Abdominal Aortic Aneurysm

An aneurysm is a localized bulge in the wall of an artery to about 50% or more of its original diameter. It can occur in a number of vessels and when it happens in the abdominal part of the aorta, it is called an abdominal aortic aneurysm.

Abdominal Aortic Aneurysm is associated with vascular processes. The incidence rate of the disease is stipulated as circa 18 / 100.000.

Presentation

Most cases are usually asymptomatic until they expand considerably or rupture. Patients may experience pain in the abdomen, flank, back or groin. This pain is often poorly characterized and unimpressive. There could also be symptoms resulting from local compression like nausea, vomiting, early satiety, urinary frequency, thrombosis from venous obstruction and back pain from erosion into adjacent vertebrae. There could be embolic phenomena like livedoreticularis. Thrombosis will produce claudication. Patient may feel a pulsatile mass in the abdomen [5].

If the aneurysm ruptures, it presents typically with back pain. There could be transient hypotension, temporary loss of consciousness and shock. If it ruptures into the vena cava, it produces symptoms like tachycardia, leg swelling and congestive heart failure. Rupture into the fourth part of the duodenum will present as upper gastrointestinal bleeding.

Workup

There is no diagnostic laboratory test for abdominal aortic aneurysm. Laboratory tests are only indicated for pre-operative management like checking transfusion requirements, the possibility of an infection, renal and liver function.

Imaging techniques are used for diagnosis. Ultrasound is the standard imaging technique and has a sensitivity of 100% when performed by skilled personnel [6].

It can also show free intraperitoneal blood. Plain abdominal radiographs may show aortic wall calcification in 50% of patients. CT scan also has a 100% sensitivity and has some advantages over ultrasound. MRI, in addition to what the CT and ultrasound does offers better imaging of branch vessels. Angiography is now used less often due to advancement in CT. Echocardiography is used in known CHD patients to assess cardiac function prior to repair [7].

Treatment

Conservative management is reserved for patients that carry a high perioperative risk. It involves controlling the underlying risk factors like beta blockers for hypertensives and serial ultrasound measurements. Also, patients who have an aneurysm that is less than 3cm may be managed conservatively [8].

Surgery is the gold standard of abdominal wall aneurysm repair and there are two methods. The open repair in which the aorta is assessed transabdominally or via the retroperitoneal space and the aorta reconstructed from within, the aneurysm sac is closed and a graft is put into the duodenum to prevent erosion [9].

The second method is endovascular repair. This involves entering the lumen of the aorta via the femoral vessels and an endograft with a stent exoskeleton placed within the lumen of the abdominal aorta aneurysm.

Prognosis

Patients who suffer rupture of the aneurysm generally have a poor prognosis and less than 50% surviving the period it takes to get to the emergency room. Patient who receive timely surgical intervention before they go into severe shock have a good survival rate. For best prognosis, the condition is best identified before it ruptures as elective repair carries a lower mortality rate. Long-term prognosis is affected by other comorbidities like chronic heart failure and chronic obstructive pulmonary disease.

Etiology

The cause of abdominal aortic aneurysm remains unclear although it is believed to be caused by degeneration of the aorta. Several factors have been identified as risk factors for this degeneration and subsequent aneurysm. The greatest risk factor is age greater than 65 years in men who have peripheral atherosclerotic disease. Other risk factors are smoking, chronic obstructive pulmonary disease, previous aneurysm repair, peripheral aneurysm, coronary artery disease and hypertension. Less common causes are Ehlers-Danlos syndrome, Marfan syndrome and collagen vascular disease. Gram-positive bacteria have been known to cause mycotic aneurysms. Rare causes include trauma, arteritis, cystic medial necrosis and pseudoaneurysms arising from anastomotic disruptions [2].

Epidemiology

Ruptured abdominal aortic aneurysm is the cause of an estimated 15,000 deaths yearly in the United States which ranks it as the 13th leading cause of the death and the 10th leading cause in men aged 55 and over. The incidence of this condition varies between countries and is as high as 8.8% in Italy. In men, the incidence increases sharply from age 50 years and in women from the age of 60 years and it peaks between the ages 75-79years in both sexes. It is commoner in Caucasians than African Americans, Asians and Hispanics [3].

