Hey, everybody, this is Rishi Agrawal.
And in this video, I'm going to be talking about anatomy.
Specifically, we're going to be talking about the branches of the thoracic aorta.
And I'm going to start with this
drawing here, and I'm going to show you what normal anatomy looks like.
Then I'm going to show you a few variants of normal anatomy.
And then I'm going to show you some abnormal cases and we'll look at CT
and angiography.
Let's start first with this drawing.
This is the ascending aorta.
This is the aortic arch.
And this is the descending aorta.
The only branches that come off of the ascending aorta
are the right coronary artery and the left main coronary artery.
The right coronary comes off of the right sinus of Valsalva,
and the left comes off of the left sinus of Valsalva.
There's also a posterior sinus,
but there's no coronary artery that comes off of the posterior sinus.
OK, then we have the ascending aorta.
The ascending aorta is covered by pericardium.
The continuation of the ascending aorta is the aortic arch.
The aortic arch begins posterior
to the right second to costoternal joint.
It arches over the left pulmonary artery and ends posterior
to the left second costoternal joint at about the level of the sternal angle.
Now there's multiple different ways that the arch branches can come off.
But for the most part, most of the time it's this configuration.
This is the most common branching pattern where you have three arteries
coming off of the aortic arch, the right brachiocephalic is the first.
The second is the left common carotid artery
and the third is the left subclavian artery.
The right brachiocephalic is usually the largest because it gives rise
to two arteries the right subclavian and the right common carotid.
Then you have the
descending aorta, which descends in the posterior mediastinum
just to the left and anterior to the vertebral bodies,
and it terminates at the level of T12 where there's the aortic hiatus.
That's where the thoracic aorta stops and the abdominal aorta begins.
You also have the thoracic duct and azygous vein
that go through this hiatus.
Now there's multiple vessels that come off of the descending aorta,
the largest of these are the posterior intercostal arteries.
These are paired arteries, but I've only drawn them in on the left.
And most of the time there's nine arteries
that go from the third rib to the 11th rib.
And then the artery
that supplies the 12th rib isn't called a posterior intercostal.
Instead, we call that the subcostal artery.
These posterior intercostal tend to come off
the posterolateral aspect of the aorta, and they go around the chest wall
along the under surface of their respective rib,
and they anastomose with the anterior intercostal arteries.
The anterior intercostal arteries are branches of the internal mammary artery,
which is also called the internal thoracic artery.
Now, notice you don't have intercostal arteries
from the first and second ribs that come directly off of the aorta.
Instead, intercostals for the first and second ribs
come off of the costocervical trunk,
which is a branch of the subclavian arteries.
And then you have the bronchial arteries, the right and left.
Bronchial arteries usually come off of the anterior
aspect of the aorta at around the level of T5-T6.
Now there's a lot of anatomic variation in the bronchial arteries,
but usually the left bronchial artery comes off of the aorta itself.
And frequently, the right bronchial artery comes off of the right third
posterior intercostal artery, which goes up and to the right.
You can also have multiple bronchial arteries so frequently
you'll have 2 left bronchial arteries and 1 or 2 right bronchial arteries.
Now, as I said, there's a lot of variation here,
and sometimes the bronchial arteries can come off of the subclavian.
Sometimes they can come off of the internal mammary.
Occasionally, they can even come off of the ascending aorta,
although that's pretty rare.
And then next, we have very small arteries
that come off of the anterior aspect of the descending aorta.
And these are esophageal arteries, pericardial arteries
and then mediastinal arteries that go to serve other organs in the mediastinum.
Like lymph nodes.
These arteries are usually pretty hard to see on CT and even on angiography.
And then last, you have the superior phrenic arteries that come off
just above the diaphragm to serve the superior aspect of the diaphragm.
These are also pretty hard to see, and they anastomose with other smaller
branches of the internal mammary artery.
I want to show you some variant anatomy that you might see.
One common normal variation is something called the bovine arch,
and that's where you have a common trunk that gives rise to the right
brachiocephalic artery and the left common carotid artery.
Now in my report, when I see this, I usually just say that there's a common
trunk that gives rise to the right brachiocephalic and left common
carotid arteries because not everybody uses that term bovine arch.
Here's what it looks like on CT.
This is the common trunk.
This is the right brachiocephalic artery.
And this is the left common carotid artery.
And then if I scroll back,
this is the left subclavian artery over here.
Another common variation is something called a four vessel arch
where the left vertebral artery arises directly off of the aorta
instead of the respective subclavian artery.
This is what it looks like on a coronal CT scan.
So right here is the right brachiocephalic artery, that's the left common carotid.
And as I scroll back that right
there is the left vertebral artery going up.
Here's what it looks like on the axial images.
So here's our normal right brachiocephalic, left common carotid.
And then as we keep going up, you can see there's two more vessels here.
So that's the left vertebral and that's the left subclavian artery.
Here's another normal
variant called an aberrant right subclavian artery.
This is where you have
the right subclavian artery coming off the distal part of the arch.
It goes behind the esophagus and then ascends to its normal position
in the supraclavicular region and then onto the arm.
In this situation, you don't have a brachiocephalic artery on the right.
Instead, the right common carotid artery arises directly
from the aortic arch.
Here's what the aberrant right subclavian artery looks like on CT.
