Perivascular space

Perivascular spaces (PVS), also known as Virchow-Robin (VR) spaces, are pial lined interstitial fluid filled spaces in the brain that surround perforating vessels. They do not have a direct connection with the subarachnoid space and in fact the fluid within them is slightly different to CSF.

On imaging they appear as as smoothly demarcated fluid-filled cysts, typically less than 5 mm in diameter, showing the same CSF attenuation or intensity and often found in the basal ganglia or midbrain.

When PVS are very numerous the brain can have a colander-like appearance referred to as etat crible (as opposed to numerous lacunes = etat lacunaire).

Overall PVSs are very common, and increasingly seen with better MRI image quality. Depending on your definition, they are seen in 50-100% of patients 2-3 and their relevance is mainly in not mistaking them for pathology.

They are usually asymptomatic. 

PVSs consist of a single or double layer of invaginated pia 8. They are typically less than 5 mm in diameter, but can reach much larger sizes, so called giant perivascular space or tumefactive perivascular space, and can exert enough mass effect to be symptomatic 1. They tend to enlarge with age and with hypertension. When very numerous the brain can have a colander-like appearance referred to as etat crible (as opposed to numerous lacunes = etat lacunaire).

Location

Most commonly they are located in the lower half of the basal ganglia especially in the anterior perforated substance along the line of the anterior commissure 3. They are also found in 1:

The cortical regions are spared. In contrast to lacunar infarcts encountered more frequently in the upper half of the putamen, perivascular spaces are seen more often in the lower half.

A special type of perivascular spaces occur in the anterior temporal lobe and can mimic cystic tumours. These are discussed separately: anterior temporal lobe perivascular spaces 9-10

Types

​​Perivascular spaces are divided into three main types 4:

  • 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 gray matter
  • type 3: located in the midbrain
Associations

They are usually idiopathic, although they are seen in greater frequency in 1,4,11:

Complications

Rarely they can cause obstructive hydrocephalus.

As they are filled with fluid similar to CSF perivascular spaces have appearances akin to water on all imaging modalities and sequences. Differentiating them from foci of encephalomalacia that result from chronic lacunar infarcts can be challenging but is important as imaging findings of ischaemia can lead to patients being put on medication such as antiplatelets therapy.

Perivascular spaces should be considered if:

  • the patients are young,
  • there is an absence of vascular risk factors, and
  • there no other changes of chronic small vessel ischaemia.
CT
  • well circumscribed fluid density spaces
  • no enhancement
  • no calcification
  • CT angiography occasionally demonstrates a traversing vessel
MRI

They follow CSF signal on all pulse sequences 7. When small the adjacent white matter is normal, thus helping to distinguish PVS from lacunar infarcts which have surrounding gliosis.

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

  • content pending

For small "run of the mill" PVSs consider:

For giant PVSs consider:

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Article Information

rID: 1863
Section: Pathology
Synonyms or Alternate Spellings:
  • Perivascular space
  • Virchow Robin spaces
  • VR spaces
  • Peri-vascular spaces
  • Peri vascular spaces
  • Virchow Robin spaces (VRS)
  • VRS
  • VR space
  • Perivascular spaces
  • Virchow-Robin space
  • Virchow-Robin spaces

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