Condition

Thoracic Aortic Aneurysm

Editors: Jinnette Dawn Abbott MD, FACC, FSCAI; Eddy Lang MDCM, CCFP(EM), CSPQ; Peter Oettgen MD

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Background Information

Description

  • Thoracic aortic aneurysm is the permanent dilation of a segment of the thoracic aorta to ≥ 150% of its normal diameter.

Also Called

  • TAA

Definitions

  • Normal adult thoracic aortic diameters:
    • Normal diameter increases with increasing age and body surface area.
    • Normal diameter may vary by 0.2-0.4 cm depending on the method of visualization and if the aortic wall is included in the measurement.
    • See approach to imaging thoracic aorta and reporting image results for guidance on accurately and reproducibly measuring aorta.
    • Mean aortic diameters based on location and imaging modality used:
      • Aortic root:
        • In females, 3.5-3.72 cm on computed tomography (CT)
        • In males, 3.63-3.91 cm on CT
        • Reference - Circulation 2010 Apr 6;121(13):e266
      • Sinus of Valsalva:
        • In females:
          • 3-3.6 cm on echocardiography
          • 2.8 cm on cardiac magnetic resonance (CMR)
        • In males:
          • 3.4-4 cm on echocardiography
          • 3.2 cm on CMR
      • Sinotubular junction:
        • In females:
          • 2.6-3.2 cm on echocardiography
          • 2.2 cm on CMR
        • In males;
          • 2.9-3.6 cm on echocardiography
          • 2.5 cm on CMR
      • Ascending aorta:
        • In males and females, 2.86 cm on chest x-ray (Circulation 2010 Apr 6;121(13):e266)
        • In females:
          • 2.7 cm on echocardiography
          • 2.6 cm on CMR
        • In males:
          • 3 cm on echocardiography
          • 2.7 cm on CMR
      • Mid-descending aorta:
        • In females:
          • 2.45-2.64 cm on CT (Circulation 2010 Apr 6;121(13):e266)
          • 2.5-2.6 cm on CMR
        • In males:
          • 2.39-2.98 cm on CT (Circulation 2010 Apr 6;121(13):e266)
          • 2.4-3 cm on CMR
      • Diaphragmatic:
        • In females, 2.4-2.44 cm on CT
        • In males, 2.43-2.69 cm on CT
        • Reference - Circulation 2010 Apr 6;121(13):e266
  • Pseudoaneurysm (also called false aneurysm) refers to dilation of the aorta due to disruption of all wall layers with extravasation of blood contained by periarterial connective tissue (not by the arterial wall). It is typically caused by blunt trauma or rapid deceleration from vehicle accidents, falls, or sports injuries (Circulation 2010 Apr 6;121(13):e266).

Types

  • Types of thoracic aortic aneurysm based on location:
    • The most common sites of involvement include:
      • Aortic root, which is most common in Marfan syndrome
      • Ascending aorta, which is proximal to the brachiocephalic artery
    • Less common sites of involvement include:
      • Transverse arch, which is involved in 10% of cases
      • Descending thoracic aorta, which is distal to the left subclavian artery
    • Thoracoabdominal aorta involves the thoracic aorta plus abdominal aorta
    • Reference - Circulation 2010 Apr 6;121(13):e266
  • Descending thoracic aortic aneurysm classification based on involving thirds of descending thoracic aorta:
    • Type A: involves proximal third
    • Type B: involves middle third
    • Type C: involves distal third
    • Type AB: involves proximal two-thirds
    • Type BC: involves distal two-thirds
    • Reference - Circulation 2010 Apr 6;121(13):e266
  • Thoracoabdominal aneurysm Crawford classification:
    • Type I: extends from the proximal descending thoracic aorta (above T6) and extends to the renal arteries (upper abdominal aorta)
    • Type II: extends from the proximal descending thoracic aorta (above T6) and extends to below the renal arteries
    • Type III: extends from the distal descending thoracic aorta (below T6 but above diaphragm) and extends into the abdominal aorta
    • Type IV: extends from below the diaphragm and involves the entire visceral aortic segment and most of the abdominal aorta
    • Reference - Circulation 2010 Apr 6;121(13):e266

Epidemiology

Who Is Most Affected

  • The mean age at diagnosis is 69 years, however females tend to be significantly older at presentation than males (Mayo Clin Proc 2009 May;84(5):465).

