Aneurysms

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Introduction0:00–0:41

The word aneurysm is based off the Greek word aneurysma, which means “dilation.” And that makes sense because aneurysms are abnormal dilations in a blood vessel.
We officially label a bulge in a blood vessel as an aneurysm when the diameter of that bulge is about one and a half times larger than the normal diameter of the blood vessel.
Aneurysms can happen to any blood vessel in your body, like the aorta, the femoral artery, the iliac artery, the popliteal artery, and cerebral arteries.
They can also happen in your veins too, but those are less common because blood pressure in veins is much much lower than in the arteries.

Types0:41–1:48

There are two major categories of aneurysms, true aneurysms and pseudoaneurysms. In true aneurysms all the layers of the blood vessel wall dilate together.
True aneurysms that balloon out symmetrically on all sides of the blood vessel are called fusiform aneurysms whereas asymmetrically shaped aneurysms balloon out to one side of the blood vessel.
This asymmetrical shape usually happens because for some reason one side of the blood vessel wall has had to put up with higher blood pressure than the rest of the vessel wall or because the wall was weaker on one side to begin with.
Asymmetrical true aneurysms can be called either “saccular” or “berry” aneurysms. You can think of pseudoaneurysms as false aneurysms as in they’re not actually aneurysms at all.
They are caused by a small hole in your blood vessel which allows blood to leak out of the vessel and form a pool of blood that looks like a fusiform or berry aneurysm depending on where the hole is and how big it is.
The blood pools because the surrounding tissues act as walls that contain the blood in one spot. Arterial aneurysms occur most commonly in the aorta with about 60% of true aortic aneurysms happening in the abdominal section of the aorta and the other 40% happening in the thoracic section.

Pathophysiology1:48–4:40

Of all the abdominal aortic aneurysms, you can find about 95% of them just below the point where the renal arteries branch off from the abdominal aorta, but above the aortic bifurcation.
That’s because there is naturally less Elastin in the walls of this part of the aorta than the rest of the aorta. Aneurysms are caused by a weakness in the blood vessel wall, so anything, really anything, that causes the wall to weaken can cause an aneurysm.
When a blood vessel wall weakens, it struggles to contain the pressure of the blood pushing against the walls, so the diameter of the blood vessel lumen increases.
On top of this, pressure on the blood vessel walls increases as the diameter of the lumen increases thanks to LaPlace’s law, making the aneurysm diameter even bigger, creating this cycle of continuous bulging.
You’ve likely experienced this when you blow up a balloon. The first breath into the balloon is tough, but the next several breaths are pretty easy.
This is why aneurysms usually get bigger over time, it’s because of this positive feedback loop. So what underlying conditions might weaken the wall of blood vessels?
Well one way is if all the layers of those blood vessel walls don’t receive oxygen. Typically the cells of the vessel walls are able to get oxygen from blood as it flows by, but in the first section of the aorta, where the walls are super thick and muscular in order to handle all that blood pressure coming from the heart, they need to have their own set of blood vessels that supply the tunica media and the tunica externa.
We call these special blood vessels vasa vasorum. In hypertension, the vasa vasorum can develop hyaline arteriolosclerosis, narrowing their lumen, causing ischemia to the aortic wall, and we end up with atrophy of the smooth muscle of the tunica media.
Overall all this weakens the aorta’s wall. The same thing can happen in blood vessels without vasa vasorum if we have a bunch of plaque building up on the tunica intima thanks to our friendly neighbourhood atherosclerosis.
Oxygen just can’t penetrate all the vessel’s walls. You see this type of aneurysm often in the abdominal aorta, where blood pressure is high and the aorta walls are nourished by passing blood.
If you think about this it’s no wonder then why both aneurysms and atherosclerosis share similar risk factors: usually people who are male, are over the age of 60, who have hypertension, and smoke.

