Hi, everybody, it's Rishi Agrawal.
In today's video,
I want to talk about the anatomy of the subclavian artery and its branches.
I'm going to start with this drawing
to show you some important points and then we'll move to a CTA
and I'll show you what these structures look like on a real patient.
Remember that the right subclavian artery
arises from the right brachiocephalic artery
and the right brachiocephalic artery bifurcates
about at the level of the right sternoclavicular joint into the right
subclavian artery and the right common carotid artery.
The left subclavian artery arises directly from the aorta.
There are a couple of important points
about the course of the subclavian arteries themselves.
First is that most of the time neither the right or the left
subclavian arteries give off any branches in the mediastinum.
Usually, the first branches will be in the lower neck.
second is that both the right and left
have this little peak that goes slightly above the clavicle for a short segment.
This is important because if you're putting in central lines
and you see that your line goes above the clavicle,
then you may have put it in the artery and not the vein.
The subclavian vein stays very close to the clavicle,
and it doesn't have this little peak that goes above.
Third is that anatomically, the subclavian artery is divided into three segments
by the anterior scalene muscle, which passes directly anterior to it.
So the part medial to the anterior scalene is part one,
and the part covered by the anterior scalene is the second part
and the part lateral to the anterior scalene is the third part.
Most of the branches come from the first part, but
you can also have branches that sometimes come off of the second and third parts.
Finally, as the subclavian artery continues
lateral to the first rib, it becomes the axillary artery.
The axillary artery
has many additional branches, which we won't cover in this video.
Now let's take a look at the branches of the subclavian artery.
The first and largest branch is the vertebral arter.
On the left,
this can occasionally come from either the aortic arch or from an early branch
point of the subclavian artery, but usually it arises
just after the subclavian artery exits the thorax.
The vertebral arteries ascend in the transverse foramen
of the cervical spine and join together to form the basilar artery.
There's an important clinical correlation with this anatomy
called subclavian steal syndrome.
This is when you have a significant stenosis of the proximal part
of the subclavian artery that becomes so bad that the flow of blood
actually reverses in the vertebral artery.
The classic history is that a patient passes out
when working out or exercising the affected arm.
This increases demand to that arm, and because of the flow reversal,
the vertebral artery pulls blood out of the circle of Willis,
causing the patient to lose consciousness.
So that's subclavian steal syndrome.
The next biggest branch of the subclavian artery is the internal
thoracic artery, also called the internal mammary artery.
This goes inferior back into the thorax, and it gives off the anterior
intercostal arteries, which anastomose with the posterior intercostal arteries.
It continues on inferiorly, just posterior to the costal cartilages,
and it divides into the superior epigastric
and musculophrenic arteries at about the sixth intercostal space.
The thyrocervical trunk arises off of the superior aspect
of the subclavian artery, usually at about the same level
as the internal thoracic artery, and it gives off many branches
and there can be a lot of variation in those branches,
but it almost always terminates in two arteries.
The inferior thyroid artery, which gives off
branches that go to the thyroid, the parathyroid, the larynx,
the esophagus and the trachea, as well as surrounding muscles.
And then the second is the ascending cervical.
So these are the two
terminal branches of the thyroid cervical trunk,
the other branches of the thyroid cervical trunk
are the lateral branches, and these are a lot more variable.
These lateral branches are the suprascapular.
The suprascapular is usually the first branch off
of the thyrocervical trunk, and then you have the dorsal
scapular.
Dorsal scapular.
And then the last one is the superficial cervical artery.
Sometimes you can see
these as independent branches from the thyrocervical trunk,
but they could also share a common trunk that then bifurcates
into the three branches, or you might see that 2
share a common trunk and then one arises independently.
These can also arise from the subclavian artery itself.
And frequently, the dorsal scapular artery arises directly from the subclavian.
The final branch of the subclavian artery is the costocervical trunk.
This divides into two branches, one
that goes superiorly, which is the deep cervical.
So the deep cervical comes from the costocervical trunk
and the superficial cervical comes from the thyrocervical trunk,
and then the branch that goes inferiorly
is the supreme intercostal.
And remember that the supreme intercostal artery
supplies the intercostals for the first and second ribs.
All right.
Now that you have this overview, let's take a look at a patient case.
This is a
CTA of the head and neck, and we're at the level of the aortic arch here.
And if I scroll up, this is the left subclavian artery.
So we're going to look at the branches of this person's left subclavian artery.
And if you're just starting out, there's a lot of branches
and they come off very close to one another.
And so it can be very easy to get overwhelmed.
