0:01

Sometimes you see a CT scan which has areas of

0:05

low density, and you don't know whether those

0:08

areas of low density represent acute infarctions,

0:12

subacute infarctions, or chronic infarctions.

0:17

Again, to make that determination, it often is

0:20

worthwhile to recommend an MRI scan because, remember,

0:24

that DWI (diffusion-weighted imaging) on an MRI scan is our

0:29

gold standard for identifying acute infarctions.

0:33

This is just that certain case.

0:36

I'm showing you the diffusion-weighted imaging

0:39

in a patient who had multiple areas of low density

0:42

on the CT scan. Here, on the diffusion-weighted imaging,

0:45

we see almost immediately that there is a

0:48

focal area of bright signal intensity in the left

0:53

posterior cerebellum. As we scroll up,

0:56

some of this is just susceptibility artifact at the

0:59

junction between the temporal bone and the brain

1:02

tissue, but we also are able to identify that there

1:08

are bright areas in the frontal lobes bilaterally.

1:13

Small dots of bright signal intensity

1:16

on the diffusion-weighted imaging.

1:19

Naturally, we would want to see this

1:22

side by side with our ADC map in order to

1:27

ensure that what we're seeing is restricted

1:31

diffusion rather than T2 shine-through.

1:36

So if we look at this with the ADC map, here's

1:40

our ADC map, and what we're looking for is dark

1:43

signal intensity, which indeed we see corresponding

1:47

to the areas of the bright signal intensity

1:51

on the diffusion-weighted imaging (DWI) package.

1:55

So what about this area?

1:59

So here is an area of encephalomalacia.

2:02

You notice that it is not bright on the DWI

2:06

sequence and is not dark on the ADC map.

2:11

So this is an old injury.

2:14

So you can see how diffusion-

2:16

weighted imaging is very helpful

2:18

in distinguishing an acute infarction, which

2:21

is going to have restricted diffusion and

2:22

low ADC, versus an old infarction, which is not

2:27

going to be bright on the DWI but is going to

2:30

show bright signal intensity on the ADC map.

2:33

We can also confirm this by looking at the T2

2:38

weighted sequence because, on the T2-weighted

2:42

sequence, we can see that there is encephalomalacia

2:46

associated with this old area of infarction.

2:50

So what to do about these multiple little

2:53

bright areas, however, bilaterally?

2:56

By virtue of seeing bilateral disease in

3:00

the middle cerebral artery distribution, right and

3:03

left, as well as an area of restricted diffusion

3:08

in the cerebellum, we would suggest that these

3:11

are occurring in multiple vascular distributions—

3:14

right and left internal carotid artery, as

3:16

well as the left vertebral artery distribution.

3:20

This tells us that the source of the

3:22

stroke is more likely to be from the heart,

3:26

rather than a carotid bifurcation.

3:28

It doesn't make sense—

3:29

it's bilateral disease, and it also

3:31

includes the vertebral arteries.

3:33

So this is a patient who likely has atrial

3:35

fibrillation or an atrial clot, or a left

3:38

ventricular clot, or potentially even a

3:41

hypercoagulable state where they're creating

3:44

multiple clots because of a, uh, coagulation problem.

3:48

So it not only gives us a sense of whether

3:51

or not this patient needs thrombectomy—no.

3:55

This also gives us a sense of where the

3:58

source of the embolic phenomenon

4:01

is occurring—most likely in the heart.

4:04

Remember that after looking at the DWI and giving a call

4:08

to the clinician that it's positive, you would normally

4:11

also look at your susceptibility-weighted imaging.

4:14

So here is our SWI sequence. On the SWI

4:19

sequence—susceptibility-weighted imaging—

4:21

blood products are dark.

4:24

So the susceptibility—the blood products are dark.

4:27

Here is that old stroke, and what we see are

4:30

areas of dark signal intensity representing

4:33

hemosiderin—old blood products—in the

4:37

right posterior frontal and parietal lobe.

4:40

There's also blood products elsewhere in this patient.

4:43

You can see here another area where there is

4:48

an area of encephalomalacia. This

4:50

little bright area around the periphery—

4:52

we would have to look at the ADC map.

4:54

It turned out that this was not dark on the ADC.

4:57

This again represented T2 shine

5:01

through of vasogenic edema and gliosis.

5:04

So these are older areas of infarction where

5:08

hemorrhage has been deposited, and that also is

5:12

typical of a patient who, for example, might have

5:15

atrial fibrillation and is on anticoagulants.

5:18

So patients who have atrial fibrillation, in order

5:20

to prevent clots from forming, will often be on

5:24

warfarin or antiplatelet drugs, and they

5:27

may have a propensity for peripheral

5:32

hemorrhage in their infarction.

5:36

So in summary, although there are areas of focal

5:43

restricted diffusion representing an acute

5:45

infarction, this is superimposed on multiple areas of

5:51

older infarction in multiple vascular

5:54

distributions associated with hemorrhage, most

5:56

likely secondary to cardioembolic phenomenon

6:01

in a patient who is on anticoagulation.