DOI: 10.1148/rg.274065722
RadioGraphics 2007;27:1071-1086
© RSNA, 2007
Virchow-Robin Spaces at MR Imaging1
Robert M. Kwee, MD and
Thomas C. Kwee, MD
1 From the Department of Radiology, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX Utrecht, the Netherlands. Received July 25, 2006; revision requested October 24 and received November 30; accepted December 4. All authors have no financial relationships to disclose.
Address correspondence to R.M.K. (e-mail: rmkwee{at}gmail.com).
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Abstract
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Virchow-Robin (VR) spaces surround the walls of vessels as they course from the subarachnoid space through the brain parenchyma. Small VR spaces appear in all age groups. With advancing age, VR spaces are found with increasing frequency and larger apparent sizes. At visual analysis, the signal intensity of VR spaces is identical to that of cerebrospinal fluid with all magnetic resonance imaging sequences. Dilated VR spaces typically occur in three characteristic locations: Type I VR spaces appear along the lenticulostriate arteries entering the basal ganglia through the anterior perforated substance. Type II VR spaces are found along the paths of the perforating medullary arteries as they enter the cortical gray matter over the high convexities and extend into the white matter. Type III VR spaces appear in the midbrain. Occasionally, VR spaces have an atypical appearance. They may become very large, predominantly involve one hemisphere, assume bizarre configurations, and even cause mass effect. Knowledge of the signal intensity characteristics and locations of VR spaces helps differentiate them from various pathologic conditions, including lacunar infarctions, cystic periventricular leukomalacia, multiple sclerosis, cryptococcosis, mucopolysaccharidoses, cystic neoplasms, neurocysticercosis, arachnoid cysts, and neuroepithelial cysts.
© RSNA, 2007
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Introduction
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The Virchow-Robin (VR) space is named after Rudolf Virchow (German pathologist, 1821–1902) (1) and Charles Philippe Robin (French anatomist, 1821–1885) (2). VR spaces, or perivascular spaces, surround the walls of vessels as they course from the subarachnoid space through the brain parenchyma. VR spaces are commonly seen at magnetic resonance (MR) imaging and may sometimes be difficult to differentiate from pathologic conditions. Knowledge of their signal intensity characteristics and localization helps in this differentiation, which is important for correct patient management.
The purpose of this article is to provide an in-depth overview of the MR imaging features of VR spaces. Specific topics outlined are the microscopic anatomy of VR spaces, dilated VR spaces, prevalence, and normal and atypical appearance of VR spaces. Subsequently, differential diagnostic considerations are discussed.
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Anatomy
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VR spaces surround the walls of arteries, arterioles, veins, and venules as they course from the subarachnoid space through the brain parenchyma (Fig 1) (1–5). Electron microscopy and tracer studies have given insight into the location of VR spaces and clarified that the subarachnoid space does not communicate directly with the VR spaces (3–5).
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Figure 1. Photomicrograph (original magnification, x20; hematoxylin-eosin stain) of a coronal section through the anterior perforated substance shows two arteries (straight arrows) with surrounding VR spaces (curved arrows).
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Arteries in the cerebral cortex are coated by a layer of leptomeninges that is subtended from the pia mater; by this anatomic arrangement, the VR spaces of the intracortical arteries are in direct continuity with the VR spaces around arteries in the subarachnoid space (Fig 2). The lack of a similar coating of leptomeningeal cells around veins in the cerebral cortex suggests that VR spaces around veins are in continuity with the subpial space (4).
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Figure 2. Drawing shows a cortical artery with a surrounding VR space crossing from the subarachnoid and subpial spaces through the brain parenchyma. The magnified view on the right shows the anatomic relationship between the artery, VR space, subpial space, and brain parenchyma.
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In contrast to arteries in the cerebral cortex, arteries in the basal ganglia are surrounded by not one but two distinct coats of leptomeninges, separated by a VR space that is continuous with the VR space around arteries in the subarachnoid space. The inner layer of leptomeninges closely invests the adventitia of the vessel wall. The outer layer abuts on the glia limitans of the underlying brain and is continuous with the pia mater on the surface of the brain and the anterior perforated substance. Veins in the basal ganglia have no outer layer of leptomeninges (similar to cortical veins), which suggests that their VR spaces are continuous with the subpial space (5).
Interstitial fluid within the brain parenchyma drains from the gray matter of the brain by diffusion through the extracellular spaces and by bulk flow along VR spaces. There is evidence from tracer studies and from pathologic analysis of the human brain that VR spaces carry solutes from the brain and are, in effect, the lymphatic drainage pathways of the brain (6).
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Dilated VR Spaces
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Dilatation of VR spaces was described by Durant-Fardel (7) in 1843. These dilatations are regular cavities that always contain a patent artery. The mechanisms underlying expanding VR spaces are still unknown. Different theories have been postulated: segmental necrotizing angiitis of the arteries or another unknown condition causing permeability of the arterial wall (8–10), expanding VR spaces resulting from disturbance of the drainage route of interstitial fluid due to cerebrospinal fluid (CSF) circulation in the cistern (11,12), spiral elongation of blood vessels and brain atrophy resulting in an extensive network of tunnels filled with extracellular water (9,13), gradual leaking of the interstitial fluid from the intracellular compartment to the pial space around the metarteriole through the fenestrae in the brain parenchyma (14), and fibrosis and obstruction of VR spaces along the length of arteries and consequent impedance of fluid flow (5).
