Abdominal Aortic Aneurysm

1 · UNDERSTAND — What is happening?

Definition and anatomy

An abdominal aortic aneurysm (AAA) is a permanent focal dilatation of the abdominal aorta, conventionally defined as a maximum diameter ≥30 mm. Most degenerative AAAs are infrarenal. For treatment planning, describe the proximal neck, maximum sac diameter, distal aorta, common/internal/external iliac arteries and access vessels.

Why it happens

AAA is a degenerative disease characterised by extracellular-matrix breakdown, inflammation and loss of medial structural integrity. The strongest clinical associations are increasing age, male sex, smoking, family history and coexistent atherosclerotic cardiovascular disease. Smoking is the most important modifiable risk factor.

Presentation

Asymptomatic: most AAAs are detected through NHS screening or incidental imaging.

Symptomatic intact AAA: new persistent abdominal, back, flank or groin pain, aneurysm tenderness, distal embolic symptoms or acute limb ischaemia features.

Suspected rupture: abdominal or back pain, collapse, syncope, hypotension, shock or a pulsatile abdominal mass. Do not wait for the full classic triad before activating the rupture pathway.

Investigations

Ultrasound is first-line for diagnosis and surveillance. In the NHS AAA Screening Programme, maximum anterior-posterior diameter is measured inner-to-inner. CTA with arterial-phase thin slices is used for operative planning once repair is being considered. In suspected rupture, bedside ultrasound can confirm an aneurysm, while CTA is appropriate when the patient is sufficiently stable and imaging will guide repair. In contemporary vascular practice, CT is usually obtained when the patient can tolerate it because it defines EVAR suitability, but imaging should not delay haemorrhage control in an unstable patient.

Useful classifications

Describe AAA as infrarenal, juxtarenal, pararenal or suprarenal; fusiform or saccular; intact, symptomatic or ruptured. Mycotic, inflammatory and saccular aneurysms behave differently from standard degenerative infrarenal AAA and need separate consideration.

2 · DECIDE — What do I do next?

1. Is this an emergency?

Suspected rupture: activate the vascular pathway immediately. Resuscitate with blood products, avoid unnecessary crystalloid, use permissive hypotension while consciousness is maintained, and obtain CTA if sufficiently stable for planning. ESVS recommends EVAR as the first option when anatomy is suitable (Recommendation 80, Class I, Level A); open repair remains essential when anatomy, access, timing or local resources make EVAR unsuitable.

Symptomatic non-ruptured AAA: admit under vascular surgery, exclude alternative causes of pain, complete rapid CTA/physiological assessment and plan urgent repair after brief optimisation when appropriate.

2. If asymptomatic, does it meet a repair threshold?

• NICE NG156: consider repair if symptomatic, ≥5.5 cm, or >4.0 cm with growth >1 cm in 1 year on inner-to-inner AP ultrasound.
• ESVS 2024: consider elective repair at ≥55 mm in men (Rec 22, Class IIa, Level C) and ≥50 mm in women (Rec 23, Class IIb, Level C). Apparent rapid growth ≥10 mm/year should be remeasured before acting (Rec 24, Class IIa, Level C).
• UK referral timing: NICE recommends vascular review within 2 weeks for AAA ≥5.5 cm and within 12 weeks for AAA 3.0–5.4 cm.

3. If below threshold

Use ultrasound surveillance and aggressive cardiovascular risk reduction. NHS screening: 3.0–4.4 cm → ultrasound in 12 months; 4.5–5.4 cm → ultrasound in 3 months; ≥5.5 cm or growth >1 cm in 12 months → vascular referral. ESVS uses sex-specific intervals: men 30–39 mm every 3 years, 40–49 mm annually, ≥50 mm every 6 months; women 30–39 mm every 3 years, 40–44 mm annually, ≥45 mm every 6 months.

4. If repair is indicated

Choose open repair, standard EVAR, complex EVAR or conservative management through shared decision-making. Key modifiers are physiological reserve, life expectancy, proximal/distal landing zones, iliac anatomy, access, renal function, previous abdominal surgery, durability, willingness for lifelong surveillance and local expertise.

