Historical Background
Juxtarenal aneurysms refer to abdominal aortic aneurysms with an infrarenal neck less than or equal to 1 cm in length, and pararenal aneurysms refer to abdominal aortic aneurysms that involve one or both orifices of the renal arteries. Browne and associates first described the design of a fenestrated graft in 1999 in which holes were placed within an endograft for deployment of uncovered balloon-expandable stents from the aortic graft into the renal arteries. The principle of fenestrated technology was extended above the infrarenal segment by Anderson in 2005 to treat aneurysms involving the visceral arteries. The first report of branched endograft used for the treatment of a thoracoabdominal aneurysm was reported in 2001 by Chuter and colleagues. Branched and fenestrated grafts offer a complete endovascular solution. Fenestrated grafts are now commercially available in the United States. As an alternative to fenestrated and branched endografts, Greenberg and associates were the first to describe a “snorkel” or “chimney graft” technique in 2003, with placement of a stent into the renal artery alongside the endograft to treat a juxtarenal aortic aneurysm. Others have extended this technique to treat pararenal aneurysms during endovascular aneurysm repair (EVAR). Hybrid, or combined open and endovascular, approaches are another option for treatment of complex aortic aneurysms involving visceral vessels and were first reported in 1999 by Quinones-Baldrich and co-workers.
Preoperative Preparation
- •
A detailed analysis is required of axial images and three-dimensional reconstructed images of the aorta using TeraRecon (San Mateo, Calif.) or M2S (West Lebanon, N.H.) devices. The radial orientation of visceral vessels is often related to in terms of the hands of a clock.
- •
The diameter of each vessel and the distance of each vessel origin from the edge of the graft, as well as from each other, are recorded. The endograft is manufactured accordingly.
- •
Preoperative hydration should be considered for patients with compromised renal function.
- •
Spinal catheter drainage is recommended if coverage of a long segment of thoracic aorta is planned in addition to treatment of the visceral segment of the aorta.
- •
Perioperative antibiotics and subcutaneous heparin for prophylaxis of deep venous thrombosis are routinely administered.
Endovascular Strategy
Endovascular repair of the visceral segment of the aorta uses stent-graft exclusion of the aneurysm with preservation of flow to important branch vessels ( 
). Flow to the renal, celiac, and superior mesenteric arteries is preserved with transarterial access. When the branch vessel arises from where the stent graft is attached, a simple hole, or fenestration in the stent graft, is sufficient. When the branch vessel arises from an aneurysmal portion of the aorta, however, flow between the stent-graft component and the branch vessel must be achieved with a branched graft to traverse the distance between the stent and the origin of the vessel.
Fenestrated Grafts
Current fenestrated stent grafts are manufactured by Cook Medical (Bloomington, Ind.). The graft is composed of woven polyester and the stent component is of stainless steel. Radiopaque markers on the front and back of the graft provide reference points for orientation. Fenestrations are categorized into three types: scallops, small fenestrations, and large fenestrations ( Fig. 27-1 ). Scallops are open to the free margin of the graft, small fenestrations occupy the spaces between stent struts, and large fenestrations are crossed by stent struts. The fenestrations are sized and positioned on the stent graft according to the relative positions of the origins of the branch vessels. Because of device constraints, with small fenestrations located between stents, the stent graft cannot be a perfect replica of aortic anatomy. Tortuosity in the path from the femoral artery to the aorta can dramatically shift the geometric relationships between the origins of the branch vessels and their corresponding fenestrations. The more fenestrations in a stent graft, the fewer degrees of freedom allowable with respect to slight adjustments in orientation during deployment. There is some flexibility in the system because of stent-graft oversizing, where the orifice of the fenestration can be forced into the proper position with a guiding catheter. The use of a bridging stent allows patency when this alignment is strained.
