A frequently encountered imaging finding in acute ischemic stroke and other cerebrovascular diseases is high-signal intensity within blood vessels on fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging sequences. Vascular hyperintensity (FVH) in FLAIR has been associated with large-vessel occlusion or stenosis.1 As opposed to other vessel signs seen in arterial insufficiency, FVH is unique in that it does not represent the thrombus, but rather is a representation of the sluggish or disordered blood flow through vessels, most often leptomeningeal collaterals.2,3 Normally in FLAIR, blood vessels have a loss of signal intensity owing to the “flow void” phenomenon in which blood protons move out of imaging section before the section-selective 180° pulse is applied, so that a spin-echo is not formed; FVH represents the relative absence of this flow void.4
Figure. A, Magnetic resonance imaging diffusion-weighted images reveal an area of increased signal in the left subcortical region. B, Fluid-attenuated inversion recovery sequences reveal vascular hyperintensity in the distal internal carotid/proximal middle cerebral artery (arrow) and more distally in the middle cerebral artery territory (arrowhead) with an absence of vessel hyperintensity in between. C, Catheter angiogram obtained 30 minutes after magnetic resonance imaging demonstrates middle cerebral artery occlusion with the distal middle cerebral artery filled from collateral channels.
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