- [Voiceover] What is a thoracic aortic aneurysm?
Well let's break that down.
An aneurysm is a permanent localized dilation of something.
In this case, of the aorta
which is the main artery in our bodies.
Now the aorta is pretty long,
it originates from the left ventricle of the heart here
and it extends down through the thorax
and in to the abdomen.
This type of aneurysm occurs in the thoracic section
of the aorta, which is about from here to about here.
Let me just orient you to what we're looking at right now.
We're looking at an anterior view
or a front view of a guy
where his chest is a little bit transparent
and we can see his heart and his major vessels,
so his major artery, the aorta,
and his major vein, the vena cava.
Let me just mention that the heart here
is supposed to be in front of the thoracic aorta,
kind of like this.
So it's supposed to look something like this
but I sort of faded it out so that we could see
the thoracic aorta really well.
Just bear in mind that the thoracic aorta
is going to be behind the heart normally.
You can get aneurysms in other sections of the aorta as well
but we're just going to look at the thoracic ones for now.
What exactly does an aneurysm looks like?
Well, it sort of looks like this.
It looks like someone came along and blew up
that part of the aorta, like a balloon almost.
You can see the walls of sort of dilated and bulged out
on both sides in this case.
Now the aorta has a lot more room in it at that area.
Just so that I really can convince you
of that dilated appearance,
here's what it looks like on an MRI.
Here's an MRI image of a thoracic aneurysm
that shows that ballooning effect really well.
So don't really worry too much
about the rest of the structures on the MRI
just sort of take note of this aorta here
and look at how dilated its walls are.
It looks like somebody actually put a golf ball
or a tennis ball in the aorta there.
We'll talk more about diagnosing aneurysms
with imaging technology a little bit later
but I'm just showing you this now
to really hammer home what it looks like.
Let me just clarify that an aneurysm
can theoretically happen in any vessel.
Not just the aorta but in any artery or vein.
Although we do see them in arteries far more commonly
than in veins
and we'll touch on why that might be
a little bit later on.
Even in terms of arteries,
they don't just happen in the aorta.
We actually see them in other arteries relatively commonly.
So yes, while the most commonly seen aneurysm
is in the aorta,
we might also see them in the iliac arteries
that deliver blood to your lower limbs.
Your popliteal artery is behind your knees,
arteries in your cerebral or your brain circulation
or your femoral artery that deliver blood to your legs.
But of the aneurysms that happen in the aorta
which is the most common place to have them,
about 40% of them happen in the thoracic regions
or the region we're talking about now.
The rest of them happen in the abdominal part of the aorta.
Now, how dilated is dilated enough
to call something an aneurysm?
Well, if you get a permanent dilation of an artery
you have at least 1 1/2 times in normal diameter
then clinically you've got yourself an aneurysm.
To give you some hard numbers here,
the average diameter of the thoracic aorta
is about 2.7 centimeters,
so you'd have an aneurysm by definition
if your aorta permanently dilated to about four centimeters
in that area.
Not all aneurysms are created equal though,
they're actually classified into true and false types.
In the true type, the entire arterial wall balloons out
and all of the layers of the wall are involved.
So the tunica's intima, media, and adventitia
they all get dilated together
and the arterial wall balloons out.
True aneurysms can also be subdivided even further
so true aneurysms that are symmetrical
are called fusiform aneurysms.
Fusiform just means spindle shaped
and that's sort of like the one I just drew.
These ones are uniform in shape.
You can also get true aneurysms that are saccular
which means that only one side of their wall
has become dilated
and that might happen if one side of the wall
for whatever reason has been chronically exposed
to higher blood pressures than the other side.
You're probably familiar with this saccular aneurysms
without even realizing it.
They're also called berry aneurysms.
So saccular because you could say
they almost look sac shaped or berry
because they can also be thought of as berry shaped
but they're the same thing.
Good, so those are the true aneurysms
fusiform and saccular.
Now, we're going to skip over
to the other type of aneurysms,
the false aneurysm.
In a false aneurysm also called a pseudoaneurysm
and pseudo just refers to the falsity of it
and you'll see what I mean in a second.
This can happen if you get a puncture in one of your vessels
from some type of trauma like an arterial injection.