So you can see we have a normal arch on the left side,
but the right subclavian artery comes off of the distal aspect of the arch.
This is the esophagus right here.
It goes right behind the esophagus.
And if we follow it up, you can see it
goes up to the right supraclavicular region and then onto the arm.
This is a patient who's had a
gated CTA, and let's just go through and see what we can identify.
So first off, this is the right coronary artery
and it's coming off of the right sinus of Valsalva This is the posterior
sinus right here and notice there's no artery that comes off of that.
This is the left sinus
and that right there is the left main coronary artery.
And then as we go up, we don't see any other arteries
coming off of the ascending aorta.
And then we have our normal arch branches right here, right
brachiocephalic, left common carotid and left subclavian.
Then as we go down,
you see a bunch of small vessels
that are coming off of the posterolateral aspect of the aorta.
Here's one right there.
There's another one.
So these are the posterior intercostal arteries.
Remember that these go from the 3rd rib to the 11th rib
and then the artery supplying the 12th rib is called the subcostal artery
and the intercostal arteries for the 1st and 2nd ribs
come off of a branch of the subclavian artery.
The first posterior intercostal should be the 3rd intercostal.
So this is the 3rd posterior intercostal right there, and we can follow it up.
It goes off to the right
and it goes to the 3rd intercostal space.
As you go further out, it gets harder and harder to see,
but that's it right there.
And if you look, there's another branch that comes off of it right there.
This artery right here is the right bronchial artery.
And if you follow that, that goes behind the right main bronchus and it continues
on posterior to the right bronchus intermedius and off to the hilum.
Now, the left bronchial artery
should come off directly from the aorta, and there it is right there.
It's hard to see because it's small,
but this right here is the left bronchial artery
coming off of the anterior aspect of the aorta.
Now I mentioned there's also small branches
that go to the esophagus,
pericardium, as well as lymph nodes.
But these are very hard to see.
This is probably one right here, right there, but it's very faint
and these are very small branches.
Let's next take a look at a normal conventional angiogram.
Here's a patient who had a conventional angio,
the catheter tip is here in the ascending aorta, the aorta looks like
it's splayed out here, but that's just because of the obliquity.
And these are the normal arch vessels so right brachiocephalic, left common
carotid, and left subclavian.
Here's another obliquity of the same thing so right
brachiocephalic, left subclavian, and left common carotid artery.
Here's an image of the catheter in the descending aorta,
and you can see there's some reflux of contrast into the arch vessels.
But mostly what's lighting up here are these posterior intercostal arteries.
And there's a vessel right here
that takes a turn downward and goes off to the right.
This is the right bronchial artery in this patient, which arises
from this third posterior intercostal artery.
You can also see in this image that the left internal mammary artery
is filling with contrast.
So this gives rise to the anterior intercostals,
which will anastomose with the posterior intercostals.
As I mentioned before, it's common to have multiple bronchial arteries,
and this patient had a common trunk that gave rise to another
right bronchial artery and the left bronchial artery here.
One important clinical correlation of this variant anatomy
is that the bronchial arteries can give rise
to feeders that go to the anterior spinal artery,
and interventional radiologists look for these feeders
because if you're doing a bronchial artery embolization
one of the known, rare, but one of the known documented complications
of bronchial artery embolization is spinal cord ischemia.
Now, let's take a look at some abnormal anatomy.
Here's a patient who has had a history of multiple pulmonary emboli.
You can see here
that there's a large vessel that comes off of the distal aspect of the arch.
And if we follow it, it goes off
and goes to the right hilum.
And this is a hypertrophied, right bronchial artery.
And you can see that there's even a pseudoaneurysm
of one of the branches here in the right hilar region.
There's many reasons why the bronchial arteries can hypertrophy.
Chronic thromboembolic pulmonary hypertension is one.
You can also see it in cases of bronchiectasis like patients
with cystic fibrosis commonly have bronchial artery hypertrophy.
Let's see if we can find the left bronchial artery here.
You can.
It's here.
This is the left bronchial artery.
It's much smaller than the right bronchial artery, but it's still hypertrophied.
Here's a patient who has an aortic coarctation, it's right here.
This patient's coarctation occurs just after
the takeoff of the left subclavian artery.
And what you'll notice is that there are large posterior intercostal arteries here.
This happens because the body is trying to get around this narrowing here,
so it wants to send blood from this side of the aorta to this side.
And because this is narrowed right here,
it has to find other channels to do that.
So remember that I mentioned that the posterior intercostal arteries
anastomose with the anterior intercostal arteries,
which are branches of the internal memory.
So in this case, these posterior intercostal arteries
are not getting blood from the descending aorta.
Instead, the blood is going from the intercostals
to the descending aorta, providing a collateral pathway in this patient.
.This is a chest X-ray of a different patient with coarctation.
And you can see here's rib notching at multiple levels.
And that's because we have hypertrophy of the posterior intercostal arteries.
And this is the third rib right here.
And notice we don't have notching in the first 1 or 2 ribs.
And that's because the intercostal arteries from the first and second rib
come from the costocervical trunk, not from the descending aorta.
OK, so that's all I wanted to show you today.
This has been an overview of the branches of the thoracic aorta.
I'll leave a link to the drawing that I did of the aorta and its branches.
And if you have any questions, please leave them in the comments below.
Thanks.