0:01

This was a patient who had hemolytic uremia syndrome.

0:05

And over the course of two days in the hospital,

0:08

became encephalopathic and somewhat obtunded.

0:10

An MRI was, was requested in part to look

0:15

for strokes or hemorrhages in the brain.

0:18

Here on the FLAIR scan, however, we

0:20

noticed almost immediately that there

0:22

was high signal intensity bilaterally

0:25

in the occipital regions that

0:27

was relatively symmetrical.

0:29

You notice that the disease goes all the

0:32

way to the periphery of the white matter.

0:34

And in this case, there is an

0:36

element of some gray matter edema.

0:39

But the disease is predominantly

0:40

a white matter disease.

0:42

It's a little worse on the

0:43

right side than the left side.

0:45

The remainder of the brain looked pretty good.

0:47

Now you can see that there was involvement

0:49

in the high parietal subcortical white

0:52

matter, again, sparing the gray matter.

0:54

We thought that this was going to be PRES, but

0:57

remember that there are potential complications

0:59

of PRES, which includes infarction,

1:02

hemorrhage, and loss of the blood-brain barrier.

1:05

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

1:10

map and get to the composite B1000 map.

1:13

You see that there is absence of high signal

1:16

intensity indicative of cytotoxic edema.

1:19

PRES is a disease of vasogenic edema,

1:23

not cytotoxic edema, so we would not

1:25

expect there to be abnormality on the DWI.

1:29

However, in severe forms, you may

1:32

actually get brain infarction.

1:34

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

1:38

And we can verify that this is indeed

1:42

vasogenic edema because, on the ADC map,

1:45

rather than dark signal restricted diffusion,

1:48

we have enhanced diffusion as bright

1:51

signal intensity in the occipital regions,

1:54

here in the subcortical white matter.

1:56

Again, you notice that this is white matter disease,

1:59

with sparing of the gray matter on the ADC map.

2:03

The next thing we would do is we would look and

2:05

see whether there was any contrast enhancement.

2:07

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

2:12

Here on the T2-weighted scan, not as well

2:15

demonstrated as with the FLAIR scan, but

2:18

it is a bilateral symmetrical disease.

2:22

So, we sometimes will say Posterior Reversible

2:26

Encephalopathy Syndrome is a misnomer.

2:28

It doesn't have to be posterior.

2:30

You can see it exclusively in the frontal lobes.

2:34

It doesn't have to be reversible.

2:37

Sometimes the patient does indeed have infarction

2:41

of the brain tissue and, therefore, permanent damage.

2:45

It doesn't necessarily have to

2:46

present with encephalopathy.

2:48

The patient may just be a little bit confused.

2:50

So, PRES—typically Posterior Reversible

2:54

Encephalopathy Syndrome—but the exceptions do occur.

Case: PRES: MRI

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