Overview

Abdominal Aortic Aneurysm, also known as AAA, is a permanent dilation of the abdominal aorta with a diameter of >1.5 times of the expected diameter. The adopted diameter that indicates AAA is 3cm or more. AAA is strongly associated with smoking and increasing age. Most of these aneurysms are fusiform and originate below the renal arteries. Rupture is associated with an overall mortality rate of 90% and 50% for those reaching hospital. Screening men over 65 reduces AAA-related mortality. Patients diagnosed with small AAA are managed with ultrasound surveillance and cardiovascular risk reduction. Patients with indications for AAA repair should be referred promptly to a vascular surgeon.^{1 2}

Abdominal aorta originates at T12 as it passes through the diaphragm

It bifurcates into the right and left common iliac arteries at L4

Branches of the descending abdominal aorta:

Aetiology and Risk Factors

• Smoking (most significant risk factor)
• Older age
• Male sex (but women rupture at smaller diameters)
• Family history
• Atherosclerosis
• Hypertension
• Hypercholesterolemia
• Other vascular aneurysm ³

Pathophysiology

Risk factors

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Chronic aortic wall inflammation

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Proteolytic imbalance – Increased Matrix metalloproteinases

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Elastin and collagen breakdown + smooth muscle apoptosis

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Aortic wall weakening

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Progressive dilation

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Eventually wall stress exceeds vessel strength and causes rupture

Classification

Anatomical:

• Suprarenal: involves origins of one or more visceral arteries but does not extend into the chest
• Pararenal: at the origin of the renal artery; the aorta at the level of superior mesenteric artery is not aneurysmal
• Juxtarenal: originates just beyond the renal arteries (<10mm)
• Infrarenal: originates distal to the renal arteries

Diameter:

• Small: <4 cm
• Medium: between 4.0 and 5.5 cm
• Large: >5.5 cm
• Very large: 6 cm or more ³

Clinical Manifestation

Asymptomatic AAA:

• Incidental finding or on routine physical examination, AXR or abdominal ultrasound
• May have a pulsatile abdominal mass on palpation
• Consider for treatment or surveillance

Symptomatic non-ruptured AAA:

• Pain in central abdomen, back, flank, pelvis, thigh or groin
• Thrombus in aneurysmal sac may be a source of emboli to lower limbs causing limb ischaemia
• Compression of surrounding structures and accompanying symptoms – left ureter, duodenum, lumbar nerve roots, IVC

Ruptured AAA – triad:

• Back/Abdominal pain
• Hypotension/collapse
• Pulsatile abdominal mass ^{1 4}

Examination

• Abdominal palpation: pulsatile abdominal mass
• Vascular examination – if limb ischaemia suspected
• Ecchymosis – may be present if AAA ruptures (indicates extensive retroperitoneal haematoma); method of description based on location:
  • Grey-Turner sign: flank ecchymosis
  • Cullen sign: periumbilical ecchymosis
  • Fox’s sign: proximal thigh ecchymosis
  • Bryant’s sign: scrotum ecchymosis ⁴

Diagnosis

• Acute Pancreatitis
• Mesenteric Ischaemia
• Ruptured gastrointestinal ulcer
• Appendicitis
• Gallstone Disease
• Nephrolithiasis
• Irritable Bowel Syndrome

Investigation

Aortic ultrasound – used for screening asymptomatic patients and symptomatic patients who are haemodynamically unstable; cannot definitively rule out ruptured AAA

CT angiogram – used for pre-op planning and patients with symptomatic AAA who are haemodynamically stable

Patients with known history of AAA and symptoms of rupture can be diagnosed based on clinical examination alone ^{1 4}

Differential diagnosis

• Acute pancreatitis
• Mesenteric Ischaemia
• Perforated peptic ulcer
• Diverticulitis
• Appendicitis
• Renal colic (nephrolithiasis)
• Irritable Bowel Syndrome
• Inflammatory Bowel Disease 

Treatment

Asymptomatic AAA:

• Cardiovascular risk reduction: smoking cessation, controlling hypertension, hyperlipidaemia, diabetes, clotting risk
• Surveillance – aortic ultrasound
• Elective surgical repair ⁵

Indications for AAA repair:

• Male with AAA of 5.5 cm or above
• Female with AAA >5.0 cm
• Aneurysm >4cm and rapid growth >1.0 cm per year
• Symptomatic AAA ^{1 5}

Risk of rupture based on aortic diameter: ⁶

Ruptured and symptomatic non-ruptured AAA – urgent surgical management:

• Emergency Endovascular Aneurysm Repair (EVAR) – placement of graft via the femoral arteries, lining the aorta and excluding the aneurysm sac; recommended in most patients
• Open repair – replacement of diseased aortic segment with a tube or bifurcated prosthetic graft via an abdominal incision; recommended for younger patients with connective tissue disorders ^{1 7}

Ruptured AAA resuscitation – restrictive resuscitation with blood products aiming for permissive hypotension – prevents worsening of bleed: higher BP would lead to higher pressure on aortic wall and disruption of temporary clot, and increase in fluid level may cause dilutional coagulopathy.

Complications 

Complications of AAA:

• Death
• Rupture
• Myocardial infarction
• Renal failure
• Lower limb embolism
• Gut ischaemia
• Abdominal compartment syndrome
• Fistula formation (eg. aorto-enteric)

Repair-related complications:

• Endoleaks
• Graft migration
• Graft infection
• Organ ischaemia

References

1. McMahon G. Abdominal aortic aneurysm. In: BMJ Best Practice [Internet]. 2025 [cited 2026 Feb 8]. Available from: BMJ Best Practice
2. Wilkinson IB, Raine T, Wiles K, Hateley P, Kelly D, McGurgan I, et al. Surgery.  Oxford Handbook of Clinical Medicine: Oxford University Press; 2024. Available from: https://doi.org/10.1093/med/9780198844013.003.0013 
3. Dalman RL, Mell M. Overview of abdominal aortic aneurysm. In: Collins KA, editor. [Internet]. [updated 2025 May 14; cited 2026 Feb 8]. Available from: UpToDate
4. Jim J. Clinical features and diagnosis of abdominal aortic aneurysm. In: Collins KA, editor. [Internet]. [updated 2024 Jul 19; cited 2026 Feb 8]. Available from: UpToDate
5. Dalman RL, Mell M. Management of asymptomatic abdominal aortic aneurysm. In: Collins KA, editor. [Internet]. [updated 2025 Sep 26; cited 2026 Feb 8]. Available from: UpToDate
6. Chung J. Epidemiology, risk factors, pathogenesis, and natural history of abdominal aortic aneurysm. In: Collins KA, editor. [Internet]. [updated 2024 May 10; cited 2026 Feb 8]. Available from: UpToDate
7. Jim J. Management of symptomatic (non-ruptured) and ruptured abdominal aortic aneurysm. In: Collins KA, editor. [Internet]. [updated 2024 Sep 3; cited 2026 Feb 8]. Available from: UpToDate