• Clinical science

Abdominal aortic aneurysm

Abstract

Abdominal aortic aneurysm (AAA) is a focal dilatation of the abdominal aorta to more than 1.5 times its normal diameter. AAAs are classified by location as either suprarenal or infrarenal aneurysms. Men of advanced age are at increased risk for their formation; smoking and hypertension are also major risk factors. AAAs are frequently asymptomatic and therefore detected incidentally. Symptomatic AAAs can manifest with lower back pain, a pulsatile abdominal mass, and a bruit on auscultation. Rupture presents with a sudden onset of severe tearing back or abdominal pain, a painful pulsatile mass, and hypovolemic shock. Abdominal ultrasound is the best initial and confirmatory test to diagnose AAAs and determine their extent. Observation, close follow-up, and reduction of cardiovascular risk factors are indicated for small aneurysms, whereas pronounced (> 5.5 cm) or rapidly expanding aneurysms require surgery. Surgical treatment involves open resection of the aneurysm with graft placement or, increasingly, endovascular stent placement. The prognosis is markedly worse if dissection or rupture of the aneurysm occurs. All men between 65 and 75 years of age with a history of smoking and men > 50 years with a positive family history should be screened once with an ultrasound to exclude an AAA.

Definition

  • Dilation of all three layers of the aortic wall (intima, media, and adventitia) to > 50% of the normal diameter[1]
    • Diameter: > 3 cm at the level of the renal arteries (see also aneurysm)

Epidemiology

  • Peak incidence: 60–70 years (rare in patients < 50 years, who account for only 1% of AAA patients)
  • 10% of male patients > 70 years suffering from hypertension
  • Sex: > : ∼ 2:1
  • More common in white populations

Epidemiological data refers to the US, unless otherwise specified.

Etiology

Classification

  • Below the renal arteries
    • Most common location , > 90%
    • 20% of aneurysms extend into the pelvic arteries.
    • Spindle-shaped or saccular (increased risk of rupture)
  • Above the renal arteries

Pathophysiology

  • Inflammation and proteolytic degeneration of connective tissue proteins; (e.g., collagen and elastin and/or smooth muscle cells) in high-risk patients → loss of structural integrity of the aortic wall; → widening of the vessel → mechanical stress (e.g., high blood pressure) acts on weakened wall tissue → dilation and rupture may occur.
  • The aneurysmatic dilatation of the vessel wall may cause disruption of the laminar blood flow and turbulence. This may cause a bruit on auscultation.
  • Possible formation of thrombi in the aneurysm → peripheral thromboembolism

References:[1][2]

Clinical features

Aortic aneurysms are mostly asymptomatic or have nonspecific symptoms. Therefore, they are often incidental findings on ultrasound or CT scan. Rupture or dissection of the aneurysm is a life-threatening condition (see “Complications” below).

  • Lower back pain
  • Pulsatile abdominal massat or above the level of the umbilicus
  • Bruit on auscultation
  • Peripheral thrombosis and distal atheroembolic phenomena (e.g., blue toe syndrome and livedo reticularis)
  • Decreased ankle brachial index

Diagnostics

  • Ultrasound: best initial and confirmatory test for AAAs [3]
    • Determines the presence, size, and extent of an aneurysm
    • Can detect a thrombus in the aneurysm[4]
    • Can detect free peritoneal blood in case of rupture
    • For follow-up and monitoring purposes
  • CT with contrast: (or MRI): determines AAA rupture, suprarenal involvement, and visceral artery involvement.
  • Other imaging: arteriography

Regular monitoring is essential, as the aneurysm size and expansion rate are strong predictors of the risk of rupture!

Differential diagnoses

Abdominal vs. thoracic aortic aneurysm
Abdominal aortic aneurysm Thoracic aortic aneurysm

Location

  • Below the renal arteries (most common)
Epidemiology
  • Advanced age
  • Predominantly men
  • More common than TAA
  • Advanced age
  • Predominantly men
Etiology
Clinical features
  • Pulsatile abdominal mass
  • Bruit on auscultation
  • Lower back pain
  • Feeling of pressure in the chest
  • Thoracic back pain
Diagnostics
  • Chest x-ray and CT with contrast
Therapy
  • Indications for repair:
    • Diameter: ≥ 5.5 cm
    • Expansion rate: ≥ 1 cm/year
    • Symptomatic aneurysm
    • Complications (e.g., rupture)
  • Indications for repair:
    • Diameter: ascending aneurysm ≥ 5.5 cm; descending aneurysm ≥ 6.5 cm
    • Expansion rate: ≥ 1 cm/year
    • Symptomatic aneurysm
    • Complications (e.g., rupture)

The differential diagnoses listed here are not exhaustive.