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Prevalence
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Small VR spaces (<2 mm) appear in all age groups. With advancing age, VR spaces are found with increasing frequency and larger apparent size (>2 mm) (15). Some studies found a correlation between dilated VR spaces and neuropsychiatric disorders (16–19), recent-onset multiple sclerosis (MS) (20), mild traumatic brain injury (21), and diseases associated with microvascular abnormalities (22).
The prevalence of VR spaces at MR imaging is also dependent on the applied technique. Heavier T2-weighted imaging results in better visualization of VR spaces (23). In addition, the use of thinner sections will demonstrate more VR spaces as well (15,24). Also, high-field-strength MR imaging is expected to have an increased clinical impact in the near future; the current magnetic field (
1.5 T) is likely to be switched to 3 or 4 T. The anticipated higher signal-to-noise ratio at higher magnetic field strengths may successfully improve spatial resolution and image contrast (25–27), leading to better visualization (and increased prevalence) of VR spaces on MR images.
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Appearance at MR Imaging
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Signal Intensity Characteristics
Visually, the signal intensities of the VR spaces are identical to those of CSF with all pulse sequences. However, when signal intensities are measured, the VR spaces prove to have significantly lower signal intensity than the CSF-containing structures within and around the brain (28), a finding consistent with the fact that the VR spaces represent entrapments of interstitial fluid. This difference in signal intensity can also be explained by partial volume effects, since a VR space with accompanying vessel is smaller than the contemporary volume of a voxel on MR images. VR spaces show no restricted diffusion on diffusion-weighted images because they are communicating compartments. T1-weighted images with substantial flow sensitivity may show high signal intensity due to inflow effects, thereby helping confirm that one is indeed dealing with VR spaces (29). VR spaces do not enhance with contrast material. In patients with small to moderate dilatations of the VR spaces (2–5 mm), the surrounding brain parenchyma generally has normal signal intensity (30,31).
Locations and Morphology
Dilated VR spaces typically occur in three characteristic locations. The first type (type I) is frequently seen on MR images and appears along the lenticulostriate arteries entering the basal ganglia through the anterior perforated substance (Figs 3, 4) (15,32). Here, the tortuous lenticulostriate arteries change direction from a lateral to a dorsomedial path and are grouped closely together. A proximal VR space, containing several vessels, is the resulting physiologic finding (33).
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Figure 3a. Bilateral type I VR spaces in a 6-year-old boy. (a) Axial proton-density–weighted image (repetition time msec/echo time msec = 2375/100) shows hyperintense areas (arrows) in the anterior perforated substance on both sides. (b) Axial fluid-attenuated inversion-recovery (FLAIR) image (6606/100) obtained at the same level shows that these areas have CSF-like content (arrows). The signal intensity of the surrounding brain parenchyma is normal. (c, d) Diffusion-weighted image (2574/81; b factor = 1000 sec/mm2) (c) and corresponding apparent diffusion coefficient map (d) show no restricted diffusion in these areas (arrows).
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Figure 3b. Bilateral type I VR spaces in a 6-year-old boy. (a) Axial proton-density–weighted image (repetition time msec/echo time msec = 2375/100) shows hyperintense areas (arrows) in the anterior perforated substance on both sides. (b) Axial fluid-attenuated inversion-recovery (FLAIR) image (6606/100) obtained at the same level shows that these areas have CSF-like content (arrows). The signal intensity of the surrounding brain parenchyma is normal. (c, d) Diffusion-weighted image (2574/81; b factor = 1000 sec/mm2) (c) and corresponding apparent diffusion coefficient map (d) show no restricted diffusion in these areas (arrows).
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Figure 3c. Bilateral type I VR spaces in a 6-year-old boy. (a) Axial proton-density–weighted image (repetition time msec/echo time msec = 2375/100) shows hyperintense areas (arrows) in the anterior perforated substance on both sides. (b) Axial fluid-attenuated inversion-recovery (FLAIR) image (6606/100) obtained at the same level shows that these areas have CSF-like content (arrows). The signal intensity of the surrounding brain parenchyma is normal. (c, d) Diffusion-weighted image (2574/81; b factor = 1000 sec/mm2) (c) and corresponding apparent diffusion coefficient map (d) show no restricted diffusion in these areas (arrows).
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Figure 3d. Bilateral type I VR spaces in a 6-year-old boy. (a) Axial proton-density–weighted image (repetition time msec/echo time msec = 2375/100) shows hyperintense areas (arrows) in the anterior perforated substance on both sides. (b) Axial fluid-attenuated inversion-recovery (FLAIR) image (6606/100) obtained at the same level shows that these areas have CSF-like content (arrows). The signal intensity of the surrounding brain parenchyma is normal. (c, d) Diffusion-weighted image (2574/81; b factor = 1000 sec/mm2) (c) and corresponding apparent diffusion coefficient map (d) show no restricted diffusion in these areas (arrows).
