The aorta is the largest artery in the body. It carries oxygen-rich blood directly from your heart to the rest of your body via its smaller branches.
Many factors, including old age, smoking, and especially atherosclerosis (a process in which plaque forms on the inside of the arterial wall), your aorta becomes more rigid over time. This reduces blood flow, gradually weakening the aortic wall until the aorta starts to lose its flexibility, finally resulting in a permanent local expansion of the lumen, called an aortic aneurysm.
Depending on where in the aorta an aneurysm is located, the two main types of aneurysms are:
- Thoracic aortic aneurysm, which can emerge anywhere within the aorta from the aortic bulb to the level of the diaphragm muscle.
- Abdominal aortic aneurysm (AAA), from the diaphragm and all the way to the place where the aorta branches into the two common iliac arteries. The typical location for AAA is just below the renal arteries, which supply the kidneys.
Clinically speaking, aneurysms can be classified as fusiform, in which case the main characteristic is that it bulges out equally on all sides, and saccular, described as a ball-shaped bulge.
One of the major challenges with aortic aneurysms is that they usually don’t produce any symptoms until they get so big that they either compress the surrounding structures, or even rupture under great pressure. Aortic rupture is a surgical emergency that quickly turns lethal unless treated immediately. To make things worse, about half of all patients with a ruptured aneurysm will die due to these complications.
The greater the size of the aneurysm, the higher the risk of rupture. Abdominal aneurysms are more likely to burst than thoracic ones, because the diameter of thoracic aneurysms grows very slowly, which means that their prognosis is good – if relatively small in diameter.
Due to the lack of symptoms, physical examinations can’t tell your doctor much, unless the aneurysm is so big that it can be sensed as a pulsating mass in your naval area. Even more serious symptoms, like chest or back pain, coughing, and hoarseness, are not characteristic enough for your doctor to make a proper diagnosis. This is the reason doctors primarily rely on imaging methods in aneurysm diagnosis.
1. Abdominal ultrasound (with color duplex sonography)
Largely available and cheap, ultrasonography is usually the first step in the diagnosis of aortic aneurysms. It doesn’t hurt, has no proven harmful effects on your body (such as ionizing radiation), and the examination lasts only about 20 minutes.
During the ultrasound exam, your doctor can precisely measure the shape and size of your aorta, along with its lumen. The fact that ultrasound makes a real-time picture of the inside of your abdomen is exploited with the help of the “Doppler effect”, a technique used to visualize blood flow and calculate its properties.
However, in some people (overweight or bloated) ultrasound waves can’t penetrate well enough for the doctors to see properly, because air, water, and fatty tissue don’t conduct these waves well enough. In these cases, patients are sent to undergo other imaging modalities.
2. A CT scan
Also called multidetector computed tomography (MDCT), it uses X-rays which pass through your body. Using a special software algorithm, the computer calculates the amount of X-rays that have been absorbed both by your body and the detectors in the machine, creating a high-resolution cross-sectional picture of your body, which can later be reconstructed in 3D.
The machine itself consists of two parts: the gantry (a donut-like part, where the X-ray tube and detectors are placed), and the moving table where the patient lays still during the procedure.
Prior to the scan, a contrast agent will be injected through your veins, which enables the creation of a better picture, along with a more informative examination.
The examination lasts for only a few minutes. You may be asked to stop breathing for a few seconds, because the picture might get blurry if the table moves.
The contrast agents are iodine-based. So, if you’re allergic to iodine or have a kidney disease which prevents iodine from being removed from the organism, you should let your doctor know that, and you’ll probably be redirected to an MRI scan, which uses different kinds of contrast agents.
3. MRI (Magnetic resonance imaging)
An imaging technique visually similar to a CT, MRI instead uses strong magnetic fields. Although relatively harmless (we’ll talk about it later), people can easily find it uncomfortable, because of very loud banging noises produced by the magnets inside the machine. Add the fact that most MRI exams can last as long as one hour, and that you have to be perfectly still the entire time, and you’ll see why some people describe this examination as “claustrophobic”. It also uses contrast agents, although these aren’t as problematic as the iodine-based ones.
A CT scan is a way cheaper and faster method, with higher resolution than the MRI, so this type of examination is usually reserved for people which need a high-resolution image of their blood vessels, but are not allowed to do a CT scan for whatever reason.
4. A chest X-ray
A method not too helpful in diagnosing issues with the aorta, mostly because an X-ray film is basically a flattened 2D image of a part of your body. This means that although you can see a shadow that may look like a widened aortic arch, for example, there is sometimes no way of telling if the heart’s shadow obscures the image.
An abdominal X-ray is of no practical use in diagnosing abdominal aortic aneurysms.
5. Transesophageal echocardiography (TEE)
A procedure where a long ultrasound transducer is placed in your esophagus. Because some parts of the thoracic aorta can be seen from it, it is used to diagnose thoracic aortic aneurysms. However, because this examination is relatively unpleasant, it’s not that widely used today, especially when there are non-invasive alternatives available.
6. Angiography (aortography)
This type of procedure is performed exclusively in a sterile operating room. A catheter is inserted into a blood vessel in your groin, arm, or leg, and is slowly pushed towards and into the aorta. Then a contrast agent is injected, which helps your medical team visualize the blood flow inside of the aorta. Although this examination can tell you very much about the status of your blood vessels, because of its complexity it’s used only in extremely complicated cases, or if other diagnostic methods fail.
These methods can tell us a lot about the location and the size of the aneurysm, as well as its relations to other arteries and internal organs.