|Atherosclerotic Aneurysm: Gross, an excellent example, natural color, external view of typical thoracic aortic aneurysms |
Image courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology
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An aortic aneurysm is a general term for any swelling (dilatation or aneurysm) of the aorta, usually representing an underlying weakness in the wall of the aorta at that location. While the stretched vessel may occasionally cause discomfort, a greater concern is the risk of rupture which causes severe pain, massive internal hemorrhage and, without prompt treatment, results in a quick death. Aneurysms often are a source of blood clots (emboli) stemming from the most common etiology of atherosclerosis.
There are 2 types of aortic aneurysms:
- Thoracic aortic aneurysm (TA), which occur in the thoracic aorta (runs through the chest)
- Abdominal aortic aneurysm (AAA), which occur in the abdominal aorta, are the most common.
- Aortic aneurysm was first discovered by Antyllus, a Greek surgeon, in the second century AD.
- In 1555, Vesalius first diagnosed AAA.
- In 1817, the first ligation was developed by Astley Cooper to treat ruptured iliac aneurysm.
- In 1888, Rudoff Matas came up with the concept of endoaneurysmorrhaphy.
- Thoraco-abdominal aorta may be classified according to Crawford classification into 5 subtypes/groups:
- Type 1: from the origin of left subclavian artery in descending thoracic aorta to the supra-renal abdominal aorta.
- Type 2: from the left subclavian to the aorto-iliac bifurcation.
- Type 3: from distal thoracic aorta to the aorto-iliac bifurcation
- Type 4: limited to abdominal aorta below the diaphragm
- Type 5 (Added by Safi's group): from distal thoracic aorta to celiac and superior mesenteric origins, but not the renal arteries.
- The pathogenesis of aortic aneurysm is characterized by progressive dilation, rupture, and dissection.
- The fibrillin-1 gene/Mutation has been associated with the development of thoracic aortic aneurysms in Marfan syndrome
- Other gene mutations coding for collagen, elastin and other elements of the extra-cellular matrix have been associated with the development of aneurysms in some genetic disorders, including Ehlers-Danlos and Alport syndromes among others.
- Mutations in the TGF-B pathway have also been described in the pathogenesis of aortic aneurysms in multiple genetic disorders, including Loeys-Dietz syndrome.
- On gross pathology, diameter enlargement, atheromatous plaques (especially in AAA), and/or dissection/rupture are characteristic findings of aortic aneurysms.
- On microscopic histopathological analysis, dilation, inflammatory signs if etiology is associated with inflammatory process, thrombus and atheroma are characteristic findings of aortic aneurysms.
Differentiating [disease name] from other Diseases
- Aortic aneurysms associated with certain high risk features and familial etiology must be differentiated from other causes as some of these aneurysms are at higher risk of rupture at earlier age.
- Aortic aneurysms should be differentiated from aortic dilation that has not reached the aneurysmal level.
Epidemiology and Demographics
- The incidence of thoracic aortic aneurysm is approximately 10 per 100,000 person-years.
- Patients of all age groups may develop aortic aneurysms.
- Abdominal aortic aneurysm is more commonly observed among patients aged 65 years old and older.
- Thoracic aortic aneurysms are commonly observed among younger patients, especially those with familial etiology.
- Thoracic aortic aneurysm affects men and women equally.
- Males are more commonly affected with AAA than females.
- The male to female ratio is approximately 4 to 1 for AAA.
- AAA usually affects individuals of the white race.
- Black individuals are less likely to develop AAA.
- Common risk factors in the development of aortic aneurysms are age, smoking, white race, atherosclerosis, and having underlying congenital disease that is associated with aortic aneurysms.
Natural History, Complications and Prognosis
- The majority of patients with aortic aneurysms remain asymptomatic for years.
- Early clinical features include abdominal pain, pulsatile abdominal mass, and chest pain.
- If left untreated, patients with progressively enlarging AAA, >0.5cm increase in size over 6 months or AAA of >5.5cm in diameter, are at increased risk of aneurysm rupture and death.
- Common complications of AAA include rupture, dissection, systemic embolization and death.
- Prognosis is generally good if screened and managed appropriately, and the 5-year survival rate of patients with repaired AAA is approximately 73%.
- The diagnosis of AAA is made when at least [number] of the following diagnostic criteria are met:
- Dilation of vessel diameter >50% its normal diameter
- Full thickness dilation: involving all three layers of the vessel
- AAA is usually asymptomatic.
- Symptoms of AAA may include the following:
- Abdominal pain
- Pulsatile abdominal mass
- Patients with ruptured AAA usually appear sick and in shock.
- Physical examination may be remarkable for:
- Pulsatile abdominal mass
- Cool extremities
- Diastolic murmur indicating aortic regurgitation from extension of TAA dissection
- There are no specific laboratory findings associated with AAA.
- An abdominal ultrasound can be diagnostic of AAA and is the imaging tool used to screen for AAA.
- Anemia can be seen in ruptured AAA.
- An abdominal ultrasound can be diagnostic of AAA and is the imaging tool used to screen for AAA
- CTA/MRA can accurately demonstrate AAA extent.
Other Diagnostic Studies
- Conventional angiogram can be used to diagnose aortic aneurysms.
- Statins are recommended in cases associated with atherosclerosis.
- Blood pressure control
- The mainstay of therapy for AAA is aneurysmal repair if diameter>5.5cm or size increased>0.5cm over 6 months.
- Surgical repair is indicated in cases of TAA dissection and progressive enlargement.
- Smoking cessation is an important measure to prevent AAA progression and rupture.
- Hannawa KK, Eliason JL, Upchurch GR. Gender differences in abdominal aortic aneurysms. Vascular. 2009;17 Suppl 1(Suppl 1):S30-9.
- Gwon JG, Kwon TW, Cho YP, Han YJ, Noh MS. Analysis of in hospital mortality and long-term survival excluding in hospital mortality after open surgical repair of ruptured abdominal aortic aneurysm. Ann Surg Treat Res. 2016;91(6):303-308.
- Wilson CT1, Fisher E, Welch HG: Racial disparities in abdominal aortic aneurysm repair among male Medicare beneficiaries. Arch Surg. 2008 May;143(5):506-10. doi: 10.1001/archsurg.143.
- Livesay JJ, Messner GN, Vaughn WK. Milestones in the treatment of aortic aneurysm: Denton A. Cooley, MD, and the Texas Heart Institute. Tex Heart Inst J. 2005;32(2):130-4.
- Lindsay ME, Dietz HC. The genetic basis of aortic aneurysm. Cold Spring Harb Perspect Med. 2014;4(9):a015909. Published . doi:10.1101/cshperspect.a015909
- Lindsay ME, Dietz HC. Lessons on the pathogenesis of aneurysm from heritable conditions. Nature. 2011;473(7347):308-16.
- John R. Frederick, Y. Joseph Woo: Thoracoabdominal aortic aneurysm. Ann Cardiothorac Surg 2012;1(3):277-285.