Abdominal aortic aneurysm

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.

• 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)

• Peak incidence: 60–70 years (rare in patients < 50 years)
• Sex: ♂ > ♀: ∼ 2:1
• More common in white populations

Epidemiological data refers to the US, unless otherwise specified.

• Risk factors
  • Advanced age
  • Smoking (most important risk factor)
  • Atherosclerosis
  • Hypercholesterolemia and arterial hypertension
  • Positive family history
  • Trauma

• Below the renal arteries
  • Most common location
• Above the renal arteries

• 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]

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 mass at 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

• 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 of acute abdomen
• Thoracic aortic aneurysm (also see table below)

The differential diagnoses listed here are not exhaustive.

Rupture^[7]

• 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^[8]

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

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