Abdominal Aortic Aneurysm
Definition
An abdominal aortic aneurysm is a focal dilatation of the infrarenal or juxtarenal aorta to at least 1.5 times its normal diameter — in practice ≥30 mm. Most are fusiform and lined with laminated thrombus; they are classified by their relation to the renal arteries, which determines whether an endovascular or open repair is anatomically possible. (sources/AD-PAD-ESC-2024, rating: very high)
It is the one aortic condition in the wiki where the key threshold rests on Level A evidence: repair is recommended at ≥55 mm in men and ≥50 mm in women. (sources/AD-AHA-2022, rating: very high)
Key Concepts
Screening
- Ultrasound screening in men ≥65 who have ever smoked — Class I, Level A, the only Level A screening recommendation in either guideline. It reduces death from ruptured AAA.
- First-degree relatives of AAA patients: screen from age 50 (I) — the familial contribution is substantial and shared with thoracic disease.
- Women ≥65 who have smoked: screening is reasonable (IIa), reflecting a lower but non-trivial prevalence.
- Opportunistic screening is recommended in patients who already have symptomatic or asymptomatic peripheral arterial disease (IIa/B) — AAA and PAD travel together.
- Men ≥65 and women ≥75 should have the abdominal aorta visualised during transthoracic echocardiography (IIa/B) — a free look during a test being done for another reason.
Surveillance intervals
| Diameter | Interval |
|---|---|
| 25–29 mm | Every 4 years (IIa) |
| 30–39 mm | Every 3 years (I) |
| Men 40–49 mm / women 40–44 mm | Annually (I) |
| Men 50–55 mm / women 45–50 mm | Every 6 months (I) |
| Beyond these, approaching repair | Individualised, often 3-monthly |
- Duplex ultrasound is the surveillance modality (I/C). CT or MRI is reserved for AAA inadequately visualised, rapid growth, or preoperative planning.
- CT is required before repair for both open and endovascular planning.
Growth and rupture
- Mean growth 0.26 cm/year, reaching 0.5 cm/year in larger aneurysms. Growth is faster in smokers and in diabetes.
- Rupture risk rises steeply above 55 mm in men and 50 mm in women — the basis for the sex-specific threshold.
- Saccular aneurysms are more malignant than fusiform at the same diameter; elective repair at ≥45 mm may be considered (IIb/C).
- Growth ≥5 mm in 6 months or ≥10 mm/year is an indication to repair (IIb/C).
- Tandem lesions are common: 20–30% of AAA patients also have a thoracic aortic aneurysm, and the femoropopliteal segment should be assessed before repair (IIa/B).
Repair threshold and modality
| Situation | Recommendation | Class |
|---|---|---|
| Asymptomatic, men ≥55 mm / women ≥50 mm | Repair | I, Level A |
| Life expectancy <2 years | Do not repair electively | III/B |
| Ruptured, anatomy suitable | EVAR over open repair | I/B |
| Unruptured, anatomy suitable, life expectancy >2 years | EVAR over open, by shared decision | IIa/B |
| Low-to-moderate risk, anatomy suitable for either | Shared decision-making, not a default | I/A |
| High perioperative risk | EVAR reasonable to reduce 30-day morbidity and mortality | IIa |
- Anatomy decides more than preference. EVAR requires adequate proximal neck, adequate iliac access and adherence to the manufacturer's instructions for use (I). Aneurysm repair outside the instructions for use is the commonest driver of late failure.
- Fenestrated EVAR is reasonable for juxtarenal anatomy in moderate-to-high-risk patients at centres with the device.
- Routine coronary angiography and systematic revascularisation before AAA repair is not recommended (III/C) — a deliberate correction of historical practice.
- At least one hypogastric artery should be preserved when treating concomitant common iliac aneurysm, to reduce pelvic ischaemia (I).
Ruptured AAA
- CT in the haemodynamically stable patient to determine suitability for EVAR (I, Level A); straight to theatre if unstable.
- EVAR over open repair where anatomy allows (I, Level A), under local rather than general anaesthesia where feasible (IIa).
- Permissive hypotension may reduce bleeding (IIa) — the same logic as damage-control resuscitation elsewhere.
- Endovascular balloon occlusion of the aorta is used as a bridge in the unstable patient.
After repair
- After EVAR: CT at 1 month; if no endoleak and no sac enlargement, duplex ultrasound at 12 months then annually; cross-sectional imaging every 5 years; follow-up indefinitely. (sources/AD-AHA-2022)
- After open repair: CT or MRI within 1 year, then every 5 years if stable (I).
- Endoleak drives reintervention: type I and type III endoleaks should be treated to achieve a seal (I); type II or V with sac expansion ≥10 mm or a failing seal should be considered for intervention (IIa).
- Medical therapy continues after repair — the patient still has systemic atherosclerosis, and the risk of a second aneurysm in another segment is real.
Medical therapy — what does and does not work
- Smoking cessation is the single most effective intervention (I/C). Growth and rupture are driven by continued smoking more than by any drug.
- Antihypertensive therapy when average SBP ≥130 or DBP ≥80 mmHg (I), which is a lower trigger than for most hypertension guidelines.
- Statin where there is evidence of atherosclerosis (I); statins may reduce AAA growth and rupture (IIa/B) — the only pharmacological growth-modifying claim with that grading.
- Beta-blockers and ARBs have not been shown to slow AAA growth in randomised trials, unlike their role in Marfan aortopathy. This is a frequent point of confusion and worth stating plainly.
- Antiplatelet therapy is for the coexisting atherosclerosis, not for the aneurysm.
Contradictions / Open Questions
- Screening is recommended for men but only "reasonable" for women, despite women having a higher rupture rate at smaller diameters and worse outcomes after rupture. The recommendation follows prevalence and cost-effectiveness modelling, not risk per aneurysm — an equity question the guidelines do not resolve.
- The 55 mm threshold is population evidence applied to individuals. In a woman at 52 mm with a saccular morphology, a family history and rapid growth, the number is close to meaningless; the guideline permits earlier repair but does not say how to weigh it.
- Medical therapy for AAA growth is largely a null result. Statins are IIa with modest evidence, beta-blockers and ARBs have failed, and the guideline's own supportive text concedes that most aneurysm trials enrolled Marfan or mixed populations.
- Surveillance intervals for 25–29 mm rest on modelling, not trials (IIa for the 4-year interval), and the boundary between "dilatation" and "aneurysm" is arbitrary at 30 mm.
- EVAR's early advantage has not been shown to persist. The guideline recommends EVAR for suitable anatomy and reasonable life expectancy but acknowledges long-term reintervention and late rupture, without resolving when open repair is preferable in a fit patient.
- Endoleak classification and management are technology-dependent and will age faster than the rest of the document.
Connections
- Related to concepts/Thoracic-Aortic-Aneurysm — the same pathology in a different segment, with different thresholds
- Related to entities/Peripheral-Artery-Disease — shared risk factors, shared screening opportunity
- Related to concepts/CLTI — the limb consequence of the same systemic disease
- Related to entities/Hypertension — the dominant modifiable driver
- Related to concepts/Atherosclerosis-Pathophysiology — the shared systemic process that links AAA to coronary and peripheral disease
- Related to concepts/Dyslipidemia-Management — the statin framework that may also slow aneurysm growth
- Related to concepts/Acute-Aortic-Syndrome — rupture is the aortic emergency that is not a dissection
- Related to concepts/Perioperative-Cardiovascular-Assessment — the population in whom repair is planned