Which diffusion-weighted MRI findings are characteristic stroke?

Updated: Nov 30, 2018
  • Author: Andrew Danziger; Chief Editor: L Gill Naul, MD  more...
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Acutely ischemic lesions demonstrate high signal of DWI and low signal on ADC maps within minutes. [87]  Diffusion-weighted images are considered to be the most reliable marker of ischemic core and can detect ischemia within 30 minutes. [13, 88, 89, 90, 91]

DWI may demonstrate high signal for several weeks. This is due to T2-weighted effects predominating over the apparent diffusion in early and subacute infarctions. [92] Confirmation with the ADC map for a corresponding area of signal loss is needed to confirm the abnormal DWI to avoid the problem of T2 “shine through.”

Falsely negative and reversible areas on diffusion images can be seen if only very mild ischemia exists, if the area of ischemia is very small, or if it is very early in the course of the ischemic event.

Abnormal signal of DWI has been reported to normalize in as little as 14 days, [93] although more recent data has observed normalization at an average of approximately 56 days. [92] However, DWI signal abnormality has been reported to last up to 72 days. This is large part due to "shine-through" effects of the T2-weighting of DWI. [92, 94]

In a study of 92 patients with erly stages of stroke, the sensitivity of DWI alone was 95% and reached 100% in conjunction with perfusion MR. [2]

In contrast, the ADC abnormality typically peaks by 3 days and pseudonormalizes during the subacute period between the 7th and 11th day after infarction and is a much more accurate assessment of infarct age. [92]

To confirm whether high signal on DWI represents acute infarction, one must match the high signal on the DWI to low signal on ADC maps (see the images below).

Noncontrast CT scan and MRI of the brain with DWI Noncontrast CT scan and MRI of the brain with DWI was performed to evaluate this 87-year-old male with history of recurrent strokes and new change in mental status. Noncontrast CT scan demonstrates a right PCA distribution hypodensity, and a hypodensity at the vertex on the right near the MCA/ACA borderzone. Both of these abnormalities are age indeterminate on the CT scan.
MRI was obtained to further clarify the findings o MRI was obtained to further clarify the findings on a noncontrast CT scan. High signal on the DWI and corresponding low signal on the ADC maps in the right frontal vertex borderzone area are seen. This signifies true restricted diffusion and an acute infarction.
The right posterior cerebral artery (PCA) distribu The right posterior cerebral artery (PCA) distribution infarction is most likely chronic. The high signal on the DWI has no corresponding low signal on the ADC map (red circle). The ADC map demonstrates slightly elevated signal in this case. The falsely persistent high signal on DWI in the absence of recent infarction is felt to be related to the partial T2-effects of DWI and is referred to as "T2 shine through."

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