Aortic Aneurysms

What are Aortic Aneurysms?

An aortic aneurysm is an abnormal bulge in the wall of the aorta, the body's largest artery (the blood vessel that carries oxygen-rich blood). Roughly the diameter of a garden hose, this artery extends from the heart down through the chest and abdominal region, where it divides into a blood vessel that supplies each leg. Although an aneurysm can develop anywhere along your aorta, most occur in the section running through your abdomen (abdominal aneurysms). The rest occur in the section that runs through your chest (thoracic aneurysms).

The weakened artery wall may stretch as blood is pumped through it from the heart. The bulge or ballooning may be symmetrical (fusiform). Occasionally an aneurysm may occur because of a localized weakness of the artery wall (saccular). Enlargement of the aorta may be only mild in degree and termed "ectasia." 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 aortic aneurysm is serious because - depending on its size - it may rupture, causing life-threatening internal bleeding. The risk of an aneurysm rupturing increases as the aneurysm gets larger. The risk of rupture also depends on the location of the aneurysm. Each year, approximately 15,000 Americans die of a ruptured aortic aneurysm. When detected in time, an aortic aneurysm can usually be repaired with surgery.

Types of Aortic Aneurysms

Aortic aneurysms are classified by shape, location along the aorta, and how they are formed. 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, and a tough outer layer called the adventitia. When the walls of the aneurysm have 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.

Shape

  • 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.


Used with the permission of Mayo Foundation

Cause

  • 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 aneurysms occur when a tear begins within the wall of the aorta, causing the three layers to separate. This is similar to what happens to a sheet of plywood that is left out in the weather. The dissection (separation of the layers) causes the wall of the aorta to weaken, and the aorta enlarges. Dissections may occur any place along the aorta and treatment depends upon the location. Frequently, 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.

Used with the permission of Mayo Foundation
Location
  • Thoracic aortic aneurysms


    The aorta is shaped like an old-fashioned walking cane with the short stem of the curved handle coming out of the heart and curling through the aortic arch which gives off branches to the head and arms. Then the aorta descends through the chest cavity into the abdomen and separates off to provide blood to the abdominal organs and both legs. Thoracic aneurysms can occur anywhere along the aorta above the diaphragm, including the ascending aorta, the aortic arch, and the descending thoracic aorta. In general, thoracic aortic aneurysms are treated by thoracic surgeons.

  • Abdominal aortic aneurysms


    Abdominal aortic aneurysms are located along the portion of the aorta that passes through the abdomen. Continuing from the thoracic aorta, the abdominal aorta carries blood down through the abdomen until it eventually splits off into two smaller arteries that provide blood to the pelvis and legs.

    Abdominal aortic aneurysms are far more common than thoracic aortic aneurysms, comprising up to 75 percent of aortic aneurysms. They can affect anyone, but are most often seen in men ages 40 to 70. Most abdominal aortic aneurysms are caused by atherosclerosis.


Used with the permission of Mayo Foundation

What causes Aortic Aneurysms?

Aortic aneurysms are most often caused by damage to the artery's wall due to atherosclerosis, commonly known as hardening of the arteries. Atherosclerosis is caused by a buildup of cholesterol and other fatty deposits in the arteries and hypertension (high blood pressure). Other causes of aortic aneurysms may include:

  • Congenital weakness of the artery wall (something you are born with)
  • Weakening of the artery wall from smoking or high blood pressure
  • Dissection or tearing of the artery wall
  • Trauma (usually falls or motor vehicle accidents)

Sometimes the cause of an aneurysm is not clear. Aneurysms may be hereditary.

What are the symptoms of Aortic Aneurysms?

Most aortic aneurysms have no symptoms. In fact, most are diagnosed on a chest X-ray or computerized tomography (CT) scan performed for evaluation of another condition, such as lung disease, or during routine exams. Symptoms may occur, however, due to the aneurysm pressing on nearby organs or tissue, or if the aneurysm leads to dissection. Symptoms of dissection include severe tearing pain in the chest or back, stroke, cold or numb extremities, or abdominal pain.

Abdominal aortic aneurysms may be diagnosed by a doctor during a physical exam, or sometimes patients notice a pulsating mass in their abdomen. The first hint of an aortic aneurysm may be an abnormal chest X-ray. Other tests that may be done to diagnose an aneurysm include:

  • Echocardiography
  • Computerized tomography (CT)
  • Magnetic resonance imaging (MRI)

How are Aortic Aneurysms treated?

