Residency · Residency · Vascular Surgery
Complex Endovascular Aortic Repair: Fenestrated and Branched Endografts
Introduction
Standard endovascular aneurysm repair (EVAR) depends on having an adequate infrarenal aortic neck to achieve a secure proximal seal. However, about 40% of patients with abdominal aortic aneurysms present with anatomy that is unsuitable for standard EVAR because their infrarenal necks are too short, angulated, or absent. Fenestrated and branched endografts (FEVAR and BEVAR) have been developed to extend the proximal seal zone into the visceral and suprarenal aorta. This advancement allows endovascular treatment of more complex aneurysms, including juxtarenal, pararenal, paravisceral, and thoracoabdominal aortic aneurysms.
Anatomy and Terminology
Aneurysm Classification by Proximal Extent
Aneurysms are classified based on their proximal extent relative to the renal arteries. Infrarenal abdominal aortic aneurysms (AAA) have a neck length of 15 mm or greater below the lowest renal artery, making them suitable for standard EVAR. Juxtarenal AAAs have a neck immediately below the renal arteries, measuring less than 15 mm, which complicates standard repair. Pararenal AAAs extend up to the level of the renal arteries themselves. Paravisceral AAAs involve the segment of the aorta from the renal arteries to the superior mesenteric artery (SMA). Thoracoabdominal aortic aneurysms (TAAA) are classified according to the Crawford system (types I-V), which categorizes them based on the extent of thoracic and abdominal aortic involvement.
Target Vessels
The key visceral branches that must be preserved when extending the proximal seal zone include the celiac artery (CA), superior mesenteric artery (SMA), right renal artery (RRA), and left renal artery (LRA). Maintaining perfusion to these vessels is critical during complex endovascular repairs.
Fenestrated Endografts (FEVAR)
Design Principles
Fenestrated endografts incorporate fenestrations—precisely positioned openings in the graft fabric that align with the ostia of target branch vessels. These fenestrations come in different sizes and configurations. Small fenestrations, typically 6-8 mm in diameter and reinforced with a nitinol ring, are used for renal arteries. Larger fenestrations, measuring 10-12 mm, accommodate the SMA and celiac artery. Scallops are U-shaped cutouts located at the proximal or distal edge of the graft; they allow vessel incorporation without the need for stenting. Each fenestration is bridged individually with a covered stent, which creates a seal between the graft and the target vessel, maintaining blood flow while preventing endoleak.
Planning and Customization
Successful FEVAR requires detailed preoperative planning using thin-slice (less than 1 mm) CT angiography with multiplanar reconstructions. Each device is custom-manufactured based on the patient's unique anatomy, with a typical production time of 6-8 weeks. Critical measurements include the aortic diameter, the clock position of each target vessel, distances between vessels, and the angulation of the aorta. To avoid delays associated with custom manufacturing, off-the-shelf fenestrated devices such as the Cook p-Branch are available for select anatomies.
Implantation Technique
The procedure is performed under general anesthesia with bilateral femoral artery access and often additional brachial artery access. Precise rotational orientation of the graft is essential and is guided by fluoroscopic landmarks and radiopaque markers on the device. After deployment, each target vessel is sequentially cannulated through the corresponding fenestration. Balloon-expandable covered stents are then placed through each fenestration into the target vessel and flared to create a tight seal with the fenestration ring.
| Feature | Fenestrated Endograft (FEVAR) | Branched Endograft (BEVAR) |
|---|---|---|
| Design | Openings (fenestrations) in graft fabric aligned with vessel ostia | Directional cuffs/limbs projecting into target vessels |
| Best suited for | Juxtarenal, pararenal aneurysms; smaller aortic diameter | TAAA; larger aortic diameter; widely spaced branches |
| Target vessel cannulation | Through fenestration (limited working room) | Through branch cuff (more working room) |
| Bridging stent | Balloon-expandable covered stent flared to fenestration ring | Covered stent into branch cuff |
| Customization | Custom-manufactured (6–8 weeks); off-the-shelf options available | Custom-manufactured; limited off-the-shelf |
| 30-day mortality | 2–5% | 5–10% |
| 5-year target vessel patency | 85–95% | 85–95% |
Branched Endografts (BEVAR)
Design Principles
Branched endografts feature cuffs or directional limbs that project from the main graft body into the target vessels. These branches provide greater working room for catheterization of target vessels compared to fenestrations and are better suited for aneurysms with larger aortic diameters and widely spaced branch vessels. Branches can be upward-directed (internal), with cuffs oriented cranially and bridged with covered stents, or downward-directed (external), with cuffs oriented caudally and accessed retrograde from brachial artery access. Helical branches have a spiral configuration that accommodates variable vessel positions.
