0:01

We've seen several examples of CT,

0:04

CTA, and CT perfusion of stroke.

0:08

We've seen examples of diffusion-weighted

0:10

MRI, MRA, and MR perfusion of stroke.

0:15

What I'd like to do is to make sure that we are all

0:17

comfortable with the non-contrast CT findings of stroke,

0:22

because that's the first scan that you're gonna see.

0:26

So on these two images,

0:28

we see the demonstration of the hyperdense blood

0:31

vessel, in this case at the distal internal carotid

0:34

artery, going into the proximal M1 segment. The dense

0:38

MCA sign on the image to the right is a more subtle

0:43

finding but one that you should learn to recognize.

0:47

This is the insular ribbon sign.

0:50

This is the normal side, the right side,

0:55

where the insula is slightly hyperdense. The gray

0:58

matter of the peri-insular tissue is slightly

1:02

hyperdense compared to the adjacent underlying white

1:06

matter. On the left side, which is the abnormal side,

1:09

the insula is not bright.

1:12

It's actually low in signal intensity.

1:14

You can see that probably best right here,

1:16

and it doesn't have the bright insular ribbon.

1:19

This is more an example of gray matter

1:22

that's kind of bright, whereas we've lost that.

1:25

These are two findings of early acute stroke

1:30

on a non-contrast CT scan.

1:33

Here is a little bit more dramatic example of a dense

1:37

MCA on a non-contrast CT—a big clot here in the MCA.

1:43

And here we see an additional

1:45

finding, which is loss of the

1:48

distinction between the basal

1:50

ganglia tissue for an acute stroke.

1:55

Notice that the caudate nucleus is low in signal

1:58

intensity on the left side compared to the

2:00

right, and the distinction between the caudate

2:03

nucleus, the anterior rim of the internal capsule,

2:07

and the subglobus pallidum has been lost.

2:14

On the left side, you'll also note the

2:17

insula on the right side is nice and bright.

2:22

Notice that the insula on the left side has lost its

2:27

normal brightness and is low in signal intensity.

2:30

So this is the basal ganglia sign as

2:33

well as the insular ribbon sign, as well

2:37

as the dense MCA sign for acute stroke.

2:41

So in looking for stroke on CT, there are lots

2:46

of different things that we would look at:

2:48

dense MCA, perfusion deficit (if we have CT

2:51

perfusion), gray-white matter blurring in the

2:54

insular ribbon, and in the basal ganglia, low

2:58

density, which we can also see, and also mass effect.

3:01

What we're also looking for is hemorrhage.

3:03

So these are the things that would be, in

3:05

general, very important to look at to

3:08

determine whether or not the patient should

3:10

go on for thrombolysis or thrombectomy.

3:13

If the stroke is greater than one-third of the middle

3:17

cerebral artery distribution, that patient has a poor

3:21

prognosis and would probably not benefit very much

3:25

from thrombectomy and thrombolysis,

3:29

even if there was a perfusion mismatch.

3:33

The presence of hemorrhage is obviously very important.

3:35

It contraindicates, in most situations,

3:38

thrombolysis. The presence of herniation,

3:42

obviously, is another situation where intervention

3:45

would be emergent to prevent the patient

3:48

from herniating and dying on that basis.

3:51

As far as the dense MCA sign goes, it's

3:54

seen in not the majority of patients who

3:57

have a middle cerebral artery stroke.

3:58

It's only in about 35 to 50%, but it

4:02

does suggest that there is likely going

4:05

to be a large volume of infarction.

4:08

Now, just the M1 segment, as you know, is where

4:11

the lenticulostriate branches will come off.

4:13

So you may see deep gray matter,

4:17

basal ganglionic infarctions

4:18

from the clot in the M1 segment.

4:21

If the patient has great collaterals for the

4:24

peripheral portions of the middle cerebral artery,

4:27

it is not a contraindication for treatment, although

4:30

it does imply that the patient may do worse.

4:34

This is an interesting graph that I think is important

4:37

with respect to reporting on the size of the clot.

4:42

The probability for successful recanalization

4:46

of occluded vessels by intravenous

4:48

thrombolysis depends on thrombus length.

4:51

If it's a three-millimeter clot, as

4:54

you can see, the success rate of

4:56

recanalization is way up here at about 85%.

4:59

Here's 90%, whereas if it's a five-millimeter

5:02

clot, and again, we're just measuring

5:03

across the distance of the bright density.

5:07

You're around a 50% probability of recanalization.

5:10

If it's eight millimeters, we're way down here at

5:13

less than a 10% chance that the patient is going to

5:17

have recanalization using intravenous thrombolysis.

5:21

So the options are, alright, well,

5:23

we're not gonna be successful.

5:24

Do we just treat the patient medically

5:27

and expectantly without thrombolysis?

5:29

Or do we suggest this is a good patient

5:32

for thrombectomy rather than thrombolysis?

5:35

Because a lot of times they're able to pull

5:37

out the clot, even if you can't dissolve

5:40

it with intravenous thrombolysis.

5:44

Additional CT findings—low density—usually means

5:46

that the stroke is older.

5:49

Here's one where it's isodense, so it's

5:51

not an old stroke. Loss of the interface in

5:54

the basal ganglia we talked about before.

5:56

This is the same image.

5:58

What I want to emphasize is that it is important

6:01

that when you are looking for strokes, you

6:04

manipulate the window and level on the CT scan because

6:08

narrow windows and levels will highlight an area

6:12

of low density and make it more apparent to you.

6:15

So you should have stroke windows preassigned

6:19

that are more like this—very kind of grainy,

6:22

high contrast—but it will show that this

6:25

caudate nucleus on the left is lower density

6:28

than the normal caudate nucleus on the right.

6:30

That's something that if you use your

6:31

standard windows might not be as obvious.

6:35

Here is another example of a patient who has

6:39

an infarct where you have loss of gray-white

6:42

differentiation in the entire middle cerebral

6:45

artery distribution on the image to the left, and

6:49

more FLAIR in the parietal lobe on the right side,

6:54

on the right-hand image.