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Abdominal Aortic Aneurysm (AAA)

NICE guideline [NG156] Abdominal aortic aneurysm: diagnosis and management. Published Mar 2020. NICE CKS Abdominal aortic aneurysm screening. Last revised: May 2024.

Background Information

  • Aneurysm: artery diameter ≥1.5 times the normal
  • AAA: permanent pathological dilation of the abdominal aorta by 1.5 times the expected diameter based on person’s sex and body size.

Conventional threshold for diagnosis of AAA is an abdominal aortic diameter of ≥3.0cm

>90% of AAAs are infrarenal (below the origin of the renal arteries).

Important risk factors include:
  • Male (6x more common than in women)
  • Advancing age
  • Smoking
  • Hypertension

Symptoms:
  • Mostly asymptomatic – most cases detected incidentally or on routinely screening
  • Abdominal / flank / back pain in minority of patients

Examination findings:
  • Aortic bruit
  • Pulsatile + expansile epigastric mass

Typical clinical features:
  • Sudden onset severe back and/or abdominal pain
    • Radiation to flank / buttocks / legs / groin possible
  • Hypotension
  • Grey Turner and/or Cullen sign

The RCEM suggests considering ruptured AAA in the following patients:
  • >50 y/o with abdominal / back pain AND hypotension
  • Known AAA with abdominal / back pain OR hypotension
 

Be aware that features of a ruptured AAA may mimic those of renal colic.

Guidelines

1st line: bedside abdominal ultrasound
  • Measure inner-to-inner maximum anterior-posterior aortic diameter
  • Can confirm AAA but cannot definitively rule out rupture
  • Abdominal aorta diameter ≥3.0 cm indicates AAA
  • Peri-aortic / free intraperitoneal / retroperitoneal fluid indicates ruptured AAA

Confirmatory: computed tomography angiography (CTA)
  • Patient must be stable
  • Abdominal aorta diameter ≥3.0 cm indicates AAA
  • Contrast extravasation from abdominal aorta indicates ruptured AAA

2 week wait referral for repair if:

  • ≥5.5 cm, or 
  • >4.0 cm + growing >1cm / year

If repair not indicated offer conservative care:
  • Risk reduction
    • Smoking cessation
    • Blood pressure control
  • Follow up and monitor with ultrasound (see screening section below for timing)

A-E approach
  • Hypotensive resuscitation (permissive hypotension)
    • Royal College of Emergency Medicine recommends aiming target systolic BP 90-120 mmHg
 
  • Involve senior + immediate bedside ultrsound
    • Referral for surgical intervention should NOT be delayed if imaging is not immediately available
    • Clinical suspicion alone is an indication for surgery
 
  • Definitive (all patients): IMMEDIATE discussion with vascular surgeon for repair

Routine screening for AAA is offered to ALL ≥65 y/o men
  • Screening modality: one-off transabdominal ultrasound
  • Measure inner-to-inner maximum anterior-posterior aortic diameter

Subsequent action depends on USS findings:
 
Aortic diameter  Interpretation Re-scanning timeframe
<3.0cm No aneurysm Discharge, no further scanning
3.0 – 4.4 cm Small AAA 12-monthly scan
4.5 – 5.4cm Medium AAA 3-monthly scan
≥5.5cm Large AAA Refer to vascular surgery

References

Author: Konstantinos 
Reviewer: 
Last edited: 28/07/25