Infrarenal AAA and Iliac Aneurysm Decision-Making and Medical Management

19.1Definition and rupture risk

An abdominal aortic aneurysm (AAA) is a focal dilatation of the infrarenal aorta to ≥3 cm. Most are asymptomatic and are detected incidentally or by screening; the principal risk is rupture, which rises steeply with increasing diameter ESVS 2024 · SVS 2018. The aneurysm wall fails through progressive transmural degeneration, characterised by fragmentation of elastin and collagen, loss of medial smooth-muscle cells, chronic inflammation, and increased matrix proteolysis Roychowdhury 2023 · Sakalihasan 2018. Clinical presentation is asymptomatic or incidental in the majority of patients. A symptomatic, tender, or painful AAA signals instability. A ruptured AAA presents with pain, hypotension, and a pulsatile abdominal mass, constituting a surgical emergency covered in adjacent chapters.

19.2Epidemiology and risk factors

In the 1990s, ultrasound screening of men aged 65 to 74 years yielded an AAA prevalence of 4% to 5%; the MASS (2002) trial detected 1,333 aneurysms among 27,147 men scanned, a prevalence of 4.9% Cornuz 2004 · MASS 2002. Contemporary screen-detected prevalence in 65-year-old men has fallen to 1.5% to 2%, a decline attributed mainly to reduced population smoking rates ESVS 2024 · Svensjö 2011. A 2011 Swedish cohort found a prevalence of 1.7%, or 2.2% including previously known cases. The disease is strongly male-predominant. The Chichester (2002) trial found a prevalence six times lower in women (1.3%) than in men (7.6%), and the ADAM (1997) screening cohort reported an odds ratio of 0.22 for female sex Chichester 2002 · ADAM 1997. Onset in women occurs roughly a decade later than in men. Population ultrasound screening of older men reduces AAA-related mortality. The MASS (2002) trial demonstrated a 42% reduction in AAA-related mortality (0.19% versus 0.33%) over a mean of 4.1 years, a benefit sustained at 13-year follow-up with a number needed to invite of 216 MASS 2012. This mortality reduction was confirmed by the Viborg (2005) trial Viborg 2005.

AAA is highly heritable. A 2010 Swedish twin study estimated heritability at 70%, with monozygotic-versus-dizygotic concordance of 24% versus 4.8% Wahlgren 2010. Familial clustering is marked, as having a first-degree relative roughly doubles the risk (relative risk 1.9) Larsson 2009. Ultrasound screening of siblings of AAA patients finds an aneurysm in 14% to 17% of brothers and 6% of sisters, supporting selective sibling screening Linné 2017. Non-syndromic infrarenal AAA is polygenic and multifactorial. The largest genome-wide association meta-analysis (2023) identified 141 risk associations, implicating lipid metabolism, extracellular-matrix dysregulation, inflammation, and vascular remodelling, and demonstrated that a polygenic risk score predicts AAA beyond clinical risk factors Roychowdhury 2023. An earlier genome-wide meta-analysis (2017) identified four AAA-specific risk loci (SMYD2, LINC00540, the PCIF1/MMP9/ZNF335 region, and ERG), with IL6R and LDLR modifying MMP9 Jones 2017. Lipids have a causal role; Mendelian-randomization analysis shows that genetically higher LDL-cholesterol (odds ratio 1.66) and triglycerides (odds ratio 1.69) raise risk, while higher HDL-cholesterol is protective (odds ratio 0.67), supporting lipid-lowering therapy Harrison 2018. AAA susceptibility loci are largely independent of generalized atherosclerosis, supporting AAA as a distinct disease. Its risk genes overlap the monogenic syndromic aortopathies through transforming-growth-factor-beta signalling, but non-syndromic infrarenal AAA remains a polygenic, multifactorial trait rather than a single-gene disorder Sakalihasan 2018.

19.3Screening and surveillance

Abdominal ultrasound is the first-line test for the detection and surveillance of infrarenal AAA. Computed tomography (CT) or magnetic resonance angiography (MRA) is reserved for operative planning, assessing anatomic suitability, or evaluating aneurysms with inadequate ultrasound windows ESVS 2024 · SVS 2018. The imaging modality changes when the clinical question changes. Surveillance asks whether a small aneurysm has enlarged within its diameter band, for which ultrasound is usually adequate. Operative planning asks whether the patient can undergo durable repair, requiring cross-sectional imaging to assess neck length, angulation, thrombus, calcification, iliac access, and distal landing zones. Poor ultrasound windows, discordant measurements, saccular morphology, or a strong clinical concern move a patient out of routine band surveillance and into targeted reassessment.

19.4Repair threshold

Elective-repair thresholds define the point at which rupture prevention usually outweighs the procedural risk of planned intervention. These values represent decision thresholds rather than emergency cut-offs; a stable 54 mm fusiform AAA in a fit man behaves similarly to a stable 55 mm aneurysm. The threshold marks the point at which the vascular team transitions from routine surveillance to actively planning elective repair ESVS 2024 · SVS 2018.

