Residency · Residency · Interventional Radiology

Aortic Aneurysm: Endovascular Repair (EVAR) Fundamentals

Definition and Epidemiology

An abdominal aortic aneurysm (AAA) is defined as a focal dilation of the aorta exceeding 3.0 cm in diameter or greater than 50% of the normal adjacent aortic diameter. The condition affects approximately 4-8% of men over age 65 and is significantly more common in males, with a male-to-female ratio of 4-6:1. Smoking is the strongest modifiable risk factor, and other important contributors include age greater than 65, male sex, family history, hypertension, and connective tissue disorders. The natural history involves progressive enlargement with an ever-increasing risk of rupture, and rupture carries an overall mortality of 65-85% when prehospital deaths are included.

Screening Guidelines

The United States Preventive Services Task Force recommends a one-time abdominal ultrasound screening for men aged 65-75 who have ever smoked. The Society for Vascular Surgery takes a broader approach, recommending screening for men and women over 65 with a smoking history, as well as men over 55 and women over 65 with a family history of AAA. Screening in targeted populations has been shown to reduce AAA-related mortality by up to 50%.

Anatomy and Classification

Location

The vast majority of AAAs (85-90%) are infrarenal, meaning they arise below the renal arteries, and these are amenable to standard EVAR. Juxtarenal aneurysms extend to the level of the renal arteries without an adequate infrarenal neck for device sealing. Pararenal aneurysms involve the renal artery origins themselves, while suprarenal aneurysms encompass the visceral segment including the SMA and celiac artery. Thoracoabdominal aneurysms extend from the thoracic aorta into the abdominal aorta and are classified using the Crawford system.

Morphology

Fusiform aneurysms are the most common type and involve symmetric dilation of the entire aortic circumference. Saccular aneurysms present as an asymmetric outpouching from one wall and carry a higher rupture risk relative to their diameter.

Rupture Risk

Annual rupture risk increases dramatically with aneurysm diameter. Aneurysms measuring 3.0-3.9 cm have essentially no annual rupture risk, while those at 4.0-4.9 cm carry a 0.5-1% annual risk. At 5.0-5.9 cm, the risk jumps to 3-15% per year, and at 6.0-6.9 cm it reaches 10-20% per year. Aneurysms exceeding 7.0 cm carry a 20-40% annual rupture risk. The standard threshold for repair is 5.5 cm in men and 5.0 cm in women, with the lower threshold in women reflecting their higher rupture risk at any given size. Repair should also be considered for rapid growth exceeding 1 cm per year or 0.5 cm in six months, saccular morphology, or any symptomatic aneurysm regardless of size.

EVAR Fundamentals

Principle

EVAR excludes the aneurysm sac from systemic blood pressure by deploying a covered stent-graft within the aorta. Blood flows through the graft lumen while the aneurysm sac is depressurized, allowing it to thrombose and potentially shrink over time. The technique requires adequate proximal and distal seal zones (landing zones) to prevent endoleak.

Anatomic Suitability (Instructions for Use)

The proximal neck must be at least 10-15 mm in length below the lowest renal artery, with a diameter of 18-32 mm, angulation less than 60 degrees, and minimal thrombus or calcification. The iliac arteries must have adequate diameter (greater than 7 mm) for device delivery and a suitable distal landing zone in the common iliac arteries with at least 10 mm of length. The iliofemoral access vessels must be large enough to accommodate the delivery system, which typically requires 16-22 French. Approximately 60% of infrarenal AAAs are anatomically suitable for standard EVAR.

Graft Configurations

The bifurcated configuration is the most common, consisting of a main body with an ipsilateral limb and a separately deployed contralateral limb. An aorto-uni-iliac (AUI) device extends the main body into one iliac artery and requires a femoral-femoral crossover bypass with contralateral iliac occlusion; this is used for hostile anatomy such as small or severely diseased iliac arteries. Fenestrated EVAR (fEVAR) uses a custom-made graft with fenestrations aligned to the renal and visceral arteries, extending the proximal seal zone for juxtarenal aneurysms. Branched EVAR employs grafts with side branches for visceral arteries and is used for thoracoabdominal and complex juxtarenal aneurysms.

Common Devices

The Medtronic Endurant/Endurant IIs is widely used and features active suprarenal fixation. The Gore Excluder is constructed with ePTFE covering, has no suprarenal fixation, and offers a low profile. The Cook Zenith has a modular design with suprarenal fixation barbs. The Endologix AFX/ALTO uses a unibody design with anatomical fixation. Each device has specific instructions for use regarding neck dimensions, angulation, and access vessel requirements.

EVAR Procedure

Technique

The procedure begins with bilateral femoral artery access, either through surgical cutdown or percutaneously using the preclose technique with Perclose devices. A stiff guidewire is advanced to the thoracic aorta, and the main body device is deployed with its proximal edge positioned just below the lowest renal artery. The suprarenal bare stent may cross the renal ostia without obstructing flow. After main body deployment, the contralateral gate is cannulated from the opposite femoral access, and the contralateral limb is deployed with overlap into the main body gate. Iliac limb extensions are placed as needed for adequate distal seal, and completion angiography is performed to assess seal, limb patency, and endoleak.

