Perivascular spaces

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Perivascular spaces, also known as Virchow-Robin 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 a slightly different composition as compared to CSF.

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

Terminology

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

Epidemiology

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

Clinical features

They are usuallyalmost invariably asymptomatic, even when quite large. Rarely, they can cause mass effect and even result in obstructive hydrocephalus.

Pathology

Perivascular spaces 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, a so called-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, perivascular spaces 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 space occurs in the anterior temporal lobe and can mimic a cystic tumour. 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 grey 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.

Radiographic features

As they are filled with a 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 antiplatelet therapy.

Perivascular spaces should be considered if:

  • patient is young
  • absence of vascular risk factors
  • 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 perivascular spaces from lacunar infarcts, which have surrounding gliosis (best seen on T2 FLAIR sequence). 

Although generally cyst-like on axial sequences, on sagittal and coronal sequences a linear radiating morphology may be seen consistent with their role in surrounding vessels.

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 are anterior temporal lobe perivascular spaces9-10. 

History and etymology

Virchow-Robin spaces are named after German pathologist Rudolf Virchow (1821–1902) and French anatomist Charles Philippe Robin (1821–1885).

Differential diagnosis

For small perivascular spaces, consider:

For giant perivascular spaces consider:

  • -<p><strong>Perivascular spaces</strong>, also known as <strong>Virchow-Robin spaces</strong>, 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 a slightly different composition as compared to CSF.</p><p>On axial imaging, they appear as smoothly demarcated fluid-filled cysts, typically less than 5 mm in diameter, showing the same attenuation or intensity as CSF and often found in the basal ganglia or midbrain.</p><h4>Terminology</h4><p>When perivascular spaces are very numerous the brain can have a colander-like appearance, referred to as <a href="/articles/tat-crible">état criblé</a> (as opposed to numerous lacunes, sometimes referred to as <a href="/articles/tat-lacunaire">état lacunaire</a>).</p><h4>Epidemiology</h4><p>Overall perivascular spaces are very common, and increasingly seen with better MRI image quality. Depending on the definition, they are seen in 50-100% of patients <sup>2-3</sup> and their relevance is mainly in not mistaking them for pathology.</p><h4>Clinical features</h4><p>They are usually asymptomatic. </p><h4>Pathology</h4><p>Perivascular spaces consist of a single or double layer of invaginated pia <sup>8</sup>. They are typically less than 5 mm in diameter but can reach much larger sizes, a so called giant perivascular space or <a href="/articles/tumefactive-perivascular-spaces-1">tumefactive perivascular space</a>, and can exert enough mass effect to be symptomatic <sup>1</sup>. They tend to enlarge with age and with hypertension. When very numerous the brain can have a colander-like appearance referred to as <a href="/articles/tat-crible">etat crible</a> (as opposed to numerous lacunes = <a href="/articles/tat-lacunaire">etat lacunaire</a>).</p><h5>Location</h5><p>Most commonly, perivascular spaces are located in the lower half of the <a href="/articles/basal-ganglia">basal ganglia</a>, especially in the anterior perforated substance along the line of the anterior commissure <sup>3</sup>. They are also found in <sup>1</sup>:</p><ul>