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The second type (type II) can be found along the path of the perforating medullary arteries as they enter the cortical gray matter over the high convexities and extend into the white matter (Figs 5, 6) (15,32).
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Figure 5a. Type II VR spaces in a 73-year-old woman. (a) Axial proton-density–weighted image (2376/100) shows multiple hyperintense foci in the centrum semiovale in both hemispheres. (b) On an axial FLAIR image (6614/100) obtained at the same level, the VR spaces are seen as hypointense dots without any surrounding high signal intensity. Note the two small lesions with a hypointense center and a hyperintense rim (arrows) in the left hemisphere; these lesions are not VR spaces but old lacunar infarctions.
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Figure 5b. Type II VR spaces in a 73-year-old woman. (a) Axial proton-density–weighted image (2376/100) shows multiple hyperintense foci in the centrum semiovale in both hemispheres. (b) On an axial FLAIR image (6614/100) obtained at the same level, the VR spaces are seen as hypointense dots without any surrounding high signal intensity. Note the two small lesions with a hypointense center and a hyperintense rim (arrows) in the left hemisphere; these lesions are not VR spaces but old lacunar infarctions.
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Figure 6a. Type II dilated VR spaces in a 6-year-old boy. (a) Axial T2-weighted image (2620/100) shows linear to punctate hyperintense areas around the occipital horns, especially on the left side (arrow). (b) FLAIR image (7572/100) obtained at the same level shows no abnormal signal intensity (arrow), in accordance with the fact that these areas are true VR spaces.
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Figure 6b. Type II dilated VR spaces in a 6-year-old boy. (a) Axial T2-weighted image (2620/100) shows linear to punctate hyperintense areas around the occipital horns, especially on the left side (arrow). (b) FLAIR image (7572/100) obtained at the same level shows no abnormal signal intensity (arrow), in accordance with the fact that these areas are true VR spaces.
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The third type (type III) appears in the midbrain. In the lower midbrain, VR spaces at the pontomesencephalic junction surround the penetrating branches of the collicular and accessory collicular arteries (Figs 7, 8). They are mainly located between the cerebral peduncles in the axial plane and correspond to the level of the tentorial margin as seen in coronal sections. In the upper midbrain, where the VR spaces are visible at the mesencephalodiencephalic junction, they appear along the posterior (interpeduncular) thalamoperforating artery or the paramedian mesencephalothalamic artery and short and long circumferential arteries originating from the upper basilar artery or proximal posterior cerebral artery (23,34,35).
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Figure 7a. Type III VR space in a 25-year-old man. (a) Axial proton-density–weighted image (2620/100) shows a hyperintense spot in the brainstem (arrow). (b) Axial FLAIR image (7292/120) obtained at the same level shows that the spot has CSF-like content without abnormal surrounding signal intensity (arrow). These findings confirm that the spot is a VR space.
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Figure 7b. Type III VR space in a 25-year-old man. (a) Axial proton-density–weighted image (2620/100) shows a hyperintense spot in the brainstem (arrow). (b) Axial FLAIR image (7292/120) obtained at the same level shows that the spot has CSF-like content without abnormal surrounding signal intensity (arrow). These findings confirm that the spot is a VR space.
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Figure 8a. Type III VR spaces in a 68-year-old man. (a) Axial proton-density–weighted image (2382/100) shows multiple punctate hyperintense areas in the brainstem (arrow). (b) Close-up T2-weighted image (4615/120) clearly shows the fine punctate pattern. (c) Axial FLAIR image (6609/100) shows the CSF-like content of the dots (arrow). No surrounding high signal intensity is seen. The typical configuration and the fact that no high signal intensity is seen on the FLAIR image confirm that the dots are VR spaces.
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Figure 8b. Type III VR spaces in a 68-year-old man. (a) Axial proton-density–weighted image (2382/100) shows multiple punctate hyperintense areas in the brainstem (arrow). (b) Close-up T2-weighted image (4615/120) clearly shows the fine punctate pattern. (c) Axial FLAIR image (6609/100) shows the CSF-like content of the dots (arrow). No surrounding high signal intensity is seen. The typical configuration and the fact that no high signal intensity is seen on the FLAIR image confirm that the dots are VR spaces.
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Figure 8c. Type III VR spaces in a 68-year-old man. (a) Axial proton-density–weighted image (2382/100) shows multiple punctate hyperintense areas in the brainstem (arrow). (b) Close-up T2-weighted image (4615/120) clearly shows the fine punctate pattern. (c) Axial FLAIR image (6609/100) shows the CSF-like content of the dots (arrow). No surrounding high signal intensity is seen. The typical configuration and the fact that no high signal intensity is seen on the FLAIR image confirm that the dots are VR spaces.
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VR spaces are mostly seen as well-defined oval, rounded, or tubular structures, depending on the plane in which they are intersected. They have smooth margins, commonly appear bilaterally, and usually measure 5 mm or less (32).
