0:01

Depending upon your institution, you may

0:04

have a protocol in which a patient gets a

0:07

non-contrast head CT scan for stroke, followed

0:11

by CT angiogram and associated CT perfusion.

0:17

Some programs will just do a non-contrast CT and a

0:21

CTA in order to define the anatomy and to determine

0:25

whether the patient is a candidate for thrombectomy and

0:29

IV thrombolysis. In this case, of the patient

0:33

who had a dense MCA on the non-contrast scan,

0:37

the patient had ordered a CT angiogram to

0:40

follow, and this was done on the same day.

0:43

So what we're seeing is a contrast-enhanced CTA of the

0:47

head and neck, and these are usually done together—both

0:50

the head and the neck together in one bolus of contrast.

0:54

Now, for

0:57

the evaluation of the patient who has a

0:59

stroke, obviously, time is of the essence.

1:02

So for the evaluation forr the CTA, generally, I go

1:06

with the thick section images to start with. So that way,

1:09

I have a sense of what's going on, and I can

1:12

get on the phone with the clinician and say, "Hey,

1:15

there's a definite thrombus here in the internal

1:17

carotid artery or in the middle cerebral artery."

1:21

So that's

1:22

thick section images because

1:24

you can scroll through them faster.

1:26

However, for the detailed anatomy that we

1:28

need to know for the overall report, I will

1:31

then go ahead and look at the thin section

1:34

images as well as the reconstructed images.

1:38

And in most cases, we're talking about

1:41

maximum intensity projection (MIP) images

1:45

of both the neck vessels to look for the

1:47

carotid bifurcation to see how stenotic

1:50

it is, as well as intracranial MIPs.

1:56

As I'm going to scroll through this, you'll

1:58

see that the way I look at a CTA is I look

2:01

at one vessel at a time, going up and down.

2:04

So here we are at the lowest-most portion, and we

2:08

have the aortic arch. I'm going to follow,

2:10

since I saw that the patient had a dense MCA

2:14

on the left side, I'm going to follow the left common

2:18

carotid artery up and down in its entirety, not

2:22

looking at the right and not looking at the vertebral

2:24

artery, just focusing on one blood vessel at a time.

2:28

So here I am, following the left

2:30

common carotid artery upward.

2:32

And we start to see the carotid bifurcation.

2:36

So I'm at the carotid bifurcation, and I have

2:38

to make an assessment of the patient's carotid

2:40

stenosis. In this case, although there is

2:44

calcified plaque that you see as these bright

2:46

little areas around the internal carotid artery,

2:49

remember, the internal carotid artery comes off

2:51

posteriorly in most patients at the bifurcation.

2:54

So there is some atherosclerotic plaque, but I'm not seeing

2:57

high-grade stenosis at all.

3:00

I'm now following the internal carotid

3:02

artery up and following it in its cervical

3:05

portion until it comes to its petrous portion.

3:09

So here we are at the petrous portion.

3:12

Little bit of irregularity in the blood vessel here.

3:15

So there is some atherosclerotic

3:17

soft plaque in the petrous internal

3:19

carotid artery, but not high grade.

3:21

I'm gonna look at this again on the thin sections.

3:24

And then we come to the cavernous

3:26

portion of the internal carotid artery.

3:27

We had seen the calcifications on the non-contrast

3:30

study, and here we see that although there are

3:33

calcifications, we are not seeing a high-grade stenosis.

3:37

I call high-grade stenosis intracranial.

3:40

Anything that's greater than 50%.

3:43

When we're looking at the carotid bifurcation, we're

3:45

usually talking about 70% as high-grade stenosis.

3:49

So we follow the cavernous internal carotid artery,

3:53

and this is the, obviously, the odontoid process right here.

3:56

So we're at the paraclinoid internal carotid artery.

3:59

We're now at the supraclinoid internal carotid artery.

4:02

And as we come to the distal portion of the internal

4:07

carotid artery at the M1-A1 junction, this is A1.

4:13

M1, we're missing M1.

4:15

So as you can see, this blood vessel, as opposed

4:19

to here, where it goes across to the M1 segment,

4:22

on the right side, on the left side, it stops.

4:25

And this is the thrombus right here.

4:29

You're seeing it as absence of contrast.

4:32

Despite that, we do see some

4:34

vessels in the Sylvian fissure.

4:37

Some of them are not filling as well as others,

4:40

because they don't have as good flow.

4:42

Some do have good flow.

4:43

And then as we continue upward in the Sylvian fissure,

4:48

we see more of the middle cerebral artery branches.

4:51

Not quite as abundant as on the

4:54

right side, but they are present.

4:56

And this is likely through

4:58

collateral circulation going upward.

5:01

So I've now evaluated the left side.

5:06

Common carotid artery, no occlusion.

5:09

Carotid bifurcation, no stenosis that

5:12

the interventionalist has to worry about.

5:14

Let's look at the right common carotid artery.

5:17

So we'll do this a little bit more quickly.

5:19

So right common carotid artery coming off

5:21

of the innominate artery, the right common

5:23

carotid artery in the neck cervical portion,

5:26

we come to the right common carotid artery bifurcation.

5:30

There is stenosis here with soft plaque,

5:33

as well as calcified hard plaque.

5:36

But once again, just visually,

5:39

this is not high-grade stenosis.

5:41

I would measure this in its minimum width,

5:45

and then compare it to the normal distal

5:49

internal carotid artery, which is here.

5:51

I would say it's probably gonna end up being

5:53

a 50% stenosis, and then following this up to

5:58

the petrous internal carotid artery, not too

6:01

bad, the cavernous internal carotid artery.

6:04

Calcified atherosclerotic plaque, but no stenosis.

6:07

Here's the M1 segment.

