Abdominal Aortic Aneurysm

Aneurysms are defined as a permanent dilation of the artery to twice the normal diameter - this is > 3cm for the abdominal aorta

Aetiology

  • The incidence increases with age - AAAs are present in 5% of the population over 60 years of age
  • Arise five times more frequently in men
  • Higher risk if patient has first degree relative with AAA
  • Aneurysms may occur secondary to atherosclerosis (most common), infection (syphilis, Escherichia coli, Salmonella) and trauma, or may be genetic (Marfan’s or Ehlers–Danlos syndrome)

Pathophysiology

  • Usually results from the degeneration of the media of the arterial wall - most commonly due to atherosclerosis
    • During the formation of atheromatous plaques, macrophages release enzymes which break down the collagen and elastin of the media → media expands
  • AAAs most commonly occur below the renal arteries (infrarenal) - 80%
  • In a ruptured AAA, the wall of the aorta completely fails and blood escapes freely into a body cavity e.g. abdominal cavity
    • Emergency - 75% fatal, most usually die before getting to hospital
    • Majority are retroperitoneal (rupture contained); intraperitoneal ruptures are rapidly fatal

Clinical presentation

Asymptomatic

  • 75% asymptomatic (incidental finding)

Symptomatic

  • Can have epigastric/central pain with no rupture or dissection
    • Pain is risk factor for rupture
  • A ruptured AAA will present as sudden onset abdominal pain radiating to back with an expansile abdominal mass

Other signs

  • Patients may present with ‘trash feet’, dusky discoloration of the digits secondary to emboli from the aortic thrombus
  • Collapse (due to hypotension)
  • Tachycardia

Investigations

Monitoring - USS

  • Shows whether there is an AAA or not, its AP diameter, and whether there is iliac involvement
  • There is a monitoring program for all men over 65 in the UK

Ruptured AAA

  • Diagnosis usually clinical - needs to be made quickly and vascular surgeon contacted
  • CT is the only imaging method which can identify a ruptured AAA

Management

Medical

  • Control of risk factors - antihypertensives, smoking cessation, lipid-lowering medication

Surgical

Asymptomatic
  • Elective surgery only performed if the AAA is > 5.5 cm in diameter - before this risk of surgery outweighs the risk of rupture
Symptomatic
  • Graft - EVAR or open lap