Atypical VR Spaces
It is reported that clusters of type II enlarged VR spaces may predominantly involve one hemisphere (36). There are even reports that describe the solely unilateral appearance of enlarged VR spaces in the high convexity (37,38).
Occasionally, VR spaces appear markedly enlarged, cause mass effect, and assume bizarre cystic configurations that may be misinterpreted as other pathologic processes, most often a cystic neoplasm. As most of these giant VR spaces border a ventricle or subarachnoid space, reports of such cases (39–41) have offered an extensive differential diagnosis that includes cystic neoplasms, parasitic cysts, cystic infarctions, nonneoplastic neuroepithelial cysts, and deposition disorders such as mucopolysaccharidosis. Salzman et al (42) presented a series of 37 patients with giant VR spaces. These spaces most often appear as clusters of variably sized cysts and are most common in the mesencephalothalamic region (Fig 9), in the territory of the paramedial mesencephalothalamic artery, and in the cerebral white matter. Giant VR spaces in the mesencephalothalamic region may cause hydrocephalus by direct compression of the third ventricle or the sylvian aqueduct (Fig 9), requiring surgical intervention (8,11,42–47).
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Figure 9a. Giant VR spaces in the mesencephalothalamic region in a 19-year-old man. (a, b) Axial (a) and sagittal (b) T2-weighted images (5970/120) show a multicystic lesion in the mesencephalothalamic region. The lesion extends from the left cerebral peduncle to the left thalamus. The content of the cysts is CSF-like. The adjacent brain parenchyma has normal signal intensity. No solid components are identified. (c) Axial gadolinium-enhanced T1-weighted image (478/18) shows no enhancement. The process has caused obstruction of the sylvian aqueduct, resulting in hydrocephalus. The size of the lesion and the degree of hydrocephalus were unchanged compared with the appearance on MR images obtained 2 years earlier.
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Figure 9b. Giant VR spaces in the mesencephalothalamic region in a 19-year-old man. (a, b) Axial (a) and sagittal (b) T2-weighted images (5970/120) show a multicystic lesion in the mesencephalothalamic region. The lesion extends from the left cerebral peduncle to the left thalamus. The content of the cysts is CSF-like. The adjacent brain parenchyma has normal signal intensity. No solid components are identified. (c) Axial gadolinium-enhanced T1-weighted image (478/18) shows no enhancement. The process has caused obstruction of the sylvian aqueduct, resulting in hydrocephalus. The size of the lesion and the degree of hydrocephalus were unchanged compared with the appearance on MR images obtained 2 years earlier.
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Figure 9c. Giant VR spaces in the mesencephalothalamic region in a 19-year-old man. (a, b) Axial (a) and sagittal (b) T2-weighted images (5970/120) show a multicystic lesion in the mesencephalothalamic region. The lesion extends from the left cerebral peduncle to the left thalamus. The content of the cysts is CSF-like. The adjacent brain parenchyma has normal signal intensity. No solid components are identified. (c) Axial gadolinium-enhanced T1-weighted image (478/18) shows no enhancement. The process has caused obstruction of the sylvian aqueduct, resulting in hydrocephalus. The size of the lesion and the degree of hydrocephalus were unchanged compared with the appearance on MR images obtained 2 years earlier.
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In one-half of cases, giant VR spaces that occur in the white matter may have surrounding signal intensity abnormality on T2-weighted or FLAIR images (42). This may be viewed as a worrisome finding and in some cases has prompted the performance of tissue biopsy. However, the abnormal signal intensity stems from reactive gliosis surrounding the enlarged VR spaces and is not an ominous finding (47).
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Differential Diagnostic Considerations
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In this section, the top differential diagnoses of dilated VR spaces are discussed. MR imaging characteristics of each disease entity are summarized, and clues to differentiate them from normal VR spaces are given.
Lacunar Infarctions
Lacunar infarctions are small infarctions lying in deeper noncortical parts of the cerebrum and brainstem. They are caused by occlusion of penetrating branches that arise from the middle cerebral, posterior cerebral, and basilar arteries and less commonly from the anterior cerebral and vertebral arteries (48,49). Sites of predilection are the basal ganglia, thalamus, internal and external capsule, ventral pons, and periventricular white matter (Figs 10, 11) (48).
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Figure 10a. Chronic lacunar infarction of the pons in a 59-year-old man. (a) Axial proton-density–weighted image (2200/100) shows a hyperintense lesion in the pons (arrow). (b) Axial FLAIR image (6614/100) shows that the lesion has a hypointense center with a hyperintense rim (arrow), an appearance that reflects gliosis.
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Figure 10b. Chronic lacunar infarction of the pons in a 59-year-old man. (a) Axial proton-density–weighted image (2200/100) shows a hyperintense lesion in the pons (arrow). (b) Axial FLAIR image (6614/100) shows that the lesion has a hypointense center with a hyperintense rim (arrow), an appearance that reflects gliosis.