6:10

Here's the A1 segment.

6:11

It looks good.

6:12

I look in the Sylvian fissure,

6:14

and the branches look fine.

6:16

Then I go down and look at the next set of

6:19

vessels, which are the vertebral arteries.

6:21

And once again, the way I would evaluate

6:23

this is just one vessel at a time.

6:25

So here we have the origin of the left vertebral artery.

6:31

That's the V1 segment.

6:33

This brightness here

6:34

is some venous contamination.

6:37

We follow the left vertebral artery in its vertebral

6:40

segment, which is called the V2 segment.

6:43

We follow that up, up, up.

6:45

Here's where it exits the vertebral segment.

6:49

So this is what's known as the V3

6:50

segment, outside the vertebral segment, but

6:53

before it enters the intracranial segment.

6:56

And as it enters the dura, this is the V

6:58

4 segment, and there are no stenoses.

7:01

Let's go back down and find the right

7:04

vertebral artery and follow it from below.

7:07

So here is the origin of the right vertebral

7:10

artery. Calcified plaque here, narrowed.

7:14

Here it comes off.

7:16

This is your right vertebral

7:18

artery that we're following.

7:19

Now entering the V2 segment, we

7:21

follow the V2 segment all the way up.

7:23

A little bit of venous, right?

7:25

Contrast here.

7:27

Here's still the vessel.

7:30

Here's the vessel coming out.

7:33

This is the V3 segment with a little

7:34

bit of calcified plaque right here.

7:37

Intracranial segment, V4 segment, which

7:39

looks fine, and it joins the basilar artery.

7:44

So at this point, I've looked at

7:45

all of the four major vessels.

7:47

I now have to look at the intracranial vasculature.

7:50

And for that, although I would look on the thin

7:53

section images, we're gonna go to the MIPs.

7:57

I like the coronal MIP the most.

7:59

This is the coronal maximum

8:01

intensity projection (MIP) image.

8:04

And we are looking at the intracranial circulation.

8:08

So that's why we're seeing the brain.

8:09

And as we come from anterior to posterior,

8:12

we see the anterior cerebral arteries.

8:15

So this is the right internal carotid artery coming

8:18

to the A1 segment and the M1 segment. These are

8:21

the middle cerebral artery branches, and we're gonna

8:24

see the connections with the anterior cerebral artery

8:26

branches on the left side internal carotid artery.

8:31

This is the A1 segment.

8:34

Now, I see a high-grade stenosis

8:37

of the left A1 segment origin.

8:40

It should be connecting to this blood vessel like this.

8:43

And there's a stenosis here.

8:46

Might even be a thrombus here.

8:48

The M1 segment is completely gone.

8:50

So here's our M1 on the right.

8:52

The M1 on the left is missing, and yet we still

8:56

do see middle cerebral artery branches, presumably

8:59

coming from either posterior cerebral artery

9:02

collaterals or anterior cerebral artery collaterals.

9:05

So the new finding is—ah, there also is a

9:09

proximal left A1 segment thrombus or

9:13

stenosis here. Thrombus.

9:15

If we see the cut within the blood vessel,

9:18

stenosis, if we see that the vessel is

9:20

narrowed, and then as we continue further

9:24

posteriorly, we come to the basilar artery.

9:27

So here's our basilar artery with the posterior

9:29

cerebral and superior cerebellar branches.

9:32

Here are the two vertebral arteries

9:35

coming together to form the basilar artery.

9:39

So this is the

9:40

V4 segment of the left and V4

9:42

segment of the right vertebral arteries.

9:45

And obviously, we would also look

9:48

at all the other projections.

9:49

So here is the occluded left middle

9:53

cerebral artery that we described before.

9:55

And you may also see this in the sagittal projection.

10:01

So coming from the left side, we're seeing the

10:05

relative paucity of branches in the Sylvian fissure,

10:10

as compared to the right side,

10:13

where you see more of these loops.

10:15

So there are some vessels that were missing

10:17

within the Sylvian fissure, likely from

10:20

a clotted vessel or diminished flow.

10:23

Here are the anterior cerebral arteries.

10:25

Here's your basilar artery coming in,

10:27

your posterior cerebral arteries.

10:28

A lot of these vessels are showing atherosclerotic

10:31

disease, as shown by irregularity to their contour.

10:35

Here's another little area of stenosis here.

10:38

In this posterior cerebral artery.

10:41

So what I'm not doing right now is showing

10:43

you the thin-section images, but you

10:47

would go through them and verify that.

10:49

The one thing that I get to with the thin-section

10:52

images is that you would be able to see more clearly

10:55

that, uh, left A1 segment stenosis and/or clot.

11:00

If you were looking at the thin-section images.

11:02

That's the type of thing that might not be

11:04

identified on the thick sections because it was

11:07

a small segment of the left A1, and so let me

11:11

just try to scroll quickly up to that level again,

11:15

following the internal carotid artery, giving

11:18

them a sense of the degree of stenosis of the

11:21

left internal carotid artery at the bifurcation.

11:24

So I would measure that and use the NASCET criteria.

11:29

That is, the narrowest part of the

11:31

internal carotid artery to a normal part.

11:34

We had worried a little bit about

11:35

the petrous internal carotid artery.

11:37

There is irregularity here and soft plaque in the petrous

11:41

left internal carotid artery, but not high-grade stenosis.

11:46

This is the internal carotid artery coming to

11:49

the occluded M1 segment and looking for the...

11:56

A1 segment.

11:57

Here's the A1, and it's right here.

12:00

It looks like I see a small low-density

12:03

area, which could be a clot right at the

12:06

A1 origin as opposed to stenosis.

12:10

It's a clot that is spanning both the

12:14

proximal A1 as well as the M1 segment.