Thoracic Aortic Aneurysm
About two inches in diameter, the aorta (the largest artery that carries oxygen-rich blood) extends from the heart (thoracic aorta) down through the chest and abdominal area (abdominal aorta), where it divides into a blood vessel that supplies each leg. In general, if the diameter of the aneurysm is more than 1.5 times the size of the normal aorta, it is called an aneurysm, an abnormal bulge in the wall of the aorta.
Ballooning or bulging of the aortic artery (aneurysm) can develop anywhere along your aorta though most occur in the section running through your abdomen and in the section that runs through your chest. A weakened artery wall may stretch as blood is pumped through it from the heart. An aneurysm may occur because of a localized weakness of the artery wall (saccular). Enlargement of the aorta may be only mild in degree (ectasia).
When a weak area of your thoracic aorta expands or bulges, it is called a thoracic aortic aneurysm (TAA). Approximately 25 percent of aortic aneurysms occur in the chest and the rest occur in the abdomen. Thoracic aneurysms affect approximately 15,000 people in the United States each year.
TAAs are serious health risks because they can burst or rupture and cause severe internal bleeding, which can rapidly lead to shock or death. If your aneurysm is large and in the section of the aorta closest to the heart, it may affect your heart valves and lead to a condition called congestive heart failure. Some patients may have more than one TAA or may also have an abdominal aortic aneurysm (AAA). Only about 20 to 30 percent of patients who get to the hospital with a ruptured TAA survive. For this reason, it is crucial to treat large aneurysms early, in order to prevent their rupture.
It is critical to notify your physician immediately if you experience any symptoms of TAA. Left untreated, a TAA may lead to a fatal rupture or organ damage. This is a life-threatening situation and you should seek medical attention immediately.
Most aortic aneurysms show no symptoms and are diagnosed on an X-ray or computerized tomography (CT) scan performed for evaluation of another condition. Symptoms may be present if the aneurysm presses on nearby organs or tissue.
If you do have symptoms, they will depend on where your aneurysm is located and how large it is. Symptoms of a TAA might mimic a heart attack. Possible symptoms may include:
- Pain in the jaw, neck, and upper back
- Chest or back pain
- Coughing, hoarseness or difficulty breathing
- If the aneurysm leads to dissection, there will probably be a severe tearing pain in the chest or back, stroke, cold or numb extremities or abdominal pain
Causes and Risk Factors
It is not known why aortic aneurysms occur although researchers understand some of the factors that contribute to their development. There is a genetic component to many aneurysms; family members of people with aneurysms are at higher risk of developing one. Regardless of the trigger, the outcome is destruction of the aortic wall, which weakens the wall and results in ballooning out of the aneurysm.
Factors that may increase your risk for aneurysm formation include:
- High blood pressure
- A family history of aneurysms
- Aging: Your risk of developing TAA increases as you age
- TAA is more common in men than in women
The larger your TAA, or the faster it grows, the more likely it is to rupture. The chance of rupture increases when your aneurysm is larger than about twice the normal diameter.
Dissection or tearing of the artery wall, known as aortic aneurysms, may also develop due to an aortic dissection, which is typically associated with high blood pressure. An aortic dissection occurs when blood flow forces the layers of the wall of your aorta apart, which weakens your aorta. The separation can extend from your thoracic aorta through your entire aorta and block arteries to your legs, arms, kidneys, brain, spinal cord, and other areas.
A problem associated with aortic dissection is that over time, the pressure of blood flow can cause the weakened area of your aorta to bulge like a balloon. Much like an over-inflated balloon, an aneurysm can stretch the aorta beyond its safety margin.
Other diseases can weaken the layers of the aortic wall, increasing the risk of aneurysms including:
Your physician will order one or more of the following tests to diagnose a TAA:
- Chest X-ray
- Echocardiography (an ultrasound of the heart)
- Duplex Ultrasound
- Magnetic resonance imaging or magnetic resonance angiography
- Computed tomography angiography (CTA) scan
Types of Aortic Aneurysms
The wall of the aorta is made up of three layers:
- A thin inner layer of smooth cells called the endothelium
- A muscular middle layer which has elastic fibers in it called the media
- A tough outer layer called the adventitia
When the wall of the aneurysm has all three layers, they are called true aneurysms. If the wall of the aneurysm has only the outer layer remaining, it is called a pseudoaneurysm. Pseudoaneurysms may occur as a result of trauma when the inner layers are torn apart.
Types of Aneurysms
- Degenerative aneurysms: Degenerative aneurysms are the most common types of aneurysms. They occur as the result of breakdown of the connective tissue and muscular layer. The cause could be cigarette smoking, high blood pressure and/or genetic conditions.
- Dissecting aneurysms: Dissecting (separating of the layers of the aorta) aneurysms occur when a tear begins within the wall of the aorta, causing the three layers to separate. The dissection causes the wall of the aorta to weaken and the aorta enlarges. A dissection may occur any place along the aorta and treatment depends upon the location. Typically, those involving the ascending aorta are treated with emergency surgery while those involving the descending thoracic aorta are treated with medication. Although dissections are uncommon, they are the most common of the acute aortic syndromes. They are lethal if left untreated.
Aortic aneurysms are classified by shape, location along the aorta, and how they are formed:
- Fusiform aneurysms: Most fusiform aneurysms are true aneurysms. The weakness is often along an extended section of the aorta and involves the entire circumference of the aorta. The weakened portion appears as a generally symmetrical bulge.
- Saccular aneurysms: Saccular aneurysms appear like a small blister or bleb on the side of the aorta and are asymmetrical. Typically they are pseudoaneurysms caused either by trauma (such as a car accident) or as the result of a penetrating aortic ulcer.
Your health-care provider will work with you to evaluate the risks of rupture and the risks of surgery. Treatment for an aneurysm depends on its size, growth rate, location and your general health.
For a small aneurysm (less than 2 inches across) with no symptoms, your physician may suggest a conservative medical approach which typically includes regularly scheduled imaging (CTA or MRA scans) of the aneurysm to follow its development. Your blood pressure and other risk factors will be closely watched for any changes.
For a large aneurysm or one that is growing more than 0.5 centimeter per year, surgery may be your best option. Your surgeon may recommend actively treating your aneurysm if it is large, is growing quickly or you have certain other types of disease such as Marfan's syndrome/ You may require active treatment sooner than patients who have small TAAs but do not have Marfan's syndrome.