Abstract
In this issue, Bertoni et al. 1 describe the use of a modular, balloon-expandable, branched aortomonoiliac device to treat an asymptomatic infrarenal aortic aneurysm in a patient with a solitary left kidney. The kidney received its blood supply from a renal artery arising from the aneurysm sac, as well as an accessory vessel arising from the right common iliac artery. These factors precluded endovascular repair with a standard infrarenal bifurcated device.
Endovascular treatment options for complex aortic aneurysm morphologies have evolved rapidly over the last decade to the point that there are now very few situations in which an endovascular option does not exist. The endovascular treatment of infrarenal aneurysms is well established, and there is now good medium-term data supporting the use of fenestrated devices for juxtarenal aneurysms.2–6 The treatment of thoracoabdominal aneurysms with combined branched and fenestrated devices is currently under evaluation in a growing number of centers worldwide, and short-term follow-up data compare favorably with the results for open repair.7–11 The evolution of the custom-designed devices used in the treatment of these aneurysms has also been rapid to the point where “off-the-shelf” branched devices for the treatment of iliac aneurysms are already available,12–14 and similar “off-the-shelf” multi-branched devices for use in thoracoabdominal aneurysms are in development. 15
To date, most branch devices studied have been of modular design and utilize self-expanding or balloon-expandable stent-grafts to bridge the gap between the endograft's branch and the target vessel. Proximal fixation is largely dependent on the radial forces exerted by the self-expanding metal struts of the main endograft at the level of the proximal sealing zone and on the barbs attached to them. Columnar forces of the bridging stent-grafts contribute to device fixation to a lesser degree. Distal displacement forces exerted on every bifurcated component are significant, largely due to the hydrostatic forces exerted on branch points where cross-sectional area decreases. An adequate seal between the various components, which is dependent mainly on radial force, is achieved by slight oversizing and by planning a long area of overlap between the components.
The use of an aortomonoiliac device by Bertoni and colleagues 1 may be of benefit in minimizing the distal displacement forces to which the device is subjected, although it mandated the use of a femoral-femoral crossover graft to perfuse the contralateral lower limb as well as the occlusion of the contralateral common iliac artery by coil embolization. It is also worth mentioning that most centers now use endografts with a metallic frame made of self-expanding stents for the treatment of such aneurysms, generally with good outcomes in terms of device integrity.16, 17 Some concerns do exist regarding the use of balloon-expandable stents as relates to stent fractures. 18
Generally speaking, it is considered desirable to have a sealing zone of at least 10 mm (and ideally up to 20 mm) in the target vessel in order to achieve an adequate seal between it and the bridging stent-graft. Most authorities on branched device technology recommend the placement of an appropriately sized bridging stent such that it overlaps with the full length of the endograft's branch while also achieving an appropriate sealing length in the target vessel. However, despite the use of a relatively short bridging stent (6×19 mm), the authors of this case report appear to have had a good result at 18-month follow-up.
The optimal follow-up modality and interval has yet to be determined with certainty for these investigational devices. Re-intervention rates in the literature to date have generally been low, but importantly there are many reports detailing “rescue” of compromised visceral vessels before they occlude, often when detected as deformities of the bridging stents on plain radiography or by increased velocities on Doppler assessment rather than on computed tomography. 19 Despite legitimate concerns for the renal function of the patient in this report, it would seem that more frequent imaging of the experimental device implanted would be appropriate, if necessary utilizing modalities that are not nephrotoxic. Nonetheless, it is gratifying to note that the imaging at 18 months demonstrated a well perfused left kidney and did not demonstrate any problems with the graft or its branch. Given that these devices are still investigational, it is important that frequent follow-up data are recorded and published until such time as the volume of the published data can inform us as to the optimal follow-up interval and modality.
In summary, it is clear that the endovascular treatment options for complex aneurysmal disease of the aorta are evolving rapidly. Technologies allowing us to maintain perfusion of vital aortic branches now are at an advanced stage of evolution but currently lack long-term follow-up data to support their routine use. In this context, it is important that authors such as Bertoni and his colleagues continue to publish their experiences of these evolving technologies in order to delineate for us their true value in the treatment of complex aortic aneurysm disease.