So I'm going to show you a little trick and that's to look at the sagittal images,
because if you look at the sagittal images,
it's a lot easier to tell what is what.
And I put these little guides up here so you can see
where we are in the axial plane. OK.
So if I scroll laterally here,
this is the subclavian artery.
Now, the first branch and the largest branch to come off
is the vertebral artery. OK.
And that's it right there.
And it usually comes off at about like the 12:00 position
if we were to take the subclavian artery and make it into a clock.
This comes off at about the 12:00 position.
Now let's keep going.
We're going laterally now
and the
next artery to come off is usually the thyrocervical trunk.
And if we were to use that clock analogy, then this would come off
somewhere between 9:00 and 12:00 somewhere, like 10:00 or 11:00.
OK, so this is the thyrocervical trunk.
Now down here just below
that between 6:00 to 9:00, like 7:00 or 8:00.
This is the internal thoracic artery.
That's the internal thoracic artery.
And then the artery that comes off posteriorly
here at maybe 1:00 or 2:00.
That's the costocervical trunk.
So if you're having trouble trying to figure out what artery is what,
look at the sagittal images because this relationship is very consistent.
Now let's look at the axials, and we will have our sagittal as up to help guide us.
So this,
I mentioned, is the vertebral artery
and that ascends in the transverse foramen of the cervical spine.
OK, so that's the vertebral artery.
Now the next one to come off this is the thyrocervical trunk.
And if we follow that, that
terminates in the inferior thyroid artery.
So it has this classic hairpin turn here.
Actually, let's let's pull up.
Let's pull up the coronal images, and I'll show that to you
because the inferior thyroid artery
has this classic hairpin turn
and it goes to the inferior aspect of the thyroid gland.
And then the next terminal artery, the second to last terminal artery
of the thyrocervical trunk is this one right here
and this one is the ascending cervical.
And if I triangulate it, you can see it on the axial.
There it is.
So that's the ascending cervical artery. OK.
And so those are the two terminal branches.
And remember, I mentioned that there's three lateral branches,
so usually the first one that comes off
is the suprascapular artery.
And let's look at the coronal images to identify that.
So this is
it right here, this is the suprascapular artery.
And if we follow that laterally, it goes off to the scapula
now because this is a neck CT, we don't have the scapula,
but this goes laterally.
And if we were to follow it, it would go to the suprascapular notch.
And on the axial images, that's it right there.
OK, this is the suprascapula artery right here.
The other branch we have to
identify is the superficial cervical artery.
And if we continue to follow this,
you can see that there's a branch that comes off here
and it goes laterally, it passes over the anterior scalene muscle.
And if we follow this artery,
it goes posterior here
and it goes deep to the trapezius muscle.
So this is the superficial cervical artery.
And then I mentioned before that the last branch is the dorsal
scapular artery, and sometimes it's hard to find these arteries.
So if you start off knowing
where it should end up, then that's another way to find it
so the dorsal scapular artery should run medial to the scapula.
This is the scapula right here, and this is it.
So if we follow this artery back, you can see that
this artery arises directly from the subclavian artery.
So in this patient, rather than arising from the thyrocervical trunk,
it arises from the subclavian artery directly, which is very common.
The internal thoracic artery
or the internal mammary artery, as I usually call it, is right here.
And you can see that arises just opposite
from where the thyrocervical trunk arises
within 1 cm of the thyrocervical trunk.
OK, so this is the thyrocervical.
This is internal thoracic.
All right.
And that leaves us one last branch, which is the costocervical trunk.
You remember that arises from the posterior aspect
of the subclavian artery, and that's it right there.
And this is best seen on the sagittal images.
So let's pull up the sagittals.
So here's the costocervical trunk.
And if I triangulate that.
That's it right there.
And let's just follow it, so this should branch into two arteries.
And there it is.
So it branches into the supreme intercostal,
so you could see that this goes below the first rib.
This is the first rib right here.
And the supreme intercostal
is the intercostal blood supply to the first and second ribs.
And then this superior branch
goes above the first rib behind the spine.
And this is the deep cervical artery.
Okay, so the deep cervical artery arises from the costocervical trunk,
and the superficial cervical artery arises from the thyrocervical trunk.
OK. And if
we continue looking at the subclavian artery,
you can see there's no more branches that arise from it.
And as we go past this line right here, that's made by the first rib.
It becomes the axillary artery.
OK, so this is the axillary artery right here,
and this is the subclavian artery right here.
All right, so I hope this helps you identify
the branches of the subclavian artery.
If you have any questions about this topic or any other thoracic
radiology topic, let me know in the comments below.
Thanks.