Abdominal aortic aneurysms

- [Voiceover] An abdominal aortic aneurysm, as the name suggests, is an aneurysm, a ballooning, that develops in the abdominal section of the aorta. So you might remember that there are true and false types of aneurysms, but when you hear abdominal aortic aneurysm, or AAA, what's most likely being referred to is a true aneurysm, a permanent dilation of the wall of the aorta. So, an aneurysm that you get in your abdominal aorta can look something like this. So, this here is a bit of your aorta. Let's say it's this section here. So, you can see that what's happened to it is that it's sort of symmetrically ballooned out on both sides, and we call an aneurysm that's ballooned out symmetrically on both sides, we call that a fusiform aneurysm. And also notice that all of the layers of the wall of the aorta are involved in this ballooning out. So, they all sort of dilate out together. So, you have the three layers of the aorta involved, the intima, the media, and the adventitia, and they all balloon out together as part of a true aneurysm. And, by the way, to be considered an aneurysm, a dilation has to be permanent, and it has to dilate the vessel out to at least 1-1/2 times its normal diameter. So, this space here would end up being 1-1/2 times the normal diameter, at least 1-1/2 times. So, do they happen in a particular place in the abdominal aorta? Well, yeah, they do. They, AAA's, most commonly occur below the renal arteries that supply the kidneys, and about 95 percent happen there, and we'll touch on why that is in a little bit. But first, let me tell you why we really don't want AAA's to occur in our aortae. Aortae, is that the plural? I'm not sure. Anyways, so it's really the potential complications of aneurysms that makes them so dangerous. For one, they can rupture, and when they rupture, they start to pour blood out of the aorta and into the tissues in the neighborhood. So, that means there's less blood able to go around the body to provide you with oxygen and glucose and other nutrients. So, if a ruptured aneurysm isn't take to the hospital right away, a lot of tissues in your body would start to become oxygen-deprived and start to get seriously damaged. And rupture is really the biggest worry about abdominal aortic aneurysms. I'm going to say AAA from now on, because abdominal aortic aneurysm is a long phrase. But anyways, I mean, I'll outline a few other complications of aneurysms in a minute, but it's really the rupture and outpouring of blood into the abdominal cavity that we worry about the most with AAA's. Okay, so why else don't we like aneurysms? They can develop clots that form inside them. Clots, also called thrombi in this case, can form when blood sort of ducks out of the normal circulation to go hang out in an aneurysm. So, this isn't such a huge problem with abdominal aneurysms, because the abdominal aorta seems to develop generally fusiform aneurysms, but you can probably see how something like a berry aneurysm, and let me just draw one of those in, so you can see how a berry aneurysm would be an awesome place for a thrombus formation, because blood just sort of gets in there and kicks back and relaxes and clots. So, these are bad because if the clot gets big enough it might occlude the blood vessel completely, so no blood can get through, and that would be bad. On top of that, bits of thrombus can break off or embolize and float around in the bloodstream, and then this would be bad, because then these little emboli can get stuck in smaller vessels and cause ischemic damage, which is damage caused by oxygen deprivation, because then they're preventing the flow of blood in that given vessel. So, yeah, I said that berry aneurysms don't usually develop in the abdominal aorta, but we still have to think about potential emboli floating around, because if you have a AAA, you may also have a saccular berry aneurysm somewhere, and a clot might be developing there. So, let me just write in here, clots can develop. And the last thing I'll mention about why aneurysms are bad is that aneurysms can compress things, and specifically, they can compress their neighbors, structures that live beside them. So particularly, in our example here, you can see how this aneurysm that we've developed here, underneath the kidneys, that might be compressing on the vena cava here in this area. This bulge here might be compressing on the vena cava here, and that means that blood can't return as easily, because remember these are veins, so blood is going to be draining up this way. So, with this sort of bulge of the aorta here, blood can't continue to drain through unhindered, through the vena cava and into the right atrium of the heart. So, they can compress things. They can compress their neighbors, and that's a problem with aneurysms. They can also cause a lot of pain. You can imagine if you have this big bulging mass in the middle of your tummy, you might be in a little bit of pain, because it's going to compress on things and trigger your neurons that sense pain. So, there's some reasons why aneurysms are not our favorite thing in the world. But why do they occur in the first place? How do they develop? Well, there's a couple reasons. So, the most common reason the aorta would balloon out here is because of something called arteriosclerosis or degenerative change. So, 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. They become more firm and hard. And a weaker, less elastic, more firm artery is less able to deal with the blood pressure wave that passes by every second. And there are three main causes that an artery would undergo arteriosclerosis or hardening, and one is atherosclerosis, which is where you get these fatty deposits on the inner lining of the artery. Calcification of the wall of the artery, where calcium just builds up on the wall of the artery as we age, that can cause the artery to stiffen as well. Chronically elevated blood pressure, chronically high blood pressure, that can cause the artery to undergo arteriosclerosis as well, because that chronically high blood pressure causes a thickening of the media layer. So, these three things are major players in the development of arteriosclerosis, which then predisposes you to development of aneurysms. But there's actually a little bit more to it. In the media, remember that middle layer of the aorta, there's lots and lots of proteins like collagen, which