Aneurysms

An aneurysm is a bulge that develops in the wall of an artery. Aneurysms usually develop in large arteries (such as the aorta), but they can develop in any artery.

Aneurysms are common. Most develop in older people, particularly in men and in people who have atherosclerosis and high blood pressure.

Most aneurysms are small and do not cause serious problems. Large aneurysms may rupture, causing bleeding. If an aneurysm in the aorta ruptures, the bleeding can be massive or fatal. When aneurysms rupture, the tissues supplied by the artery are deprived of blood and thus oxygen and nutrients. Occasionally, aneurysms of the aorta result in dissection of the aorta's wall.

See the figure Aneurysms in the Aorta.

Because blood does not flow normally through aneurysms, blood clots (thrombi) can develop and block blood flow through them. Part of a clot may break off, travel through the bloodstream (becoming an embolus), and eventually block a small artery in another part of the body. Occasionally, an aneurysm presses on adjacent body structures, producing pain or causing tissues to break down (deteriorate).

Most aneurysms, if detected early, can be treated. Treatment is more likely to be effective if it is given before an aneurysm ruptures.

In older people, aneurysms most commonly develop in the part of the aorta that is in the abdomen. They are called abdominal aortic aneurysms. The second most common site is the popliteal artery, located at the back of the knee. Aneurysms may also develop in the part of aorta that is in the chest. They are called thoracic aortic aneurysms. Aneurysms can develop in the arteries that lead from the aorta to the leg arteries (iliac arteries), the main arteries of the thighs (femoral arteries), arteries in the neck (carotid arteries—which carry blood to the brain), and the heart's arteries (coronary arteries). Aneurysms can develop in the arteries within the brain, but these aneurysms usually cause symptoms and are diagnosed and treated before age 65.

Causes

In older people, most aneurysms develop because the arteries have been weakened by years of atherosclerosis. High blood pressure (which puts added pressure on arteries) and cigarette smoking (which can damage arteries) make aneurysms more likely to develop. High blood pressure also tends to make existing aneurysms enlarge and sometimes rupture.

Symptoms

Often, aneurysms do not produce symptoms until just before they rupture.

Before an abdominal aortic aneurysm ruptures, a pulsing sensation may be felt in the abdomen. Typically, when the aneurysm begins to rupture, pain is first felt as a deep, penetrating pain in the back or abdomen. The area over the aneurysm may become tender. As the rupture progresses, it often causes sudden, excruciating pain in the lower abdomen and back. If the resulting internal bleeding is severe, the person rapidly goes into shock, often losing consciousness and collapsing. Sometimes an aneurysm causes mild pain in the back or abdomen that comes and goes. The pain is usually caused by a series of small ruptures that become covered with blood clots.

Thoracic aortic aneurysms may become very large without causing symptoms. Symptoms vary but can include pain (usually high in the back), coughing, and wheezing. Rarely, a person coughs up blood if an aneurysm presses on an airway wall, causing it to break down. Swallowing may be difficult and hoarseness may develop if an aneurysm presses on the lower part of the throat.

Rupture of a thoracic aortic aneurysm usually causes excruciating pain high in the back. The pain may radiate down the back and into the abdomen as the rupture progresses. Pain may also be felt in the chest and arms. Internal bleeding may cause the person to rapidly go into shock.

Usually, aneurysms in arteries in the limbs do not cause pain unless they rupture, and they rupture much less often. But if blood clots develop and part of the clot breaks off and blocks a small artery, the skin over areas beyond the blockage may become pale and cool. If the blockage persists, gangrene may develop in the limb, which sometimes must be amputated.

Diagnosis

Aneurysms, particularly abdominal aortic aneurysms, may be found unexpectedly when a doctor performs a physical examination or a test for another reason. A doctor checks the aorta by pressing deeply on the abdomen. If the aorta feels unusually large or is pulsing too forcefully, the doctor suspects an abdominal aortic aneurysm. With a stethoscope placed over the aneurysm, the doctor can sometimes hear a whooshing sound (bruit).

