Definition and epidemiology
An abdominal aortic aneurysm (AAA) is a permanent, localized dilation of the abdominal aorta with a diameter at least 1.5 times normal, generally defined as 3 cm or greater. Most (about 90%) are infrarenal, arising below the renal arteries.
- Prevalence increases sharply with age; most common in men over 65
- Male-to-female ratio approximately 4-6:1
- Prevalence in screened populations has declined in recent decades, likely due to falling smoking rates
- Rupture risk rises steeply with increasing diameter, especially above 5.5 cm
AAA is largely a disease of older smokers with atherosclerotic risk factors, distinguishing it from thoracic aortic aneurysms, which more often relate to connective tissue disease or bicuspid aortic valve.
- AAA defined as aortic diameter ≥3 cm, most commonly infrarenal
- Smoking is the strongest modifiable risk factor; diabetes is inversely associated
- One-time ultrasound screening recommended for men 65-75 who ever smoked
- Classic rupture triad: abdominal/back pain, hypotension, pulsatile mass
- Repair threshold: ≥5.5 cm in men, ≥5.0 cm in women, or rapid growth
- Hemodynamically unstable patient with suspected rupture goes straight to OR, not imaging
- EVAR has lower perioperative mortality but requires lifelong surveillance for endoleak
- Mortality of ruptured AAA remains very high (>80%) even with emergency repair
Etiology and risk factors
The dominant mechanism is degenerative, driven by chronic inflammation and proteolytic degradation of the aortic wall matrix, closely associated with atherosclerosis.
Major risk factors
- Smoking — strongest modifiable risk factor; also increases growth rate and rupture risk
- Age over 65
- Male sex
- Family history of AAA (first-degree relative)
- Hypertension
- Atherosclerosis / dyslipidemia
Less common causes
- Connective tissue disorders (Marfan syndrome, Ehlers-Danlos syndrome, type IV)
- Vasculitis (Takayasu arteritis, giant cell arteritis)
- Mycotic (infected) aneurysm, e.g., from Salmonella or Staphylococcus bacteremia
- Trauma
Notably, diabetes mellitus is inversely associated with AAA, an exception worth remembering for exams.
Pathophysiology
AAA formation involves a combination of chronic transmural inflammation, destruction of elastin and collagen in the media and adventitia, and smooth muscle cell loss.
- Matrix metalloproteinases (MMPs), particularly MMP-2 and MMP-9, degrade elastin and collagen, weakening the wall
- Chronic inflammatory infiltrate (macrophages, T cells) perpetuates proteolysis
- Loss of elastin reduces wall compliance and promotes progressive dilation
- Laplace's law: wall tension increases with radius, so as the aneurysm enlarges, tension rises further, accelerating growth and rupture risk
- Mural thrombus commonly forms within the dilated segment and can embolize distally
Clinical features
Most AAAs are asymptomatic and found incidentally on imaging or screening.
When symptomatic
- Vague abdominal, back, or flank pain
- Palpable, pulsatile, nontender periumbilical mass
- Early satiety or symptoms from compression of adjacent structures (rare)
Ruptured or symptomatic (impending rupture)
- Sudden severe abdominal or back pain
- Hypotension and syncope
- Pulsatile abdominal mass
- This triad (pain, hypotension, pulsatile mass) is classic for rupture, though all three are present in only a minority of cases
- Rupture can be contained (retroperitoneal), temporarily limiting blood loss and allowing transient hemodynamic stability, or free into the peritoneal cavity, causing rapid hemodynamic collapse
- Flank or periumbilical ecchymosis (Grey Turner or Cullen sign) is classically taught with retroperitoneal hemorrhage (most often hemorrhagic pancreatitis) and can rarely be seen with retroperitoneal AAA rupture, but it is a late, inconsistent finding that develops over hours to days and should not be relied on for acute diagnosis
Diagnosis
Screening
- One-time abdominal ultrasound for men aged 65-75 who have ever smoked (strong recommendation, USPSTF and major vascular societies)
- Selective screening considered for men who never smoked with a family history, and discussed individually for women with risk factors
Imaging
- Abdominal ultrasound — initial test for diagnosis and surveillance; inexpensive, no radiation
- CT angiography — gold standard for preoperative planning, precise sizing, and assessing anatomy (neck length, involvement of renal/iliac arteries)
- MR angiography — alternative when contrast or radiation is contraindicated
Suspected rupture
- Hemodynamically unstable patient with a known or suspected AAA should go directly to the operating room; imaging should not delay life-saving surgery
- If stable enough, CT angiography confirms rupture and guides emergency repair
Surveillance intervals (typical consensus)
| Diameter | Follow-up |
|---|---|
| 3.0-3.9 cm | Ultrasound every 2-3 years |
| 4.0-4.9 cm | Ultrasound every 12 months |
| 5.0-5.4 cm | Ultrasound or CT every 6 months |
| ≥5.5 cm (men) / ≥5.0 cm (women) | Elective repair |
Differential diagnosis
- Renal colic — flank pain, but with hematuria and normal pulsatile mass
- Acute pancreatitis — epigastric pain, elevated lipase, no pulsatile mass
- Perforated peptic ulcer — peritonitis, free air on imaging
- Mesenteric ischemia — pain out of proportion to exam, elevated lactate
- Diverticulitis — localized left lower quadrant pain and tenderness
- Musculoskeletal back pain — lacks hemodynamic instability or pulsatile mass
- Aortic dissection — tearing pain, often radiating to back, blood pressure differential between limbs
Management
Management depends on size, symptoms, and growth rate.
