An abdominal aortic aneurysm (AAA) is a permanent, abnormal dilation of the abdominal aorta — the body's largest artery, which carries oxygenated blood from the heart through the abdomen to the pelvis and lower extremities. An aneurysm is defined as a focal dilation exceeding 1.5 times the expected normal aortic diameter, with a threshold of 3.0 cm commonly used in practice. As an AAA enlarges, the mechanically weakened aortic wall faces exponentially increasing rupture risk — and rupture carries an overall mortality of 80–90%, with the majority of patients dying before reaching the operating room.
Abdominal aortic aneurysm is part of a broader spectrum of arterial aneurysmal disease that can affect multiple vascular territories simultaneously. Splenic artery aneurysm — the most common visceral artery aneurysm — is frequently discovered alongside aortic disease on the same abdominal MRI. Nutcracker syndrome involves the left renal vein — which crosses the aorta — and must be identified when aortic anatomy is evaluated. Mural thrombus within an AAA can embolize distally, causing renal or renal parenchymal infarction. MR angiography provides the complete anatomic roadmap of the aorta and its branch vessels — including the renal arteries that define the proximal repair boundary — in a single radiation-free examination.
Causes
Atherosclerosis and aortic wall degeneration.
The primary pathophysiology of AAA is progressive degeneration and remodeling of the aortic media — the middle structural layer of the aortic wall — driven by chronic inflammation, proteolytic enzyme activity (particularly matrix metalloproteinases MMP-2 and MMP-9), and oxidative stress. This leads to fragmentation and loss of elastin and collagen within the aortic wall, reducing its tensile strength and allowing the lumen to progressively dilate under systemic blood pressure. Atherosclerotic plaque accumulates in the intima and contributes to chronic transmural inflammation. Mural thrombus — the laminated blood clot that accumulates within the aneurysm sac adjacent to the true lumen — does not protect against rupture and may harbor inflammatory cells that actively promote wall degradation.
Risk factors.
Smoking is by far the most powerful modifiable risk factor — the risk of AAA is 3–5 times higher in smokers vs. non-smokers, and current or former smoking is present in approximately 75% of AAA patients. Male sex confers a 4–5 fold higher AAA risk than female sex, though women with AAA have higher rupture rates at smaller sizes than men — the sex-specific repair threshold is lower in women (5.0 cm vs. 5.5 cm for men). First-degree family history of AAA approximately doubles individual risk. Hypertension and hypercholesterolemia contribute through their effects on atherosclerosis and aortic wall stress. Genetic connective tissue disorders — Marfan syndrome (FBN1), Loeys-Dietz syndrome (TGFBR1/2), Ehlers-Danlos syndrome type IV (COL3A1) — produce aneurysms at younger ages through primary structural protein defects rather than atherosclerosis. Interestingly, diabetes mellitus appears to be inversely associated with AAA — possibly through advanced glycation end-products (AGEs) crosslinking and stiffening the aortic wall, paradoxically reducing dilation despite accelerating atherosclerosis.
Symptoms
The majority of AAAs are entirely asymptomatic throughout their natural history, growing at an average rate of 2–3 mm per year for small aneurysms and 3–5 mm per year for larger ones — discovered only when screening ultrasound or incidental abdominal imaging is performed. The classic symptomatic triad — a pulsating epigastric mass, abdominal or back pain, and hypotension — is a late and ominous presentation indicating impending or actual rupture. Contained rupture (retroperitoneal hematoma with temporarily preserved hemodynamics) may allow a brief window for emergency intervention; free rupture into the peritoneal cavity produces immediate hemodynamic collapse with very high mortality even with rapid surgical response. Chronic contained aneurysm symptoms — dull, deep, persistent abdominal or lumbar back pain — may occur from pressure on adjacent structures or from stretching of the aortic wall, and should be evaluated urgently when they develop in a patient with a known AAA. Distal embolization of mural thrombus can cause acute limb ischemia (blue toe syndrome), renal infarction, or mesenteric ischemia.
Diagnosis
One-time abdominal ultrasound screening is recommended by the USPSTF for all men aged 65–75 who have ever smoked — a grade B recommendation based on the 43% reduction in AAA-specific mortality from screening programs. Ultrasound is the screening modality of choice: inexpensive, widely available, highly accurate for AAA detection, and radiation-free. Once an AAA is identified, periodic surveillance ultrasound tracks growth rate — the rate of growth is itself a risk factor for rupture independent of absolute size.
An MRI of the abdomen with MR angiography (MRA) is the most comprehensive radiation-free evaluation of the abdominal aorta. MRI measures maximum aortic diameter precisely (the critical metric for repair decisions), characterizes mural thrombus morphology and volume, identifies inflammatory changes in the aortic wall (inflammatory AAA — a rare variant with periaortic fibrosis and retroperitoneal involvement), and maps the anatomic boundaries of the aneurysm relative to the renal arteries (infrarenal neck length and diameter), common iliac arteries, and access vessels — the critical planning information for EVAR. Phase-contrast MRA quantifies aortic flow and identifies hemodynamically significant renal artery stenoses that may require treatment at the time of aortic repair. MRI is particularly valuable for serial surveillance in younger patients with connective tissue disorders who would accumulate significant radiation from repeated CT angiography over decades of follow-up. CT angiography remains the predominant pre-procedural planning modality at most vascular surgery centers given its speed and spatial resolution.
