00:01
Although we've already seen
the mediastinum.
00:03
We're going to revisit
the posterior mediastinum.
00:06
Starting with some
superficial stuff,
then some deep stuff.
00:09
Now that we've had a greater
understanding of the rest
of the mediastinum.
00:15
So let's go back and look
at the vagus nerves.
00:19
So the vagus nerves, as we know are
descending from the neck area
down into the thorax, and
eventually into the abdomen.
00:25
And here we see the right vagus
nerve, and the left vagus nerve.
00:30
And we also know that there are
what are called recurrent branches.
00:34
Recurrent laryngeal branches
that we're going to deal with.
00:37
But before we see those,
we know that distally
they're going to form a plexus
over the esophagus called
the esophageal plexus.
00:46
But that recurrent laryngeal
that we saw is wrapping under
the aortic arch on the left.
00:52
But the aortic arch is
an asymmetric structure.
00:54
So let's look at this in a
little bit greater detail.
00:58
On the right side,
we see the right vagus nerve
coming down to the level
of the right subclavian artery.
01:05
And then if we blink that out,
we can actually see
the right recurrent
laryngeal nerve here
wrapping underneath
the right subclavian artery
to head back towards
the trachea in the larynx.
01:17
But on the left side
is quite a bit different.
01:19
We have the left vagus nerve
coming down a lot further
before it gives off the left
recurrent laryngeal nerve.
01:28
And that's because of
embryology essentially.
01:32
The recurrent laryngeal nerve
started out very symmetric
early in development,
but because of regression
of some right sided structures,
and ended up higher up
underneath the subclavian.
01:42
But on the left side,
we had that thing called the ductus
which becomes ligamentum arteriosum.
01:48
And it sort of traps
the left recurrent laryngeal nerve
underneath the aortic arch.
01:55
Now, let's look at some
deep structures
of the posterior mediastinum.
02:01
If we look deeply into
the posterior mediastinum,
we see a lot of important veins.
02:06
We already know that the IVC
is bringing deoxygenated blood
from below the heart.
02:12
And the SVC is bringing
deoxygenated blood
from above the heart.
02:17
What about the area in between?
That's something
we have to deal with.
02:21
Importantly, we have
intercostal veins in between.
02:24
And what they're going to do
is drain into the Azygous veins.
02:28
And on the right side, they can
drain directly into the azygous
because it's a
right sided structure.
02:34
But on the left, they have
to do something a little different.
02:37
Inferiorly, they're going to
drain into the Hemiazygous vein.
02:41
And then superiorly into the
accessory hemiazygous vein,
and those will cross over the
midline, over to the right side
to reach the azygous vein.
02:51
If we look at a lateral view,
we can see the arrangement
of the SVC receiving this
azygous vein from posterior.
03:02
And there's also an exception
to this rule, generally speaking,
where the first also called supreme
or highest intercostal artery
takes a shortcut and instead drains
directly into
the brachiocephalic vein
instead of the azygous vein
Another important deep structure
of the posterior mediastinum
are the paired sympathetic trunks
going along either side
of the vertebral column,
in between which will find
a lymphatic structure called
the thoracic duct.
03:33
This thoracic duct is going to
go all the way through the thorax
up towards some venous
structures.
03:41
Notably, it's going to join
at the junction
of the left internal jugular vein
and the left subclavian vein,
so that all that lymphatic fluid
it's draining
can enter the venous system.
03:53
So again, we have
the thoracic duct
draining most of
the lymphatic fluid,
especially all of this stuff
coming from the abdomen.
04:01
But we have a smaller duct
on the right simply called
the right lymphatic duct.
04:06
And it's draining into the same
location but on the right side.
04:11
So what this does
is essentially drain
the right upper part of the body,
including the right upper limb,
right thorax, and right head
and neck.
04:21
Whereas, the thoracic duct
handles essentially everything else.