Classical options to address visceral target vessels in endovascular repair of complex abdominal (AAA) and thoracoabdominal (TAAA) aortic aneurysms with customized grafts (F/BEVAR), include fenestrations (holes in the stent-graft) and directional side-branches.1 Fenestrations are preferred for target vessels that have a close to 90-degree take-off from the aorta, and when the main stent-graft at the level of the target vessel is adjacent to the wall or with only a short gap to bridge. Exact positioning of the main stent-graft with alignment of the fenestration to the target vessel is mandatory and needs to be achieved by repositioning of the stent-graft, and catheterization can be tedious. Directional side branches are preferred when target vessels have a steep downward take-off angle and/or when there is a larger gap to be bridged, which is often the case in extensive TAAA. Other advantages of directional side-branches include a better seal and fixation for the bridging covered stent, and a less critical positioning of the branch with regard to the target vessel.
Inner branches were introduced more recently as an option to address visceral arteries that were regarded as “unsuitable” for either fenestrations or standard directional branches. Inner branches have a cylindrical part inside the main graft, and a fish mouth-like external opening. In the Cook device, this fish mouth opening is fixed to the Z-Stent of the graft. Whenever possible, inner branches are fitted with an indwelling wire (Fig. 1).
Potential advantages of inner branches compared to “standard” branches include a lower risk of squashing in angulated and narrow aortic anatomies, the option to keep the main graft wide to combine them with fenestrations, and the ability to start lower in the thoracic aorta to reduce aortic coverage length. Potential disadvantages include a more vertical path within the main aortic graft that may lead to a sharper kink of the bridging stent, and some limitations in positioning since they have to fit inside the Z-stent of the Cook graft.
Inner branches can provide an extra option for target vessels that present with a steep downward take-off in a narrow aortic lumen where there is not enough room to plan using standard branches. Inner branches can be also an option in narrow and angulated anatomies, particularly for the renal arteries, where exact planning and orientation of a fenestration can be tedious due to the angulation. A combination of inner branches for the renal arteries with two fenestrations for the SMA and the celiac artery is a useful option to consider in particular anatomies. This configuration provides the advantage of a more “forgiving” solution for the renal arteries compared to fenestrations, along with a short proximal aortic coverage, reducing the risk for spinal cord ischaemia. Another useful configuration consists of three fenestrations for the renal arteries and the SMA and one inner branch for the celiac artery.
Inner branches have also been used in post-dissection thoracoabdominal aortic aneurysms, where the use of standard branches can be associated with more technical difficulties due to the presence of a very narrow true lumen.
Our early experience with inner branches with the Cook Platform for the visceral arteries has shown an excellent technical success rates. Estimated patency at one year was 91.9 ± 4.5% with slightly higher occlusion rates observed at the initial cases compared to standard branches.2 The use of more kink-resistant bridging stents in the later cases of our experience was associated with a significant improvement in patency rates.
In our experience, inner branches are an additional very useful option to address “difficult” target vessels in particular anatomies. A combination with fenestrations rather than a graft with inner branches only seems to be the most commonly used configuration in our practice, and we still try to plan fenestrations whenever possible, given their superiority in terms of patency rates compared to branches. To our opinion, inner branches should not be used in all cases, but one should plan carefully to use inner branches in specific anatomies where fenestrations or standard branches may be more difficult or impossible to plan.