UK versus Europe

NICE: offer open surgical repair for unruptured AAA meeting repair criteria unless open repair is contraindicated; consider EVAR when abdominal copathology or patient-specific considerations make EVAR preferable, or when open repair is contraindicated.

ESVS: for most patients with suitable anatomy and reasonable life expectancy, EVAR should be considered the preferred modality (Rec 65, Class IIa, Level B). For patients with long life expectancy, open repair should be considered the preferred modality (Rec 66, Class IIa, Level B). This is the core NICE–ESVS divergence trainees should know.

IFU rule: elective EVAR outside the manufacturer’s instructions for use is not recommended (ESVS Rec 57, Class III, Level C).

3 · JUSTIFY — Why is that the correct decision?

Why not repair every small AAA?

The UK Small Aneurysm Trial and ADAM trial showed no survival advantage from early open repair of small asymptomatic AAAs compared with surveillance. Early-EVAR trials such as CAESAR and PIVOTAL likewise did not demonstrate a mortality benefit from intervening before conventional thresholds; PIVOTAL is helpful but had short mean follow-up, so it should not be over-read.

Why does diameter still dominate?

Rupture risk rises with increasing diameter, but diameter is a surrogate rather than a complete risk model. Symptoms, rapid growth, sex, morphology, family history, physiological reserve and competing mortality matter. ESVS grades the standard male threshold as Class IIa/Level C and the lower female threshold as Class IIb/Level C; the evidence base is limited for both.

EVAR versus open repair

EVAR-1 showed an early peri-operative survival advantage for EVAR: the 2004 30-day operative mortality report found 1.6% mortality after EVAR versus 4.6% after open repair by per-protocol analysis. This early advantage is not a durable all-cause survival advantage.

In the 15-year EVAR-1 follow-up, overall total mortality did not differ significantly, but beyond 8 years open repair had lower total mortality and lower aneurysm-related mortality. The late aneurysm-related excess after EVAR was mainly driven by secondary sac rupture. DREAM and OVER support the same practical teaching point: EVAR reduces early physiological insult but trades that for device durability, re-intervention and lifelong surveillance.

Rupture evidence

The IMPROVE trial found no significant 30-day mortality difference between an endovascular strategy and open repair for ruptured AAA (35.4% versus 37.4%), with a prespecified sex interaction favouring EVAR in women. Current practice therefore uses an EVAR-first approach when anatomy is suitable while maintaining open capability.

Guideline perspective

ESVS 2024 is the main contemporary European vascular framework. NICE NG156 is central for UK practice and is more restrictive regarding elective EVAR. Complex EVAR should have explicit consent, audit and governance arrangements, including registry entry where required.

4 · PERFORM — How do I execute the plan?

Before intervention

• Review CTA with centreline measurements: neck length/diameter/angulation, thrombus/calcification, renal/visceral anatomy, iliac landing zones and access. For elective disease, get CTA when the ultrasound threshold for repair is met rather than using early CT to push borderline AAAs over threshold.
• Assess cardiac, respiratory and renal risk; frailty and functional reserve often matter more than age alone.
• Optimise smoking cessation, blood pressure and secondary cardiovascular prevention. ESVS recommends cardiovascular risk-factor management for all AAA patients, including smoking cessation, blood-pressure control, statin and antiplatelet therapy, and lifestyle advice.
• For elective repair, continue established single antiplatelet therapy where appropriate (ESVS Rec 40, Class IIa, Level B). Do not run elective AAA repair on dual antiplatelet therapy or oral anticoagulants unless there is a deliberate peri-operative plan (ESVS Rec 41, Class III, Level C).
• NICE advises not to routinely offer pre-operative beta-blockers solely for AAA repair.
• Consent for mortality, cardiac/respiratory/renal complications, bleeding/transfusion, bowel or limb ischaemia, sexual dysfunction, wound complications and further procedures. For EVAR specifically discuss endoleak, migration, limb occlusion, radiation/contrast exposure, re-intervention and lifelong imaging.

EVAR — execution principles

Obtain safe arterial access, deploy a suitably sized device within IFU with secure proximal and distal seal, preserve pelvic perfusion where possible, and confirm aneurysm exclusion and limb patency on completion imaging. Device-specific technique belongs in the EVAR Procedure Guide.

