Abdominal aortic aneurysm screening
Exam Tips
- Know UK screening eligibility: routinely offered to all men in the year they turn 65; men >=66 can self-refer if not previously screened.
- Memorise ultrasound thresholds and follow-up: <3.0 cm discharge, 3.0-4.4 cm annual, 4.5-5.4 cm every 3 months, >=5.5 cm vascular referral.
- In OSCE counselling, balance benefit (reduced rupture death via early detection) against harms (anxiety, overdiagnosis, operative complications).
- Primary care role is often examined: identify unscreened eligible men, support self-referral, optimise BP/lipids/smoking, and reinforce surveillance attendance.
- For visual recall, review a standard vascular surgery figure showing infrarenal AAA anatomy and ultrasound diameter measurement planes.
Definition
Abdominal aortic aneurysm (AAA) is a permanent, pathological dilatation of the abdominal aorta, usually infrarenal, defined in practice as an aortic diameter of 3.0 cm or more on imaging. In UK screening, the condition is typically asymptomatic until late, but rupture carries very high mortality, so population ultrasound screening aims to detect aneurysms before rupture and route patients into surveillance or elective vascular care.
Pathophysiology
AAA develops through chronic degeneration of the aortic media with elastin/collagen breakdown, smooth-muscle cell loss, inflammation, and proteolytic remodeling of the vessel wall. Smoking, age-related arterial damage, and hypertension accelerate wall stress and expansion (Laplace relationship: increasing radius raises wall tension), making progressive dilatation and eventual rupture more likely, particularly in infrarenal segments where wall structure and flow patterns are more vulnerable.
Risk Factors
- Male sex
- Age >= 65 years
- Current or previous smoking (risk rises with cumulative exposure)
- Hypertension
- Family history of AAA (higher inherited risk)
- Atherosclerotic disease (coronary/cerebrovascular/peripheral arterial disease)
- Hyperlipidaemia
- Chronic obstructive pulmonary disease
- Diabetes mellitus
Clinical Features
Symptoms
- Usually none (most screen-detected AAAs are asymptomatic)
- If expanding: abdominal, flank, or back pain
- If rupture: sudden severe abdominal/back pain, collapse, syncope
Signs
- Pulsatile expansile abdominal mass (not always palpable)
- Hypotension/tachycardia in rupture
- Shock with possible abdominal tenderness in ruptured AAA
Investigations
Management
Lifestyle Modifications
- Smoking cessation support (highest-yield intervention for slowing growth and reducing cardiovascular risk)
- Heart-healthy diet with reduced saturated fat intake
- Regular exercise for small/medium AAA if clinically stable
- Weight optimisation
- BP and cardiovascular risk-factor control in primary care
Pharmacological Treatment
Antiplatelet (secondary cardiovascular prevention where indicated)
- Aspirin 75 mg once daily
- Clopidogrel 75 mg once daily (if aspirin not tolerated/contraindicated)
Not a direct aneurysm-shrinking therapy; used to reduce overall vascular events when indicated. Avoid/seek specialist advice in active bleeding or very high bleeding risk.
Lipid lowering
- Atorvastatin 20-80 mg once daily (commonly 40-80 mg for secondary prevention)
Use for cardiovascular risk reduction in line with UK lipid guidance; monitor liver enzymes and adverse effects (e. g, myalgia).
Antihypertensives
- Ramipril 2.5 mg once daily, titrate to 10 mg once daily
- Amlodipine 5 mg once daily, increase to 10 mg once daily
- Indapamide 2.5 mg once daily (or 1.5 mg MR once daily)
Treat hypertension to guideline targets; check renal function/electrolytes with ACE inhibitors. Avoid ACE inhibitors in pregnancy; caution in bilateral renal artery stenosis.
Smoking cessation pharmacotherapy
- Nicotine replacement therapy: e. g, 21 mg/24 h patch daily then step down
- Varenicline: 0.5 mg once daily days 1-3, 0.5 mg twice daily days 4-7, then 1 mg twice daily for 11 weeks
- Bupropion SR: 150 mg once daily for 6 days then 150 mg twice daily
Choose with shared decision-making and contraindication check. Bupropion is contraindicated in seizure disorders/eating disorders; varenicline may cause nausea/vivid dreams and needs renal dose adjustment.
Surgical / Interventional
- Refer large AAA (>=5.5 cm in men), symptomatic AAA, or rapidly expanding aneurysm for vascular surgery review.
- Elective endovascular aneurysm repair (EVAR) for anatomically suitable patients; requires lifelong imaging surveillance for endoleak/device complications.
- Open surgical repair when anatomy is unsuitable for EVAR or based on patient-specific risk-benefit assessment.
- Emergency repair (EVAR or open) for rupture where feasible; discuss peri-operative mortality risk urgently.
- Safety/contraindications: operative approach depends on frailty, severe cardiopulmonary comorbidity, renal function, and anatomical suitability; iodinated contrast for EVAR/CTA needs caution in severe CKD or contrast allergy.
Complications
- Rupture with haemorrhagic shock and high mortality
- Thromboembolism/distal embolisation
- Progressive expansion with pain
- Post-operative complications: myocardial infarction, stroke, acute kidney injury, endoleak (after EVAR), graft infection (rare)
Prognosis
Screen-detected small/medium AAAs have better outcomes because they enter structured surveillance and risk-factor management. Prognosis worsens with increasing diameter and faster growth; rupture is frequently fatal (around 80% do not survive), while elective repair carries substantially lower mortality than emergency surgery.
Sources & References
🏥BMJ Best Practice(1)
✅NICE Guidelines(1)
- Abdominal aortic aneurysm screening[overview]