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Figure 11a. Acute and chronic lacunar infarctions in a 66-year-old man. (a) Axial proton-density–weighted image (2385/100) shows multiple high-signal-intensity lesions bilaterally in the basal ganglia, internal capsule, and thalamus (arrows). The signal intensity of the periventricular white matter is abnormally increased. (b) Axial FLAIR image (6608/100) shows multiple small high-signal-intensity lesions and hypointense lesions surrounded by hyperintense rims in the same region (arrows). (c) Apparent diffusion coefficient map shows a recent infarction in the posterior limb of the right internal capsule (arrow).
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Figure 11b. Acute and chronic lacunar infarctions in a 66-year-old man. (a) Axial proton-density–weighted image (2385/100) shows multiple high-signal-intensity lesions bilaterally in the basal ganglia, internal capsule, and thalamus (arrows). The signal intensity of the periventricular white matter is abnormally increased. (b) Axial FLAIR image (6608/100) shows multiple small high-signal-intensity lesions and hypointense lesions surrounded by hyperintense rims in the same region (arrows). (c) Apparent diffusion coefficient map shows a recent infarction in the posterior limb of the right internal capsule (arrow).
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Figure 11c. Acute and chronic lacunar infarctions in a 66-year-old man. (a) Axial proton-density–weighted image (2385/100) shows multiple high-signal-intensity lesions bilaterally in the basal ganglia, internal capsule, and thalamus (arrows). The signal intensity of the periventricular white matter is abnormally increased. (b) Axial FLAIR image (6608/100) shows multiple small high-signal-intensity lesions and hypointense lesions surrounded by hyperintense rims in the same region (arrows). (c) Apparent diffusion coefficient map shows a recent infarction in the posterior limb of the right internal capsule (arrow).
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In the upper two-thirds of the anterior perforated substance and basal ganglia, cavities in brain specimens usually appear to be lacunar infarctions. Large VR spaces found in the inferior third of the anterior perforated substance and basal ganglia are invariably VR spaces around branches of lenticulostriate arteries (type I VR spaces) (32).
Lacunar infarctions tend to be larger than VR spaces and often exceed 5 mm. However, no consistent cutoff value with high diagnostic accuracy has been reported in the literature, to our knowledge. In contrast to VR spaces, lacunar infarctions are generally not symmetric (30,32,33,50). It is difficult to distinguish lacunar infarctions from VR spaces by means of shape. However, wedge-shaped holes are more likely to be lacunar infarctions (50).
Lacunar infarctions can be differentiated from VR spaces by signal intensity characteristics. An acute lacunar infarction (12 hours up to 7 days) appears as a small high-signal-intensity region on T2-weighted and FLAIR images and as a hypointense area on T1-weighted images. High signal intensity is seen on diffusion-weighted images with corresponding low signal intensity on the apparent diffusion coefficient map (Fig 11). Enhancement is variable.
A chronic lacunar infarction is better defined and has high signal intensity on T2-weighted images and low signal intensity on T1-weighted images. On FLAIR images, a hyperintense lesion or a lesion with a hypointense center and a hyperintense rim reflecting gliosis is seen (Figs 10, 11). Diffusion-weighted images are normal. Enhancement may persist up to 8 weeks after the acute event (51).
Cystic Periventricular Leukomalacia
Periventricular leukomalacia, usually seen in premature infants, is a leukoencephalopathy resulting from a pre- or perinatal hypoxic-ischemic event. In the acute stage, white matter undergoes vascular congestion and coagulative necrosis. Cavitation then occurs within necrotic regions. End-stage periventricular leukomalacia has a typical appearance at MR imaging (Fig 12): T2-weighted and FLAIR images show abnormally increased signal intensity in the periventricular white matter. There is marked loss of periventricular white matter, predominantly in the periatrial regions, and compensatory focal ventricular enlargement adjacent to regions of abnormal white matter signal intensity. The involvement tends to be symmetrical. Corpus callosal thinning can be seen as a secondary manifestation. There is relative sparing of the overlying cortical mantle. In more severe cases, cavitated infarcts have replaced the immediate periventricular white matter (52,53). These cystic components have surrounding gliosis, easily depicted on FLAIR images, which distinguishes them from enlarged VR spaces (Fig 12).
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Figure 12a. Cystic periventricular leukomalacia in a 3-year-old boy with a history of perinatal asphyxia who had delayed motor and mental development and epilepsy. (a) Axial proton-density–weighted image (2611/100) shows hyperintense lesions predominantly in the right peritrigonal area (straight arrow) but also in the left peritrigonal area (curved arrow). These lesions could be mistaken for type II VR spaces. (b) Coronal FLAIR image (11,000/140) shows gliosis around the cystic lesions (arrows), a characteristic finding in end-stage cystic periventricular leukomalacia.
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Figure 12b. Cystic periventricular leukomalacia in a 3-year-old boy with a history of perinatal asphyxia who had delayed motor and mental development and epilepsy. (a) Axial proton-density–weighted image (2611/100) shows hyperintense lesions predominantly in the right peritrigonal area (straight arrow) but also in the left peritrigonal area (curved arrow). These lesions could be mistaken for type II VR spaces. (b) Coronal FLAIR image (11,000/140) shows gliosis around the cystic lesions (arrows), a characteristic finding in end-stage cystic periventricular leukomalacia.
