A numerical flow experiment for assessing the risk of rupture in anterior communicating artery aneurysms in relation to aneurysm projection.

Anterior communicating artery (AcoA) aneurysms may project in different directions - anterior, posterior, superior, or inferior - each of which can substantially alter intra-aneurysmal flow patterns and potentially influence rupture risk. The present study investigates the impact of aneurysm projection direction on hemodynamic characteristics associated with rupture and thrombosis. Transient computational fluid dynamics (CFD) simulations were performed using idealized, parametric models of AcoA aneurysms with four defined projection types: anterior (toward the frontal lobe), posterior (toward the optic chiasm), superior (toward the hypothalamus), and inferior (toward the skull base). Two aneurysm sizes were analyzed. Blood was modeled as a non-Newtonian, shear-thinning fluid under pulsatile flow conditions representative of physiological cerebral circulation. Key hemodynamic parameters, including wall shear stress and its spatial gradient, pressure, velocity, vorticity, relative residence time, viscosity, and blood washout were evaluated over multiple cardiac cycles. While global cerebral flow distribution remained unchanged, aneurysm projection produced marked differences in intra-aneurysmal hemodynamics. Anteriorly projecting aneurysms exhibited higher velocities, stronger vortical structures, elevated wall shear stress, and rapid blood washout, indicating a rupture-prone flow environment. In contrast, inferiorly projecting aneurysms demonstrated low velocity, high viscosity, reduced vorticity, and prolonged blood residence time, consistent with conditions favoring intrasaccular thrombosis. These projection-dependent patterns were preserved across both aneurysm sizes. Aneurysm projection direction is a critical determinant of AcoA aneurysm hemodynamics, independent of size. Anterior projections are associated with flow conditions linked to increased rupture risk, whereas inferior projections promote flow stagnation and thrombotic potential. These findings highlight the importance of incorporating projection-specific hemodynamic assessment into aneurysm risk stratification beyond size-based criteria.