The vessel starts to leak blood outside of it's walls
so now you got a hole in one of your vessels.
What happens next is that blood will leak out
of the lumen of the vessel and in to the tissue
and it will start to collect between the actual vessel
in the surrounding tissues
so you get this one sided ballooning happening.
That's a false aneurysm because it's not actual dilation
of the vessel but it does have a similar shape
as an actual aneurysm.
Also this false aneurysm ballooning
can happen on both sides of the vessel,
if you have a leak on both sides.
Now that you know all about what thoracic aneurysms are
maybe we should look at why they're not really the best
thing to have happen inside of us.
Why are they such a bad thing?
Well it's really the potential complications of aneurysms
that can make them so dangerous.
Let me just clear off some room here.
For one, they can rupture.
To develop an aneurysm in the aorta
there has to be some weakness of the wall going on
that can predispose an aneurysm to rupture as well.
When they rupture they spill blood out of the circulation
and in to the tissues surrounding the aneurysm
and when blood spills out of the vascularture
there's less blood able to get around the body
to do its job.
So if a ruptured aneurysm isn't dealt with emergently
among other problems that would crop up
your body tissues would start to become oxygen deprived
and sustained irreversible damage.
They can also develop clots that form inside of them
and that's a process called thrombus formation.
Thrombi or clots, they form when blood's allowed
to slow down and hang out
instead of rushing around like normal.
You can probably see something like a berry aneurysm
would be an awesome place for thrombus formation
because blood just gets in there
and gets the kickback and relax and clot.
These are bad because if it the clot gets big enough
it might occlude the blood vessel completely
so no blood can get through.
On top of that, bits of thrombus can break off
or embolize and float around in the bloodstream.
This is bad because in this little emboli
can get stuck in smaller vessels
and cause ischemic damage.
Damage caused by oxygen deprivation
because then these emboli are preventing blood
from getting through that vessel
and supplying blood to whatever organ or structure
it's supposed to be supplying blood to.
Aneurysms can compress things
so they can compress other structures
that are running by them.
For example in the thorax, the vena cava runs
right beside the aorta.
An aneurysm here in the thorax, if it got big enough
it might start to compress the vena cava
and compromise or slow down venous return to the heart.
There's a few reasons why aneurysms
are not are favorite thing.
Why do aneurysms occur in the first place?
Well there's a couple reasons,
the most common reason the aorta would balloon out here
is because of something called arteriosclerosis
or degenerative change.
That just means that the walls of the aorta
start to change from normal
where they're nice and strong and elastic
and they start to get weaker and less elastic.
A weaker, less elastic aorta or any artery for that matter
is less able to deal with the blood pressure wave
that passes by every second.
Let me give you some background here.
Recall that the aorta has three layers
the adventitia on the outside,
the media in the middle,
and the intima on the inside.
In the media, there's lots and lots of proteins
like collagen which give the aorta its tensile strength
and elastin that gives it its elastic recoilability
to spring back to normal
after a blood pressure wave passes by.
Two things about this,
it's related to developing an aneurysm.
First, as we descend down the aorta
we have relatively less collagen and elastin
than we do up at the top here.
To add to that, as people get older
there's some degeneration of the collagen and elastin.
So not only is the aorta becoming slightly dilated
and weaker because some collagen is degenerating
but the aorta also ends up not being able to spring back
to its normal shape as it used to be able to
after a blood pressure wave passes by.
Second, according to the Law of LaPlace
which you might have learned from your Physics teacher,
dilation of a tube results an increased wall tension
from whatever fluid is inside that tube.
In our case here, the fluid is blood
that's rushing through it pretty high pressure.
Remember we've just left the heart
and that blood pressure causes a wall to dilate even more.
There's a pretty bad cycle that goes on here
to cause an aneurysmal dilation.
The wall weakens which causes it
to be more prone to dilating
and the more dilated it gets, the more prone it is
to becoming more dilated
because then it isn't able to cope with the blood pressure.
There are other causes too of aneurysm.
To name just a few, previous aortic dissection
might cause an aneurysm to develop
because remember then aortic dissection
is already a defect in the vessel wall,
so it won't be as strong as it was before the dissection
so you could develop an aneurysm there.