Treatment for an aneurysm depends on its size and location and your general health. If the aneurysm is small and you have no symptoms, your physician may suggest a "watch-and-wait" approach with regularly scheduled images of the aneurysm to check the size. However, if your aneurysm is large enough, or if the aneurysm is growing more than 1 centimeter (cm) per year, surgery may be your best option. Your health-care provider will work with you to evalulate the risks of rupture and the risks of surgery.

Medical Treatment of Aortic Dissections

The aorta is composed of three layers. Aortic dissections occur when the layers separate (the way plywood will separate if left out in the rain). When dissections occur, patients typically experience severe pain in the chest or back which may be described as tearing discomfort. This most frequently takes them to the emergency room, where the diagnosis may be made.

Dissections may involve the ascending aorta alone, the descending thoracic and abdominal aorta alone, or the entire aorta. The risk of death depends on the extent of the dissection. It is highest for those aneurysms involving the ascending aorta. For that reason, most of these aneurysms are treated surgically as an emergency. Dissections of the descending thoracic aorta can often be treated with blood pressure control. The medical treatment of aortic dissection includes aggressive control of blood pressure and heart rate while the aorta heals. The risk of death with medical treatment of descending thoracic aortic dissection is about 10 percent. If surgery is required, however, the risk is higher at about 30 percent. Every effort is therefore made to treat these patients with medication.

Once the acute dissection has healed, adequate control of blood pressure may eliminate the need for surgery. Lifelong monitoring of diameter of the aorta is required because a previously dissected descending thoracic aorta may enlarge and rupture.

Open abdominal or open chest surgery

The accepted standard treatment for aneurysm once it meets the indications for surgery is replacement of that portion of the aorta with an artificial graft. Typically a graft is made from DacronTM, a material that will not wear out. The graft is sewn in place with a permanent suture material.

The operation, including the incision that is made, depends on the location of the aneurysm. If the aneurysm is close to the aortic valve, an incision in the front of the chest such as a median sternotomy may be used. If the aneurysm is close to the valve, the aortic valve may have to be repaired or replaced. Surgery on the aortic arch is usually done from the front as well. If the aneurysm involves the descending thoracic aorta, which lies in the left chest, or the thoracic abdominal aorta, an incision on the left side of the chest will likely be required. If the aneurysm is confined to the abdomen, then an incision either in the abdomen, or on the side or flank may be used.

Endovascular surgery

In recent years, a treatment has been developed to repair an aneurysm without major surgery. Many surgeons have been using less invasive endovascular surgery on abdominal aortic aneurysms. The procedure results in less blood loss, less trauma to the aorta, and fewer (or no) days in intensive care. Because results with endovascular repair of abdominal aortic aneurysms have been encouraging, similar techniques are being developed for the treatment of thoracic aortic aneurysms as well.

Endovascular surgery may benefit those who need surgery but are at high risk of complications because of pre-existing medical problems. However, not every person is a good candidate for this procedure. The appropriate choice of procedure, open versus endovascular, depends on many factors and is best determined by the medical team in consultation with the patient.

In endovascular surgery, a synthetic graft (stent-graft consisting of a polyester tube inside a metal cylinder) is attached to the end of a thin tube (catheter) that is inserted into the bloodstream, usually through an artery in the leg. Watching the progress of the catheter on an X-ray monitor, the surgeon threads the stent-graft to the weak part of the aorta where the aneurysm is located.
Once in place, the graft is expanded. The stent-graft reinforces the weakened section of the aorta to prevent rupture of the aneurysm. The metal frame is expanded like a spring to hold tightly against the wall of the aorta, cutting off the blood supply to the aneurysm. The blood now flows through the stent-graft, avoiding the aneurysm. The aneurysm typically shrinks over time.

What is the prognosis for an aortic aneurysm?

Medical Treatment of Aortic Dissections

The risk of death with medical treatment of descending thoracic aortic dissection is about 10 percent. If surgery is required, the risk is higher, however, at about 30 percent. Every effort is therefore made to treat these patients with medication.

Once the acute dissection has healed, adequate control of blood pressure may eliminate the need for surgery. Lifelong monitoring of diameter of the aorta is required because a previously dissected descending thoracic aorta may enlarge and rupture.

Open abdominal or open chest surgery

The length of the operation and the risks involved depends on the extent of the repair required, and on the patient's general health. Recovery time varies. Most people need at least a month or six weeks to recover from aneurysm surgery. The length of the hospital stay depends on the patient's condition and the operation performed, but it is typically a week.

Endovascular surgery

Although endovascular surgery reduces recovery time to a few days, it still carries risk. And because the procedure is fairly new, long-term results are unknown. Complications can occur with this procedure, namely blood leaking from the graft, known as endoleak. For this reason, patients who have repair of their aortic aneurysms with stent-grafts are initially required to return for monitoring every six months.

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