What is the Aorta?
The aorta is the largest artery in the body, transporting oxygenated blood from the heart to the brain, chest, and abdominal organs and to the legs. The portion of the aorta in the chest from the heart to the diaphragm is known as the Thoracic Aorta. The portion from the diaphragm to the pelvis is the Abdominal Aorta. It is an elastic blood vessel which stretches and contracts in relation to the pulsation of blood out of the heart.
The Thoracic Aorta has 4 distinct parts:
Aortic Root – Lies in the front portion of the chest below the sternum. It starts at the level of the heart and includes the aortic valve and the portion where the coronary arteries arise called the Sinus of Valsalva.
Ascending Aorta – Starts above the Sinus of Valsalva and extends to the first branch supplying blood to the head.
Aortic Arch – Curved portion of the aorta involving the 3 vital branches to the head, neck and arms.
Descending Thoracic Aorta – is located in the back. It starts after the last branch to the head and extends to the level of the diaphragm. It gives off multiple branches to the chest wall and spinal cord.
What are causes of aortic aneurysm:
- Genetic – family history of thoracic aneurysm and dissection
- Connective tissue disorders – Marfan’s syndrome/Ehlers-Danloss syndrome
- Vascular inflammation – giant cell arteritis, takayasu arteritis, behcet’s disease, syphillis
- Aortic dissection
- Trauma – car accident, fall from height, blunt chest trauma
- Weightlifting – high intensity
What are risk factors which can cause increased rate of growth of aneurysms:
- Hypertension – associated in >70% of aortic dissections (IRAD)
- Increasing age
- Bicuspid or unicuspid aortic valve – congenital
- Renal failure
- Previous aneurysm repair
- Turner Syndrome
What are indications for aortic surgery:
- Type A (ascending) aortic dissection, which is an emergency issue
- Ascending aortic diameter > 4.5 cm in patients with Marfan syndrome or other connective tissue disorders.
- Ascending aortic diameter > 5.0 to 5.5 cm in patients without Marfan syndrome
- Descending and thoracoabdominal atherosclerotic aortic aneurysm diameter > 6 cm, or Type B aortic dissection complicated by impaired blood flow, rupture, or rapid expansion
- Dissecting descending thoracic aortic aneurysm diameter > 5.0 cm
- Expansion rate > 1 cm per year
What surveillance is necessary for aortic aneurysms:
The vast majority (nearly 90 percent) of aortic aneurysms identified through imaging tests are small in diameter (less than 3.5 cm) and are unlikely to burst. However, for others, surgical intervention is recommended when the probability of rupture in the next year exceeds the risks of the operation or if a patient is experiencing pain or other symptoms caused by the compromised blood flow to major arterial branches, regardless of aneurysm size. Patients with aneurysms of the ascending or aortic root associated with regurgitation (leakage) of the aortic valve may also be advised to undergo early intervention, which would likely involve combined repair procedures.
Patients should be followed up with serial imaging studies for surveillance. When a thoracic aortic aneurysm is first detected, it is not possible to determine the rate of growth. Repeat imaging in the first 6-12 months after initial study is recommended. If the aneurysm is unchanged in size, it is then reasonable to evaluate the rate of imaging and space them out accordingly. It is reasonable in most cases to obtain imaging studies on an annual basis. In those without predisposing conditions (i.e. Marfan or acute aortitis), thoracic aortic aneurysms are usually slow to grow so annual imaging is sufficient for surveillance. Depending on the growth of the aneurysm, if there is significant growth, the imaging interval may be decreased to keep a closer eye on the growth rate.