Numerical modeling is an effective tool for preoperative planning. The present work is devoted to a retrospective analysis of neurosurgical treatments for the occlusion of cerebral aneurysms using flow-diverters and hemodynamic factors affecting stent endothelization. Several different geometric approaches have been considered for virtual flow-diverters deployment. A comparative analysis of hemodynamic parameters as a result of computational modeling has been carried out basing on the four clinical cases: one successful treatment, one with no occlusion and two with in stent stenosis. For the first time, a quantitative assessment of both: the limiting magnitude of shear stresses that are necessary for the occurrence of in stent stenosis (MaxWSS > 1.23) and for conditions in which endothelialization is insufficiently active and occlusion of the cervical part of the aneurysm does not occur (MaxWSS < 1.68)–has been statistacally proven (p < 0.01).

Abdominal aortic aneurysm is a widespread disease of cardiovascular system. Predicting a moment of its rupture is an important task for modern vascular surgery. At the same time, little attention is paid to the comorbidities, which are often the causes of severe postoperative complications or even death. This work is devoted to a numerical study of the haemodynamics of the model geometry for possible localizations of abdominal aortic aneurysm: on the aortic trunk or on its bifurcation. Both rigid and FSI numerical simulations are considered and compared with the model aortic configuration without aneurysm. It is shown that in the case of localization of the aneurysm on the bifurcation, the pressure in aorta increases upstream. Moreover, only in the case of a special geometry,when the radii of the iliac arteries are equal (r 1 = r 2), and the angle between them is 60 degrees, there is a linear relationship between the pressure in the aorta above the aneurysm and the size of the aneurysm itself: the slope of the straight line is in the interval a ∈ (0.003; 0.857), and the coefficient of determination is R 2 ⩾ 0.75. The area bounded by the curve of the ‘pressure–velocity’ diagram for the values of velocity and pressure upstream in the presence of an aneurysm decreases compared to a healthy case (a vessel without an aneurysm). The simulation results in the rigid and FSI formulations agree qualitatively with each other. The obtained results provide a better understanding of the relationship between the geometrical parameters of the aneurysm and the changing of haemodynamics in the aortic bifurcation and its effect on the cardiovascular system upstream of the aneurysm.

Highlights. Small cerebral aneurysms (<3 mm), which make up the majority of aneurysms, rupture more frequently, although medium (>3 mm) and giant (>15 mm) aneurysms and have a higher risk of rupture. This article proves for the first time that the rupture risk criteria developed for giant cerebral aneurysms do not work for small aneurysms. The development of small aneurysms in patients was analyzed and measured morphological features of aneurysms were compared with their calculated hydrodynamic characteristics.Aim. To study the dynamics of development of small cerebral aneurysms, to assess the applicability of existing methods for calculating the risk of rupture, to formulate new clarifying hypotheses for calculating the risk of rupture of small cerebral aneurysms.Methods. Patient data were provided by the Federal Center for Neurosurgery, Novosibirsk. CT angiography was performed using a Philips Ingenuite CT scanner (Philips Medical Systems, USA, 128 slices). Aneurysm size dynamics was assessed by measuring three main sizes with an accuracy of 0.1 mm using the IntelliSpace Portal Philips software environment. Numerical calculations were carried out using ANSYS CFX 2020R2.Results. Hemodynamic characteristics change according to the changes of the aneurysm dome. In the case when morphological characteristics of the aneurysm have not changed, a change in the geometry of the patient's circle of Willis (coW) is observed: the curvature of the arteries, the angles of bifurcations (the structure of coW remained unchanged). The PHASES score (absolute risks of rupture for aneurysms) was found to be unusable for the considered aneurysms.Conclusion. This work formulates and morphologically and hydrodynamically confirms for the first time in the volunteers that the change in risk estimates for such aneurysms is fundamentally affected, even insignificantly, by the change in the circle of Willis: a change in the curvature of individual segments of the cerebral arteries, as well as the angles of their bifurcations. The results obtained are aimed at modifying the existing risk criteria for rupture of cerebral aneurysms.