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.
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).
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:
- substantia nigra
- dentate nucleus
- subinsular region: "subinsular bright spots"
- corpus callosum and cingulate gyrus
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.
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
They are usually idiopathic, although they are seen in greater frequency in 1,4,11:
- mucopolysaccharidoses, e.g. Hunter disease, Hurler disease
- some muscular dystrophies
- traumatic brain injury
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.
- 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 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.
History and etymology
- content pending
For small "run of the mill" PVSs consider:
- choroid fissure cyst
- rim of gliosis seen best on FLAIR 8
- neutral or negative mass effect
- typically upper two-thirds of basal ganglia (due to infarcts of perforating end arteries)
chronic small vessel ischaemic disease
- typically periventricular and subcortical
- cyst with a dot sign
- CNS cryptococcosis: if multiple
For giant PVSs consider:
- 1. Salzman KL, Osborn AG, House P et-al. Giant tumefactive perivascular spaces. AJNR Am J Neuroradiol. 2005;26 (2): 298-305. AJNR Am J Neuroradiol (full text) - Pubmed citation
- 2. Song CJ, Kim JH, Kier EL et-al. MR imaging and histologic features of subinsular bright spots on T2-weighted MR images: Virchow-Robin spaces of the extreme capsule and insular cortex. Radiology. 2000;214 (3): 671-7. Radiology (full text) - Pubmed citation
- 3. Jungreis CA, Kanal E, Hirsch WL et-al. Normal perivascular spaces mimicking lacunar infarction: MR imaging. Radiology. 1988;169 (1): 101-4. Radiology (abstract) - Pubmed citation
- 4. Kwee RM, Kwee TC. Virchow-Robin spaces at MR imaging. Radiographics. 2007;27 (4): 1071-86. doi:10.1148/rg.274065722 - Pubmed citation
- 5. Ogawa T, Okudera T, Fukasawa H et-al. Unusual widening of Virchow-Robin spaces: MR appearance. AJNR Am J Neuroradiol. 1995;16 (6): 1238-42. Pubmed citation
- 6. Papayannis CE, Saidon P, Rugilo CA et-al. Expanding Virchow Robin spaces in the midbrain causing hydrocephalus. AJNR Am J Neuroradiol. 2003;24 (7): 1399-403. Pubmed citation
- 7. Brant WE, Helms CA. Fundamentals of Diagnostic Radiology. Lippincott Williams & Wilkins. (2007) ISBN:0781761352. Read it at Google Books - Find it at Amazon
- 8. Osborn AG, Preece MT. Intracranial cysts: radiologic-pathologic correlation and imaging approach. Radiology. 2006;239 (3): 650-64. Radiology (full text) - doi:10.1148/radiol.2393050823 - Pubmed citation
- 9. Rawal S, Croul SE, Willinsky RA et-al. Subcortical cystic lesions within the anterior superior temporal gyrus: a newly recognized characteristic location for dilated perivascular spaces. AJNR Am J Neuroradiol. 2014;35 (2): 317-22. doi:10.3174/ajnr.A3669 - Pubmed citation
- 10. Lim AT, Chandra RV, Trost NM et-al. Large anterior temporal Virchow-Robin spaces: unique MR imaging features. Neuroradiology. 2015;57 (5): 491-9. doi:10.1007/s00234-015-1491-y - Pubmed citation
- 11. Inglese M, Bomsztyk E, Gonen O et-al. Dilated perivascular spaces: hallmarks of mild traumatic brain injury. AJNR Am J Neuroradiol. 2005;26 (4): 719-24. AJNR Am J Neuroradiol (full text) - Pubmed citation