Endovascular Repair of Juxtarenal (Chimney), Infrarenal, and Iliac Artery Aneurysms

Patient Selection

The introduction of EVAR as a lesser invasive alternative to open aortic aneurysm repair has not changed the indications for repair. Repair is undertaken when AAAs reach 5 to 5.5 cm in diameter; however, certain anatomic criteria need to be met for successful EVAR to occur. The most important area of interest is the proximal aortic neck. A cylindrical neck of at least 15 mm in length measured from the renal arteries, with a diameter of 33 mm or less is preferred. In addition, the neck should be relatively free of thrombus and calcification because these interfere with apposition of the stent-graft against the aortic luminal surface. Neck angulation, defined as the angle between the infrarenal aorta and the neck of the aneurysm, of greater than 60 degrees can also interfere with the ability to achieve a proximal seal. The distal landing zone has several elements that require evaluation. The aortic bifurcation should be large enough to accommodate both limbs of the bifurcated stent-graft, preferably greater than 22 mm in diameter. The maximal iliac artery diameter must be at least 2 mm smaller than the largest limb size available. Several manufacturers produce iliac limbs with flared diameters, allowing for preservation of the internal iliac artery, and this is referred to as the bell-bottom technique. If the common iliac artery is short or aneurysmal and external iliac artery landing is required, internal iliac artery embolization is performed to prevent an endoleak. Typically, unilateral hypogastric artery occlusion is well tolerated. If a patient has bilateral common iliac artery aneurysms, repair should be staged to avoid complications with pelvic ischemia. In practice, discussions with patients about potential hip and buttock claudication, as well as erectile dysfunction, should be undertaken preoperatively. Access for delivery of the device is another important consideration. The diameter of the femoral and iliac vessels must be of sufficient size for traversal of the sheath delivery system. Preoperative assessment of the patient's imaging, as well as careful consideration of the device manufacturer's specifications in regard to outer diameter of the delivery system, will allow the formulation of an access strategy. Alternatively, iliac conduits and retroperitoneal approaches have expanded the application of EVAR beyond traditional femoral approaches; that is, iliac artery tortuosity should be routinely assessed because severe degrees may necessitate adjunctive maneuvers such as brachiofemoral access techniques to straighten and “rail” the system. The ability to navigate difficult anatomy has been greatly improved by modern stiff wires. Any patient whose intestinal circulation is based on the inferior mesenteric artery (in the instance of celiac and superior mesenteric artery [SMA] occlusions) should also not undergo EVAR. Patients who have accessory renal arteries are not routinely disqualified from EVAR consideration, unless their coverage would likely affect renal function. In patients who have diabetes mellitus and an elevation of their baseline creatinine, covering even small accessory renals may result in deterioration of renal function. Patients who are reluctant to undergo the surveillance protocol should not be considered for EVAR, because the need for secondary intervention following EVAR is not insignificant.

Endovascular Treatment of Juxtarenal Aortic Aneurysms

Juxtarenal refers to AAAs extending up to the renal arteries with an infrarenal neck less than or equal to 1 cm in length. Pararenal is sometimes used interchangeably with juxtarenal and refers to AAAs that involve the origins of the renal arteries. In contrast, suprarenal AAAs extend above the renal arteries, and paravisceral aneurysms involve the SMA and/or the celiac artery. Although these aneurysms historically required an open approach, the drive of industry and technology, as well as a comorbid patient population, have motivated the expansion and use of endovascular approaches for repair. This chapter discusses treatment of juxtarenal and pararenal aneurysms using off-the-shelf components to extend the seal zone, with so-called “chimney” or “snorkel” stents. Fenestrated grafts also offer a “totally endovascular” solution, but require time (weeks) to manufacture. Branched grafts are only available to patients enrolled in a clinical trial, or as part of investigational device exemption, and take 6 to 8 weeks to manufacture, provided the patient meets protocol-defined anatomic and clinical constraints. The latter endografts are discussed in a separate chapter.

Renal artery stenting via the encroachment or snorkel (or chimney) technique allows preservation of renal blood flow when treating juxtarenal aneurysms with traditional infrarenal stent-grafts. This chapter outlines these endovascular approaches to treating juxtarenal aneurysms.

Setting

Endovascular AAA repair can be done in a hybrid operating room with fixed C-arm positioning, in an operating room using a portable C-arm, or in an interventional or cardiac catheterization suite. EVAR has been described with regional block, local anesthesia, and general anesthesia. Although traditionally performed through either one or two femoral artery cutdowns, the advent of smaller delivery systems have allowed percutaneous technique to be increasingly employed, decreasing the morbidity of the procedure even further.