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Multiple Sclerosis
MS lesions may be located anywhere in the central nervous system. Lesions in the periventricular and juxtacortical white matter correspond to the location of type II VR spaces. In addition, individual MS plaques often appear as ovoid lesions, mimicking the shape of dilated VR spaces (Fig 13). However, MS lesions are usually arranged like fingers pointing away from the walls of the lateral ventricles (Dawson fingers) and can easily be distinguished from enlarged VR spaces by signal intensity characteristics. In the acute stage, MS lesions are isointense or mildly hypointense to brain parenchyma on T1-weighted images. In the chronic phase, they have a hypointense center with a mildly hyperintense rim on T1-weighted images. T2-weighted and FLAIR images demonstrate hyperintense lesions. Both solid and ring enhancement may occur. Enhancement is dependent on the current degree of inflammation (54).
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Figure 13a. Ovoid MS lesion of the centrum semiovale in a 49-year-old man. Axial proton-density–weighted (2624/100) (a) and FLAIR (7291/120) (b) images show a hyperintense lesion (arrow) in the right centrum semiovale. Other MS lesions were located behind the left occipital horn and in the basal ganglia and brainstem.
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Figure 13b. Ovoid MS lesion of the centrum semiovale in a 49-year-old man. Axial proton-density–weighted (2624/100) (a) and FLAIR (7291/120) (b) images show a hyperintense lesion (arrow) in the right centrum semiovale. Other MS lesions were located behind the left occipital horn and in the basal ganglia and brainstem.
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Cryptococcosis
Cryptococcosis is an opportunistic fungal infection caused by Cryptococcus neoformans, affecting the central nervous system in human immunodeficiency virus–seropositive patients and in patients with other immunocompromised states. Central nervous system infection can be either meningeal or parenchymal. Infection usually starts as meningitis, most pronounced at the base of the brain (55,56). The infection often provokes little inflammatory reaction, owing to the host’s immunity and to the immunosuppressive effect of the organism’s capsule (55–57). Infection of the meninges may spread to the adjacent brain through the subarachnoid space or along the ependymal surface.
As the infection spreads along the VR spaces, they may become distended with mucoid, gelatinous material that originates from the organism’s capsule (56). Therefore, cryptococcosis should be considered in the differential diagnosis in any immunocompromised patient with dilated VR spaces. Larger collections of organisms and gelatinous capsular material in the VR spaces have been termed gelatinous pseudocysts (55,56). Mass lesions representing cryptococcomas may occur, particularly in the deep gray matter (55).
Imaging findings are primarily manifestations of meningitis. Hydrocephalus often develops as a result of the acute meningeal exudate and may also occur in the course of the infection because of meningeal adhesions. Punctate hyperintense areas representing dilated VR spaces or cryptococcomas are frequently seen in the basal ganglia, thalami, and midbrain on T2-weighted images (Fig 14) (55,56). On FLAIR images they are also hyperintense, making it possible to differentiate them from normal VR spaces. Contrast enhancement is uncommon (58). On diffusion-weighted images, there may be restricted diffusion in some of the lesions due to the high viscosity of their contents.
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Figure 14. Cryptococcosis in a 58-year-old woman with headaches and fever who was seropositive for human immunodeficiency virus. Parasagittal T2-weighted image (5963/120) shows multiple dilated VR spaces in the region of the basal ganglia (arrowheads). C neoformans was cultured from the CSF.
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Mucopolysaccharidoses
The mucopolysaccharidoses are inherited disorders of metabolism characterized by enzyme deficiency and inability to break down glycosaminoglycan (GAG), which results in the accumulation of toxic intracellular substrate. Clinical features are mental and motor retardation, macrocephaly, and musculoskeletal deformities. The urinary GAG level is elevated. Brain atrophy and abnormalities of the white matter may be present.
Typically, the VR spaces are dilated by accumulated GAG, which results in a cribriform appearance of the white matter, corpus callosum, and basal ganglia on T1-weighted images. Occasionally, arachnoid cysts (due to meningeal GAG deposition) are seen. On T2-weighted and FLAIR images, the dilated VR spaces are isointense to CSF (Fig 15). However, the surrounding white matter may show increased signal intensity, representing gliosis, edema, or de- or dysmyelination (Fig 15). The latter helps in differentiating them from normal VR spaces. In addition, MR spectroscopy shows a broad peak around 3.7 ppm (higher than the chemical shift of myoinositol), considered to contain signals from accumulated GAG (59–61).
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Figure 15a. Hurler syndrome (mucopolysaccharidosis type I) in a 2-year-old boy with typical external features of this syndrome. A classic Hurler mutation with severe  -L-iduronidase deficiency was demonstrated. (a) Axial proton-density–weighted image (3835/150) shows dilated VR spaces in both hemispheres (arrowheads). (b) Coronal FLAIR image (6381/100) shows increased signal intensity in the surrounding brain parenchyma (arrows); this finding indicates that the spaces are not normally dilated VR spaces. There is also increased CSF space frontally.