Incidence/Prevalence

  • STUDY SUMMARY
    incidence of degenerative nondissecting thoracic aortic aneurysm about 0.13% in Minnesota, United States from 1980 to 1994
    COHORT STUDY: JAMA 1998 Dec 9;280(22):1926

  • STUDY SUMMARY
    annual incidence of combined thoracic aortic aneurysm and dissection increased in Sweden between 1987 and 2002
    COHORT STUDY: Circulation 2006 Dec 12;114(24):2611

Risk Factors

  • Hypertension (Circulation 2010 Apr 6;121(13):e266)
  • Smoking (Circulation 2010 Apr 6;121(13):e266)
  • Genetic disorders associated with medial degeneration, including:
  • Risk factors for mycotic thoracic aortic aneurysm include:
    • IV drug use (Emerg Radiol 2014 Apr;21(2):191)
    • Presence of potential sources of infection, including:
      • Infective endocarditis
      • Prosthetic valve endocarditis
      • Infection contiguous to the aorta, such as vertebral osteomyelitis or gastroenteritis caused by salmonella
      • Reference - Circulation 2016 Nov 15;134(20):e412
    • Increased susceptibility to infection due to damage to endothelium caused by congenital abnormality, such as cystic necrosis or coarctation of aorta (Circulation 2016 Nov 15;134(20):e412)

Possible Risk Factors

  • STUDY SUMMARY
    current fluoroquinolone use associated with increased risk of thoracic aortic aneurysm and thoracic aortic dissection
    SYSTEMATIC REVIEW: Am J Med 2017 Dec;130(12):1449

  • STUDY SUMMARY
    current, past, or any prior-year fluoroquinolone use associated with increased risk of aortic aneurysm or dissection and risk may be greater with longer duration of use, in patients > 70 years old, and in women
    CASE-CONTROL STUDY: JAMA Intern Med 2015 Nov 1;175(11):1839

  • STUDY SUMMARY
    oral fluoroquinolone use associated with increased risk of aortic aneurysm but not aortic dissection compared to amoxicillin use
    COHORT STUDY: BMJ 2018 Mar 8;360:k678

  • STUDY SUMMARY
    fluoroquinolone monotherapy may not increase risk of aortic aneurysm or aortic dissection compared to other antibiotic monotherapies in adults with infections where fluoroquinolone use is indicated
    NESTED CASE-CONTROL STUDY: JAMA Intern Med 2020 Sep 8 early online

Associated Conditions

  • Atherosclerosis
  • Chronic kidney disease (CKD) in adults (Eur Heart J 2014 Nov 1;35(41):2873)
  • Diabetes mellitus (Eur Heart J 2014 Nov 1;35(41):2873)
  • Dyslipidemia (Eur Heart J 2014 Nov 1;35(41):2873)
  • Respiratory illness (Eur Heart J 2014 Nov 1;35(41):2873)
  • Other cardiovascular conditions, including:
    • Bicuspid aortic valve
    • Aberrant right subclavian artery
    • Coarctation of the aorta
    • Right aortic arch
    • Reference - Circulation 2010 Apr 6;121(13):e266
  • Inflammatory diseases, including:

Etiology and Pathogenesis

Causes

  • Most thoracic aortic aneurysms are caused by dilatation of the aorta due to degenerative disease of the media, but idiopathic aneurysms can occur (Circulation 2010 Apr 6;121(13):e266).

Pathogenesis

  • Thoracic aortic aneurysm formation involves medial degeneration characterized by all of the following:
    • Disruption and loss of elastic fibers
    • Loss of smooth muscle in the aortic media
    • Increased deposition of proteoglycans
  • Medial degeneration may initially be an adaptive response to wall stress in the aortic dilation zone.
Aortic aneurysm

Image 1 of 4

Aortic aneurysm

Gross specimen of a longitudinal section through a thoracic aorta with aneurysm.

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