The 5.5 cm threshold rests on randomised evidence that repairing smaller aneurysms confers no survival benefit. The UK Small Aneurysm Trial and the ADAM trial each showed that early elective open repair of 4.0 to 5.5 cm AAAs gave no survival advantage over ultrasound surveillance ADAM 2002 · UKSAT 2002. Randomised data likewise show no benefit from early EVAR of small aneurysms CAESAR 2011.

Clinical assessment involves a three-step evaluation: determining if the aneurysm has reached the society threshold for the patient's sex and population, assessing if the anatomy is suitable for a durable repair, and evaluating whether the patient's fitness and preference make elective repair a better option than continued surveillance. Atypical morphology or growth alters this calculus. Factors that bring repair forward include rapid expansion, saccular shape, symptoms, poor measurement reliability, or impending loss of an endovascular option. Conversely, very high operative risk, hostile or non-durable anatomy, or limited life expectancy defer intervention even when the diameter exceeds the threshold ESVS 2024 · SVS 2018. Real-world practice analyses document a drift away from the 5.5 cm reference point in some centers, highlighting the need to distinguish legitimate patient individualisation from threshold erosion Ramirez 2024 · Threshold compliance 2025.

19.5Choosing surveillance, EVAR, open repair, or no repair

EVAR depends on anatomy that allows a durable seal. The proximal aortic neck must offer adequate length, an acceptable diameter and limited angulation, and little circumferential thrombus or calcification, while the iliac arteries must permit safe device access and a sound distal landing zone. A short, severely angulated, conical, or heavily diseased neck, or narrow and tortuous access vessels, makes a standard infrarenal endograft unlikely to seal durably and points the decision toward open repair or a more complex fenestrated or branched solution covered elsewhere ESVS 2024 · SVS 2018.

Open surgical repair remains the more durable reconstruction. It is generally preferred when endovascular anatomy is unfavourable and when the patient is fit enough to tolerate laparotomy and aortic clamping with a long life expectancy ahead. Current guidance recognises the trade-off plainly: EVAR carries an early survival and recovery advantage that narrows over the years and commits the patient to lifelong surveillance and reintervention for endoleak, sac growth, or device failure, whereas open repair asks more of the patient at operation but is far less likely to need later aortic reintervention KVSS 2026 · ESVS 2024 · SVS 2018.

Three randomised trials define this trade-off. In EVAR-1, 30-day operative mortality was 1.7% for EVAR versus 4.7% for open repair, but the early survival benefit was lost by about two years, and on long-term follow-up EVAR carried higher aneurysm-related and total mortality driven by late secondary sac rupture EVAR-1 2016 · EVAR-1 2004. DREAM reported perioperative mortality of 1.2% for EVAR versus 4.6% for open repair, with survival equal by two years and out to six years DREAM 2010 · DREAM 2004. OVER confirmed the early perioperative advantage for EVAR with no long-term survival difference OVER 2012.

A decision not to repair is a legitimate pathway, not a failure of care. When operative risk is prohibitive or competing illness makes rupture an unlikely cause of death, neither EVAR nor open repair improves the outlook, and best medical therapy with symptom-based review is the right plan even when the diameter sits above the threshold ESVS 2024. EVAR-2 tested this directly: in patients unfit for open repair, EVAR did not improve survival over no intervention, reducing aneurysm-related death but leaving all-cause mortality unchanged because of competing comorbidity EVAR-2 2010.

Two situations move the decision outside this elective framework. In a ruptured or acutely symptomatic aneurysm, modality selection is dominated by haemodynamic stability, the immediate anatomy, and local capability rather than long-term durability, and it runs through the emergency pathway. An infected or mycotic aneurysm is a separate problem: when source control is needed, open debridement and reconstruction is often favoured, although endovascular repair has a role as a bridge in the unstable patient or as a definitive option in selected anatomy ESVS 2024 · SVS 2018. An inflammatory aneurysm should not be treated as open-favouring by default; the dense periaortic inflammation that makes open dissection hostile can instead make EVAR the more attractive option when the anatomy is suitable.

Sex shapes the choice as well as the threshold. Women tend to have smaller and more angulated infrarenal necks and smaller iliac access vessels, which lowers the proportion eligible for standard EVAR and raises the relative role of open repair or more complex endovascular planning ESVS 2024 · SVS 2018. The final recommendation is a shared decision that weighs anatomy, fitness, life expectancy, the durability the patient needs, the burden of lifelong surveillance, and the patient's own priorities, rather than diameter alone.

