Flow diverters are a recent addition to the range of endovascular devices now available for the treatment of intracranial aneurysms. The FIAT trial aims at comparing flow diversion to best standard treatment in the context of a randomised controlled trial. Best standard treatment may include any of the following and will be left to the treating physician to decide : 1) conservative management; 2) coiling with or without high porosity stenting; 3) parent vessel occlusion with or without bypass; 4) surgical clipping. If the only treatment alternative is deemed to be flow diversion for compassionate use, then randomisation will not be carried out, but patient will enter a registry and her data recorded according to same schedule as randomised patients.