Branched Grafts
Unlike fenestrated grafts, branched stent grafts allow a zone of overlap between the main stent graft and the covered stent within the branch vessel, preventing component separation and endoleak. The orientation of the branch component is parallel to the axis of the primary stent graft and aorta, and in most cases, the inner orifice of the branch is cranial to the origin of the target vessel. The relatively indirect route allows more flexibility in cannulation of the branch vessels compared with the fenestrated approach and is the preferred approach when targeting a greater number of branch vessels. Generally, the target vessels are caudally oriented; thus the branches of the stent graft are typically caudally oriented and more easily cannulated through the brachial approach ( Fig. 27-2 , A ). Occasionally, the renal arteries are cranially oriented, dictating a different branch takeoff from the main graft, and are more easily cannulated compared with the femoral approach.
Endovascular Technique
Fenestrated Graft Implantation
Fenestrated grafts consist of a fenestrated main body component, a bifurcated component, and bridging stents. Bilateral common femoral arteries are exposed, and the patient is systemically heparinized. The delivery system of the fenestrated stent graft is inserted, and an aortogram is performed. The stent graft is then positioned and oriented to match each fenestration with the appropriate target vessel. The sheath is withdrawn, and then the stent graft is deployed and repositioned as appropriate.
Wire and catheter traversal through the fenestration into the target vessel is achieved, followed by transgraft bridging sheath insertion into the target vessel. The constraining trigger wire on the upper attachment system is then removed, the delivery system is withdrawn, and the bridging stent is deployed and ballooned to create a flared end. The infrarenal bifurcated stent graft is then inserted and deployed.
Branched Graft Implantation
There are three major components of the branched stent-graft system: a thoracoabdominal component with multiple branches for each visceral artery, an infrarenal aortic component consisting of a main aortic trunk and two iliac limbs, and small stent grafts used to extend each branch of the thoracoabdominal component into the visceral branches of the aorta. After bilateral femoral artery exposure and systemic heparinization, the thoracoabdominal stent-graft delivery system is inserted over a stiff wire and an angiographic catheter is inserted through the contralateral side. An aortogram is performed to locate the celiac artery, and the thoracoabdominal stent graft is positioned with the distal end 1 to 2 cm above the celiac artery orifice. The sheath is withdrawn, and a confirmatory arteriogram is performed before removal of safety wires, releasing both ends of the stent graft. The delivery system is removed. Attention is then directed toward cannulating the graft branches.
Because most branches are caudally oriented, most cannulations are performed from the brachial or axillary artery. Cranial-oriented branches may be cannulated from the femoral approach. Brachial access is achieved with a short 7-Fr sheath. The descending thoracic aorta is catheterized, and a stiff guidewire is inserted. The short sheath is exchanged for a long 10-Fr Flexor sheath. Using a combination of a smaller sheath or guiding catheter and an angled catheter, branches of the stent graft are cannulated, followed by access into the corresponding visceral artery. The guidewire is exchanged for a long Rosen wire, and a sheath or guiding catheter is advanced at least 2 cm into the visceral artery. The catheter is exchanged for the delivery system of the visceral extension. The visceral extension is deployed with 15-mm overlap into the visceral artery, as well as the branch of the stent graft ( Fig. 27-2 , B ). These steps are repeated for all involved visceral arteries.
The infrarenal component is then deployed into the thoracoabdominal component, followed by deployment of the iliac limbs ( Fig. 27-2 , C ). A completion arteriogram is performed; all sheaths, wires, and catheters are removed; and the brachial artery repaired. If cannulation of the branches proves difficult and time consuming, this portion of the procedure may be delayed for hours or days, given that visceral perfusion is maintained through the perigraft space.
Snorkel or Chimney Graft Technique
In some patients the stent graft partially covers the renal artery orifice and adjunctive renal artery stenting is required. In the “encroachment” technique the superior margin of the stent graft is pushed inferiorly by the renal stent. In the snorkel technique a covered stent is deployed parallel to the main stent graft, protruding proximally, like a chimney, to preserve flow to the branch vessel covered by the graft. The snorkel technique provides an alternative to fenestrated stent grafts in urgent cases or to reestablish flow to a branch vessel unintentionally compromised during EVAR ( Fig. 27-3 ). Transbrachial access is critical for the snorkel maneuver.
