DW imaging reliability in acute stroke

DW imaging reliability in acute stroke.—Conventional computed tomography (CT) and MR imaging cannot be used to reliably detect infarction at the earliest time points. The detection of hypoattenuation on CT scans and hyperintensity on T2-weighted MR images requires a substantial increase in tissue water. For infarctions imaged within 6 hours after stroke onset, reported sensitivities are 38%–45% for CT and 18%–46% for MR imaging. For infarctions imaged within 24 hours, the authors of one study  reported a sensitivity of 58% for CT and 82% for MR imaging.

DW images are very sensitive and specific for the detection of hyperacute and acute infarctions, with a sensitivity of 88%–100% and a specificity of 86%–100% . A lesion with decreased diffusion is strongly correlated with irreversible infarction. Acute neurologic deficits suggestive of stroke but without restricted diffusion are typically due to transient ischemic attack, peripheral vertigo, migraine, seizures, intracerebral hemorrhage, dementia, functional disorders, amyloid angiopathy, and metabolic disorders .

Although, after 24 hours, infarctions usually can be detected as hypoattenuating lesions on CT and hyperintense lesions on T2-weighted and fluid-attenuated inversion recovery MR images, DW imaging is useful in this setting, as well. Older patients commonly have hyperintense abnormalities on T2-weighted images that may be indistinguishable from acute lesions. However, acute infarctions are hyperintense on DW images and hypointense on ADC maps, whereas chronic foci are usually isointense on DW images and hyperintense on ADC maps due to elevated diffusion (Fig). In one study in which there were indistinguishable acute and chronic white matter lesions on T2-weighted images in 69% of patients, the sensitivity and specificity of DW imaging for detection of acute subcortical infarction were 94.9% and 94.1%, respectively.

 Differentiation of acute white matter infarction from nonspecific small-vessel ischemic changes. This patient had onset of symptoms 2 days prior to imaging. Top: Transverse DW images  in the top row clearly demonstrate the acute infarction (arrowheads) in the putamen and corona radiata. Bottom: Fluid-attenuated inversion recovery (FLAIR) images demonstrate multiple white matter lesions in which acute (arrowhead) and chronic lesions (arrows) cannot be differentiated.