give the aorta its tensile strength, so its ability to withstand pressure, and elastin that gives the aorta its elastic recoil ability, to spring back to normal after a blood pressure wave passes by. And as we descend down the aorta, and particularly in the abdominal aorta region, we have less collagen and elastin than we do up at the top, even in perfectly healthy aortas. So, the lower parts of the aorta are, therefore, more prone to developing aneurysms just as it is, and on top of that, as we 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. So, remember earlier I said that 95 percent of AAA's happen below the renal arteries, well this is why. There's not as much collage or elastin there, compared to higher parts of the aorta. So, it's a lot more predisposed. Furthermore, once you've developed that slight bulging of the aorta, in most people it tends to enlarge over time, and that's because according to the Law of Laplace, dilation of a tube causes increased tension on its walls by the fluid that's inside. So, that increased tension on the walls might cause it to balloon out even further and so on. It sort of progresses like a vicious cycle. So, what are the risk factors for developing aneurysms? Atherosclerosis, that deposition of fatty substances along the walls of the aorta, that's a risk factor. That will increase your odds of developing an aneurysm. Smoking, that's a huge risk factor. Partly because it contributes to atherosclerosis and partly because it directly damages the walls of your arteries. So, I'll write that in red, because that one is extra bad. Hypertension, so pathologically high blood pressure, that's a risk factor. COPD is a risk factor, so chronic obstructive pulmonary disease. And let me draw your attention to this. Smoking actually causes atherosclerosis to get worse, and it causes hypertension to get worse, and smoking is the major cause of COPD. So, you can see that just by eliminating smoking you're reducing your risk of developing an aneurysm in a huge way. Another risk factor is being male. Simply by being male, and the reasons are not entirely known, but males are almost five times more likely to get aneurysms than females, which is just great. And age is a risk factor. If you're over 65 years old, or 65 years young, as my father-in-law likes to say it, then you are at an increased risk of developing an aneurysm, and that's because older people tend to have stiffer aortas, so that's partly because of the calcification, so the deposition of calcium within the walls of the aorta that we talked about earlier and partly because there's just been more degeneration of that collagen and elastin over time. Genetics is also a risk factor. So, when I say genetics, I'm referring to a family history, a positive family history. So, if a first-degree relative has developed an aneurysm, then you're at an increased risk of developing an aneurysm, and also other genetic reasons. So, if you have a genetic condition that causes malformation of your collagen and elastin, would predispose you to developing an aneurysm. How do you know if you have a AAA? Well, if you do have one, chances are you won't know about it, because most people with AAA's are asymptomatic. Most AAA's are either discovered incidentally on abdominal x-rays, during a routine physical exam sometimes, or, unfortunately, because of a rupture. But let's try to group our potential symptoms into two main groups. Symptoms that you might get with an intact aneurysm, so an aneurysm that hasn't ruptured, and symptoms that you might get with a ruptured aneurysm. So, the main thing with an intact aneurysm is that it just really causes a constant pain in the abdomen. So, AAA's can cause severe, constant pain in your abdominal region. So, you can get pain in your abdomen and your lower back or even your sides and your groin, but some people actually describe feeling a pulse in their abdomen as well. They might actually feel a pulsatile, sort of expansive mass in their abdomen, whereas symptoms of a ruptured aneurysm are a little bit worse. So, if you have a ruptured AAA, you need to be taken to a hospital right away. If someone has a ruptured AAA, besides usually experiencing a lot of pain in the abdomen, they might develop hypotension, and that's because blood is leaking out of the circulatory system. So, blood pressure can't be maintained. They might develop tachycardia or markedly increased heart rate, and this would happen because the heart senses that the blood pressure has gone down, so it's trying to work harder and faster to move blood around the body. Syncope, otherwise known as fainting, that might happen because not being able to maintain blood pressure means that blood may not be able to get up to the brain, which would cause a faint. Shock might occur, which is where body tissues don't get enough oxygen, because they're not getting enough blood. So, we really don't want to have these things happen to us. So, how do we go about diagnosing aneurysms in the abdominal aorta? Well, it's usually through a combination of physical exam and imaging. On physical exam, the healthcare professional might look for an expansile pulsatile mass in the abdomen, just using their hands, but it's not always easy to feel, partially because the aorta is a pretty deep structure. Remember, it sits right in front of your spine, all the way behind all of your abdominal organs. And it's partially because some patients might carry some weight around their abdomen, and that makes it more difficult to feel if there's an aneurysm there. But on imaging, which is a lot more sensitive and specific for aneurysms, AAA's are usually first assessed by ultrasound. Ultrasounds use sound waves to create pictures of structures inside your body. So, the ultrasound can give you a really good indication of whether there's a AAA there, and in some cases, even whether or not it's ruptured. Another good thing about ultrasound is that it can be done super quickly at the hospital, if there's a suspected rupture. CT, or computed tomography scans, are used to diagnose AAA's, to check exactly where a given one might be and to see what its diameter is, because that will help to determine what sort of treatment it gets. MRI's can also really accurately evaluate the entire aorta, and that's to look for the exact location and extent of the aneurysm, and they also 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.