Open repair — execution principles

Expose the aorta, obtain proximal and distal control, replace the aneurysmal segment with a tube or bifurcated graft as dictated by distal disease, restore flow and assess bowel and lower-limb perfusion. Detailed exposure, clamping and anastomotic technique belong in the Open AAA Repair Procedure Guide.

Rupture execution principles

Use a permissive hypotension policy until proximal control, the patient losing consciousness or definitive haemorrhage control. If CTA confirms suitable anatomy, move rapidly to EVAR; if not, move to open repair. Local anaesthesia may be considered for ruptured EVAR when feasible.

5 · MANAGE — What can go wrong and how do I respond?

Immediate postoperative priorities

Monitor haemodynamics, urine output, renal function, haemoglobin, lactate, limb perfusion and abdominal findings. ESVS recommends early ICU/HDU monitoring for all open AAA repairs and high-risk EVAR patients (Rec 69, Class I, Level C).

Complication → recognise → act

• Bleeding: falling haemoglobin, shock, abdominal distension → resuscitate, correct coagulopathy and return to theatre/angiography when ongoing.
• Renal injury: oliguria/creatinine rise after contrast, hypotension or clamping → optimise perfusion, avoid nephrotoxins, investigate obstruction/renal artery compromise when suspected.
• Lower-limb ischaemia: pain, pallor, absent pulses → urgent imaging or re-intervention for graft limb kinking, thrombosis or embolisation.
• Colonic ischaemia: abdominal pain/distension, bloody diarrhoea, acidosis or sepsis → urgent assessment. After ruptured AAA repair, ESVS recommends considering flexible sigmoidoscopy when colonic ischaemia is suspected (Rec 84, Class IIa, Level B); do not delay laparotomy if transmural ischaemia is likely.
• Endoleak after EVAR: type I and III are high-pressure failures and usually require prompt correction; type II is commonly observed unless associated with significant sac enlargement. Type V/endotension remains a diagnosis of exclusion.
• Graft infection: fever, pain, raised inflammatory markers, perigraft gas/fluid or fistulation → urgent aortic MDT, microbiology and definitive source-control planning.

Surveillance

After standard EVAR, obtain early postoperative CTA within 30 days to assess seal, overlap and endoleak risk. Low-risk patients may move to low-frequency imaging during the first 5 years, but ESVS now recommends long-term imaging follow-up for all EVAR patients regardless of initial risk stratification. NICE adds a practical safety rule: if an endoleak is suspected, use CTA or contrast-enhanced ultrasound when CTA is contraindicated; a negative colour duplex ultrasound alone does not exclude endoleak.

After open repair, monitor clinically and follow local long-term imaging practice for para-anastomotic aneurysm, graft infection and progression elsewhere in the aorto-iliac tree.

6 · REMEMBER — What must I retrieve instantly?

AAA: 10 things to retrieve instantly

1. Definition: abdominal aorta ≥30 mm.
2. NHS surveillance: 3.0–4.4 cm yearly; 4.5–5.4 cm every 3 months; ≥5.5 cm or growth >1 cm/year → vascular referral.
3. NICE repair triggers: symptomatic, ≥5.5 cm, or >4.0 cm plus >1 cm growth in 1 year.
4. ESVS sex thresholds: men ≥55 mm (IIa/C); women ≥50 mm (IIb/C).
5. Rapid growth: remeasure before acting; measurement variation is common.
6. CTA timing: plan repair with CTA once the ultrasound threshold is met; AP CTA is often about 4 mm larger than AP ultrasound.
7. UK–Europe split: NICE defaults to open repair when suitable; ESVS is more EVAR-supportive in anatomically suitable patients with reasonable life expectancy.
8. IFU: elective EVAR outside IFU is not recommended.
9. Rupture: permissive hypotension, CTA if stable enough, EVAR first if anatomy suitable.
10. EVAR evidence: early survival advantage; late sac rupture/reintervention risk; lifelong surveillance.

Memory hook

The 5 S’s: Symptoms, Size, Speed of growth, Sex, Suitability for repair. If you cannot state all five, you are not ready to decide.