Intraoperative Assessment

Completion angiography is mandatory after every EVAR. The operator must assess for type I endoleak (which requires immediate treatment), type II endoleak (which is usually observed), and any limb kinking or stenosis. Intravascular ultrasound may be used to confirm sizing and graft apposition to the aortic wall.

Endoleaks

Classification

Type I endoleaks result from an inadequate seal at the proximal (Ia) or distal (Ib) attachment site. These are high-pressure leaks that require immediate treatment, which may include balloon molding, extension cuff placement, Palmaz stent deployment, or conversion to open repair. Type II endoleaks involve retrograde flow into the aneurysm sac from branch vessels such as lumbar arteries or the inferior mesenteric artery. They are the most common type and are usually benign; treatment is only indicated if the sac grows by more than 5 mm. Treatment options include transarterial embolization via the SMA-to-IMA pathway, translumbar direct sac puncture with embolization, or a transcaval approach. Type III endoleaks arise from graft defects including fabric tears or component disconnection and require treatment with relining using additional graft components. Type IV endoleaks represent graft fabric porosity, are transient and seen only intraoperatively, and are self-limited. Type V endoleak, also called endotension, describes sac expansion without a detectable endoleak on imaging and remains a controversial entity that may represent an occult type II or pressure transmission through thrombus.

Surveillance Protocol

Standard surveillance involves CTA at 1 month, 6 months, 12 months, and then annually. If the graft is stable with no endoleak at one year, some centers transition to duplex ultrasound surveillance to reduce radiation and contrast exposure. Sac enlargement greater than 5 mm on any follow-up study warrants investigation for endoleak. Lifelong surveillance is mandatory, and this is a key distinction from open surgical repair.

Key Trials

EVAR-1 (2004, long-term follow-up)

This trial compared EVAR with open repair for AAA greater than 5.5 cm in fit patients. EVAR demonstrated lower 30-day mortality (1.7% vs. 4.7%), but the survival advantage eroded by 2-3 years and there was no long-term survival benefit. EVAR also had higher reintervention rates.

DREAM Trial (2004)

This trial produced similar findings: EVAR offered lower perioperative mortality with no long-term survival advantage.

OVER Trial (2009)

This VA study confirmed lower perioperative mortality for EVAR with similar long-term outcomes. Notably, patients younger than 70 years had better long-term survival with open repair.

Implications

EVAR is the preferred approach for patients at high surgical risk. Open repair may be preferred for young, fit patients because it avoids the lifelong surveillance burden and carries lower reintervention rates.

<image>Illustration of a standard bifurcated EVAR graft deployed within an infrarenal abdominal aortic aneurysm. The image shows an anteroposterior view of the abdominal aorta with the aneurysm sac in gray, the EVAR graft with suprarenal bare stent fixation, the main body fabric below the renal arteries, and bifurcated limbs extending into the common iliac arteries. The renal arteries, SMA, and IMA origin (covered by the graft) are labeled. An inset magnifies the proximal seal zone showing at least 15 mm of healthy infrarenal neck with the graft fabric apposed to the aortic wall.</image>

<image>Diagram of the five types of endoleak after EVAR. Five panels: Type I shows high-pressure leak at the proximal (Ia) or distal (Ib) attachment site with arrows indicating flow direction; Type II shows retrograde flow from a lumbar artery and the IMA filling the aneurysm sac; Type III shows a defect in the graft fabric or disconnection between modular components; Type IV shows diffuse blush through the graft porosity; Type V shows sac expansion without visible contrast leak. Each panel is color-coded by clinical significance (red for requires treatment, yellow for observe, green for self-limited).</image>

<image>Comparison of the proximal landing zone anatomy for EVAR suitability. Three illustrations: (1) Favorable anatomy with a long (>15 mm) parallel infrarenal neck with minimal angulation, labeled as suitable for standard EVAR; (2) Hostile neck with short neck (<10 mm), severe angulation (>60 degrees), and circumferential thrombus, labeled as high risk for type Ia endoleak; (3) Juxtarenal aneurysm with no infrarenal neck, labeled as requiring fenestrated EVAR. Key measurements (neck length, neck diameter, angulation angle) are annotated on each illustration.</image>

Clinical Pearls

EVAR trades lower perioperative mortality for lifelong surveillance and higher reintervention rates compared with open repair. Type I and III endoleaks are high-pressure leaks that must be treated immediately because they negate the protective effect of the graft. Type II endoleaks are the most common type and are usually benign, warranting intervention only when the aneurysm sac is growing. Patient anatomy determines EVAR suitability, with neck length, angulation, and access vessels being the critical factors. Percutaneous EVAR using the preclose technique is increasingly standard and reduces wound complications compared with femoral cutdown. Young, fit patients may be better served by open repair to avoid lifelong surveillance and reintervention. EVAR is not a cure; it is lifelong disease management.

References

• EVAR Trial Participants. Endovascular versus open repair of abdominal aortic aneurysm (EVAR Trial 1). N Engl J Med 2010
• Lederle FA et al. Open versus endovascular repair of abdominal aortic aneurysm (OVER trial). N Engl J Med 2009
• Defined by the SVS Practice Guidelines on Abdominal Aortic Aneurysm. J Vasc Surg 2018
• Defined by the ESVS Clinical Practice Guidelines on AAA Management 2024
• Defined by the Defined by the SIR/SVS Reporting Standards for Endovascular Aortic Repair

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