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Figure 15b. Hurler syndrome (mucopolysaccharidosis type I) in a 2-year-old boy with typical external features of this syndrome. A classic Hurler mutation with severe -L-iduronidase deficiency was demonstrated. (a) Axial proton-density–weighted image (3835/150) shows dilated VR spaces in both hemispheres (arrowheads). (b) Coronal FLAIR image (6381/100) shows increased signal intensity in the surrounding brain parenchyma (arrows); this finding indicates that the spaces are not normally dilated VR spaces. There is also increased CSF space frontally.
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Cystic Neoplasms
Giant dilatations of the VR spaces may cause mass effect and assume bizarre configurations that may be misinterpreted as a cystic brain tumor (39–42). However, cystic brain tumors often have solid components, may enhance with contrast material, mostly show surrounding edema, and have contents that usually are not equal to CSF, as can be seen on FLAIR images (Fig 16). They generally exhibit low signal intensity on diffusion-weighted images with corresponding high apparent diffusion coefficient values (62–64). When the lesions in question occur in a characteristic location along the path of a penetrating vessel, follow CSF signal intensity with all sequences, do not enhance with contrast material, and have normal adjacent brain parenchyma, their appearance is virtually always pathognomonic of giant VR spaces (Fig 9) (42). Still, differentiation between giant VR spaces and cystic brain tumors is sometimes difficult and follow-up MR imaging may be useful.
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Figure 16a. Desmoplastic pilocytic astrocytoma of the right thalamus, cerebral peduncle, and brainstem in a 15-year-old girl. (a, b) Axial proton-density–weighted (2374/100) (a) and FLAIR (6614/100) (b) images show a large mass with solid (arrow) and cystic (arrowheads) components. (c) Axial gadolinium-enhanced T1-weighted image (598/18) shows inhomogeneous enhancement of the solid component (arrow) and rim enhancement of the cystic components (arrowheads). Obstruction of the third ventricle has caused hydrocephalus.
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Figure 16b. Desmoplastic pilocytic astrocytoma of the right thalamus, cerebral peduncle, and brainstem in a 15-year-old girl. (a, b) Axial proton-density–weighted (2374/100) (a) and FLAIR (6614/100) (b) images show a large mass with solid (arrow) and cystic (arrowheads) components. (c) Axial gadolinium-enhanced T1-weighted image (598/18) shows inhomogeneous enhancement of the solid component (arrow) and rim enhancement of the cystic components (arrowheads). Obstruction of the third ventricle has caused hydrocephalus.
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Figure 16c. Desmoplastic pilocytic astrocytoma of the right thalamus, cerebral peduncle, and brainstem in a 15-year-old girl. (a, b) Axial proton-density–weighted (2374/100) (a) and FLAIR (6614/100) (b) images show a large mass with solid (arrow) and cystic (arrowheads) components. (c) Axial gadolinium-enhanced T1-weighted image (598/18) shows inhomogeneous enhancement of the solid component (arrow) and rim enhancement of the cystic components (arrowheads). Obstruction of the third ventricle has caused hydrocephalus.
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Neurocysticercosis
Cysticercosis is the most common parasitic infection of the central nervous system, caused by the larval stage of the pork tapeworm Taenia solium. Fluid-filled oval cysts with an internal scolex (cysticerci) may be located in the brain parenchyma (gray-white matter junction, but also in the basal ganglia, cerebellum, and brainstem), subarachnoid space, ventricles, or spinal cord.
MR imaging findings of neurocysticercosis are variable, depending on the stage of evolution of the infection. Lesions can be seen at different stages in the same patient.
In the initial vesicular stage, a cystic lesion is isointense to CSF with all MR sequences, resembling an enlarged VR space. However, a discrete eccentric scolex (hyperintense to CSF) may be seen (Fig 17). In general, the lesions do not enhance in this stage.
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Figure 17. Parenchymal neurocysticercosis in the vesicular stage in a 17-year-old boy. Axial T1-weighted image (605/18) shows a cystic lesion with an eccentrically located scolex (arrow), a finding pathognomonic of neurocysticercosis.
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In the colloidal vesicular stage, the cyst is mildly hyperintense to CSF. Mild to marked surrounding edema may be seen. A thick cyst wall enhances, including the scolex.
In the granular nodular stage, a thickened retracted cyst wall is seen, which may have nodular or ring enhancement. Edema decreases.
In the nodular calcified stage, the lesion is shrunken and completely calcified, appearing hypointense with all MR sequences. Gradient-echo sequences are very useful to demonstrate the calcified scolex (65–67).
Arachnoid Cysts
Arachnoid cysts represent intra-arachnoid CSF–containing cysts that do not communicate with the ventricular system. The most common supratentorial locations for an arachnoid cyst are the middle cranial fossa, the perisellar cisterns (Fig 18), and the subarachnoid space over the convexities. On MR images, arachnoid cysts appear as well-defined nonenhancing masses that are isointense to CSF with all sequences, including diffusion-weighted imaging (68). They can be differentiated from enlarged VR spaces by their typical location.
