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Abdominal Aortic Aneurysm (AAA)

Clinical Subject Page

Abdominal aortic aneurysm (AAA)

ICD-10

I71.4

Specialty

Cardiology

Onset

Chronic

Reviewed

June 2026

On This Page

Overview

Abdominal aortic aneurysm (AAA) is a localized dilation of the abdominal aorta measuring ≥3.0 cm in diameter or ≥50% greater than the normal vessel diameter, resulting from weakening of the aortic wall and increasing the risk of rupture.

Etiology & Risk Factors

  • Etiology & Risk Factors

    Etiology

    • Atherosclerosis (most common)
    • Chronic hypertension
    • Smoking-related vascular degeneration
    • Connective tissue disorders (Marfan, Ehlers-Danlos)
    • Inflammatory aortitis
    • Infectious (mycotic) aneurysm
    • Previous aortic trauma

    Risk Factors

    • Age ≥65 years
    • Male sex
    • Smoking (strongest modifiable risk factor)
    • Hypertension
    • Family history of AAA
    • Hyperlipidemia
    • Coronary artery disease
    • Peripheral arterial disease

Pathophysiology

      • Inflammation and proteolytic degeneration of collagen, elastin, and smooth muscle cells weaken the abdominal aortic wall.
      • Loss of wall strength leads to progressive widening (aneurysm).
      • Mechanical stress (especially from hypertension) further enlarges the aneurysm and may cause rupture.
      • The dilated vessel disrupts laminar blood flow, producing turbulent flow.
      • Mural thrombi may develop within the aneurysm and cause peripheral thromboembolism.

      Simple Flow

      Wall degeneration → Weak abdominal aortic wall → Aneurysm formation → Turbulent blood flow → Thrombus formation ± Rupture

Clinical Presentation

  1. Symptoms

    • Usually asymptomatic
    • Chest pain
    • Back pain
    • Hoarseness
    • Dysphagia
    • Dyspnea
    • Cough

    Signs

    • Early diastolic murmur (aortic regurgitation)
    • Features of connective tissue disorders
    • Signs of compression of adjacent structures
    • Hypotension or shock (rupture)

History Taking

  • Key Questions

    • Sudden abdominal or back pain?
    • Pulsatile abdominal sensation?
    • History of smoking?
    • Hypertension?
    • Family history of AAA?
    • Previous aneurysm?
    • Syncope or dizziness?
    • Peripheral vascular disease?

    Red Flags

    • Sudden severe abdominal or back pain
    • Hypotension
    • Syncope
    • Pulsatile abdominal mass
    • Signs of hemorrhagic shock

Physical Examination

Inspection

  • May show a visible pulsation in thin patients

Palpation

  • Pulsatile abdominal mass (classic finding)

Auscultation

  • Abdominal bruit

General Examination

  • Assess peripheral pulses
  • Check for signs of hypovolemic shock if rupture is suspected

If Rupture Occurs

  • Hypotension
  • Tachycardia
  • Severe abdominal or back pain
  • Signs of shock

Investigations

  • Laboratory

    • CBC
    • Renal function
    • Coagulation profile
    • Blood type & crossmatch (if rupture suspected)

    Imaging

    • Abdominal ultrasound (screening & surveillance)
    • CT angiography (gold standard for diagnosis and operative planning)

    Additional Tests

    • ECG (exclude cardiac causes)
    • Chest X-ray (if indicated)