  • +<p><strong>Perivascular spaces</strong>, also known as <strong>Virchow-Robin spaces</strong>, 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 a slightly different composition as compared to CSF.</p><p>On axial imaging, they appear as smoothly demarcated fluid-filled cysts, typically less than 5 mm in diameter, showing the same attenuation or intensity as CSF and often found in the basal ganglia or midbrain.</p><h4>Terminology</h4><p>When perivascular spaces are very numerous the brain can have a colander-like appearance, referred to as <a href="/articles/tat-crible">état criblé</a> (as opposed to numerous lacunes, sometimes referred to as <a href="/articles/tat-lacunaire">état lacunaire</a>).</p><h4>Epidemiology</h4><p>Overall perivascular spaces are very common, and increasingly seen with better MRI image quality. Depending on the definition, they are seen in 50-100% of patients <sup>2-3</sup> and their relevance is mainly in not mistaking them for pathology.</p><h4>Clinical features</h4><p>They are almost invariably asymptomatic, even when quite large. Rarely, they can cause mass effect and even result in <a href="/articles/obstructive-hydrocephalus">obstructive hydrocephalus</a>.</p><h4>Pathology</h4><p>Perivascular spaces consist of a single or double layer of invaginated pia <sup>8</sup>. They are typically less than 5 mm in diameter but can reach much larger sizes, a so-called giant perivascular space or <a href="/articles/tumefactive-perivascular-spaces-1">tumefactive perivascular space</a>, and can exert enough mass effect to be symptomatic <sup>1</sup>. They tend to enlarge with age and with hypertension. When very numerous the brain can have a colander-like appearance referred to as <a href="/articles/tat-crible">etat crible</a> (as opposed to numerous lacunes = <a href="/articles/tat-lacunaire">etat lacunaire</a>).</p><h5>Location</h5><p>Most commonly, perivascular spaces are located in the lower half of the <a href="/articles/basal-ganglia">basal ganglia</a>, especially in the anterior perforated substance along the line of the anterior commissure <sup>3</sup>. They are also found in <sup>1</sup>:</p><ul>
  • -<li>some muscular dystrophies</li>
  • -<li>traumatic brain injury</li>
  • -</ul><h5>Complications</h5><p>Rarely, they can cause <a href="/articles/obstructive-hydrocephalus">obstructive hydrocephalus</a>.</p><h4>Radiographic features</h4><p>As they are filled with a 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 antiplatelet therapy.</p><p>Perivascular spaces should be considered if:</p><ul>
  • +<li>some <a title="muscular dystrophy" href="/articles/muscular-dystrophy">muscular dystrophies</a>
  • +</li>
  • +<li><a title="Traumatic brain injury" href="/articles/traumatic-brain-injury">traumatic brain injury​</a></li>
  • +</ul><h4>Radiographic features</h4><p>As they are filled with a 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 antiplatelet therapy.</p><p>Perivascular spaces should be considered if:</p><ul>
  • -</ul><h5>MRI</h5><p>They follow CSF signal on all pulse sequences <sup>7</sup>. When small, the adjacent white matter is normal, thus helping to distinguish perivascular spaces from lacunar infarcts, which have surrounding <a href="/articles/gliosis">gliosis</a> (best seen on T2 FLAIR sequence). </p><p>Although generally cyst-like on axial sequences, on sagittal and coronal sequences a linear radiating morphology may be seen consistent with their role in surrounding vessels.</p><p>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.</p><h4>History and etymology</h4><p>Virchow-Robin spaces are named after German pathologist <strong>Rudolf Virchow</strong> (1821–1902) and French anatomist <strong>Charles Philippe Robin</strong> (1821–1885).</p><h4>Differential diagnosis</h4><p>For small perivascular spaces, consider:</p><ul>
  • +</ul><h5>MRI</h5><p>They follow CSF signal on all pulse sequences <sup>7</sup>. When small, the adjacent white matter is normal, thus helping to distinguish perivascular spaces from lacunar infarcts, which have surrounding <a href="/articles/gliosis">gliosis</a> (best seen on T2 FLAIR sequence). </p><p>Although generally cyst-like on axial sequences, on sagittal and coronal sequences a linear radiating morphology may be seen consistent with their role in surrounding vessels.</p><p>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.</p><p>The exception to the 'no surrounding high T2 signal' rule is are <a href="/articles/anterior-temporal-lobe-perivascular-spaces">anterior temporal lobe perivascular spaces</a> <sup>9-10</sup>. </p><h4>History and etymology</h4><p>Virchow-Robin spaces are named after German pathologist <strong>Rudolf Virchow</strong> (1821–1902) and French anatomist <strong>Charles Philippe Robin</strong> (1821–1885).</p><h4>Differential diagnosis</h4><p>For small perivascular spaces, consider:</p><ul>
  • -<a href="/articles/cns-cryptococcosis-1">CNS cryptococcosis</a>: if multiple</li>
  • +<a href="/articles/cns-cryptococcosis-2">CNS cryptococcosis</a>: if multiple</li>
  • -<li>cystic neoplasm(s) <sup>1,8</sup><ul><li>they rarely exhibit similar CSF intensity on all MRI sequences</li></ul>
  • +<li>cystic neoplasms <sup>1,8</sup><ul><li>they rarely exhibit similar CSF intensity on all MRI sequences</li></ul>

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