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Case: PRES: MRI

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This was a patient who had hemolytic uremia syndrome.

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And over the course of two days in the hospital,

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became encephalopathic and somewhat obtunded.

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An MRI was, was requested in part to look

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for strokes or hemorrhages in the brain.

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Here on the FLAIR scan, however, we

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noticed almost immediately that there

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was high signal intensity bilaterally

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in the occipital regions that

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was relatively symmetrical.

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You notice that the disease goes all the

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way to the periphery of the white matter.

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And in this case, there is an

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element of some gray matter edema.

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But the disease is predominantly

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a white matter disease.

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It's a little worse on the

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right side than the left side.

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The remainder of the brain looked pretty good.

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Now you can see that there was involvement

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in the high parietal subcortical white

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matter, again, sparing the gray matter.

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We thought that this was going to be PRES, but

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remember that there are potential complications

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of PRES, which includes infarction,

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hemorrhage, and loss of the blood-brain barrier.

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So, on the DWI scan, we go past the B0

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map and get to the composite B1000 map.

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You see that there is absence of high signal

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intensity indicative of cytotoxic edema.

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PRES is a disease of vasogenic edema,

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not cytotoxic edema, so we would not

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expect there to be abnormality on the DWI.

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However, in severe forms, you may

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actually get brain infarction.

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That occurs in less than 10 percent of cases of PRES.

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And we can verify that this is indeed

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vasogenic edema because, on the ADC map,

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rather than dark signal restricted diffusion,

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we have enhanced diffusion as bright

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signal intensity in the occipital regions,

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here in the subcortical white matter.

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Again, you notice that this is white matter disease,

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with sparing of the gray matter on the ADC map.

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The next thing we would do is we would look and

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see whether there was any contrast enhancement.

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And in this case, it was a non-contrast MR only.

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Here on the T2-weighted scan, not as well

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demonstrated as with the FLAIR scan, but

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it is a bilateral symmetrical disease.

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So, we sometimes will say Posterior Reversible

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Encephalopathy Syndrome is a misnomer.

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It doesn't have to be posterior.

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You can see it exclusively in the frontal lobes.

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It doesn't have to be reversible.

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Sometimes the patient does indeed have infarction

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of the brain tissue and, therefore, permanent damage.

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It doesn't necessarily have to

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present with encephalopathy.

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The patient may just be a little bit confused.

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So, PRES—typically Posterior Reversible

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Encephalopathy Syndrome—but the exceptions do occur.

Report

Faculty

David M Yousem, MD, MBA

Professor of Radiology, Vice Chairman and Associate Dean

Johns Hopkins University

Tags

Neuroradiology

MRI

Emergency

Brain

Acquired/Developmental

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