Fenestrated Stent-Grafting of Juxtarenal Aortic Aneurysms



Fenestrated Stent-Grafting of Juxtarenal Aortic Aneurysms


Mohamad Hamady



Introduction


Continuous developments in endovascular treatment of abdominal and thoracic aortic aneurysm, together with growing experience and encouraging results, have paved the way for emergence of a new generation of stent-grafts that allow extension of the proximal landing zone and preservation of renal and visceral arteries.


Since the first report of fenestrated endovascular repair of aortic aneurysms (FEVAR) by Park et al. in 1996,1 several large published series and multicenter studies have demonstrated high technical success and promising short- and midterm results. But FEVAR also represents unique challenges to the endovascular interventionalist. These include appropriate patient selection, accurate endograft planning, and demanding technical skills.



Indications and Anatomic Suitability


Clinical indications for FEVAR include aneurysm diameter of 5.5 cm or more, rapidly enlarging aneurysm at a rate of 5 mm over 6 months or 1 cm over 1 year, aneurysm neck 15 mm or less, and patients deemed unfit for open surgery. High-risk patients for major vascular surgery include patients with significant pulmonary disease, poor renal function, severe coronary or heart valve disease, and hostile abdomen.2


Ideal anatomy for FEVAR includes aortic diameter of 20 to 32 mm at the level of the renal arteries, neck angulation of less than 45 degrees, iliac artery diameter of 7 mm or more, and iliac angulation of 85 degrees or less. The renal arteries should be 4 mm or larger to avoid stent thrombosis. Renal artery or superior mesenteric artery (SMA) ostial stenosis should be handled with great care and is considered an adverse anatomic feature.



Contraindications


There is no absolute contraindication, but the presence of an adverse anatomic feature could make the procedure difficult and increase procedural comorbidity. If there are three or more adverse anatomic features, the procedure could be extremely difficult or impossible.3 Symptomatic or ruptured aneurysm is not suitable for this technology because stent-graft manufacture can take at least 6 weeks. Recent development of off-the-shelf devices may enable their use for symptomatic aneurysms, but it is hard to envisage that ruptured aneurysm would be suitable.4



Devices


The first commercially available fenestrated stent-graft is the Cook device. It is a composite system that consists of a proximal custom-made component, a bifurcated component, and two iliac limbs. The system is based on the original Zenith platform (Cook Medical, Bloomington, Ind.), which is made of woven polyester fabric sutured to stainless-steel Gianturco stents.


The proximal component contains two or three fenestrations and a scallop (Fig. 48-1). Rarely, there are four fenestrations. There are two types of fenestrations, small and large. The small fenestration is 6 mm in width and 6 or 8 mm in height. It is reinforced with a nitinol ring and should be 15 mm or more from the proximal edge of the fabric. The large fenestration is 8 to 12 mm in diameter and should be 10 mm or more from the edge of the graft. The scallop is 6 to 12 mm in depth and 10 mm wide. It is also reinforced with a nitinol ring and has gold radiopaque markers. The bare spring (which contains fixation barbs) is located within the top cap. This, together with one or two posterior diameter reducing ties, assists device orientation until final deployment.



The small fenestrations and scallop have no struts across them. The small fenestrations are intended to be stented. This stenting serves two goals: migration resistance and sealing. The large fenestration can have struts crossing the fenestration.


The proximal fenestrated component has some important radiopaque markers: an anterior check mark, three anterior vertical markers, and three posterior horizontal markers.


Bare metallic stents or covered stents may be used to bridge the gap between the fenestrations and target branch vessels. The choice of side branch stent depends on the distance of the side vessel from the aneurysm and the presence of mural thrombus. Uncovered balloon-expandable stents may be preferred over covered stents if the distance from the renal artery or the SMA to the aneurysm is 5 mm or more and/or if the mural thrombus is not severe enough to cause poor opposition of the stent to the side wall. The nitinol ring and overdilation of the stent after deployment of the side branch stent using an oversized balloon help seal the renal or SMA stent against the graft wall and resist future migration. However, many operators prefer to use covered stents in all cases.



New Devices


At least two new devices have been introduced recently to overcome certain limitations and shortfalls of the existing commercially available Cook device. Although these devices are awaiting full evaluation through multicenter studies and/or randomized trials, they clearly provide the endovascular community with a wider range of options and take endovascular treatment of challenging aneurysms a step further.



Custom-Made Fenestrated Anaconda Device (Vascutek, Terumo, Japan)


This fenestrated device was developed on the background of the original Anaconda device.5,6 Its proximal end is positioned suprarenally, and this part of the device provides the seal and fixation by means of hooks and rings. The anterior valley is oriented to cradle the SMA and/or celiac trunk. The fenestrations are made in the unsupported part of the fabric, which gives more flexibility to orient the fenestration according to the circumferential orientation of the renal or SMA vessels. The typical device encompasses two renal fenestrations supported by nitinol rings and marked by four radiopaque markers (Fig. 48-2). However, an SMA fenestration can be added to increase the coverage length in shorter landing zones. Our initial experience with this device shows that potential advantages include the ability to (1) accommodate more difficult anatomy and angulation and (2) partially reposition the top device after cannulating one vessel so that the device can be reoriented, and the next fenestration faces the second vessel. The device also gives the operator the option of cannulating the fenestration antegradely prior to full device deployment, since there is no closed top cap. However, the delivery system profile is still relatively large, similar to the Cook fenestrated stent.




Ventana Fenestrated System (Endologix, Irvine, Calif.)


The Ventana endograft is based on the conventional Endologix aortic endograft, which is based on a different concept of fixation and seal. Use of the aortic bifurcation as a point of anatomic fixation for the bifurcation of the graft, and the separate seal achieved through placement of a proximal extension that overlaps with the bifurcation graft, allows two separate benefits. The first benefit is fixation, based upon the aortic bifurcation rather than the proximal diseased aorta. This morphology also maintains the aortic bifurcation should interventions across the bifurcation for occlusive disease be required in the future. The second advantage is resistance to migration of the proximal segment because there is no “baffle” for the aortic flow to push against.


Based upon these concepts, the Ventana fenestrated device uses a proximal fenestrated extension that seals with a bifurcation graft seated at the aortic bifurcation. The initial design of the device was produced with the aim of allowing placement in various individuals without the need for specific individual graft creation or off-the-shelf devices. All fenestrations and the scallop are marked with radiopaque markers to allow for ease of visualization, and the stent-graft can be rotated and oriented appropriately in vivo using a highly torquable low-friction delivery system. The delivery system includes prepositioned sheaths through the fenestrations that allow cannulation of the renal branches with catheters prior to graft deployment. After positioning catheters and wires in the renal arteries, the prepositioned sheaths can be advanced into the renal arteries and the graft positioned with the scallop at the level of the SMA. Deployment of the main body is followed by placement of the covered renal stents to complete the procedure.



Procedure Planning


Planning is one of the most important prerequisites for successful FEVAR. A thorough understanding of the axial anatomy, stent-graft features, and practical knowledge about the behavior of the graft inside the patient are needed.


Full computed tomographic angiography (CTA) of the aorta should be acquired with 1- to 2-mm slice thickness, using a modern 16 or more multidetector CT scanner. The images are reconstructed using a variety of commercially available three-dimensional (3D) software packages. The center-of-flow line is used to straighten the aorta and correct for angulations.


The following is a guide for planning for the Cook device, although the process is not grossly different for other fenestrated devices.

Dec 23, 2015 | Posted by in INTERVENTIONAL RADIOLOGY | Comments Off on Fenestrated Stent-Grafting of Juxtarenal Aortic Aneurysms
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