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Abdominal aortic aneurysms are one of the few truly preventable medical emergencies. Early detection and surgical repair of these lesions is vital as a ruptured AAA has a very slim chance of survival.


Key Points

  • An Aneurysm is an abnormal, localised dilatation of an endothelial lined vascular structure.
  • An Abdominal Aortic Aneurysm or AAA is an aneurysm located on the abdominal aorta.
  • Present in 5% of men over 70 years old
  • AAA’s are much more common in men than females (9:1)
  • Ruptured AAA is the 10th most common cause of death (of men) in the UK.

Aetiology

Associated with:

  • Smoking
  • Hypertension
  • Family history
  • Marfan’s syndrome
  • Ehlers-Danlos syndrome

Signs and Symptoms

Abdominal Aortic Aneurysms present in one of three ways;

  • Asymptomatic (60%)
  • Symptomatic (10%)
  • Ruptured (30%)

Asymptomatic AAAs are commonly found incidentally after patients undergo routine imaging or physical examination. Commonly AXRs, ultrasounds, CTs and MRIs detect undiagnosed AAAs.

Symptomatic AAAs commonly present with central abdominal pain, back pain, distal embolic events (due to aneurysmal emboli formation) and rarely aortic occlusion (due to thrombus formation).

Ruptured AAAs present with severe and sudden onset epigastric pain, sudden unexplained hypotension, unexplained collapse, sweating associated with a pulsatile abdominal mass. MEDICAL EMERGENCY, call for help.


Pathology

The pathological events causing AAAs are poorly understood.

  • AAAs are ‘true aneurysms’, meaning they involve all three layer of the artery (the intima, media and adventitia).
  • 95% of all AAAs occur infrarenally (ie distal to the origin of the renal arteries)
  • 15% of AAAs involve the dilatation of the common iliac arteries.
  • Between 5-10% of AAAs are ‘inflammatory’ and are associated with gross inflammatory changes in the surrounding retroperitoneal area (making surgical revision more challenging).

Investigations

If an aneurysm is suspected then an abdominal ultrasound is the best method of gaining an approximate (+/- 0.5 cm) AP (back to front) diameter of the aneurysm. This is the method used in the AAA screening program, as is it cheap, safe and simple to do.

Once an aneurysm is detected the patient should be monitored by half-yearly abdominal ultrasound scans until the AAA reaches an AP diameter of greater than 5.0 cm, at which point they should be referred for a CT angiogram.

CT angiography (CTA) is used to generate a highly detailed image of the aneurysm with the surrounding visceral arteries and associated structures. Which is generally used in preparation for surgical repair of the AAA. CTA is not suitable for AAA screening programs because of radiation exposure and cost.


Management

Management options involve:

  • Monitoring
  • Endovascular aneurysm repair
  • Open repair

AAA management is based on ‘The UK small aneurysm trial’ that concluded the risk of aneurysm repair outweighed the risk of rupture until the aneurysm reached greater than 5.5 cm in AP diameter. Before this point is reached the patient should be monitored with regular ultrasound scans.

When the AAA reaches an AP diameter of greater 5.5 cm then there are two main surgical options available: an open repair or an endovascular aneurysm repair (EVAR).

An open AAA repair involves replacing the aneurysmal section of aorta with a new prosthetic graft. A long midline incision from below the xiphisternum to above the pubic bone is required. 30-day mortality is between 5-10%.

EVAR involves placing a stent graft inside the aneurysm via a femoral arteriotomy. It has a much-improved short-term outcome with a reduced hospital stay compared to an open repair. It is however a very expensive procedure.

The study ‘EVAR 1’ showed that open repairs have worse short term mortality than EVAR but a much lower long term reintervention rates when compared to EVAR.


Epidemiology

  • AAAs is far more common in men than women (9:1).
  • It is the 10th biggest killer of men in the UK.
  • They are present in 4% of men over 65 and 5% of men over 70.
  • Risk of rupture is 1% annually for AAAs between 4-5.5 cm in diameter.
  • Risk of rupture increases with diameter.

References

McLatchie et al, Oxford Handbook of Clinical Surgery, 4th ed, 2013.

James-Garden et al, Principle and Practice of Surgery, 6th ed, 2012.