Thoracic aortic aneurysms

- [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.