Diagnosis

Abdominal Aortic Aneurysm (AAA) · Diagnostic Criteria

DEFINED AS INFRARENAL AORTIC DIAMETER ≥3.0 cm (OR ≥1.5x EXPECTED NORMAL) Most AAAs are infrarenal and asymptomatic until rupture. Diagnosis and surveillance rely on abdominal ultrasound (screening/monitoring) and CT angiography (pre-operative planning, suspected rupture). Measurements taken outer-wall-to-outer-wall, perpendicular to the aortic long axis.
Diagnostic Approach
1
Screen
One-off abdominal ultrasound screening recommended for men aged 65–75 (esp. ever-smokers). Often otherwise found incidentally on imaging or exam (pulsatile abdominal mass).
Screening
2
Confirm & Measure
Abdominal ultrasound is first-line for diagnosis/surveillance (cheap, no radiation). CT angiography for pre-operative planning or suspected rupture/symptomatic AAA.
Imaging
3
Classify & Localise
Determine extent — infrarenal (most common, ~90%), juxtarenal, suprarenal, or thoracoabdominal. Assess relationship to renal and iliac arteries for repair planning.
Anatomic mapping
4
Risk Stratify
Assess size, growth rate, symptoms, and comorbidities to determine surveillance interval vs urgent surgical referral.
Integration
Category Diameter Action
Normal infrarenal aorta <3.0 cm No follow-up required
Small AAA 3.0–4.4 cm Annual ultrasound surveillance; address cardiovascular risk factors
Medium AAA 4.5–5.4 cm Ultrasound surveillance every 3 months; vascular surgery referral
Large AAA ≥5.5 cm Elective surgical repair indicated (open or EVAR) regardless of symptoms
Rapid expansion ≥1 cm/year or ≥0.5 cm in 6 months Treat as high risk — expedite surgical referral regardless of absolute size
Symptomatic AAA (pain, tenderness) Any size Urgent CT angiography and surgical referral — treat as impending rupture
Ruptured AAA Any size Surgical emergency — classic triad: abdominal/back pain, pulsatile mass, hypotension
Risk Factors
Smoking — strongest modifiable risk factor
Age >65 and male sex — incidence rises sharply with age, ~4–6x more common in men
Hypertension & atherosclerosis — chronic wall stress and degenerative change
Family history — first-degree relative with AAA increases risk significantly
Connective tissue disease — Marfan, Ehlers-Danlos (less common cause than for TAA)
COPD & peripheral arterial disease — shared atherosclerotic risk profile
Screening & Surveillance Notes
One-off USS screening — recommended for men at age 65 in many national programmes (e.g. NHS AAA screening)
Average growth rate — ~0.2–0.3 cm/year, faster as diameter increases
Repair decision — based on diameter threshold, growth rate, and patient fitness for surgery, not symptoms alone
EVAR vs open repair — EVAR has lower perioperative mortality but requires suitable anatomy and lifelong surveillance for endoleak
Smoking cessation — single most effective intervention to slow growth and reduce rupture risk
Home / Home / Clinical Cases / Cardiovascular System Clinical Cases / Abdominal Aortic Aneurysm (AAA)
Related Topics

Plaque

Management

Medical Management

  • Smoking cessation
  • Blood pressure control
  • Statin therapy
  • Antiplatelet therapy (if indicated)
  • Regular imaging surveillance for small aneurysms

Surgical Management

  • Endovascular aneurysm repair (EVAR)
  • Open surgical repair
  • Immediate repair for ruptured AAA
  • Elective repair for symptomatic or large aneurysms (typically ≥5.5 cm in men, or rapidly expanding aneurysms)

Complications

    • Aneurysm rupture
    • Massive hemorrhage
    • Thromboembolism
    • Distal limb ischemia
    • Aortic dissection (rare)
    • Death

Prognosis

  • Small AAAs have a good prognosis with surveillance.
  • Risk of rupture increases markedly with aneurysm size and expansion rate.
  • Ruptured AAA has a very high mortality despite emergency surgery. 

Key Points / Clinical Pearls

    • Smoking is the strongest modifiable risk factor for AAA.
    • Ultrasound is the preferred screening test.
    • CT angiography is the imaging modality of choice before repair.
    • AAA is defined as an abdominal aortic diameter ≥3.0 cm.
    • Elective repair is generally recommended at ≥5.5 cm in men or for symptomatic/rapidly expanding aneurysms.
    • Ruptured AAA is a surgical emergency with high mortality.
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