Sex distribution
Age distribution

Pathophysiology

The main reason for this condition is failure of elastin and collagen, the structural proteins of the aorta. The loss of structural integrity and widening of the lumen begins with a degeneration of the media. There are different mechanisms responsible for development of abdominal aortic aneurysm [4].

The number of elastin layers reduces from the thoracic to the infrarenal aorta, leading to medial thinning. Also, as an individual ages, there is an increase in the concentration of proteolytic enzymes relative to the concentration of their inhibitors. This causes the media to degrade by way of increased proteolytic activity. Another mechanism is the role of metalloproteinase enzyme responsible for tissue remodeling. In aneurysm walls, there is increased activity of this enzyme. The action of immunoreactive proteins are also thought to be responsible for aneurysm formation. There is high correlation of this condition with atherosclerosis. This may be due to the atherosclerosis causing obstruction of the vasa vasorum which may lead to weakening of the aortic wall, loss of elastic recoil and degenerative ischemic changes.

Prevention

This includes cessation of smoking, treatment of hypertension, healthy low-fat diet, regular exercise and screening of men aged 65 and above with ultrasound [10].

Summary

This condition is relatively common and life threatening. As the size of an aneurysm grows, the risk of rupture increases. It is usually asymptomatic, producing symptoms only when there is significant dilatation or eventual rupture [1].

Patient Information

Definition: This is a swelling of a part of the large artery in the abdomen. It is mostly seen in men above 65 years and is a potentially fatal condition. If it ruptures, it may kill even before the patient can access emergency care.

Cause: they include, smoking, hypertension, atherosclerosis, men over 65years, chronic obstructive lung disease, alcohol, infection and trauma.

Symptoms: they are usually not symptomatic until they rupture. When there are symptoms, it includes pain, they include pain in the abdomen, back, sides and groin. This pain is usually hard to define. There could also be a palpable mass which may be pulsating.

Diagnosis: This is done by the use of imaging techniques like ultrasound, CT scan, MRI and Angiography. They show the aneurysm and complications if they are present.

Treatment: The main treatment is surgical. It could be open when the aorta is accessed through a large abdominal or retroperitoneal incision or endograft repair which involves entering the aorta through a tiny incision in an artery.

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References

  1. Wanhainen A. How to define an abdominal aortic aneurysm--influence on epidemiology and clinical practice. Scand J Surg 2008; 97:105.
  2. Singh K, Bønaa KH, Jacobsen BK, et al. Prevalence of and risk factors for abdominal aortic aneurysms in a population-based study : The Tromsø Study. Am J Epidemiol 2001; 154:236.
  3. Wilmink AB, Quick CR. Epidemiology and potential for prevention of abdominal aortic aneurysm. Br J Surg 1998; 85:155.
  4. Wassef M, Baxter BT, Chisholm RL, Dalman RL, Fillinger MF, Heinecke J, et al. Pathogenesis of abdominal aortic aneurysms: a multidisciplinary research program supported by the National Heart, Lung, and Blood Institute. J Vasc Surg. Oct 2001;34(4):730-8.
  5. Muluk SC, Gertler JP, Brewster DC, et al. Presentation and patterns of aortic aneurysms in young patients. J Vasc Surg 1994; 20:880.
  6. Guirguis-Blake JM, Beil TL, Senger CA, Whitlock EP. Ultrasonography screening for abdominal aortic aneurysms: a systematic evidence review for the U.S. Preventive Services Task Force. Ann Intern Med 2014; 160:321.
  7. Daly KJ, Torella F, Ashleigh R, McCollum CN. Screening, diagnosis and advances in aortic aneurysm surgery. Gerontology. Nov-Dec 2004;50(6):349-59.
  8. Brewster DC, Cronenwett JL, Hallett JW Jr, Johnston KW, Krupski WC, Matsumura JS. Guidelines for the treatment of abdominal aortic aneurysms. Report of a subcommittee of the Joint Council of the American Association for Vascular Surgery and Society for Vascular Surgery. J Vasc Surg. May 2003;37(5):1106-17.
  9. Stanley, J. Open surgical treatment of pararenal abdominal aortic aneurysms. In: Aortic Aneurysms, Contemporary Cardiology, Upchurch, G, Criado, E. (Eds), Humana Press, 2009. p.159
  10. Wilmink TB, Quick CR, Day NE. The association between cigarette smoking and abdominal aortic aneurysms. J Vasc Surg 1999; 30:1099.

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