Aortic aneurysm

Resident Survival Guide

Aortic aneurysm
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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For patient information on Thoracic aortic aneurysm, click here

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1], Associate Editor(s)-in-Chief: Lina Ya'qoub, MD Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Overview

An aortic aneurysm is a dilation of the aorta in which the aortic diameter is ≥ 3.0 cm, 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 which are often fatal. Aneurysms often are a source of blood clots (emboli) stemming from the most common etiology of atherosclerosis.

Classification

There are 2 types of aortic aneurysms: thoracic and abdominal. These can be further classified according to the respective part of the vessel that's been affected:

• 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.
  • Suprarenal - not as common, often more difficult to repair surgically due to the presence of many aortic branches;
  • Infrarenal - often more easily surgically repaired and more common;
  • Pararenal - aortic aneurysm is infrarenal but affects renal arteries;
  • Juxtarenal - infrarenal aortic aneurysm that affects the aorta just below the renal arteries.

Thoracoabdominal aortic aneurysm may also 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: from distal thoracic aorta to celiac and superior mesenteric origins, but not the renal arteries.

Historical Perspective

Aortic aneurysm was first recorded by Antyllus, a Greek surgeon, in the second century AD. In the Renaissaince era, in 1555, Vesalius first diagnosed an abdominal aortic aneurysm. The first publication on the pathology with case studies was published by Lancisi in 1728. Finally, in 1817, Astley Cooper was the first surgeon to ligate the abdominal aorta to treat a ruptured iliac aneurysm. In 1888, Rudoff Matas came up with the concept of endoaneurysmorrhaphy.

Pathophysiology

The aortic aneurysms are a multifactorial disease associated with genetic and environmental risk factors. Marfan's syndrome and Ehlers-Danlos syndrome are associated with the disease, but there are also rarer syndromes like the Loeys-Dietz syndrome that are associated as well. Even in patients that do not have genetic syndromes, it has been observed that genetics can also play a role on aortic aneurysms' development. There has been evidence of genetic heterogeneity as there has already been documented in intracranial aneurysms. The genetic alterations associated with these genetic syndromes are the following:

Genetic diseases associated with aortic aneurysms

Disease	Involved Cellular Pathway	Mutated Gene(s)	Affected Protein(s)
Ehlers-Danlos syndrome type IV	Extracellular Matrix Proteins	COL3A1	Collagen type III
Marfan's syndrome	Extracellular Matrix Proteins	FBN1	Fibrillin-1
Loeys-Dietz syndrome	TGF-β Pathway	TGFBR1/TGFBR2
Aneurysm-Osteoarthritis Syndrome		SMAD3	SMAD3
Autosomal Dominant Polycystic Kidney Disease	Ciliopathy	PKD1PKD2	Polycystin 1 Polycystin 2
Turner Syndrome	Meiotic Error with Monosomy, Mosaicism, or De Novo Germ Cell Mutation	45X 45XO	Partial or Complete Absence of X Chromosome
Bicuspid Aortic Valve with TAA	Neural Crest Migration	NOTCH1	Notch 1
Familial TAA	Smooth Muscle Contraction Proteins	ACTA2	α-Smooth Muscle Actin
Familial TAA with Patent Ductus Arteriosus	Smooth Muscle Contraction Proteins	MYH11	Smooth Muscle Myosin
Familial TAA	Smooth Muscle Contraction Proteins	MYLK	Myosin Light Chain Kinase
Familial TAA	Smooth Muscle Contraction Proteins	PRKG1	Protein Kinase c-GMP Dependent, type I
Loeys-Dietz Syndrome variants	TGF-β Pathway	TGF-βR1TGF-βR2SMAD3TGF-β2TGF-β3

• 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

In the United States alone 15,000 people die yearly due to aortic aneurysms and it is the 13th leading cause of death. 1-2% of the population may have aortic aneurysms and prevalence rises up to 10% in older age groups. The disease varies according to where it takes place. In the thorax, the aortic arch is the less affected segment (10%) and the most common is the ascending aorta (50%). Regarding abdominal aneurysms, the infrarenal segment aortic aneurysms are three times more prevalent than the aortic aneurysms and dissections.

Regarding other factors as age, abdominal aortic aneurysms usually present 10 years later than thoracic aortic aneurysms. Both lesions are more present in men, but the proportion is much higher regarding abdominal aortic aneurysms (6:1 male:female ratio) in comparison to thoracic ones.

Abdominal aortic aneurysms also affect patients differently regarding race, as they are more prevalent among whites than blacks, asians and hispanics. It also seems to be declining in prevalence as evidenced by a Swedish study that found out a 2% prevalence of abdominal aortic aneurysms in comparison to earlier studies which reported 4-8%, probably due to risk-factor modification.

Risk Factors

• 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%.

Diagnosis

Diagnostic Criteria

• 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

Symptoms

• AAA is usually asymptomatic.
• Symptoms of AAA may include the following:

• Abdominal pain
• Pulsatile abdominal mass
• Hypotension
• Shock
• Death

Physical Examination

• Patients with ruptured AAA usually appear sick and in shock.
• Physical examination may be remarkable for:

• Pulsatile abdominal mass
• Hypotension
• Tachycardia
• Shock
• Cool extremities
• Diastolic murmur indicating aortic regurgitation from extension of TAA dissection

Laboratory Findings

• 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.

Imaging Findings

• 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.

Treatment

Medical Therapy

• Statins are recommended in cases associated with atherosclerosis.
• Blood pressure control

Surgery

• 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.

Prevention

• Smoking cessation is an important measure to prevent AAA progression and rupture.

Related Chapters

• Aortic Dissection
• Thoracic Aortic Aneurysm
• Abdominal Aortic Aneurysm
• Aneurysm

References

• 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.