So this is an introduction
of a man who has had a catastrophic event
in his abdominal aortic aneurysm. It has started
to rupture. This can lead to hemorrhage and
be fatal if not taken care of urgently either
with surgery or with angioplasty with a placement
of a stent.
So what is the definition of an aneurysm?
An aneurysm is an abnormal dilation of a blood
vessel to greater than one and half times
its normal size. The normal size of the aorta
is between 3 and 3.5 cm depending on the size
of the person. When one sees these with an
ultrasound sometimes there is actually clot
in them and sometimes that clot can embolize
and cause problems in the peripheral arterial
system of the legs. Commonly, an abdominal
aorta is usually approximately just 2 cm to
3 cm in diameter. When it gets to 3 to 3,
we are really talking about an aneurysmal
dilatation of the abdominal aorta. Sometimes
since the wall of the aorta is weakened, a
tear can develop and you can have a dissection
starting from the point of the aneurysm. Size
and location may vary. One can have aneurysms
of the aorta in the chest. One can have aneurysms
of the abdominal aorta and there can be aneurysms
of peripheral arteries that can also rupture.
For example, femoral artery aneurysm or popliteal
Here we see a little cartoon. First of all
the normal aorta with its intima, the inner
lining the endothelial inner lining, the media
which is the smooth muscle layer, and then
the adventitia which holds the blood vessel
in place. You see here a true aneurysm in
which there is a bulge from the vessel wall
and in fact often the bulging part of the
vessel wall is thinned and abnormal in structure.
However, the wall remains in place. In a false
aneurysm rupture has already occurred and
only thing preventing blood from escaping
from the aorta is a clot or some fat and fibrous
tissue that is formed. This is called a pseudoaneurysm
and the outer layer is not containing the
vessel wall. It's containing clotted blood
and sometimes some fibrous, some scar tissue.
These are very likely to rupture they are
an urgent reason for either surgery or angioplasty.
Here are two example of thoracic aortic aneurysm.
In the first form, the saccular or berry just
like berry, the fruit, is a little bulge off
the side of the aorta. Berry aneurysms can
also occur in the blood vessels of the brain
and when they rupture they are often fatal
because brain haemorrhage, cerebral haemorrhage
is a very, very serious and frequently fatal
condition. You can see that the little berry
aneurysm, the little sac there, that pouches
out from the ascending aorta just a above
the aortic valve appears as a little round
nubbin on the aorta. This is in comparison
to the fusiform aortic aneurysm in which the
entire circumference of the aorta is involved
as opposed to a little nubbin sticking off.
The entire ascending aorta is dilated in this
little cartoon that shows a fusiform aneurysm.
The widening of this part of the entire blood
vessel contains blood vessel wall. There is
no rupture here but there is weakening and
often thinning of the vessel wall in both
of these forms of aneurysms. So because of
these weakening they are at increased risk
of rupturing. And of course rupturing can
lead to fatal internal hemorrhage.
Let's look at the abdominal aortic aneurysm
because that is the most common as we will
talk about in a moment. It is an exceedingly
common event particularly in elderly folks
who have atherosclerosis. The abdominal aortic
aneurysm often referred to as a AAA occurs
in the abdominal aorta, the overwhelming majority
of them 85% to 90%, occur below the kidney.
So below the renal artery. They are diameters
again as we said before greater than 3 cm
and generally when they get beyond 4 cm in
diameter there is a high risk of rupture.
Remember that the normal-sized aorta is 2
cm on average, 2 cm to 2.5 cm depending on
a person’s size so that when the aorta gets
to 3 it is clearly an aneurysm, and when it
gets to 4 there is a high risk of rupture.
And aortic dissection on the other hand
is not so much a thinning of the wall and
a widening of the aorta but an actual tear
in the inner lining of the aorta allowing
the blood in the channel, in the lumen of
the aorta or other blood vessel to get into
the wall of the aorta. And in the sense just
like a surgeon dissects with a finger, the
blood passes down through the wall of the
aorta and sometimes breaks out again through
the outer wall leading to a hemorrhage which
is frequently fatal. This is a very serious
medical emergency requiring urgent medical
or angioplasty repair because ruptures are
very, very high risk. It can partially heal
itself with a false aneurysm that is with
a clot but it is still high risk to go on
at a later date and rupture with fatal hemorrhage.
And again a dissection results from a tear
that starts in the intima, giving the blood
access to the internal layers of the aorta
and forcing them apart and of course, there
can be fatal hemorrhage with this. There is
a very high risk of fatal hemorrhage.