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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- AAA = aortic diameter ≥3 cm (normal infrarenal aorta ~2 cm). Most are infrarenal, fusiform, and asymptomatic
- NHS AAA Screening Programme: single abdominal US offered to all men aged 65 in England
- Surveillance: 3.0–4.4 cm (yearly USS), 4.5–5.4 cm (3-monthly USS). Consider repair at ≥5.5 cm (NICE NG156)
- Elective repair: endovascular (EVAR) or open surgical — EVAR has lower perioperative mortality but higher reintervention rate
- Ruptured AAA: severe sudden abdominal/back pain + hypotension + pulsatile abdominal mass → emergency surgical repair; >80% mortality overall
Overview
An abdominal aortic aneurysm (AAA) is a permanent localised dilatation of the abdominal aorta exceeding 50% of the normal diameter (generally taken as ≥3 cm). Over 90% are infrarenal. The pathogenesis involves degeneration of the aortic media with loss of elastin and smooth muscle, likely driven by inflammation, proteolytic enzymes (matrix metalloproteinases), and atherosclerosis. The risk of rupture increases exponentially with aneurysm size: <1% per year for aneurysms <5.5 cm but 25–30% per year for those >7 cm. Ruptured AAA is a surgical emergency with overall mortality exceeding 80%.
Epidemiology
AAA affects approximately 5–8% of men and 1–2% of women over 65. The prevalence has been declining, likely due to reduced smoking rates. Risk factors include male sex (6:1), age >65, smoking (strongest modifiable risk factor), hypertension, family history (first-degree relative with AAA), and other atherosclerotic disease. AAA rupture causes approximately 6,000 deaths per year in the UK. The NHS AAA Screening Programme has been shown to reduce AAA-related mortality by approximately 50% in screened populations.
Clinical Features
Symptoms
Usually asymptomatic — detected incidentally on imaging or through screening
Vague abdominal or back pain (expanding or symptomatic aneurysm)
RUPTURED AAA: sudden severe central abdominal pain radiating to back, often with collapse
Syncope or shock (hypovolaemia from rupture)
Signs
Pulsatile, expansile abdominal mass above the umbilicus (expansile = expands in two planes — distinguish from transmitted pulsation)
Ruptured AAA: haemodynamic instability (hypotension, tachycardia), peritonism, Grey Turner sign (flank bruising)
Signs of distal embolisation (blue toe syndrome, livedo reticularis)
Investigations
First-line
Abdominal ultrasoundFirst-line screening and surveillance tool. Measures AP diameter. Safe, non-invasive, highly accurate
Second-line
CT angiography (CTA)Pre-operative planning — defines anatomy, neck length (EVAR suitability), branch vessel involvement, iliac anatomy
BloodsFBC, U&Es, coagulation, group and save/crossmatch
Specialist
MR angiographyAlternative to CT if contrast allergy or renal impairment
EchocardiographyPre-operative cardiac risk assessment
1
NHS AAA Screening Programme
- Single abdominal ultrasound offered to all men aged 65 in England
- Women and younger men may self-refer if at high risk
- <3 cm = normal, discharged from screening
- 3.0–4.4 cm (small): annual USS surveillance
- 4.5–5.4 cm (medium): 3-monthly USS surveillance
- ≥5.5 cm (large): refer to vascular surgery for consideration of repair
2
Conservative management (all AAA patients)
- Smoking cessation (most important modifiable risk factor for growth and rupture)
- Optimise cardiovascular risk: statin, antiplatelet, BP control
- Best medical therapy — no drug has proven to reduce AAA growth rate
3
Elective repair (≥5.5 cm or rapidly expanding >1 cm/year or symptomatic)
- Endovascular aneurysm repair (EVAR) — lower perioperative mortality (~1–2%), shorter hospital stay, but requires lifelong CT surveillance and higher reintervention rate
- Open surgical repair — durable long-term result, perioperative mortality ~4–5%, no need for long-term imaging surveillance
- Choice depends on anatomy (EVAR requires suitable neck), fitness, patient preference
4
Ruptured AAA — emergency management
- Permissive hypotension (target SBP 70–80 mmHg) — avoid aggressive fluid resuscitation
- Activate major haemorrhage protocol, crossmatch blood urgently
- Emergency open repair or emergency EVAR (if anatomically suitable and available)
- Overall mortality >80% (including prehospital deaths); in-hospital operative mortality ~40–50%
Complications
- Rupture: Life-threatening haemorrhage — >80% overall mortality
- Distal embolisation: Thrombus or atheromatous debris → blue toe syndrome, renal impairment, mesenteric ischaemia
- Aortoenteric fistula: Erosion into duodenum (usually post-repair) → massive GI haemorrhage
- Graft infection: Post-operative, rare but serious
- Endoleak: Persistent blood flow into aneurysm sac post-EVAR — requires surveillance and possible reintervention
UKMLA Exam Tips
- 1Pulsatile EXPANSILE mass in the abdomen + sudden back pain + hypotension = ruptured AAA → emergency surgery, do NOT wait for CT if haemodynamically unstable
- 2Screening: men aged 65, single USS. Threshold for repair: ≥5.5 cm
- 3EVAR = lower perioperative mortality but needs lifelong CT surveillance; open repair = more durable but higher perioperative risk
- 4Permissive hypotension in ruptured AAA — do not give excessive IV fluids (worsens haemorrhage)
- 5An expansile mass pushes your hands APART (AAA); a transmitted pulsation pushes your hands UP (mass overlying aorta)
- 6Triad of ruptured AAA: sudden severe abdominal/back pain + hypotension + pulsatile abdominal mass
practicetest your knowledge on abdominal aortic aneurysmApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — cardiovascular and beyond.
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