神经影像与临床
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imaging and clinical 8
•
VR spaces surround the walls of arteries, arterioles, veins, and venules as they course from the subarachnoid space
through the brain parenchyma . Electron microscopy and
the penetrating branches of the collicular and accessory collicular arteries .
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
brain injury , and diseases associated with microvascular
abnormalities.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 . In addition, the use of thinner sections will demonstrate more VR spaces
• •
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. 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 . The second type (type II) can be found along the path of the perforating medullary
than the CSF-containing structures within and around the brain , 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
arteries as they enter the cortical gray matter over the high convexities and
extend into the white matter .The third type (type III) appears in the midbrain. In the lower midbrain, VR spaces at the pontomesencephalic junction surround
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.
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 . VR spaces do not enhance with contrast material. In patients with small to
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 . The lack of a similar coating of leptomeningeal cells around veins in the cerebral cortex
•
Dilatation of VR spaces was described by Durant-Fardel in 1843. These dilatations are regular cavities that always contain a pat百度文库nt artery. The mechanisms underlying expanding VR spaces are still unknown. Different theories
•
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) . Some studies found a correlation between dilated VR spaces and neuropsychiatric disorders , recent-onset multiple sclerosis (MS) , mild traumatic
elongation of blood vessels and brain atrophy resulting in an
extensive network of tunnels filled with extracellular water , gradual leaking of the interstitial fluid from the intracellular
have been postulated: segmental necrotizing angiitis of the
arteries or another unknown condition causing permeability of the arterial wall , expanding VR spaces resulting from disturbance of the drainage route of interstitial fluid due to cerebrospinal fluid (CSF) circulation in the cistern , spiral
• 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
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 . Interstitial fluid within the brain
parenchyma drains from the gray matter of the brain
Photomicrograph (original magnification, ×20; hematoxylin-eosin stain) of a coronal section through the anterior perforated substance shows two arteries (straight arrows) with surrounding VR spaces (curved arrows).
as well . Also, high-field-strength MR imaging is expected to
have an increased clinical impact in the near future; the current
• Signal Intensity Characteristics
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 . Arteries in the cerebral cortex are coated by a layer of leptomeninges that is
•
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
•
VR spaces surround the walls of arteries, arterioles, veins, and venules as they course from the subarachnoid space
through the brain parenchyma . Electron microscopy and
the penetrating branches of the collicular and accessory collicular arteries .
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
brain injury , and diseases associated with microvascular
abnormalities.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 . In addition, the use of thinner sections will demonstrate more VR spaces
• •
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. 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 . The second type (type II) can be found along the path of the perforating medullary
than the CSF-containing structures within and around the brain , 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
arteries as they enter the cortical gray matter over the high convexities and
extend into the white matter .The third type (type III) appears in the midbrain. In the lower midbrain, VR spaces at the pontomesencephalic junction surround
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.
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 . VR spaces do not enhance with contrast material. In patients with small to
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 . The lack of a similar coating of leptomeningeal cells around veins in the cerebral cortex
•
Dilatation of VR spaces was described by Durant-Fardel in 1843. These dilatations are regular cavities that always contain a pat百度文库nt artery. The mechanisms underlying expanding VR spaces are still unknown. Different theories
•
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) . Some studies found a correlation between dilated VR spaces and neuropsychiatric disorders , recent-onset multiple sclerosis (MS) , mild traumatic
elongation of blood vessels and brain atrophy resulting in an
extensive network of tunnels filled with extracellular water , gradual leaking of the interstitial fluid from the intracellular
have been postulated: segmental necrotizing angiitis of the
arteries or another unknown condition causing permeability of the arterial wall , expanding VR spaces resulting from disturbance of the drainage route of interstitial fluid due to cerebrospinal fluid (CSF) circulation in the cistern , spiral
• 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
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 . Interstitial fluid within the brain
parenchyma drains from the gray matter of the brain
Photomicrograph (original magnification, ×20; hematoxylin-eosin stain) of a coronal section through the anterior perforated substance shows two arteries (straight arrows) with surrounding VR spaces (curved arrows).
as well . Also, high-field-strength MR imaging is expected to
have an increased clinical impact in the near future; the current
• Signal Intensity Characteristics
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 . Arteries in the cerebral cortex are coated by a layer of leptomeninges that is
•
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