Define Abdominal Aortic Aneurysm. Describe its clinical features and management.

The Concept & Definition

An aneurysm is a permanent, localised dilatation of an artery to more than 1.5 times its normal diameter. An abdominal aortic aneurysm (AAA) therefore means an abdominal aorta of 3 cm or more (the normal aorta is ~2 cm), most commonly located below the renal arteries (infrarenal). It is a true aneurysm (involving all three layers of the wall) and is degenerative in origin. Its whole clinical importance lies in the risk of rupture, which is usually fatal.

Risk Factors

Risk factors are increasing age, male sex, smoking, hypertension, a family history, and connective-tissue disorders (e.g. Marfan syndrome). Smoking is a particularly strong association.

Clinical Features

• Asymptomatic — the majority, found incidentally or on screening as a pulsatile, expansile abdominal mass.
• Symptomatic (unruptured) — abdominal or back pain (may herald expansion or impending rupture).
• Ruptured AAA — the classic triad of sudden severe abdominal/back pain, hypotension/collapse, and a pulsatile expansile abdominal mass — a catastrophic emergency with very high mortality.

Screening & Investigation

Because rupture is lethal but elective repair is safe, screening is offered (in the UK, a single ultrasound for men at 65). Ultrasound is used for diagnosis, screening and surveillance, while CT angiography gives precise size and anatomy for planning repair and is used to confirm rupture in the stable patient.

Management

• Small aneurysms (< 5.5 cm) — surveillance with ultrasound plus risk-factor control (stop smoking, control blood pressure), since the rupture risk is low.
• Large (≥ 5.5 cm), symptomatic, or rapidly expanding aneurysms — elective repair, either open surgical graft repair or endovascular aneurysm repair (EVAR — a stent-graft placed via the femoral arteries).
• Ruptured AAA — emergency repair (open or emergency EVAR) in those who reach theatre, though mortality remains high.

WHY Size Determines Repair

The 5.5 cm threshold is not arbitrary but reflects the balance of two risks. Below ~5.5 cm the annual risk of rupture is low — lower than the risk of the repair operation itself — so surveillance is safer. Above 5.5 cm, or when the aneurysm is expanding rapidly (>1 cm/year) or causing symptoms, the rupture risk rises steeply and exceeds the operative risk, so repair becomes worthwhile. Wall tension rises with diameter (Laplace's law), which is the physical basis for this size-dependent rupture risk.

Open Repair VS Evar

The two repair options have trade-offs worth knowing. Open repair replaces the aneurysmal segment with a prosthetic graft through a laparotomy — durable but with greater operative stress and a longer recovery. EVAR (endovascular aneurysm repair) deploys a stent-graft via the femoral arteries — less invasive with lower short-term mortality, but it requires lifelong surveillance for complications such as endoleak (persistent flow into the sac) and needs suitable anatomy. The choice depends on the patient's fitness and the aneurysm's shape.

The Ruptured Aaa as a Mimic

A crucial clinical point is that a ruptured or leaking AAA is a great mimic — it can present like renal colic, an acute abdomen, or back pain, and a wrong diagnosis is fatal. Therefore any man over 60 with sudden abdominal or back pain, collapse, or a first presentation of 'renal colic' should have an AAA excluded (by examining for a pulsatile mass and prompt imaging). The stable patient gets a CT; the unstable one with a known/obvious AAA goes straight to theatre.

A Note on Thoracic & Other Aneurysms

For completeness, aneurysms occur elsewhere and share the same principles. Thoracic aortic aneurysms (more often associated with connective-tissue disease or hypertension) and popliteal aneurysms (which tend to thrombose or embolise rather than rupture, threatening the limb, and are frequently bilateral) are the other important sites. A false (pseudo) aneurysm — a contained leak walled off by surrounding tissue, often after arterial puncture or trauma — differs from a true aneurysm in not involving all wall layers. Recognising these broadens the concept beyond the abdominal aorta.

• AAA = aorta ≥3 cm (aneurysm = >1.5× normal); usually infrarenal.
• Elective repair threshold ≈ 5.5 cm (or symptomatic/rapidly expanding); options = open graft or EVAR.
• Ruptured AAA triad: sudden abdominal/back pain + hypotension/collapse + pulsatile expansile mass (emergency).

Most are asymptomatic until rupture — hence screening.

• AAA = permanent localised dilatation of the aorta ≥3 cm (>1.5× normal); usually infrarenal, true aneurysm, degenerative.
• Risk: age, male, smoking, hypertension, family history, connective-tissue disorders.
• Usually asymptomatic (pulsatile expansile mass); ruptured AAA triad = pain + shock + pulsatile mass (emergency, high mortality).
• Ultrasound for diagnosis/screening/surveillance (screen men at 65); CT angiography for planning/rupture.
• <5.5 cm → surveillance + risk factors; ≥5.5 cm/symptomatic/rapidly expanding → elective repair (open or EVAR); ruptured → emergency repair.