Overview of Abdominal Aortic Aneurysm Imaging
Abdominal Aortic Aneurysms, abbreviated as AAAs, are a health condition that usually affects over 1.3% of people above the age of 50. More specifically, the incidence of AAA escalates to higher than 12% for senior men. An AAA develops when the large blood vessel at the back of the abdomen, called the aorta, becomes weak and inflates like a balloon.
When an AAA ruptures, it can be very serious, even fatal, with a death rate between 50-95%. The risk of death increases every minute, making it extremely important to catch and treat it quickly. However, nearly 30% of such cases are not correctly identified at first, mostly because physical symptoms may not clearly point towards AAA. Upon examination, only a disappointing 65% are accurately determined and less than 25% of patients show the three classic signs: low blood pressure, stomach pain and a throbbing feeling in their abdomen.
Due to these reasons, doctors make use of point of care ultrasound to timely and accurately diagnose the condition, as this method has been successful in about 94-99% cases. In fact, a research study has confirmed that bedside ultrasound, an average-sized sound wave technology used to look at organs in the body, is about as accurate as a CT scan when measuring the size of an AAA. It is a quick, safe and effective way to diagnose, as it can be completed in less than 5 minutes. Even more crucially, the use of ultrasound in this way has substantially reduced the mortality rate from AAA by 20-60%.
Anatomy and Physiology of Abdominal Aortic Aneurysm Imaging
The abdominal aorta, a large blood vessel, enters your abdomen through an opening known as the aortic hiatis, located just below the breastbone. It lies at the front of the backbone, and runs parallel to a large vein called the inferior vena cava. The aorta goes on to divide into two iliac arteries around the level of the belly button. As it travels down the abdomen, the aorta shrinks and moves closer to the surface of the body, and also branches out to provide smaller arteries that supply blood to various parts of the body including the stomach, liver, kidneys and lower intestines.
An aneurysm is a swelling or enlargement of a blood vessel, in this case the aorta, that’s caused by the weakening of the blood vessel wall. An enlargement greater than 3 cm is identified as an abdominal aortic aneurysm (AAA). There are two main types of AAA: fusiform and saccular. The majority of AAAs are fusiform which means they are evenly swollen around the whole circumference of the aorta. Saccular aneurysms, on the other hand, are more like local bulges or balloon-like outgrowths on the vessel, which are often due to infections.
Nearly 90% of AAAs are found below the kidneys, though the kidneys’ blood vessels can sometimes be hard to see with an ultrasound. Scanning the aorta to where it divides can help the doctors make sure they have seen the entire aorta.
Why do People Need Abdominal Aortic Aneurysm Imaging
If you experience low blood pressure, abdominal pain, and observe a pulsing mass in your belly area, this could be a sign of an emergency condition – but only a quarter of individuals will notice all these signs at once.
Doctors might consider performing an ultrasound, a non-invasive scan that captures images of internal organs, on the abdominal aorta – a major blood vessel that supplies blood to the abdomen, pelvis, and legs – under the following conditions:
– You are older than 50 and are experiencing pain in your chest, abdomen, lower back, groin; kidney pain; blood in your urine; or a condition known as ‘hydronephrosis’ where your kidneys swell because of a buildup of urine.
– You’ve had a cardiac arrest.
– You have low blood pressure.
– You’ve fainted.
– Blood clots are blocking the blood supply in your legs.
– You have weakness or decreased sensation in your legs.
Doctors might also suggest an ultrasound scan if you’re not showing any symptoms but fall into specific high-risk categories.
The United States Preventative Services Task Force (USPSTF) & The American Academy of Family Physicians (AAFP) recommend ultrasound scans for:
– Men over 65, who have smoked at any point in their lives.
The Society for Vascular Surgery recommends an ultrasound scan for:
– All men aged above 65.
– Men over 55 who have a family history of “AAA” – an abdominal aortic aneurysm, which is an enlarged area in the lower part of the aorta.
– Women over 65, who either have a family history of AAA or have smoked at any point in their lifetime.
Risk factors for aortic conditions that might necessitate a scan include:
– Being older than 50.
– Having a family history of AAA.
– Being male.
– Having high blood pressure.
– Being a smoker.
– Having coronary artery disease, which is damage or disease in your heart’s major blood vessels.
– Having diabetes.
– Having high lipids (fats) in the blood.
– Having peripheral arterial disease, a condition of the blood vessels that supply the legs and feet.
When a Person Should Avoid Abdominal Aortic Aneurysm Imaging
There are no known reasons why a person can’t have an ultrasound test to look at the large blood vessel in their belly, called the abdominal aorta.
Equipment used for Abdominal Aortic Aneurysm Imaging
The aorta, a major blood vessel in the body, can be examined using a special type of ultrasound called a sonogram. This process happens in real-time and uses something called B-mode imaging, which is set for the abdomen. They use a device known as a curvilinear transducer, which works well because it uses lower-frequency sound waves that can penetrate deeper into the body.
Another type of device, called a phased array transducer, may also be used. In some cases, especially with thinner individuals, a linear probe may be used because it can give more detailed images.