Treatment

Conservative

  • Reduction of cardiovascular risk factors
    • Optimal blood pressure levels (< 120/80 mm Hg)
    • Cessation of smoking
  • Follow-up for AAA: (aneurysm surveillance): see table below
Diameter of AAA Follow-up
< 3 cm No further follow-up
3–4 cm Ultrasound every year
4–4.5 cm Ultrasound every 6 months
4.5–5.5 cm Ultrasound every 3 months

Surgical

  • Indications for repair
    • Elective repair: for asymptomatic AAAs with any of the following criteria[5]
      • Diameter > 5.5 cm
      • Aneurysm expanding ≥ 1 cm per year
      • Diameter between 4–5.5 cm in young individuals with minimal operative risks and good estimated life expectancy.
    • Emergency repair:
      • Symptomatic aneurysm (indicative of imminent rupture or a leaking AAA)
      • Acutely symptomatic : emergency operation (see “Complications” below)
  • Procedures
    • Endovascular aneurysm repair (EVAR)
      • Preferred over open surgery; esp. in patients with high operative risk
      • Minimally invasive procedure that can be performed under local anesthesia
      • An expandable stent graft is placed intraluminally under fluoroscopic guidance via the femoral or iliac arteries at the site of the aneurysm.
    • Open repair: a laparotomy is performed and the dilated segment of the aorta is replaced with a tube graft or Y-prosthesis (bifurcated synthetic stent graft)

References:[1]

Complications

Rupture[6]

  • Risk factors: large diameter, rapid expansion, and smoking
  • Clinical features
    • Impending rupture or contained leak
      • Throbbing abdominal or low back pain radiating to the flank, buttocks, legs, or groin
      • Grey turner sign (ecchymosis of the affected flank area)
      • Cullen sign (periumbilical ecchymosis)
    • Manifested rupture
      • Hypovolemic shock (in case of a free, non-covered rupture)
      • Sudden onset of severe tearing back or abdominal pain with radiation to the flank, buttocks, legs, or groin
      • Painful pulsatile mass
      • Nausea, vomiting
      • Syncope
      • Hematuria
  • Diagnosis: ultrasound, contrast CT → extravasation of contrast agent
  • Treatment: open emergency surgery (gold standard) or endoscopic treatment
  • Prognosis: high mortality rate (∼ 90% if AAA rupture occurs outside of the hospital)
  • Embolism: from thrombotic material of the aneurysm
  • Aortic dissection

Postoperative complications[7]

  • Ischemia of the bowel, kidneys, and spinal cord
  • Prosthetic graft infection
  • Aortoenteric fistula

We list the most important complications. The selection is not exhaustive.

Prevention

  • Screening for abdominal aneurysm with abdominal ultrasound
    • One-time screening in men aged 65 to 75 years with a history of smoking
    • Individuals ≥ 50 years with positive family history

References:[1][8]

  • 1. Rahimi SA. Abdominal Aortic Aneurysm. In: Rowe VL. Abdominal Aortic Aneurysm. New York, NY: WebMD. http://emedicine.medscape.com/article/1979501. Updated December 19, 2016. Accessed February 6, 2017.
  • 2. Kumar V, Abbas AK, Aster JC. Robbins & Cotran Pathologic Basis of Disease. Philadelphia, PA: Elsevier Saunders; 2014.
  • 3. Dent B, Kendall RJ, Boyle AA, Atkinson PR. Emergency ultrasound of the abdominal aorta by UK emergency physicians: a prospective cohort study. Emerg Med J. 2007; 24(8): pp. 547–549. doi: 10.1136/emj.2007.048405.
  • 4. Jang T. Bedside Ultrasonography Evaluation of Abdominal Aortic Aneurysm. In: Taylor CR. Bedside Ultrasonography Evaluation of Abdominal Aortic Aneurysm. New York, NY: WebMD. http://emedicine.medscape.com/article/1977715-overview#showall. Updated September 20, 2015. Accessed February 6, 2017.
  • 5. Brewster DC, Cronenwett JL, Hallett JW Jr, Johnston W, Krupski WC, Matsumura JS. Guidelines for the treatment of abdominal aortic aneurysms. J Vasc Surg. 2003; 37(5): pp. 1106–1117. doi: 10.1067/mva.2003.363.
  • 6. Agabegi SS, Agabegi ED. Step-Up To Medicine. Baltimore, MD, USA: Lippincott Williams & Wilkins; 2013.
  • 7. Maleux G, Koolen M, Heye S. Complications after endovascular aneurysm repair. Semin Intervent Radiol. 2009; 26(1): pp. 3–9. doi: 10.1055/s-0029-1208377.
  • 8. Upchurch GR. Abdominal Aortic Aneurysm. Am Fam Physician. 2006; 73(7): pp. 1198–1204. url: http://www.aafp.org/afp/2006/0401/p1198.html.
  • Karow T, Lang-Roth R. Allgemeine und Spezielle Pharmakologie und Toxikologie. Dr. med. Thomas Karow (2012 und 2013); 2010.
  • Kliegman RM, Stanton BF, Geme JS, Schor NF, Behrman RE. Nelson Textbook of pediatrics. Elsevier (2011); 2011.
last updated 08/31/2018
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