Intracranial aneurysms, particularly large and giant, fusiform or recurrent 
aneurysms are increasingly treated with flow diverters (FDs), a recently 
introduced and approved neurovascular device. While some rare cases may not be 
treated any other way, in most patients a more conventional, conservative, or 
validated approach such as coiling, parent vessel occlusion, or surgical 
clipping exists. Only a randomized clinical trial can answer the question of 
which treatment option leads to better patient outcomes.We report the design of 
the FIAT study, a clinical care trial aiming to compare angiographic and 
clinical outcomes following treatment with a Flow-Diverter or with the best 
conventional treatment option. The FIAT study will include both a randomized and 
a registry portion. Patients will be proposed randomization to either FD 
stenting or best conventional treatment option (observation, coiling, stenting, 
or clipping) as determined by the treating physician. FIAT will recruit a total 
of 338 patients, to show that i) FD stenting can be performed with an 
'acceptable' immediate complication rate of less than 15% morbidity and 
mortality (defined as mRS > 2); ii) FD stenting can increase from 75 to 90% the 
proportion of patients with a "good outcome", defined as complete or 
near-complete occlusion of the aneurysm AND a good clinical outcome (mRS ≥ 2) at 
one year, as compared to the best conventional option. The FIAT study provides a 
scientific and ethical context to care for patients eligible for flow-diversion 
therapy.