Haemodynamic effects of proximal neck angulation in abdominal aortic aneurysms: a numerical study

An abdominal aortic aneurysm (AAA) is an enlarging dilation of the abdominal aorta at signifi-cant risk of rupture and death. During normal physiological conditions, pulsatile blood flow in the abdominal aorta displays largely laminar patterns, albeit localized disturbances due to branching vessels and geometric variations. The existence of an aneurysm also distorts vascular structure, leading to sophisticated flow dynamics that could foster disease progression. In the present study, haemodynamics in three-dimensional AAA models were studied with the help of computational fluid dynamics (CFD). Idealized aneurysm geometries with four extreme proximal neck angulations were taken into consideration with laminar flow and rigid arterial wall assump-tion. Simulations were carried out over the entire cardiac cycle to preserve the pulsatile flow's unsteadiness. Post-processing methods were used to analyse velocity distribution, pressure fields, streamlines, and wall shear stress (WSS). The findings showed that marked angulation of the proximal aortic neck caused asymmetric flow patterns, turbulence, and blood recirculation in the aneurysm sac, espe-cially during diastole. Low and oscillatory WSS regions were mapped, which are implicated to cause endothelial dysfunction and wall degeneration, whereas zones of high WSS indicated pos-sible localized vascular weakening. These results illustrate that vessel angulation greatly enhances disturbed hemodynamics in AAA, thus augmenting the risk of wall weakening and rupture. This study outlines the promise of CFD-based simulations to deliver mechanistic insights into aneurysm behavior and progression and to provide a non-invasive means of assessing rupture risk and to guide clinical decision-making.