Classification
AAA is classified by size (which determines rupture risk and repair threshold) and anatomic location (which determines repair approach).
- Small AAA (3.0–4.4 cm): Annual rupture risk <1%. Surveillance with ultrasound every 12 months. Intensive cardiovascular risk factor modification.
- Moderate AAA (4.5–5.4 cm): Annual rupture risk 1–3%. Ultrasound every 6 months. Continue risk modification; repair planning discussions initiated.
- Large AAA (?5.5 cm in men, ?5.0 cm in women): Annual rupture risk 5–15% and rising sharply with size. Repair recommended in patients with acceptable surgical risk. Growth >1 cm/year at any size is an independent indication for repair regardless of absolute diameter.
- Infrarenal AAA: Origin below both renal arteries (~95% of all AAA). Most amenable to standard EVAR with a sufficient infrarenal neck (>10–15 mm) for graft seal.
- Juxtarenal/Pararenal/Suprarenal AAA: Aortic neck at or above the renal arteries. Requires fenestrated or branched EVAR (FEVAR/BEVAR) or open surgical repair. Higher procedural complexity.
Treatments
Management is guided by aneurysm size, growth rate, anatomy, patient surgical risk, and life expectancy.
Surveillance and cardiovascular risk factor modification: Small and moderate AAAs are managed with periodic imaging surveillance and aggressive risk factor modification. Smoking cessation is the most impactful single intervention — it reduces AAA growth rate by approximately 20% and is associated with lower overall cardiovascular mortality. Statin therapy reduces AAA growth rate and is recommended for all AAA patients given their high cardiovascular risk burden. Antihypertensive therapy (preferably beta-blockers or ACE inhibitors) controls aortic wall stress. Antiplatelet therapy reduces cardiovascular events.
Endovascular aneurysm repair (EVAR).
EVAR — the placement of a fabric-covered self-expanding stent graft through bilateral femoral arterial access — has become the predominant AAA repair technique, accounting for over 80% of elective repairs in the United States. The stent graft is deployed to bridge the aneurysm sac, redirecting aortic blood flow through the graft and excluding the aneurysm sac from arterial pressure. EVAR requires suitable anatomy — adequate infrarenal neck length (?10–15 mm), acceptable neck angulation, and iliac access vessels of sufficient caliber. Advantages include shorter hospital stay (1–2 days vs. 5–7 days for open repair), faster recovery, and lower 30-day mortality (0.5–1.5% vs. 3–5% for open repair). The main limitation is the need for lifelong annual CT or MRI surveillance to detect endoleaks — persistent perfusion of the aneurysm sac outside the stent graft — which can perpetuate rupture risk if untreated. Type II endoleaks (retrograde flow from lumbar or inferior mesenteric artery collaterals) are the most common and often resolve spontaneously; Type I and III endoleaks (seal zone or graft fabric failures) require reintervention.
Open surgical repair.
Open repair — clamping the aorta above the aneurysm, opening the sac, and sewing in a prosthetic Dacron graft — provides the most durable long-term repair, essentially eliminating endoleak risk and reducing the lifelong surveillance burden. It remains the treatment of choice for patients with anatomy unsuitable for EVAR, younger patients expected to outlive EVAR durability data, and cases of inflammatory or infected (mycotic) AAA. The trade-off is higher early perioperative risk — 30-day mortality of 3–5% at experienced centers — and longer recovery (4–6 weeks). Long-term survival after open repair is equivalent to or better than EVAR in fit patients.
Emergency repair of rupture.
Ruptured AAA is one of the most time-critical surgical emergencies in medicine — every minute of delay worsens outcome. Immediate transfer to an operating room is mandatory. EVAR under local anesthesia (if anatomy permits) is increasingly favored for hemodynamically unstable patients — it can be established faster than open repair in experienced centers and may reduce blood loss. Permissive hypotension (target systolic BP 70–90 mmHg) is maintained until aortic control is achieved. Overall 30-day mortality for ruptured AAA is 40–50% even at experienced centers — emphasizing the critical importance of elective detection and repair before rupture occurs.
Surveillance after repair.
EVAR patients require lifelong annual imaging — CT angiography or MRI/MRA — to monitor for endoleaks, graft migration, limb occlusion, and aneurysm sac enlargement. Patients with open repair require less frequent surveillance (every 5 years) but still benefit from periodic imaging to detect juxtaanastomotic pseudoaneurysm formation and new aneurysm development in other arterial segments.
Get an MRI to Confirm Your Diagnosis
Before surgical planning or starting treatment, a clear MRI diagnosis ensures the right path forward. First Look MRI offers self-pay Abdomen MRI scans — no doctor's order or insurance required — at our locations in Georgia, Texas, and Colorado.