Abdominal aortic aneurysms are usually diagnosed and measured using ultrasonography. Computed tomography (CT) and magnetic resonance imaging (MRI) are sometimes used. A thoracic aortic aneurysm can be diagnosed using CT, MRI, or transesophageal echocardiography (in which an imaging device is passed down the throat into the esophagus). Angiography of the aorta may be needed. For this test, dye is injected through a long, thin tube (catheter) that is inserted into a vein and threaded to the aorta. Then x-rays are taken. The dye outlines the aneurysm.

Aneurysms of leg arteries can be accurately diagnosed using ultrasonography or CT. Angiography is accurate and provides even more details about the aneurysm. But usually, angiography is done only when surgery to repair the aneurysm is being planned.

Because the chance of an aneurysm rupturing without warning often depends on its size, tests may have to be repeated periodically to see whether the aneurysm is enlarging. For example, if an abdominal aortic aneurysm is more than 1½ inches (4 centimeters) wide, ultrasonography or CT should be done every 6 months.

Treatment

Controlling blood pressure as closely as possible with drugs can help prevent an aneurysm from enlarging. Beta-blockers, which decrease the force of the heart's contraction, are particularly useful.

Whether surgery to repair or remove an unruptured aortic aneurysm is advisable depends on which risk is greater: the risk of surgery or the risk of aneurysm rupture. For example, if an abdominal aortic aneurysm is larger than 2 inches (5 centimeters) wide and the person is otherwise in good health, surgery is usually necessary. Surgery is also done if the aneurysm causes pain.

For an unruptured abdominal aortic aneurysm, surgery to repair the aorta may be done. It often involves making an incision into the abdomen and inserting an artificial tube (graft) inside the aorta without removing the aneurysm. This procedure prevents rupture of the aneurysm. For an unruptured thoracic aortic aneurysm, the aneurysm must be surgically removed through an incision in the chest.

Surgery to repair aneurysms has risks. The average chance of dying during repair of an abdominal aortic aneurysm is about 1 in 20. Certain conditions increase the chance of death during surgery. They include older age and heart, lung, or kidney disorders (which are common among people with aneurysms). For people without any of these conditions, the chance of death is about 1 in 50. Surgery to remove thoracic aortic aneurysms can be comparably risky.

A new, nonsurgical technique (called endovascular repair) can be used to repair unruptured abdominal aortic aneurysms. After numbing the insertion site with a local anesthetic, the doctor inserts an artificial tube into an artery near the top of the leg and guides it into the aneurysm. The tube is similar to the one inserted during surgery, but it is collapsed, so that it can fit into a blood vessel. Once inside the aneurysm, the tube expands, forming a new channel for blood flow. This technique appears to be effective.

If an aneurysm causes pain, surgery is usually necessary because rupture is very likely. If an abdominal or thoracic aortic aneurysm ruptures, the only chance for survival is emergency surgery. The goal of emergency surgery is to replace the ruptured part of the aorta with a graft. Even with surgery, rupture of an abdominal or a thoracic aortic aneurysm is fatal more than half of the time. Death often results from loss of blood.

Leg artery aneurysms, whether ruptured or not, are usually repaired surgically. The risk of death during surgery is slight, and if surgery is not done, the risk of losing the leg is high because clots can form and block blood flow.

Outlook

Aneurysms tend to enlarge, particularly if subjected to the wear and tear caused by high blood pressure. However, they tend to enlarge slowly. The larger the aneurysm, the greater the chance of rupture. Rupture is unlikely for abdominal aortic aneurysms smaller than 2 inches (5 centimeters) wide, for thoracic aortic aneurysms smaller than 2½ inches (6 centimeters) wide, and for most leg artery aneurysms. Abdominal aortic aneurysms larger than 3 inches (7½ centimeters) are likely to rupture eventually and without warning.