Aortic aneurysm

Causes and risk factors

• Age over 55 years (Risk increases with age)
• A family history of AAA is particularly concerning
• Smoking
• High blood pressure

Pathogenesis

Most aneurysms are caused by a breakdown in the proteins that provide the structural strength to the wall of the aorta. These proteins, called collagen and elastin can gradually deteriorate with age, but inflammation that is associated with atherosclerosis can accelerate this process even in younger people. There are also naturally occurring enzymes that cause the breakdown of collagen and elastin. An excess of these enzymes or other conditions that activate these enzymes may also contribute to the formation of an aneurysm, or its sudden growth. In rare cases an aneurysm may be caused by infection (mycotic aneurysms). There is still much to be learned about the cause of aneurysms and their growth, but fortunately we have successful, permanent treatments for AAA when they occur. Vascular surgeons have performed much of the basic research on aneurysm formation.

Types of Aortic Aneurysms

Aortic aneurysms are classified by shape, location along the aorta, and how they are formed.

True aneurysms and pseudoaneurysms

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

Occasionally an aneurysm may occur because of a localized weakness of the artery wall (saccular). 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.

Location

• Thoracic aortic aneurysm (TAA)

A TAA is a diseased, weakened, and bulging section of the aorta in the chest. This condition, if not treated, could result in a rupture of the aorta, leading to life-threatening internal bleeding. The aneurysm may be caused by vascular disease, injury, or a genetic defect of the tissue. TAA is sometimes found in people with Marfan?s syndrome, which is characterized by many anomalies including elongated bones. It is also associated with Turner syndrome, which results from a missing X chromosome and is associated with dwarfism and arrested sexual development in addition to aortic aneurysm. TAA also can run in families independent of those two syndromes. Because it is difficult to diagnose victims often die young. People with TAA remain unaware of the risk they face because the slowly enlarging aorta does not cause any symptoms until it has reached a critical diameter. At that point, the aorta dissects or ruptures, both of which are life-threatening. Typically, the patient develops chest pain and usually goes to an emergency department to seek treatment.

• Abdominal aortic aneurysm (AAA)

More than 90% of abdominal aortic aneurysms originate below the renal arteries. The diameter is the most important predictor of aneurysm rupture with up to a 40% risk of rupture over 5 years for aneurysm > 5 cm. When they do rupture they tend to rupture leftward and posteriorly.

Symptoms and signs

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.

Screening

When aortic aneurysms are diagnosed early, treatment is safe and effective and the aneurysm is cured. AAA can be diagnosed by a simple ultrasound scan that can be performed in a few minutes without risk or discomfort.

Men between the ages of 65 and 75 who are or have been smokers should have a one-time ultrasound to screen for abdominal aortic aneurysm, according to a new recommendation from the U.S. Preventive Services Task Force. Nearly 70 percent of men in this age group have smoked and would benefit from routine screening to check for aneurysms.

Diagnosis

Most patients have no symptoms at the time an AAA is discovered. Aneurysms are often detected on tests that were performed for entirely different reasons. 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. Although AAA can be detected by physical examination, most are diagnosed today using an ultrasound scan or CAT scan, simple exams that are non-invasive and can be done as an outpatient. Magnetic resonance imaging (MRI) can also help. These exams also tell us about the size of the aneurysms ? the key element to determine the need for treatment. Since major surgery was required in the past to repair an aortic aneurysm, that decision depended upon a comparison of the risk of rupture with risk of the surgery itself. Most doctors agree that for someone in good health, an AAA larger than 5 centimeters in diameter (about the size of a lemon) needs treatment. Smaller aneurysms may also need treatment if they cause symptoms (like back pain or abdominal pain), or tests show that the aneurysm has rapidly grown larger.

Treatment

1. Watch and wait

When detected in time, most ruptures can be prevented by repairing the aneurysms with an operation. Treatment for an aneurysm depends on its size and location and the general health of the person. If the aneurysm is small and without symptoms, a "watch-and-wait" approach may be suggested with regularly scheduled images of the aneurysm to check the size. However, if the aneurysm is large enough, or if the aneurysm is growing more than 1 centimeter per year, surgery may be the best option.

Women are more likely than men to die from aortic dissection according to one of the first studies of its kind reported. Aortic 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.

2. Medical treatment

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.

3. Endovascular repair of AAA

Recent advances in catheter-based technologies have led to exciting new treatments for aortic aneurysms. Now, endovascular grafting technology allows surgeons to repair the AAA by delivering a graft through a small incision in the groin, rather than the traditional major open surgery. The endovascular method, approved by the FDA in 1999, allows the graft to be delivered via a catheter (tube) inserted in a groin artery. In the operating room, x-ray guidance is used for proper positioning of the graft. The graft is then expanded inside the aorta and held in place with metallic hooks rather than sutures. The hospital stay is usually only one or two days, and most patients can return to work or normal daily activities in about a week. Even patients with serious medical problems, once thought to be too sick, or too frail to have surgery for AAA, may have their aneurysm repaired using an endovascular graft. This can avoid the need for major open surgery and also eliminate the risk of fatal rupture if the AAA was not treated at all. It?s very important for patients to know that endovascular grafting may not be possible in every case. Endovascular grafts are specially manufactured and don?t ?fit? for every case. Also, in many cases, standard surgery is still the best since we don?t have 50 years of experience with these newer procedures like we do with surgery. There may still be serious problems we haven?t anticipated.

4. Surgical resection

Surgery is usually required to repair an AAA, but modern, catheter-based technologies using endovascular grafts have made treatment less invasive in many cases. The combination of early diagnosis and modern treatment of aortic aneurysms can save countless lives lost due to aneurysm rupture each year.

Surgical treatment of AAA has been performed for almost 50 years and is a successful and durable procedure. In surgery the diseased part of the aorta is replaced with a Dacron or Teflon graft that is carefully matched to the normal aorta and is sewn in place by the surgeon. While ultimately curative, this operation requires a major abdominal incision and general anaesthesia, and the hospital stay averages 7-10 days for most patients. Even after uncomplicated surgery, it is often a month or two before patients can return to a full and normal life. Nevertheless, more than 90% of patients make a full recovery from surgery. After more than half a century of experience with these procedures we know that once patients have recovered, their aneurysms are permanently cured.

Follow up

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.

Prognosis and survival

Because the abdominal aorta is such a large blood vessel, a ruptured abdominal aneurysm is a life-threatening event. Fortunately, not all aneurysms rupture. Many grow very slowly and cause no symptoms or problems for many years. However, all have the potential to rupture and thus must be identified and treated or watched very carefully. The combination of earlier diagnosis with safer, simpler, and ever more successful treatments can prevent needless deaths due to ruptured abdominal aortic aneurysms. Timely suspicion and consultation with the family doctor and a simple ultrasound test can tell whether a person has aneurysm.

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.

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.

Recent news and research

Cocaine users in their mid-40s are found to have more than four times the risk of coronary artery aneurysms as non-users as per the Journal of the American Heart Association. It is believed that cocaine predisposes to coronary artery aneurysms, and then the aneurysms themselves may predispose to heart attacks.

The Food and Drug Administration has approved a new device called GORE TAG Endoprosthesis System that is intended to prevent ruptures of descending thoracic aneurysms by making a new path for blood flow. It is the first endovascular grafting system approved to treat aneurysms of the thoracic aorta.

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