What's The Difference Between Ascending And Aortic Arch Aneurysms?

The aorta is the largest artery in the human body, whose purpose is to transfer high-oxygen blood from the heart to the rest of your body. On its way, it branches into smaller arteries that supply the arms, head, almost all of the internal organs, and legs. Upon exiting the heart via the aortic bulb, the aorta first ascends, then bends over the heart, descends all the way through the diaphragm muscle to the lower abdomen, finally splitting into two arteries that supply the legs and pelvic organs. The diaphragm divides the aorta into two main sections – thoracic and abdominal.

The thoracic part of the aorta is also divided into four segments, due to small differences in their size, shape, and properties:

• Aortic bulb (root) which incorporates aortic valves and small blood vessels for the heart itself.
• Ascending aorta, which spans from the root of the aorta up to its first branch.
• Aortic arch, which begins from the first branch (brachiocephalic trunk), goes under the trachea and the esophagus, on its way branching into three arteries that supply the head, neck, and arms.
• Descending aorta, which lowers down, giving branches for the ribs.

The wall of the aorta is composed of three layers: the smooth inner layer, elastic and muscular middle layer, and the outer layer, mostly made of collagen.

What is an aortic aneurysm?

If all three layers of the aortic wall take part in the process, it’s called a true aneurysm. If there is a rupture of the wall and a blood collection is formed between the middle and the outer layer, that’s a false aneurysm (or pseudoaneurysm). A dissecting aneurysm is formed when there is a tear in the inner layer, and then the blood splits the outer and the middle layer, ripping them apart.

Aneurysms can also be fusiform, when the aneurysm expands out equally on all sides, or saccular, where a balloon-like formation bulges only on one side of the aorta.

How do you get ascending or aortic arch aneurysms?

Unlike in descending and abdominal parts of the aorta, where atherosclerosis is the key cause of aneurysms, in ascending aorta the main culprit can be found in the form of cystic medial necrosis (CMN).

CMN can also be seen in some connective tissue disorders, such as Marfan or Ehlers-Danlos syndrome. Other than the aorta itself, CMN can also cause problems with patients with bicuspid aortic valve, an inherited condition where there are two leaflets of the aortic valve instead of three. CMN can also be inherited, resulting in “familial thoracic aortic aneurysm syndrome”.

Other factors contributing to aneurysm formation in the ascending aorta include a syphilis infection, Turner syndrome, aortic inflammatory diseases, chronic dissections, and traumas.

How are ascending and aortic arch aneurysms diagnosed?

Aneurysms generally don’t show any symptoms, at least when they are small in diameter, and a physical examination rarely gives more information about the disease. The symptoms depend on the size and the location of the aneurysm. Aortic valve insufficiency (where the aortic valve basically leaks blood back to the heart) and chest pain can be seen in patients with ascending aortic aneurysms, whereas patients with an aortic arch aneurysm show symptoms similar to patients who have narrowed neck arteries.

This is why imaging methods are a superior method of diagnosing and monitoring aneurysms. They include:

• A chest X-Ray, where you can initially assume that an aneurysm exists. In ascending aneurysms, the structures over the heart seem wider, unlike in aortic arch aneurysms, where the arch structures are highlighted.
• Ultrasound. Unlike transesophageal echocardiography (TEE), used with thoracic aorta and dissection diagnosis, ascending aorta and the valves are checked using transthoracic echocardiography (TTE), a quick and painless method where an ultrasound probe is put on your chest, and the soundwaves are transformed into visual images on the monitor in real time.
• A CT scan can measure the size, location and give numerous other information about the aneurysm and the surrounding structures with great precision. This method uses X-rays, but don’t worry, because the benefits from this method outweigh the risks.
• An MRI scan gives similar results as a CT, even with more efficiency, but unfortunately the examination can take a very long time, and an MRI exam is way more expensive.
• Aortography is used when the anatomy and the flow of the aorta is necessary, although it is not widely used, because it is somewhat more uncomfortable than the other imaging methods.

How are ascending and aortic arch aneurysms treated?

If the aneurysm is relatively small, regular checkups are performed once or twice a year. Because of the complicated nature of surgery, operative treatment is reserved for those patients with large aneurysms who have already developed symptoms. Meanwhile, it is essential to control your blood pressure, both by using medications (beta blockers or statins) and avoiding heavy physical activities.

In patients with large aneurysms, surgery is the only treatment. Surgery for an ascending aortic aneurysm is indicated if the diameter is larger than seven centimeters, or six centimeters in patients with Marfan syndrome or other complications, because these aneurysms tend to rupture more easily. The rupture of the aneurysm requires immediate surgery, although the procedure is very risky, and more than half of patients with a ruptured aneurysm die even before they get to the hospital.

There are two main types of ascending aortic aneurysm surgeries:

• Aortic aneurysm repair, an open type of surgery, where the dilated part of the ascending aorta is replaced with a synthetic graft. Depending on the location of the aneurysm, this procedure can involve reconstruction of the aortic valve, or spare it entirely. During this operation, circulation and oxygen levels are controlled by a cardiopulmonary bypass (CBP) pump, also known as a heart-lung machine 
• Endovascular aortic repair (EVAR), done under local anesthesia by placing a stent inside the part of the dilated wall via a catheter. The whole procedure is monitored with the help of imaging methods, such as a CT or ultrasound. Although the recovery period is a lot shorter than in open surgery, not every aneurysm can be replaced using this method.

The surgery itself comes with a lot of risks and complications, even death, especially if the aneurysms are complex. Patients might also have accompanying diseases, or belong to some of the risk groups. Therefore, it is essential to maintain a healthy lifestyle and diet, and immediately stop smoking if you belong to this population. Your blood vessels will be grateful.