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usmle step 2 ck

Abdominal Aortic Aneurysm

Pathologic dilation of the abdominal aorta >=3 cm (or >50% of normal diameter), most commonly infrarenal, with risk of rupture proportional to size

Review date
reviewed 2026-05-04
Reading time
5 min read
Author
Dr Kola Tytler MBBS CertHE MBA MSt MRCGP
Cardiovascularcommonlong-term-condition
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Condition details
Cardiovascular
common
5 min read
reviewed 2026-05-04
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About This Page

This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.

Key points

  • USPSTF: one-time ultrasound screening for men aged 65-75 who have EVER smoked (Grade B)
  • Most AAAs are asymptomatic — discovered incidentally or on screening
  • Rupture risk increases exponentially with size: <4 cm = <1%/year, 5-5.9 cm = 3-15%/year, >=6 cm = 20-40%/year
  • Elective repair indicated at >=5.5 cm (men) or >=5.0 cm (women), or growth >0.5 cm in 6 months
  • Ruptured AAA: classic triad of abdominal/back pain + hypotension + pulsatile abdominal mass — emergent surgical repair, do NOT delay for imaging if hemodynamically unstable

Overview

An abdominal aortic aneurysm is defined as dilation of the abdominal aorta to >=3 cm or >50% greater than the normal adjacent diameter. Over 90% are infrarenal in location. The pathogenesis involves degenerative changes in the aortic wall with loss of elastin and smooth muscle, chronic inflammation, and proteolytic destruction of the media. AAA is strongly associated with smoking and atherosclerotic risk factors, though it is a distinct process from occlusive atherosclerosis.

Epidemiology

Prevalence is ~4-8% in men >65 who have smoked. Men are affected 4-6x more than women. Risk factors: smoking (strongest, 5-8x risk), age >65, male sex, white race, family history (first-degree relative with AAA increases risk 2x), hypertension, and peripheral artery disease. Ruptured AAA accounts for ~15,000 deaths/year in the US with overall mortality ~80% (including pre-hospital deaths). Elective repair mortality is ~1-5%.

Clinical Features

Symptoms
Most are asymptomatic — incidental finding on imaging or screening
Vague abdominal or back pain (may indicate expansion or impending rupture)
Ruptured AAA: sudden severe abdominal/flank/back pain + hemodynamic instability
Distal embolization: blue toe syndrome, livedo reticularis (atheroemboli from mural thrombus)
Signs
Pulsatile, expansile abdominal mass (sensitivity depends on size and body habitus — more difficult in obese patients)
Abdominal bruit (not reliable)
Ruptured: hypotension, tachycardia, abdominal distension/tenderness, Grey Turner sign (flank ecchymosis)

Investigations

First-line
Abdominal ultrasoundScreening and surveillance modality of choice. Sensitivity ~95-100% for detecting AAA. USPSTF: one-time screening for men 65-75 who have ever smoked
CT angiography (CTA)Pre-operative planning: precise sizing, anatomy (suprarenal extension, iliac involvement), relationship to renal/mesenteric arteries, suitability for EVAR vs open repair
Second-line
CT abdomen/pelvis without contrastCan detect AAA incidentally, but CTA is preferred for surgical planning
Specialist
MRAAlternative to CTA if contrast allergy or renal insufficiency. Good for planning but less spatial resolution than CTA

Management

SVS/ACC 2018 AAA Guideline + USPSTF 2019 Screening Recommendation
1
Screening
  • USPSTF Grade B: one-time ultrasound for men aged 65-75 who have ever smoked
  • Selective screening for men 65-75 who have never smoked (USPSTF Grade C)
  • Insufficient evidence for women who have never smoked; consider for women 65-75 with smoking history or family history
2
Surveillance (small AAA, not meeting repair threshold)
  • 3.0-3.9 cm: ultrasound every 2-3 years
  • 4.0-4.9 cm: ultrasound every 6-12 months
  • 5.0-5.4 cm: ultrasound or CT every 6 months; vascular surgery consultation
  • All sizes: smoking cessation, statin, BP control, optimize cardiovascular risk factors
  • No evidence that beta-blockers slow AAA growth
3
Elective repair indications
  • Diameter >=5.5 cm in men or >=5.0 cm in women
  • Growth rate >0.5 cm over 6 months or >1 cm/year
  • Symptomatic aneurysm (pain suggesting expansion)
  • Saccular morphology (higher rupture risk at smaller sizes)
  • EVAR (endovascular): preferred if anatomy suitable — lower 30-day mortality than open (~1-2% vs 4-5%). Requires lifelong surveillance for endoleak
  • Open repair: if anatomy not suitable for EVAR, younger patients (better long-term durability), concurrent aortoiliac occlusive disease
4
Ruptured AAA — emergency
  • Permissive hypotension (SBP 70-90) until OR — aggressive fluid resuscitation may worsen bleeding
  • Emergent surgical repair: open or EVAR depending on availability and anatomy
  • Massive transfusion protocol: 1:1:1 ratio of PRBC:FFP:platelets
  • Do NOT delay for CT if diagnosis is clinically obvious and patient is unstable — go directly to OR
  • CT only if hemodynamically stable and diagnosis uncertain

Complications

  • Rupture: Most feared — ~80% overall mortality. Risk proportional to size
  • Distal embolization: Mural thrombus fragments cause blue toe syndrome, renal infarction, mesenteric ischemia
  • Aortoenteric fistula: Usually between AAA graft and duodenum — herald GI bleed then massive hemorrhage
  • Post-EVAR endoleak: Persistent blood flow into aneurysm sac. Type I/III require re-intervention; Type II (most common) often observed
  • Post-repair complications: Colonic ischemia (IMA ligation), spinal cord ischemia, renal failure, graft infection
USMLE Step 2 CK Exam Tips
  • 1USPSTF screening: one-time US for men 65-75 who have EVER smoked. This is tested frequently
  • 2Ruptured AAA triad: abdominal/back pain + hypotension + pulsatile mass. Unstable = OR immediately, no CT
  • 3Repair threshold: >=5.5 cm men, >=5.0 cm women, or rapid growth (>0.5 cm/6 months)
  • 4EVAR has lower perioperative mortality but requires lifelong surveillance. Open repair is more durable
  • 5Blue toe syndrome with palpable pedal pulses = atheroemboli from proximal source (AAA, aortic plaque)
  • 6If a patient had prior AAA repair and presents with GI bleeding: think aortoenteric fistula (graft erosion into duodenum)

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regional clinical guidance

Abdominal Aortic Aneurysm: guidance by region

Recommendations, thresholds and pathways can differ. Open the page written for the jurisdiction you need.

United StatesAbdominal aortic aneurysmCardiovascular · reviewed 2026-08-20

Verified Sources & References

SVS/ACC 2018 AAA Guideline
USPSTF 2019 AAA Screening Recommendation
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