Connective tissue disorders like Marfan syndrome
or Ehlers-Danlos syndrome
where some of your structural proteins like your collagen
don't form properly.
That would predispose you to an aneurysm.
Atherosclerosis would predispose you
to developing an aneurysm.
That's the pathological deposition
of cholesterol particles onto the inside
of your arteries and the cholesterol deposition
will kick off this inflammatory cascade
and cause the walls of any vessel that happens in
to weaken and predispose that vessel
to developing an aneurysm.
By now you must be asking what you can do
to avoid developing an aneurysm.
Well, there's a few things that are associated
with development of aneurysms
and these are called risk factors.
Here are a few of the major risk factors.
Atherosclerosis is a big risk factor.
Smoking is also a big risk factor
for development of aneurysms
partly because it contributes to atherosclerosis development
and partially because it directly damages the walls
of your arteries.
Hypertension is another risk factor.
COPD or chronic obstructive pulmonary disease,
that's another risk factor.
Smoking can actually cause atherosclerosis to get worse.
It causes COPD and it can cause hypertension.
You can see a trend here, smoking is a pretty huge
risk factor since it already contributes
to all of the other risk factors that we have on our list.
Being male is a risk factor,
so that's something I still have to come to terms with.
Males are almost five times more likely to get aneurysms
than females and it's not entirely known why
but that's what we see.
Age is a risk factor.
Being older than 65 years old predisposes you
to developing aneurysms and that's because older people
tend to have stiffer aortas,
so that's partly because of calcification
which is the deposition of calcium within the walls
of the aorta that happens as you get older
and partly because there's been more degeneration
of the collagen and elastin over time
like we talked about earlier.
Genetics also plays a role, so if you have any of those
connective tissue disorders we talked about earlier
or if you've had a family history of people
in your family developing aneurysms,
then that puts you at a greater risk of developing one.
How do you know if you have a thoracic aneurysm?
Well if you do have one, chances are you won't know about it
because 75% of people with this are asymptomatic.
Most thoracic aneurysms are either discovered incidentally
on imaging or unfortunately because of a rupture
but let's try to group our symptoms into two main groups.
Let's say we will have a group of symptoms
associated with an intact aneurysm
and a group of symptoms associated
with a ruptured aneurysm.
Let's look at the intact aneurysm
and we're assuming that the aneurysm has reached a size
where it can actually cause symptoms.
If you develop an aneurysm in this part of the aorta here
in the upper part of the aorta
then it might compress on structures in that area.
You might compress your recurrent laryngeal nerve
and that nerve controls your vocal chords.
If you compress that nerve, you might end up
with a hoarse voice or you might compress your vena cava
and you'd have compromised vena's return
or you might compress your trachea or your esophagus
and then you might have airway or esophageal obstruction.
The compression will also often cause pain
in the region of the aneurysm.
Now symptoms of a ruptured aneurysm,
so hypotension or pathologically low blood pressure
is one of the major symptoms
and this is because blood is leaking out
of your circulatory system at this point.
So you can't maintain pressure in what's supposed
to be a closed pressured system, your circulation.
Syncope, also known as fainting,
that might happen because not being able to maintain
your blood pressure means you might not be able to get blood
up to your brain and that would cause you to faint.
Hemoptysis, that's coughing up blood.
That might happen if the aneurysm erodes
into the trachea nearby
or hematemesis, that's vomiting up blood.
That might occur if the aneurysm erodes into the esophagus
also nearby, so we don't want these things to happen to us.
How might we go about finding these little guys
before they rupture?
Well the most sensitive and specifically
of finding a thoracic aneurysm is through imaging.
You could get a chest x-ray.
Radiologist will look for signature shadows
and opacities that appear on an x-ray
that suggest thoracic aortic aneurysm.
You could get a CT scan, CT
or computerized tomography scans
can quickly and accurately evaluate the entire aorta
to look for the exact location extent of the aneurysm.
MRIs can also really accurately evaluate
the entire aorta to look for the exact location in extent
of the aneurysm.
MRIs don't expose the patient to any radiation
but they take a bit longer to do,
they're less readily available
and they cost more than CT scans do.