title: Computational fluid dynamics analysis of flow reduction induced by flow-diverting stents in intracranial aneurysms: a patient-unspecific hemodynamics change perspective.
abstract: OBJECTIVE
  Flow-diverter stents (FDSs) have been used effectively to treat large neck and complex saccular aneurysms on the anterior carotid circulation. Intra-aneurysmal flow reduction induces progressive aneurysm thrombosis in most patients. Understanding the degree of flow modification necessary to induce complete aneurysm occlusion among patients with considerable hemodynamics variability may be important for treatment planning.
  
  
  METHODS
  Patients with incidental intracranial saccular aneurysms who underwent FDS endovascular procedures were included and studied for a 12 months' follow-up period. We used computational fluid dynamics on patient-specific geometries from 3D rotational angiography without and with virtual stent placement and thus compared intra-aneurysmal hemodynamic problems. Receiver operating characteristic analysis was used to estimate the stent:no-stent minimum hemodynamic ratio thresholds that significantly (p≤0.05) determined the condition necessary for long-term (12 months) aneurysm occlusion.
  
  
  RESULTS
  We included 12 consecutive patients with sidewall aneurysms located in the internal carotid or vertebral artery. The measured porosity of the 12 deployed virtual FDSs was 83±3% (mean±SD). Nine aneurysms were occluded during the 12 months' follow-up, whereas three were not. A significant (p=0.05) area under the curve (AUC) was found for spatiotemporal mean velocity reduction in the aneurysms: AUC=0.889±0.113 (mean±SD) corresponding to a minimum velocity reduction threshold of 0.353 for occlusion to occur. The 95% CI of the AUC was 0.66 to 1.00. The sensitivity and specificity of the method were ∼99% and ∼67%, respectively. For both wall shear stress and pressure reductions in aneurysms no thresholds could be determined: AUC=0.63±0.16 (p=0.518) and 0.67±0.165 (p=0.405), respectively.
  
  
  CONCLUSIONS
  For successful FDS treatment the post-stent average velocity in sidewall intracranial aneurysms must be reduced by at least one-third from the initial pre-stent conditions.
authors.affiliation: Interventional Neuroradiology Unit, Service of Neuroradiology, University of Geneva Hospitals and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Rafik
authors.initials: R
authors.lastname: Ouared
authors.affiliation: PLADEMA-CONICET, Universidad Nacional del Centro de la Provincia de Buenos Aires, Tandil, Argentina.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Larrabide
authors.affiliation: Interventional Neuroradiology Unit, Service of Neuroradiology, University of Geneva Hospitals and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Olivier
authors.initials: O
authors.lastname: Brina
authors.affiliation: Interventional Neuroradiology Unit, Service of Neuroradiology, University of Geneva Hospitals and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Pierre
authors.initials: P
authors.lastname: Bouillot
authors.affiliation: Interventional Neuroradiology Unit, Service of Neuroradiology, University of Geneva Hospitals and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Gorislav
authors.initials: G
authors.lastname: Erceg
authors.affiliation: Interventional Neuroradiology Unit, Service of Neuroradiology, University of Geneva Hospitals and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Hasan
authors.initials: H
authors.lastname: Yilmaz
authors.affiliation: Interventional Neuroradiology Unit, Service of Neuroradiology, University of Geneva Hospitals and Faculty of Medicine, Geneva, Switzerland.
authors.forename: Karl-Olof
authors.initials: KO
authors.lastname: Lovblad
authors.affiliation: Interventional Neuroradiology Unit, Service of Neuroradiology, University of Geneva Hospitals and Faculty of Medicine, Geneva, Switzerland.|Division of Neuroradiology, Joint Department of Medical Imaging, University Health Network, University of Toronto, Toronto, Ontario, Canada.|Division of Neurosurgery, Department of Surgery, University Health Network, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Vitor
authors.initials: V
authors.lastname: Mendes Pereira
keywords: Aneurysm; Blood Flow; Flow Diverter; Stent