FRCS prompts

Do not quote diameter alone. State symptoms, growth, sex, anatomy, fitness, life expectancy and patient preference. For EVAR, describe neck, seal zones, iliac anatomy, access and whether the plan is within IFU. For open repair, state clamp level, tube versus bifurcated graft and how you will assess bowel and limb perfusion.

1. Wanhainen A, Van Herzeele I, Bastos Gonçalves F, et al. Editor’s Choice – European Society for Vascular Surgery (ESVS) 2024 Clinical Practice Guidelines on the Management of Abdominal Aorto-Iliac Artery Aneurysms. Eur J Vasc Endovasc Surg. 2024;67(2):192–331. doi:10.1016/j.ejvs.2023.11.002. PMID: 38307694.
2. National Institute for Health and Care Excellence. Abdominal aortic aneurysm: diagnosis and management. NICE guideline NG156. Published 19 March 2020; last updated 19 March 2020.
3. NHS England. NHS abdominal aortic aneurysm screening: care pathway. Published 1 June 2015; last updated 27 October 2025.
4. The UK Small Aneurysm Trial Participants. Mortality results for randomised controlled trial of early elective surgery or ultrasonographic surveillance for small abdominal aortic aneurysms. Lancet. 1998;352:1649–1655. doi:10.1016/S0140-6736(98)10137-X.
5. Lederle FA, Wilson SE, Johnson GR, et al.; Aneurysm Detection and Management Veterans Affairs Cooperative Study Group. Immediate repair compared with surveillance of small abdominal aortic aneurysms. N Engl J Med. 2002;346:1437–1444. doi:10.1056/NEJMoa012573.
6. Greenhalgh RM, Brown LC, Kwong GPS, Powell JT, Thompson SG; EVAR Trial Participants. Comparison of endovascular aneurysm repair with open repair in patients with abdominal aortic aneurysm (EVAR trial 1), 30-day operative mortality results: randomised controlled trial. Lancet. 2004;364:843–848. doi:10.1016/S0140-6736(04)16979-1.
7. EVAR Trial Participants. Endovascular aneurysm repair versus open repair in patients with abdominal aortic aneurysm (EVAR trial 1): randomised controlled trial. Lancet. 2005;365:2179–2186. doi:10.1016/S0140-6736(05)66627-5.
8. Patel R, Sweeting MJ, Powell JT, Greenhalgh RM; EVAR Trial Investigators. Endovascular versus open repair of abdominal aortic aneurysm in 15-years’ follow-up of the UK endovascular aneurysm repair trial 1 (EVAR trial 1): a randomised controlled trial. Lancet. 2016;388:2366–2374. doi:10.1016/S0140-6736(16)31135-7.
9. De Bruin JL, Baas AF, Buth J, et al.; DREAM Study Group. Long-term outcome of open or endovascular repair of abdominal aortic aneurysm. N Engl J Med. 2010;362:1881–1889. doi:10.1056/NEJMoa0909499.
10. Lederle FA, Freischlag JA, Kyriakides TC, et al.; OVER Veterans Affairs Cooperative Study Group. Long-term comparison of endovascular and open repair of abdominal aortic aneurysm. N Engl J Med. 2012;367:1988–1997. doi:10.1056/NEJMoa1207481.
11. Cao P, De Rango P, Verzini F, et al.; CAESAR Trial Group. Comparison of surveillance versus aortic endografting for small aneurysm repair (CAESAR): results from a randomised trial. Eur J Vasc Endovasc Surg. 2011;41:13–25. doi:10.1016/j.ejvs.2010.08.026.
12. Ouriel K, Clair DG, Kent KC, Zarins CK; PIVOTAL Investigators. Endovascular repair compared with surveillance for patients with small abdominal aortic aneurysms. J Vasc Surg. 2010;51:1081–1087. doi:10.1016/j.jvs.2009.10.113. Mean follow-up was approximately 20 months.
13. IMPROVE Trial Investigators. Endovascular or open repair strategy for ruptured abdominal aortic aneurysm: 30 day outcomes from IMPROVE randomised trial. BMJ. 2014;348:f7661. doi:10.1136/bmj.f7661.

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