Putting the decision in order

1. Decide surveillance versus repair. Below the threshold and without symptoms, rapid growth, or saccular change, continue surveillance; move toward repair once the threshold is reached or those features appear.
2. Before committing to a repair, ask whether to repair at all. Prohibitive operative risk, limited life expectancy, or patient goals that outweigh the benefit point to a deliberate no-repair pathway with best medical therapy.
3. If repair is appropriate, assess endovascular suitability against the device instructions for use and the durability of the seal: proximal neck length, diameter, and angulation, thrombus and calcification, iliac access, and a sound distal landing zone, together with the patient's ability to attend lifelong follow-up.
4. Choose open repair when the anatomy is unsuitable or non-durable for a standard endograft, or when a fit patient with a long life expectancy prioritises a durable repair and accepts the larger operative insult.
5. Adjust for the exceptions before settling the plan: rupture or symptoms move to the emergency pathway, female sex with smaller or more angulated anatomy narrows the endovascular options, infection or inflammation reshape the choice as above, and the patient's own priorities are weighed throughout KVSS 2026 · ESVS 2024 · SVS 2018.

19.6Medical therapy

Medical management in AAA targets cardiovascular risk reduction rather than aneurysm shrinkage. While drug therapies may modify overall survival, none removes the need for diameter-based surveillance or timely surgical repair assessment ESVS 2024. Smoking cessation is the single most effective intervention. Continued smoking accelerates aneurysm expansion by roughly 0.35 mm per year and raises rupture risk, and guidelines give a strong recommendation for cessation support, combining behavioural intervention with pharmacotherapy, in every patient with an AAA. Blood-pressure control alongside statin and antiplatelet therapy is recommended for global cardiovascular risk SVS 2018.

Mechanistic support for the inverse association between glucose-lowering therapy and AAA is derived from laboratory work on AAA patient-derived smooth-muscle cells, but this has not yet translated into an aneurysm-specific clinical indication Metformin smooth muscle 2025. Statin therapy is consistently associated with improved survival in observational follow-up of AAA cohorts, but the patient must understand the endpoint is vascular risk control, not anatomical stabilisation.

19.7Iliac aneurysm

Iliac aneurysm management relies on answering three distinct questions. First, is the iliac aneurysm isolated or part of an infrarenal AAA repair plan? Second, does it involve the common iliac artery, where distal seal and expansion risk dominate, or the internal iliac (hypogastric) artery, where pelvic perfusion and rupture risk dominate? Third, can at least one internal iliac artery be preserved without compromising durable exclusion? Answering these determines the operative strategy before committing to an aortic plan ESVS 2024 · Huang 2008.

Isolated internal iliac aneurysms carry a risk of rupture even without a visualised endoleak on imaging and warrant repair on their own terms, regardless of the infrarenal aortic diameter Regus 2023 · Internal iliac rupture 2022. Operative strategies must protect pelvic perfusion. Bilateral loss of hypogastric flow causes disabling buttock claudication and carries a risk of severe pelvic ischemia. Therefore, iliac branch devices or endovascular hypogastric repair should be utilised when the anatomy allows for the preservation of internal iliac perfusion Kliewer 2019 · Huilgol 2011. The entire iliac reconstruction must be explicitly planned prior to aortic intervention to ensure durability of the distal seal.

19.8Shared decision-making

The society threshold establishes when elective repair should be formally considered; shared decision-making establishes whether immediate repair, further surveillance, or additional assessment best fits the patient's anatomy, fitness, sex, and personal priorities Shared decision making 2023 · Shared decision making 2019. Quality-of-life data from the CAESAR (2011) trial found no clear advantage for early endovascular repair of small AAAs over careful surveillance. Consequently, the technical feasibility of early EVAR does not displace the safety strategy of threshold-based observation CAESAR 2011.

A structured shared-decision conversation provides the patient with four specific elements: where the aneurysm sits relative to the relevant society threshold, whether the measurement is reliable and growth is confirmed, what repair entails for their specific anatomy (including procedural durability and follow-up requirements), and what continued surveillance means (the next imaging date, the triggers for earlier assessment, and the symptoms that demand urgent review) Shared decision making 2023 · Shared decision making 2019.

The timeline for intervention is frequently modified by patient-specific factors. Clinical features that reasonably open the repair decision earlier include saccular morphology, confirmed rapid growth, strong family history of AAA, borderline anatomy where delay might sacrifice an endovascular option, and concomitant iliac disease approaching its own threshold. Conversely, the decision to operate is deferred in patients with severe competing illness, stable slow aneurysm growth, high-risk or non-durable anatomy, or an informed preference for continued surveillance.

19.9Areas of controversy

Current debate in AAA management focuses on the optimal repair thresholds, particularly the sex-specific disparities and whether lower cut-offs are justified in women ESVS 2024 · SVS 2018. The true efficacy of medical therapy remains contested, specifically regarding the lack of trial-proven statin growth-rate modification and whether the observed mechanism of metformin in smooth-muscle cells translates into clinical benefit Metformin smooth muscle 2025 · Hosseini 2022. The routine implementation and yield of selective familial and sibling screening also generate ongoing discussion Linné 2017. Finally, real-world registry data highlight controversy over threshold erosion, as documented drift toward sub-threshold repair continues to challenge strict adherence to society guidelines Ramirez 2024 · Threshold compliance 2025.