Abdominal Aortic Aneurysm Causes, Abdominal Aortic Aneurysm Effects, Abdominal Aortic Aneurysm Symptoms, Abdominal Aortic Aneurysm Diagnosis, Abdominal Aortic Aneurysm Prognosis & Treatments

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Abdominal Aortic Aneurysm

Definition

Q. What is Abdominal Aortic Aneurysm?
Ans. The aorta is the largest artery in your body, and it carries oxygen-rich blood pumped out of, or away from, your heart. Your aorta runs through your chest, where it is called the thoracic aorta. When it reaches your abdomen, it is called the abdominal aorta. The abdominal aorta supplies blood to the lower part of the body. In the abdomen, just below the navel, the aorta splits into two branches, called the iliac arteries, which carry blood into each leg.

When a weak area of the abdominal aorta expands or bulges, it is called an abdominal aortic aneurysm (AAA). The pressure from blood flowing through your abdominal aorta can cause a weakened part of the aorta to bulge, much like a balloon. A normal aorta is about 1 inch (or about 2 centimeters) in diameter. However, an AAA can stretch the aorta beyond its safety margin as it expands. Aneurysms are a health risk because they can burst or rupture. A ruptured aneurysm can cause severe internal bleeding, which can lead to shock or even death.

Less commonly, Abdominal Aortic Aneurysm can cause another serious health problem called embolization. Clots or debris can form inside the aneurysm and travel to blood vessels leading to other organs in your body. If one of these blood vessels becomes blocked, it can cause severe pain or even more serious problems, such as limb loss.

Each year, physicians diagnose approximately 200,000 people in the United States with AAA. Of those 200,000, nearly 15,000 may have AAA threatening enough to cause death from its rupture if not treated.

Fortunately, especially when diagnosed early before it causes symptoms, an AAA can be treated, or even cured, with highly effective and safe treatments.

Epidemiology of Abdominal Aortic Aneurysm
Abdominal Aortic Aneurysm is uncommon in individuals of African, Asian, and Hispanic heritage.

There are 15,000 deaths yearly in the U.S. secondary to AAA rupture. The frequency varies strongly between males and females. The peak incidence is among males around 70 years of age, the prevalence among males over 60 years totals 2-6%. The frequency is much higher in smokers than in non-smokers (8:1), and the risk decreases slowly after smoking cessation. Other risk factors include hypertension and male sex. In the U.S., the incidence of AAA is 2-4% in the adult population. AAA is 4-6 times more common in male siblings of known patients, with a risk of 20-30%.

Rupture of the AAA occurs in 1-3% of men aged 65 or more, the mortality is 70-95%.

Etiology of Abdominal Aortic Aneurysm
The exact causes of the degenerative process remain unclear. There are, however, some theories and risk factors defined.

Genetic Influences: The influence of genetic factors is highly probable. The high familial prevalence rate is most notable in male individuals. There are many theories about the exact genetic disorder that could cause higher incidence of AAA among male members of the affected families. Some presumed that the influence of alpha 1-antitrypsin deficiency could be crucial, some experimental works favored the theory of X-linked mutation, which would explain the lower incidence in heterozygous females. Other theories of genetic etiology were also formulated.
Hemodynamic Influences: Abdominal aortic aneurysm is a focal degenerative process with predilection for the infrarenal aorta. The histological structure and mechanical characteristics of infrarenal aorta differ from those of the thoracic aorta. The diameter decreases from the root to the bifurcation, and the wall of the abdominal aorta also contains a lesser proportion of elastin. The mechanical tension in abdominal aortic wall is therefore higher than in the thoracic aortic wall. The elasticity and distensibility also decline with age, which can result in gradual dilatation of the segment. Higher intraluminal pressure in patients with arterial hypertension markedly contributes to the progression of the pathological process.
Atherosclerosis: The AAA was long considered to be caused by atherosclerosis, because the walls of the AAA are frequently affected heavily. However, this theory cannot be used to explain the initial defect and the development of occlusion, which is observed in the process.
Other Causes: Other causes of the development of AAA include: infection, trauma, arteritis, cystic medial necrosis (m. Erdheim) and connective tissue disorders (e.g. Marfan syndrome, Ehlers-Danlos syndrome).

Symptoms

Symptoms of Abdominal Aortic Aneurysm
Although you may initially not feel any symptoms with Abdominal Aortic Aneurysm, if you develop symptoms, you may experience one or more of the following:

A pulsing feeling in your abdomen, similar to a heartbeat.
Severe, sudden pain in your abdomen or lower back. If this is the case, your aneurysm may be about to burst.
On rare occasions, your feet may develop pain, discoloration, or sores on the toes or feet because of material shed from the aneurysm.

If your aneurysm bursts, you may suddenly feel intense weakness, dizziness, or pain, and you may eventually lose consciousness. This is a life-threatening situation and you should seek medical attention immediately.

Causes

Causes of Abdominal Aortic Aneurysm
Physicians and researchers are not quite sure what actually causes an Abdominal Aortic Aneurysm to form in some people. The leading thought is that the aneurysm may be caused by inflammation in the aorta, which may cause its wall to weaken or break down. Some researchers believe that this inflammation can be associated with atherosclerosis (also called hardening of the arteries) or risk factors that contribute to atherosclerosis, such as high blood pressure (hypertension) and smoking. In atherosclerosis fatty deposits, called plaque, build up in an artery. Over time, this buildup causes the artery to narrow, stiffen and possibly weaken. Besides atherosclerosis, other factors that can increase your risk of Abdominal Aortic Aneurysm include:

Being a man older than 60 years
Having an immediate relative, such as a mother or brother, who has had Abdominal Aortic Aneurysm
Having high blood pressure
Smoking

Your risk of developing Abdominal Aortic Aneurysm increases as you age. Abdominal Aortic Aneurysm is more common in men than in women.

