I'm gonna talk to you now about an uncommon,
but very important emergency, aortic dissection.
So the definition of aortic dissection
is a separation of the normal layers of the aorta
with accumulation of blood between those layers.
As you can see in this image,
the normal aortic wall is made up of three layers.
The adventitia on the outside, the media in the middle,
and the intima on the inside which is directly adjacent to the blood
that would normally flow through the aorta.
When the aorta dissects, there's a tear in the intima
that allows blood to intercalate into the media
and that's what causes the dissection
with accumulation of blood between those layers.
Aortic dissection like I said is pretty rare.
There's only between 5 and 30 cases per million people per year,
and in the United States we only see about 2000 cases annually
across the whole country.
It's most common in middle aged patients
particularly in the age range from 50 to 65,
and it's much more common in men than it is in women.
For every one woman who gets an aortic dissection,
three men will suffer from the same disease.
In the United States it's more common in African-Americans,
a little bit less common in whites and least common in Asians.
And there's a definite familial predisposition.
There are a number of hereditary conditions
that increase the risk for aortic dissection
particularly those that affect connective tissue.
So how does aortic dissection work?
There's a couple of different mechanisms by which the aorta can dissect.
One of which is formation of an entrance tear in the intima,
so basically you get a little hole in the intima
which allows blood to escape from the aortic lumen
into the wall creating a true lumen and a false lumen
that are right next to each other,
separated only by that thin layer of intima.
Another thing that can happen is rapture of the vasa vasorum.
So the vasa vasorum provides blood supply to the aorta itself
and basically when those small vessels
that run through the aortic wall rupture,
you can get bleeding directly into the aortic wall
and formation of the self-contained hematoma inside the wall.
Lastly, atherosclerotic disease can cause aortic dissection
because basically you develop an atherosclerotic plaque that ulcerates,
allowing bleeding inside of the wall of the aorta.
Besides this there are also other mechanisms of aortic dissection.
Changes in the media without any entrance injury of the intima
can result in dissection. These changes can include cystic medial
necrosis or abnormalities in the architecture of the
medial elastic fibers.
Also there are genetic abnormalities in the elastic fiber
and elastin protein possible. All these changes can result
in aortic dissection without the formation of a false and a true lumen.
However you get your aortic dissection.
It's a really dangerous disease process
beause it's associated with a number of important complications.
One thing that can happen with the dissection
is you can get compression of the true lumen of the aorta
if the hematoma inside the wall is large enough.
So basically, you get enlargement of the hematoma
with mechanical compression of the true lumen
and that can lead to hypoperfusion of any organ distal
to where the lumen is obstructed.
You can also get aneurysmal dilation of the false lumen,
so as that false lumen gets bigger, and bigger, and bigger,
it can balloon out and the wall can weaken creating risk of rupture.
Raptures of the aorta as you can imagine can be rapidly fatal.
You can also get propagation of the dissection.
So wherever along the course of the aorta the dissection starts,
it can move either distally or proximally.
When it moves proximally down into the aortic arch and the heart itself,
you can get aortic valvular insufficiency,
cardiac tamponade, or myocardial ischemia.
If the dissection involves the vessels that lead up into the head and neck,
you can get stroke.
And if it involves the abdominal vessels
you can get renal or mesenteric ischemia.
There are a number of risk factors
that predispose patients to aortic dissection.
Basically anything that increases the aortic wall stress
can cause weakening of the intima and predispose to bleeding.
So hypertension is probably the single
most important risk factor for dissection.
You can also see it in patients with atherosclerotic disease because again,
that increases wall stress and weakens the intima.
Cocaine use, Aortic valvular disease, and pregnancy.
There are also conditions that weaken the intima itself.
So connective tissue disorders, syphilitic aortitis
which is pretty rare in this day and age but we still see it occasionally.
And also traumatic injuries of the aorta
particularly rapid decelerations.
So cars that strikes stationary objects,
the heart swings forward in the chest wall
causing mechanical strain on the wall of the aorta
leading to intimal tear and dissection.