Abdominal Aortic Aneurysm
Progressive weakening and dilatation of the abdominal aortic wall beyond 3cm, which enlarges silently under rising wall tension until it ruptures, a catastrophic emergency defined by pain, hypotension and a pulsatile mass.
In a nutshell
AAA is progressive wall weakening causing dilatation. Wall tension rises with radius (Laplace), so bigger aneurysms grow faster and rupture risk accelerates. Rupture is a catastrophic emergency (pain, hypotension, pulsatile mass) needing immediate theatre.
Classic presentation
An asymptomatic pulsatile abdominal mass found incidentally, or sudden severe abdominal or back pain with hypotension and a pulsatile mass in rupture.
Key points
- Screening is a single ultrasound offered to men aged 65, because men have far higher prevalence.
- Wall tension rises with radius (law of Laplace), so growth and rupture risk accelerate as the aneurysm enlarges; surveillance intervals shorten accordingly.
- The rupture triad is pain, hypotension and a pulsatile abdominal mass; this is a clinical diagnosis in the unstable patient, do not wait for imaging.
- The elective repair threshold (around 5.5cm) balances rupture risk against operative risk.
- Smoking cessation and blood pressure control slow growth even when the aneurysm is too small for repair.
First-line investigation
Abdominal ultrasound: quick, non-invasive, and measures aortic diameter directly.
First-line management
In suspected rupture: immediate resuscitation and emergency transfer to theatre without delay. Electively: surveillance and repair at the size threshold.
Exam traps
- A stable patient with a known AAA and new pain still needs urgent same-day imaging; do not assume it is unrelated.
- Do not delay transfer to theatre for CT in a haemodynamically unstable patient with suspected rupture; clinical diagnosis and immediate crossmatch take priority.
- A ruptured AAA can mimic renal colic with loin pain: always consider it in an older patient with new loin pain and collapse.
Educational content pending clinical review. Not medical advice.