Diagnosis

Diagnosis of Abdominal Aortic Aneurysm
Abdominal Aortic Aneurysm are commonly divided according to their size and symptomatology. An aneurysm is usually considered to be present if the measured outer aortic diameter is over 3 cm (normal diameter of aorta is around 2 cm). The natural history is of increasing diameter over time, followed eventually by the development of symptoms (usually rupture). If the outer diameter exceeds 5.5 cm, the aneurysm is considered to be large. For aneurysms under 5.5 cm, the risk of rupture is low, so that the risks of surgery usually outweigh the risk of rupture. Aneurysms less than 5.5 cm are therefore usually kept under surveillance until such time as they become large enough to warrant repair, or develop symptoms. The vast majority of aneurysms are asymptomatic. The risk of rupture is high in a symptomatic aneurysm, which is therefore considered an indication for surgery. Possible symptoms include low back pain, flank pain, abdominal pain, groin pain or pulsating abdominal mass. The complications include rupture, peripheral embolisation, acute aortic occlusion, and aortocaval (beteween the aorta and inferior vena cava) or aortoduodenal (between the aorta and the duodenum) fistulae. On physical examination, a palpable abdominal mass can be noted. Bruits can be present in case of renal or visceral arterial stenosis.

As most of the AAAs are asymptomatic, their presence is usually revealed during an abdominal examination for another reason - the most common being abdominal ultrasonography. A physician may also detect the presence of an AAA by abdominal palpation. Ultrasonography provides the initial assessment of the size and extent of the aneurysm, and is the usual modality for surveillance. Preoperative examinations include CT, MRI and special modes thereof, like CT/MR angiography. Angiography may be useful also, as an additional method of measurement for the planning of endoluminal repair. Note that an aneurysmal aorta may appear normal on angiogram, due to thrombus within the sac.

Pathophysiology of Abdominal Aortic Aneurysm
The most striking histopathological changes of aneurysmatic aorta are seen in tunica media and intima. These include accumulation of lipids in foam cells, extracellular free cholesterol crystals, calcifications, thrombosis, and ulcerations and ruptures of the layers. There is an adventitial inflammatory infiltrate. However, the degradation of tunica media by means of proteolytic process seems to be the basic pathophysiologic mechanism of the AAA development. Some researchers report increased expression and activity of matrix metalloproteinases in individuals with AAA. This leads to elimination of elastin from the media, rendering the aortic wall more susceptible to the influence of the blood pressure.

Treatment

Treatment of Abdominal Aortic Aneurysm
If your Abdominal Aortic Aneurysm is small, your physician may recommend "watchful waiting," which means that you will be monitored every 6-12 months for signs of changes in the aneurysm size. Your physician may schedule you for regular CT scans or ultrasounds to watch the aneurysm. This method is usually used for aneurysms that are smaller than about 2 inches (roughly 5.0 to 5.5 centimeters) in diameter. If you also have high blood pressure, your physician may prescribe blood pressure medication to lower the pressure on the weakened area of the aneurysm. If you smoke, you should obtain help to stop smoking. An aneurysm will not "go away" by itself. It is extremely important to continue to follow up with your physician as directed because the aneurysm may enlarge to a dangerous size over time. It could eventually burst if this is not detected and treated.

Open Surgical Aneurysm Repair
A vascular surgeon may recommend that you have a surgical procedure called open aneurysm repair if your aneurysm is causing symptoms, or is larger than about 2 inches (roughly 5.0 to 5.5 centimeters), or is enlarging under observation. During an open aneurysm repair, also known as surgical aneurysm repair, your surgeon makes an incision in your abdomen and replaces the weakened part of your aorta with a tube-like replacement called an aortic graft. This graft is made of a strong, durable, man-made plastic material, such as DacronÂ®, in the size and shape of the healthy aorta. The strong tube takes the place of the weakened section in your aorta and allows your blood to pass easily through it. Following the surgery, you may stay in the hospital for 4 to 7 days. Depending upon your circumstances, you may also require 6 weeks to 3 months for a complete recovery. More than 90 percent of open aneurysm repairs are successful for the long term.

Endovascular Stent Graft
Instead of open aneurysm repair, your vascular surgeon may consider a newer procedure called an endovascular stent graft. Endovascular means that the treatment is performed inside your artery using long, thin tubes called catheters that are threaded through your blood vessels. This procedure is less invasive, meaning that your surgeon will usually need to make only small incisions in your groin area through which to thread the catheters. During the procedure, your surgeon will use live x-ray pictures viewed on a video screen to guide a fabric and metal tube, called an endovascular stent graft (or endograft), to the site of the aneurysm. Like the graft in open surgery, the endovascular stent graft also strengthens the aorta. Your recovery time for endovascular stent grafting is usually shorter than for the open surgery, and your hospital stay may be reduced to 2 to 3 days. However, this procedure requires more frequent follow-up visits with imaging procedures, usually CT scans, after endograft placement to be sure the graft continues to function properly. Also, the endograft is more likely to require periodic maintenance procedures than does the open procedure. In addition, your aneurysm may not have the shape that is suitable for this procedure, since not all patients are candidates for endovascular repair because of the extent of the aneurysm, or its relationship to the renal (kidney) arteries, or other issues. While the endovascular stent graft may be a good option for some patients who have suitable aneurysms and who have medical conditions increasing their risk, in some other cases, open aneurysm repair may still be the best way to cure AAA. Your vascular surgeon will help you decide what is the best method of treatment for your particular situation.

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