Preparing for Abdominal Aortic Aneurysm Imaging
Whenever you have a sonogram, the doctor needs to set everything up just right to get a good picture of what’s inside your body. In this case, we’re talking specifically about getting a sonogram of your abdominal aorta, which is a major blood vessel in your abdomen. First, the doctor will have you lay flat on your back on a bed that’s adjusted to their waist level. They’ll make the room darker and put a special gel on your skin.
They’ll then use the sonogram machine to find a part of your spine called the ‘vertebral body.’ It should appear bright with a shadow behind it on the sonogram. Once it’s found, the doctor will use it as a guide to adjust the settings of the machine to get better images. As they move the sonogram device lower down your body towards your belly button, they will need to adjust the machine’s settings because your aorta will be closer to the surface of your body in these areas.
The doctor might need to press down firmly to move any bowel gas that’s in the way of seeing your aorta clearly. Also, they may need to adjust other machine settings or change the angle of the machine’s probe to get clearer images. If there’s still something blocking the view, like a part of your bowel, they can try moving the machine towards your feet and then angling it upwards. The opposite technique can also be done. Sometimes, turning you to lay on your left side can help them see better too.
However, there are a few people (about 5%) who may not have a visible aorta using this method due to unique aspects of their body. If this happens, doctors have other advanced imaging techniques like a CT scan or an MRI scan that can be used to supplement the evaluation.
How is Abdominal Aortic Aneurysm Imaging performed
An ultrasound is a way to take pictures of your body using sound waves. To do an ultrasound of your abdominal aorta, which is the main blood vessel in your belly, the technician will start by placing a device called a transducer below the bottom part of your breastbone in a horizontal position. They will then do a scan covering the entire aorta that goes down to where the aorta splits at your belly button level. The technician may need to take several video images to capture the whole aorta. In this process, they also measure how wide your aorta is at its largest spot from outer wall to outer wall. It’s important that the ultrasound device is perfectly straight across from the aorta for the most accurate measurements.
While doing the ultrasound, the technician will also be looking for any blood clots, known in medical terms as thrombus. These appear as bright spots within the aorta. They are easily missed, so they need to be paid close attention to. Often clots are seen along the front and side wall of the aorta, and they may cause a second channel within the aorta that make it look like the aorta is narrower than it actually is.
If you are in a critical condition, your doctors will also use ultrasound to check for fluid that shouldn’t be there in your belly. It is important to know that most abdominal aortic aneurysms, a condition where the aorta balloons out, rupture in an area of your belly where ultrasound cannot routinely evaluate. However, combining ultrasound with the doctor’s clinical judgement, can correctly identify ruptured aneurysms in almost all cases.
The ultrasound also checks for aortic dissection, which is a serious condition where the inner layer of aorta tears and blood surges through this tear causing the inner and middle layers of the aorta to separate. The ultrasound can see this as a wave-like flap of tissue within the aorta. If this is seen, then your blood pressure will need to be managed very strictly, and surgery might be needed urgently.
Possible Complications of Abdominal Aortic Aneurysm Imaging
There aren’t any known issues or risks that come from using ultrasound technology to check your abdominal aorta, which is the main artery in your abdomen. However, there may be some limitations. These can include physical factors like body size and the presence of gas in your intestines, as well as how experienced the person running the ultrasound is. If the ultrasound doesn’t give a clear enough picture, doctors might consider other, more advanced imaging techniques, but this will depend on your specific body condition at the time of the test.
What Else Should I Know About Abdominal Aortic Aneurysm Imaging?
Most of the time, an abnormal expansion or bulge in the wall of the large blood vessel in your abdomen (abdominal aortic aneurysm) occurs below the blood vessels that lead to your kidneys (renal arteries). When doctors perform a scan to check this, they scan down to “the point where a blood vessel splits into two paths” (bifurcation). This ensures they can see the full picture of the large blood vessel (aorta).
There can be a blood clot inside your blood vessel (intraluminal thrombus). If a blood clot is present, it is important to include it when measuring the size of the aneurysm.
Sometimes, there might be tears in the innermost layer of the artery (intimal flaps) which are tell-tale signs of aortic dissections, a severe condition where the inner layer of the aorta tears.
In some cases, it might be hard to tell the difference between the aorta and the large vein that carries de-oxygenated blood from the lower half of your body back to your heart (Inferior Vena Cava or IVC). Typically, the aorta, which has a pulse, is thicker, can’t be easily pressed down, and is located closer to the middle of your body than the IVC. The IVC, on the other hand, is thinner, can be pressed down, and may appear to have a pulse due to its closeness to the aorta and due to normal breathing. To tell them apart, doctors may use a special kind of ultrasound (pulsed-wave Doppler) to ensure they recognize the pulsating flow of the aorta from the slightly varying flow of the IVC due to breathing.
Although these kinds of aneurysms are normally behind the abdominal cavity (retroperitoneal), when doctors think an aneurysm might have burst (ruptured AAA), they might perform an ultrasound of the right upper part of the abdomen to check for abnormal amounts of fluid.