Although EVAR is being performed increasingly using a percutaneous technique, having immediate access to an open vascular set is paramount and at times lifesaving, should intraoperative issues arise, and where open conversion is required. General anesthetic is also preferred when attendant open adjunctive procedures such as femoral-femoral artery bypass grafting, iliac conduit, or local femoral endarterectomy is planned. Because EVAR is being performed increasingly in much older comorbid patients with less than ideal anatomy, the need for sophisticated operative imaging to optimize precision deployment, as well as a surgical preparedness for potentially catastrophic access issues, underscores the importance of the operating room or hybrid suite in performing these procedures. The outcomes of EVAR for ruptured AAA have also been favorable, particularly in institutions where a systematic algorithm ensures that the appropriate endovascular team is alerted when a ruptured aneurysm is identified in the emergency room. It is clear that, in this subset of patients, having the ability to convert from an endovascular to an open approach should the patient rapidly deteriorate, is an important consideration. Of paramount importance to the success of every aortic endovascular program is identifying and training a dedicated endovascular team of nurses, operating room scrub technicians, and radiology technologists.

Endovascular Stent-Graft Planning and Placement for Infrarenal Aortic Aneurysms

Axial imaging is obtained via computed tomography (CT) angiography or magnetic resonance angiography provided that the patient does not have renal insufficiency. Three-dimensional reconstructions performed by Terra Recon (Foster City, CA), Vitrea (Vital Images), Leonardo (Siemens), or M2S (Lebanon, NH) have become the standard and are used to measure the distance from the lowest renal artery to the aortic bifurcation, the lowest renal artery to the ipsilateral hypogastric artery, and the lowest renal artery to the contralateral hypogastric artery ( Figs. 42.1 and 42.2 ). Diameter measurements of the neck and of the common iliac arteries are then performed. It is important at this time to note the extent of neck angulation and rotation of the juxtarenal aorta to optimize accurate endograft deployment. Broeders and Blankensteijn describe a simple technique to optimize imaging prior to endograft deployment. The juxtarenal aorta should be visualized in the sagittal plane to measure the degree of craniocaudad angulation ( Fig. 42.3 ). The axial sections are then used to measure the degree of aortic neck rotation ( Fig. 42.4 ). These angle calculations should be noted to ensure that the C-arm is orthogonal to the takeoff of the lowest renal artery. The tortuosity of the vessels, the degree of calcification, and any thrombus is also noted. Circumferential thrombus or calcification will prevent complete apposition of the stent-graft to the aortic wall and thus compromise the ability to achieve a proximal seal. Using 10% to 20% proximal graft oversizing, the stent-graft devices are housed in relatively large sheaths that require bilateral groin incisions and femoral artery repair or percutaneous access that is closed with vascular closure devices. After introduction of the delivery system over a stiff wire to the juxtarenal aorta, an aortogram is performed, and under “roadmap” guidance, the main body of the stent-graft is positioned and deployed just under the lowest renal artery. With modular bifurcated grafts, care is taken to insert and deploy the main body of the graft with the contralateral gate deployed in an anterolateral position, which is optimal for subsequent retrograde cannulation. Once the contralateral gate is deployed, it is cannulated, and efforts are made to ensure that the catheter is indeed within the stent-graft and not behind the graft in the aneurysm sac. When deploying devices with separate suprarenal fixation, a magnified aortogram is performed at this time to confirm the location and position of the renal arteries. Cranial obliquity is usually required to ensure that the origin of the lowest renal artery is seen in an orthogonal orientation. Once the suprarenal stent is deployed, the stiff wire is placed up the contralateral limb and a pelvic arteriogram with the C-arm at an oblique angle of 15 to 20 degrees to the other side is performed to demonstrate the origin of the contralateral hypogastric artery. The contralateral iliac limb is then deployed taking care to preserve flow to the internal iliac artery. The remainder of the main body or ipsilateral limb is deployed. In an obligate three-piece system, another pelvic arteriogram is performed in the opposite obliquity to demonstrate the takeoff of the ipsilateral internal iliac artery. The junctions are ballooned, and stiff wires are removed before the completion of arteriography to ensure that limb kinking is not a concern. Graft limb kinking is of particular concern in individuals with external iliac landing because of concomitant iliac artery aneurysms or small iliac artery diameters. Any type I or III endoleaks should be addressed in the operating room. Type I endoleaks can be addressed with proximal extensions, large-diameter bare stents, or simple ballooning. Type III endoleaks can be addressed with bridging pieces or repeated ballooning. Type II endoleaks can be observed, as the majority of them resolve with conservative management within 6 to 12 months. Completion arteriography should demonstrate both renal and hypogastric artery patency and good flow down both iliac limbs. In the setting of small calcified aortic bifurcations (<20 mm diameter), adjunctive bilateral kissing balloon angioplasty should be a consideration.

Endovascular Repair of Common and Internal Iliac Artery Aneurysms

The relationship between aneurysm diameter and rupture risk is not as well delineated for iliac aneurysms as it is for the abdominal aorta. However, it is generally agreed that repair should be undertaken when the diameter reaches 3.0 to 4.0 cm in size.