TAAA Applications
BEVAR facilitates fully endovascular treatment of Crawford extent I-IV thoracoabdominal aneurysms. To reduce the risk of spinal cord ischemia, multiple staged procedures may be necessary. BEVAR is often combined with thoracic stent grafts to achieve complete aortic coverage in these extensive aneurysms.
Complications
Target Vessel Related
Complications related to target vessels include target vessel instability, which occurs when there is loss of seal at the fenestration-stent interface, potentially causing a type III endoleak. Branch occlusion due to thrombosis of bridging stents is reported in 3-8% of renal branches. Target vessel stenosis can result from kinking or compression of bridging stents.
Endoleak
Endoleaks are classified by type. Type I endoleaks result from inadequate proximal or distal seal and require intervention. Type II endoleaks arise from branch vessel back-bleeding, such as lumbar arteries or the inferior mesenteric artery, and are usually benign. Type III endoleaks occur due to fabric tears or component disconnections and necessitate treatment. A unique complication of fenestrated repair is gutter leak, which occurs when there is flow between the bridging stent and the fenestration ring.
Spinal Cord Ischemia
The risk of spinal cord ischemia increases with the extent of aortic coverage and the number of intercostal arteries sacrificed. The incidence is approximately 5-10% for extent II TAAA repairs. Prevention strategies include staged procedures, cerebrospinal fluid (CSF) drainage, permissive hypertension with mean arterial pressure (MAP) greater than 80 mmHg, and maintenance of pelvic perfusion by preserving at least one internal iliac artery. Perioperative management of spinal drains aims to keep CSF pressure below 10 mmHg.
Renal Complications
Renal complications include contrast-induced nephropathy due to the high volumes of contrast used during these procedures. Occlusion of renal artery branches may lead to renal infarction. Perioperative acute kidney injury occurs in 10-20% of cases.
Outcomes
Technical success rates for FEVAR and BEVAR range from 90-97% in experienced centers. Thirty-day mortality is 2-5% for FEVAR in juxtarenal and pararenal aneurysms and 5-10% for BEVAR in thoracoabdominal aneurysms. Target vessel patency at five years is 85-95% overall, with renal branches demonstrating lower patency than mesenteric branches. Freedom from reintervention is 70-80% at five years. These outcomes are strongly influenced by center volume and operator experience.
Surveillance
Postoperative surveillance includes CT angiography at 1 month, 6 months, and annually thereafter. Duplex ultrasound of target vessels is performed between CT scans to monitor for endoleak, branch vessel patency, aneurysm sac behavior, and stent-graft migration. Renal function is assessed at each follow-up visit by measuring creatinine and glomerular filtration rate (GFR).
Key Clinical Pearls
Fenestrated and branched endografts have significantly expanded the scope of endovascular repair to include complex aortic aneurysms that previously required open surgery. The most critical factor for successful FEVAR and BEVAR is meticulous preoperative planning using thin-slice CT angiography. Preventing spinal cord ischemia demands a multimodal approach that includes staged procedures, CSF drainage, hemodynamic optimization, and preservation of pelvic perfusion. These complex procedures should be performed in high-volume centers with dedicated teams experienced in advanced endovascular techniques. Lifelong imaging surveillance is essential to detect complications such as endoleak, branch occlusion, and aneurysm sac growth.
References
- Defined, Defined, et al. "Fenestrated and branched endovascular aortic repair for complex aortic aneurysms." J Vasc Surg. 2017;66(6):1587-1597.
- Defined, Defined, et al. "Outcomes of fenestrated EVAR for juxtarenal aneurysms." J Vasc Surg. 2018;68(3):683-694.
- Defined, Defined, et al. "Spinal cord ischemia after complex endovascular aortic repair." J Vasc Surg. 2019;70(5):1665-1675.
- Defined, Defined, et al. "Branched endografts for thoracoabdominal aortic aneurysms: current evidence." Eur J Vasc Endovasc Surg. 2020;59(2):197-209.