Causes4:40–6:40

If we look at tertiary syphilis, it affects the vasa vasorum as syphilis causes inflammation in the tunica intima of the vasa vasorum (which again are those blood vessels that deliver oxygen to the thick walls of larger blood vessels), ultimately leading to a narrower lumen and restricting blood supply to the vessel walls of the thoracic aorta, causing atrophy.
By the way, the name for this vasa vasorum inflammation is endarteritis obliterans. If you were to look at the vasa vasorum in tertiary syphilis, you’d see the inflammation causes fibrosis and scarring on the walls creating this cool to look at, but less cool to have tree-bark like texture.
Other bacterial infections can also cause aneurysms, which we label as mycotic aneurysms. The bacteria from an infection somewhere else in the body can break off from the main infection and travel around in the blood.
Usually these embolic bacteria will get stuck in the intracranial arteries, visceral arteries, or the arteries feeding the arms and legs.
There the bacteria enter and weaken the blood vessel walls, leading to, you guessed it, an aneurysm. Some of the bacteria that commonly cause mycotic aneurysms are, and these can be tricky to pronounce, so bare with me, Bacteroides fragilis, Pseudomonas aeruginosa, and anything in the Salmonella species.
You’ll also see mycotic aneurysms are a complication of infective endocarditis. But it’s not limited to just bacteria.
Infection from the fungi Aspergillus, Candida, and Mucor are also a common cause of mycotic aneurysms. Genetic disorders affecting your body’s ability to properly form connective tissue like fibrillin or collagen also weaken the blood vessel walls, so people with Marfan’s syndrome have weakened blood vessel walls because the elastic properties found within fibrillin is impaired.
And people with Ehlers-Danlos syndrome are more likely to develop aneurysms because their ability to form collagen proteins is disrupted.

Complications6:40–9:19

Alrighty then. So intact aneurysms are usually okay, and don’t cause any symptoms.
I say usually because the bulging blood vessel can compress other organs or vessels around it. So if an aneurysm compressed a major vein like the inferior or superior vena cavae, it could decrease the amount of blood returning to the heart.
Usually though the big worry with aneurysms is the possibility that they might explode, or more like rupture, but it’s more fun to say explode.
When an aneurysm ruptures, it’s like having a water main break. Blood is spewing out from the hole in the blood vessel and less blood is flowing downstream to the cells that need it, which causes ischemia in that downstream tissue.
In thoracic aneurysms specifically, a very serious complication can occur if the aneurysm is right above the aortic valve.
As the aneurysm dilates, it pulls on the walls around the aortic valve preventing the aortic valve from closing properly, and allowing blood from within the aorta to flow back into the ventricle during ventricular diastole.
This particular condition is called aortic insufficiency, and can also cause a high-pitched brassy like cough because the left recurrent laryngeal nerve which wraps around the aorta is stretched by that expanding diameter of the aorta.
I don’t have that audio clip for that brassy cough sound, but it’s pretty distinct when you hear it. Moving on to the brain.
If an aneurysm ruptures in the brain, blood will pool into the subarachnoid space putting pressure on the brain tissue and irritating the meninges, causing symptoms like a very sudden and intense headache, and the inability for someone to flex their neck forward.
Another point on the list of terrible things aneurysms can cause is blood clots. As blood flows past the aneurysm, some of the blood might pull over into the extra lumen space caused by the aneurysm itself.
This blood isn’t being pushed along the blood vessel as quickly as the rest of the blood, and when blood stays still for too long, it likes to clot.
Given enough time the blood clot might become so big it blocks off the entire blood vessel, causing tissue ischemia, or it could break into smaller pieces called emboli and get wedged in a smaller blood vessel, also causing ischemia.
As an aside, it’s kinda of nifty that the clotting property of blood is really useful to stop blood from leaking out of our blood vessels, but it just also happens to be really really deadly if it stops the blood from moving altogether.
Honestly blood coagulation could be the plot for the third installment of the Speed movies. Ok, back on track, abdominal aortic aneurysms sometimes have signs and symptoms, and sometimes they don’t, even if the aneurysm has ruptured.

Signs and Symptoms9:19–9:19

Signs and Symptoms9:19–9:56

Really severe pain in the left flank which includes the abdomen, chest, lower back, as well as the groin, a pulsating mass that is in time with the heartbeat somewhere in this painful region, and hypotension occur in about 50% of aneurysms that have ruptured and are considered the classical sign of an abdominal aortic aneurysm.
Thoracic aorta aneurysms usually don’t have any symptoms, although sometimes they can cause severe chest, back, and abdominal pain.

Diagnosis and treatment9:56–10:16

And there you go, that’s aneurysms. Aneurysms can be asymptomatic, and are sometimes diagnosed incidentally when an individual gets an imaging study for another reason.
Usually they’re seen best on an ultrasound, CT scan, or MRI. If an aneurysm is present and large enough to cause risk to an individual, it can be treated surgically.

Review10:16–10:55

All right, as a quick recap... Aneurysms are blood-filled bulges that form in weakened areas of the blood vessel walls.
Left untreated, aneurysms can burst, causing uncontrolled internal bleeding or excessive blood clotting. Based on the size and location of an aneurysm, surgical treatment may be necessary.