virchow (1821–1902) 15 and French anatomist Charles-Philippe Robin (1821–1885) who described them further in 1851 and 1859, respectively 16,20. Interestingly, Virchow and Robin disagreed on whether or not these spaces directly communicated with the subarachnoid space. Over a century and a half later, this remains an unresolved question 20

For small perivascular spaces, consider:

For giant perivascular spaces consider:

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