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Figure 18. Arachnoid cyst in the perisellar cistern area in a 16-year-old girl. Axial FLAIR image (7292/120) shows a well-defined, round cyst with CSF-like content in the suprasellar cistern (arrow).
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Neuroepithelial Cysts
Neuroepithelial cysts are rare and benign lesions, mostly asymptomatic. Their etiology is controversial but developmental anomalies are likely. Lesions are spherical to ovoid, measure up to several centimeters in size, and may have mass effect. They are lined with thin epithelium and have a CSF-like content. On the basis of pathologic studies, neuroepithelial cysts are regarded as ependymal in origin (69). Neuroepithelial cysts may involve the lateral ventricles or fourth ventricle, with which they do not communicate (intraventricular cysts). They can also be found within the cerebral hemispheres, thalamus (Fig 19), midbrain, pons (Fig 20), and cerebellar vermis and in the medial temporal lobe in or near the choroidal fissure (choroidal fissure cysts) (Fig 21) (70,71).
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Figure 19. Neuroepithelial cyst of the thalamus in a 53-year-old woman with migraine headaches. Axial FLAIR image (7291/120) shows a multiloculated cyst with CSF-like signal intensity in the right thalamus (arrow). The adjacent brain parenchyma has normal signal intensity. Note that this lesion could also be an enlarged VR space. A final diagnosis can be made with certainty only after pathologic study.
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Figure 20a. Neuroepithelial cyst of the cerebral peduncle and pons in a 60-year-old woman with epilepsy. Axial T1-weighted (30/13) (a) and coronal FLAIR (11,000/140) (b) images show a cyst with CSF-like content in the left cerebral peduncle (arrow). The adjacent tissue has normal signal intensity. The cyst has a diameter of 15.7 mm as measured on the coronal FLAIR image (b). This benign lesion probably represents a neuroepithelial cyst, although it could also be a huge VR space.
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Figure 20b. Neuroepithelial cyst of the cerebral peduncle and pons in a 60-year-old woman with epilepsy. Axial T1-weighted (30/13) (a) and coronal FLAIR (11,000/140) (b) images show a cyst with CSF-like content in the left cerebral peduncle (arrow). The adjacent tissue has normal signal intensity. The cyst has a diameter of 15.7 mm as measured on the coronal FLAIR image (b). This benign lesion probably represents a neuroepithelial cyst, although it could also be a huge VR space.
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Figure 21. Choroidal fissure cyst in a 1-week-old boy. Axial T1-weighted spectral presaturation inversion-recovery image (5094/30) shows a medial temporal lobe cyst with CSF-like content arising in the choroidal fissure (arrow).
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MR imaging confirms the CSF-like signal behavior of the cyst with all sequences and allows exclusion of adjacent brain edema, soft-tissue mass, and gliosis in or around the cyst. There is no enhancement with contrast material (70,71). Differentiation between neuroepithelial cysts and enlarged VR spaces can be made with certainty only by pathologic study.
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Conclusions
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VR spaces surround the walls of the vessels as they course from the subarachnoid space through the brain parenchyma. They can be seen on MR images in all age groups. They may become markedly enlarged. Knowledge of their signal intensity characteristics and localization helps in differentiating them from different pathologic conditions.
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Footnotes
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Abbreviations: CSF = cerebrospinal fluid, FLAIR = fluid-attenuated inversion recovery, GAG = glycosaminoglycan, MS = multiple sclerosis, VR = Virchow-Robin
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References
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- Virchow R. Ueber die Erweiterung kleinerer Gefaesse. Archiv Pathol Anat Physiol Klin Med 1851; 3:427–462.[CrossRef]
- Robin C. Recherches sur quelques particularités de la structure des capillaires de l’encephale. J Physiol Homme Anim 1859;2:537–548.
- Hutchings M, Weller RO. Anatomical relationships of the pia mater to cerebral blood vessels in man. J Neurosurg 1986;65:316–325.[Medline]
- Zhang ET, Inman CB, Weller RO. Interrelationship of the pia mater and the perivascular (Virchow-Robin) spaces in the human cerebrum. J Anat 1990;170:111–123.[Medline]
- Pollock H, Hutchings M, Weller RO, Zhang ET. Perivascular spaces in the basal ganglia of the human brain: their relationship to lacunes. J Anat 1997;191:337–346.[CrossRef][Medline]
- Schley D, Carare-Nnadi R, Please CP, Perry VH, Weller RO. Mechanisms to explain the reverse perivascular transport of solutes out of the brain. J Theor Biol 2006;238:962–974.[CrossRef][Medline]
- Durant-Fardel M. Traite du ramollissement du cerveau. Paris, France: Balliere, 1843.
- Poirier J, Barbizet J, Gaston A, Meyrignac C. Thalamic dementia: expansive lacunae of the thalamo-paramedian mesencephalic area—hydrocephalus caused by stenosis of
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Abstract
Introduction
