Endovascular treatment with flow diverters may fail to occlude experimental bifurcation aneurysms

Animal models may explain how stents and flow diverters (FDs) may succeed or fail to treat bifurcation aneurysms.

In vitro studies were designed to anticipate device deformations in bifurcations. Large, wide-necked bifurcation aneurysms were constructed in 21 animals and treated 4-8 weeks later using stents and FDs in various combinations, forming four main groups: parent artery to right branch flow diversion (RBFD, n = 6), parent artery to left branch flow diversion (LBFD, n = 6), Y flow diversion (YFD, n = 4), and compared with high-porosity Y-stenting (YHPS, n = 4). The results include immediate and follow-up angiography at 3 months, followed by grading of the extent of neointimal coverage of devices at pathology.

In vitro, all braided devices showed varying porosities according to characteristic zones. FDs can be compacted to decrease porosities, but a limiting factor is the constant presence of a more porous transition zone. In vivo, 3/6 RBFD, 4/6 LBFD, and 2/4 YFD treated aneurysms had decreased in size by 3 months, while those treated with YHPS increased in size (P = 0.15). There was a significant correlation between device porosities and extent of neointimal coverage (r = 0.639, P = 0.002), and between porosities and angiographic evolution (r = -0.655, P = 0.002), but not between neointima formation and angiographic evolution (r = -0.278, P = 0.235). Failures could be explained in all cases by the presence of leaks or holes in the neointima at the level of the transition zones.

FDs did not successfully treat most bifurcation aneurysms, at least in this animal model.