PassFinals
Vascular Surgery

Abdominal Aortic Aneurysm

An abdominal aortic aneurysm (AAA) is a focal abdominal-aortic dilatation that is often silent until it becomes symptomatic or ruptures; management is determined by symptoms, diameter, growth, anatomy, operative risk and patient preference.

In a nutshell

AAA is often silent, but new abdominal or back pain, collapse or a pulsatile mass may indicate symptomatic or ruptured disease. Use immediate bedside aortic ultrasound and urgent regional vascular discussion for suspected rupture. For unruptured disease, surveillance is annual at 3.0 to 4.4 cm and every 3 months at 4.5 to 5.4 cm; consider repair if symptomatic, rapidly growing or 5.5 cm or larger.

Classic presentation

An asymptomatic aneurysm found on screening or incidental imaging, or sudden abdominal/back pain with collapse or hypotension in rupture; the complete triad of pain, hypotension and a pulsatile mass is not required.

Key points

  • AAA is defined for teaching and NHS surveillance as an inner-to-inner maximum anterior-posterior aortic diameter of 3.0 cm or more on ultrasound.
  • In suspected symptomatic or ruptured AAA, offer immediate bedside aortic ultrasound and discuss immediately with a regional vascular service if AAA is seen, or if ultrasound is unavailable or non-diagnostic and suspicion remains.
  • Once accepted for emergency assessment, the person should leave the referring unit within 30 minutes of the transfer decision; consider restrictive volume resuscitation during transfer.
  • Small AAA (3.0 to 4.4 cm) is usually rescanned yearly; medium AAA (4.5 to 5.4 cm) every 3 months; refer 5.5 cm or larger or growth over 1 cm in 12 months.
  • Consider repair when symptomatic, asymptomatic and over 4.0 cm with growth over 1 cm in a year, or asymptomatic and 5.5 cm or larger.
  • NICE offers open repair for eligible unruptured AAAs; EVAR or conservative management may be considered when open repair is contraindicated or individual factors favour another approach.
  • After EVAR, surveillance is required. A suspected endoleak needs contrast-enhanced CTA, or contrast-enhanced ultrasound if CTA is contraindicated; a negative colour-duplex scan alone does not exclude it.
  • Smoking cessation and hypertension management are core risk-reduction measures; manage wider cardiovascular risk using current NICE guidance rather than an invented AAA-specific drug regimen.

First-line investigation

Immediate bedside aortic ultrasound for suspected symptomatic or ruptured AAA; outpatient abdominal ultrasound for suspected asymptomatic AAA and surveillance.

Management

Suspect rupture and transfer

  • Immediate bedside aortic ultrasound and regional vascular discussion; resuscitate and transfer urgently, with restrictive volume resuscitation considered during transfer.1,5

Confirm and stage

  • Use ultrasound for diagnosis and surveillance; use thin-slice arterial-phase CTA for elective repair planning and consider it for suspected rupture only when appropriate for repair assessment.1

Monitor size and reduce risk

  • Annual ultrasound at 3.0 to 4.4 cm, three-monthly at 4.5 to 5.4 cm, plus smoking cessation, hypertension management and wider cardiovascular risk reduction.1,2,6

Plan repair when indicated

  • Consider repair if symptomatic, rapidly growing or 5.5 cm or larger; choose open repair, EVAR or conservative management through specialist shared decision-making based on anatomy and operative risk.1

Surveil after EVAR and safety-net

  • Tailor post-EVAR surveillance, investigate suspected endoleak with contrast-enhanced CTA or contrast-enhanced ultrasound, and give urgent advice for new severe pain or collapse.1,3

Exam traps

  • Do not wait for the full rupture triad: collapse or new abdominal/back pain in a high-risk person can be enough to trigger the AAA pathway.
  • A non-diagnostic bedside ultrasound does not rule out rupture; discuss immediately with the regional vascular service if suspicion remains.
  • Do not send an unstable patient for routine CT before urgent vascular discussion and transfer; CTA is for repair planning when clinically appropriate.
  • The 5.5 cm threshold is measured inner-to-inner on the maximum anterior-posterior ultrasound diameter; symptoms and growth can justify repair below this size.
  • A negative colour-duplex ultrasound alone does not exclude an endoleak after EVAR.
  • Women have lower prevalence but higher rupture risk at a given diameter; do not use sex to dismiss the diagnosis.

Illustrations

Law of Laplace and aneurysm growthDiagram showing wall tension rising with radius, illustrating why larger aneurysms grow faster and rupture more readily.PassFinals · original
Ruptured abdominal aortic aneurysm on CTAxial CT showing a large calcified abdominal aortic aneurysm with adjacent retroperitoneal haemorrhage (arrows).James Heilman, MD, Wikimedia Commons · CC-BY-SA-3.0
Abdominal aortic aneurysm on ultrasoundAbdominal ultrasound measuring the maximal anteroposterior aortic diameter, the modality used by the national AAA screening programme.Mikael Häggström, M.D. Author info, Wikimedia Commons · CC0

Key sources

  1. NICE NG156: Abdominal aortic aneurysm: diagnosis and management (NG156 recommendations)Published 19 Mar 2020
  2. NHS AAA Screening Programme: care pathway (England screening pathway updated 27 October 2025)Published 27 Oct 2025 | Updated 27 Oct 2025
  3. NHS: Abdominal aortic aneurysm (NHS symptoms and treatment information)
  4. NHS: Abdominal aortic aneurysm screening (NHS screening information and surveillance intervals)Updated 11 Nov 2024
  5. NICE NG156: Emergency transfer and permissive hypotension recommendations (NG156 recommendations 1.3.1 to 1.3.6)Published 19 Mar 2020
  6. NICE NG238: Cardiovascular disease: risk assessment and reduction, including lipid modification (NG238 recommendations)Published 14 Dec 2023

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.