Causes and Risk Factors of Aortic Aneurysms

December 15, 2008 at 11:00 am

Definition of Aortic Aneurysms

An aortic aneurysm is a weak spot in the wall of the aorta, the primary artery that carries blood from the heart to the head and extremities

Description of Aortic Aneurysms

An aneurysm is an abnormal enlargement of a blood vessel.
Some 15,000 Americans die suddenly each year from rupture of an aneurysm in the aorta, which is the ninth leading cause of death in men over age 55. Aortic aneurysms are four times more common in men than in women and usually occur in those over age 50. Approximately one percent of men between the ages of 55 and 64 will have a significant aneurysm, and the likelihood increases to about four to six percent of those men over the age of 75.

The aorta is the largest artery in the body. All of the blood leaving the heart to go to the body leaves through the aorta and is then distributed to the smaller arteries. The aorta leaves the heart traveling towards the head, then makes a u-turn, and travels down the body just to the left of the spine before branching into two arteries in the pelvis which feed the separate leg. An aortic aneurysm is a weak spot in the wall of the aorta allowing the vessel to expand which increases in diameter.

Aneurysms are first classified by where they occur in the body. If they are in the thorax (above the diaphragm), they are thoracic aortic aneurysms. Aneurysms below the diaphragm are abdominal aortic aneurysms. Abdominal aortic aneurysms are further classified into those that extend above the renal arteries and those that do not (infrarenal).

They are then classified by whether or not they involve a dissection, a tear in the inner lining of the artery. Blood is then pushed into this tear under pressure from the heart which causes the tear to expand. This tear may extend in between the three concentric walls of the artery and travel down through the walls creating a new channel. The new channel may become so big that it compresses the normal flow of blood depriving organs of blood flow and oxygen.

More commonly, aneurysms do not start with a large tear, but result from a gradual weakening in the walls, especially of the muscular lining that maintains the shape of the vessel. With this weakness, the wall stretches further and the constant pressure from the pumping blood causes it to slowly expand.

Causes and Risk Factors of Aortic Aneurysms

Most aneurysms occur in older patients with a history of hypertension and atherosclerosis. However the causes of aneurysms are poorly understood.

Thoracic aortic dissections or aneurysms can occur in young people. The dissecting tear can begin as the result of trauma such as a car accident. Patients with Marfan’s syndrome (a problem with collagen which makes the vessels weak) or with an abnormal aortic valve, which increases stress on the artery, can cause it to dilate. Several basketball players have undergone surgery to correct this type of aneurysm. The actor John Ritter reportedly had an abnormal valve which led to an aortic dissection.
The causes of abdominal aortic aneurysms are less well-understood. The wall may become weak because atherosclerosis (cholesterol deposits) make the artery less healthy and cause it to weaken. Some studies have suggested low-grade inflammation in the arterial wall slowly digests the wall making it weak. There are some families that have multiple aneurysms suggesting that at least some cases are related to a genetic disorder.

 Symptoms of Aortic Aneurysms

Aneurysms can be small, or grow to the size of a grapefruit. Most produce no symptoms, especially when small. The most common symptom is a throbbing, or pulsation, in the abdomen. Sometimes, abdominal or lower back pain occurs.

Dissections, or dissecting aneurysms, on the other hand often cause excruciating pain. Those that occur in the chest may be mistaken for a heart attack and the two are occasionally related. The pain of this dissection is often described as “ripping” or “tearing”. It may travel, first being located in the chest, then moving to the back between the shoulder blades, and then lower in the body. Similarly, dissections in the abdominal aorta cause a traveling pain that tends to start at the level of the stomach and then migrates down, often to one leg or the other.
Aneurysms may also cause symptoms when they embolize. The inside layer of the ballooning section will usually be lined with blood that has clotted; if a piece of this clot breaks loose it is called an emboli. The symptoms associated with embolization will vary depending on where the embolus goes – if it goes to the brain, it will cause a stroke. More often, it will travel down the legs towards the feet. The area of the leg downstream from the clot will become cool, pale, and usually painful. It will eventually take on a bluish discoloration if the problem is not corrected.
Aneurysms may also rupture – the ballooning segment may pop. This is usually a fairly catastrophic event. Severe pain is usually followed quickly by low blood pressure and then death. This happens because the blood leaves the arteries and bleeds internally.

 Diagnosis of Aortic Aneurysms

There are two ways to diagnose an aneurysm prior to it causing symptoms: through physical examination or through a medical imaging study. During a physical examination, your doctor should listen to your abdomen and palpate (feel) your abdomen. Some aneurysms create a bruit, which is a certain kind of noise, that can be heard with a stethoscope. The palpation can be felt at about the level of the belly button. Even large aneurysm can be impossible to feel in subjects with a large amount of abdominal fat. On the other hand, thin people may be able to feel, or even see, the pulsations in their abdomen. In this case, one simply needs to measure how wide the area of pulsation is to determine whether or not it is normal.
Oftentimes, aneurysms are detected during some sort of imaging study. For instance, a doctor orders a CAT scan to look at the kidneys and the aneurysm is seen, or it is seen on a chest X-ray in someone thought to have pneumonia.

If an aneurysm is found or suspected, it should be further studied with some sort of dedicated imaging study. This may be a CAT scan, an MRI, or an ultrasound depending on its location. It is important to known how big the aneurysm is (its greatest diameter) and where it begins and where it ends.

Treatment of Aortic Aneurysms

The treatment for an aneurysm depends on many factors: where it is, how big it is, how quickly it is enlarging, and whether or not it has caused any symptoms. The major decision is whether or not surgery is needed to correct it.

For small aneurysms that are found incidentally, the treatment is usually watchful waiting. This involves medications to control blood pressure and repeating an imaging study in approximately six months. If it is increasing rapidly in size, surgery may need to occur sooner. Aneurysms less than four centimeters (cm) in diameter can be safely monitored, and those bigger than six cm should usually be repaired. There is a gray area in the middle; treatment for these size aneurysms will depend on many factors, especially the degree of risk of the surgery for each particular patient.
Some physicians will prescribe a blood thinner, such as coumadin, in addition to blood pressure medications. This medication will hopefully break apart any blood clots before they can cause damage, but there is a risk of too much bleeding.Immediate surgery is usually required for a dissecting aortic aneurysm, especially those in the thorax. Aneurysms that start further down the aorta may be managed with medications.

If surgery is necessary, the type of surgery and the degree of risk of the surgery depend on the location of the aneurysm. If it is in the thorax near the heart, the surgery may require cardiopulmonary bypass which increases the risk of the surgery. In the abdomen, if the aneurysm starts below the renal arteries, it may be repaired by inserting a synthetic graft. This material (similar to Gore-Tex) is attached to a small tube and threaded up from the leg and positioned inside of the aneurysm. When it is deployed, it creates a strong inner lining to the aorta, preventing it from expanding further or rupturing. This procedure does not involve a large incision and the recovery time is fairly quick, but it should only be done by someone with a fair deal of experience with the procedure. If the aneurysm involve the renal arteries, an open surgery is necessary to repair it and ensure that blood flow to the kidneys is maintained.

 Questions To Ask Your Doctor About Aortic Aneurysms

  • Where is the aneurysm located?
  • What type of aneurysm is it?
  • What is its size?
  • Is it rapidly growing?
  • What threat does it pose?
  • Is surgery indicated?
  • What are the risks involved?
  • How often have you performed this surgery?
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Angiotensin II, atherosclerosis, and aortic aneurysms Aneurysm


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