There is an urgent need to offer the new tool afforded by FDs to patients currently presenting with a difficult aneurysm, in a context that can offer protection from over-optimistic perspectives, fashion, learning curves and marketing. Only a randomized clinical trial can offer such protection as well as provide an answer to the question of which treatment option leads to better patient outcomes. The primary hypothesis is that flow diversion can be performed with an "acceptable" immediate complication rate, defined as less than 15% morbidity and mortality (modified Rankin Score > 2 at 3 months), AND increase the number of patients experiencing successful therapy, defined as complete or near complete occlusion of the aneurysm from 75 to 90%.