Asymptomatic, small AAA
- Surveillance imaging per size-based intervals (see Diagnosis)
- Smoking cessation — most important intervention to slow growth and reduce rupture risk
- Blood pressure control and statin therapy for cardiovascular risk reduction (does not reliably shrink the aneurysm but reduces overall cardiovascular events)
- Beta-blockers may be used for cardiovascular risk reduction, though evidence for slowing aneurysm growth specifically is limited
Indications for elective repair
- Diameter ≥5.5 cm in men, ≥5.0 cm in women (some European guidelines use lower women's thresholds)
- Rapid growth (>1 cm/year or >0.5 cm in 6 months)
- Symptomatic aneurysm (pain, tenderness) regardless of size
- Saccular morphology (higher rupture risk at smaller size)
Repair options
- Endovascular aneurysm repair (EVAR) — stent graft placed via femoral access; lower perioperative morbidity and mortality, preferred when anatomy is suitable, but requires lifelong surveillance imaging for endoleak
- Open surgical repair — direct replacement with a prosthetic graft; more durable long-term, preferred in young, fit patients or unfavorable anatomy for EVAR
- Choice between EVAR and open repair should be individualized based on anatomy, surgical risk, and patient preference; guideline bodies (ESVS, SVS) both endorse EVAR for suitable candidates but emphasize shared decision-making
Ruptured AAA
- Immediate resuscitation and emergent repair (open or endovascular if feasible and hemodynamically tolerated)
- Permissive hypotension during transport/resuscitation to avoid exacerbating bleeding before definitive repair
- Mortality remains high even with prompt intervention
Complications and prognosis
- Rupture — the feared complication; overall mortality for ruptured AAA (including prehospital deaths) exceeds 80%, even with emergency surgery
- Distal embolization from mural thrombus causing limb ischemia ("trash foot")
- Aortoenteric fistula — rare, presents with GI bleeding, especially after prior aortic graft
- Post-EVAR endoleak — persistent blood flow into the aneurysm sac outside the graft, requiring surveillance and sometimes reintervention
- Graft infection — rare but serious after open or endovascular repair
With timely elective repair, long-term survival is favorable; untreated large aneurysms carry a substantial annual rupture risk that rises steeply above 5.5-6 cm.
AAA risk factors — think "SMASH": Smoking, Male, Age, Sixty-plus, Hypertension/family History
Practice questions
1. A 70-year-old man with a 40-pack-year smoking history undergoes a screening abdominal ultrasound that reveals a 4.2 cm infrarenal aortic aneurysm. He is asymptomatic and has well-controlled blood pressure. Which is the most appropriate next step in management?
2. A 68-year-old woman presents to the emergency department with sudden severe back pain and dizziness. Blood pressure is 80/50 mmHg, heart rate is 125/min, and a pulsatile abdominal mass is palpated. Which is the most appropriate immediate next step?
3. A 72-year-old man undergoes elective EVAR for a 6 cm infrarenal AAA. One year later, routine CT surveillance shows persistent flow into the aneurysm sac outside the stent graft, with a slight increase in sac diameter. Which complication is most likely?
Frequently asked questions
What causes an abdominal aortic aneurysm?
AAA results mainly from chronic inflammation and enzymatic degradation of elastin and collagen in the aortic wall, strongly linked to atherosclerosis and smoking. Other contributors include aging, hypertension, genetic predisposition, and family history. Less common causes include connective tissue disorders, vasculitis, infection (mycotic aneurysm), and trauma. Diabetes is unusual among vascular risk factors in that it appears protective against AAA.
What are the first symptoms of an abdominal aortic aneurysm?
Most AAAs cause no symptoms at all and are found incidentally on imaging or screening. When symptoms do occur, they are typically vague abdominal, flank, or back pain, sometimes with a palpable pulsatile mass. Sudden severe pain with hypotension suggests rupture or impending rupture and is a medical emergency requiring immediate evaluation.
How is an abdominal aortic aneurysm diagnosed?
AAA is diagnosed primarily with abdominal ultrasound, which is used for both initial detection and ongoing surveillance. CT angiography provides more detailed anatomy and is used for surgical planning once an aneurysm is found or suspected to be large or symptomatic. Screening ultrasound is recommended for men aged 65-75 who have ever smoked.
Is an abdominal aortic aneurysm curable?
AAA cannot be reversed with medication, but it can be effectively treated with surgical or endovascular repair once it reaches a size or growth rate that warrants intervention. Small aneurysms are monitored with surveillance imaging and risk-factor control, especially smoking cessation. Successful elective repair generally restores normal life expectancy, whereas rupture carries very high mortality.
AAA vs aortic dissection — what is the difference?
An AAA is a dilation of the aortic wall that can rupture, while an aortic dissection is a tear in the inner layer of the aortic wall allowing blood to split the layers apart, which can occur in a normal-caliber or aneurysmal aorta. Dissection classically causes sudden tearing pain radiating to the back with pulse or blood pressure differences between limbs, whereas AAA is usually silent until rupture causes pain, hypotension, and a pulsatile mass.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: I71.3
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.