Type Iv Thoracoabdominal aneurysms : What ’ s next ?

T he classic anatomic definition of a Crawford type IV thoracoabdominal aortic aneurysm (TAAA) is that of aneurysms extending from the 12th intercostal space to the iliac bifurcation involving the visceral aortic segment and the origins of the renal, superior mesenteric, and celiac arteries.1 In the endovascular era, however, some investigators have moved away from this strict anatomic criteria and instead use a functional one that considers the required extent of aorta covered by the endograft when repairing the aneurysm.2 For example, a suprarenal aneurysm (by anatomic criteria) that is repaired endovascularly and requires branch stents to all four visceral vessels and aortic coverage to the supraceliac aorta would be considered functionally a type IV repair by some experts in the field.2,3 Traditionally, type IV TAAAs have been treated with open surgery. However, with the introduction and evolution of endovascular aneurysm repair, several treatment alternatives using endovascular therapy alone or in combination with open surgery have been developed to repair these complex aneurysms. These treatment modalities are evolving, new techniques and devices are continuously being introduced, and old ones are being updated and improved upon. The general trend is toward a less invasive approach, which improves patient outcomes, recovery time, and quality of life. In this article, we discuss the current options for treating type IV TAAAs and focus on what the future holds for these complex aneurysms. PARALLEL ENDOGRAFT ENDOVASCULAR REPAIR The Snorkel/Chimney/Sandwich Technique In 2011, Kolvenbach et al4 reported their multi-institutional experience of nine thoracoabdominal aneurysms repaired with the “sandwich technique.” Three of these TAAAs were type IV. Because endovascular techniques have become routine in the daily practice of vascular surgeons and interventionists, many feel confident using these techniques as a quick bailout procedure in urgent or emergent situations in high-risk patients whose lives may be at risk and are unfit for surgery. While this treatment option is technically feasible, there are no reported data on midor long-term results, making its use in the elective setting questionable. It must also be emphasized that there is a large difference in complexity of repair between juxtarenal aneurysms and TAAAs, and that a parallel graft repair of a type IV TAAA may require placement of covered stents into all four visceral vessels. The issue of endoleaks associated with these parallel grafts, as well as the durability of the branches, remains unresolved, and their midand long-term outcomes are unknown.