Exploration of the effect of morphology and location on hemodynamics of small aneurysms: a variable-controlled study based on two cases with tandem aneurysms.

Introduction: Small aneurysms are usually treated with a flow diverter alone, without coils. However, some continue to exhibit incomplete occlusion after treatment, even after an extended period. This study aimed to investigate the effects of aneurysm morphology and location on the hemodynamic parameters related to poor outcomes.

Methods: Two patients with tandem aneurysms were enrolled. Flow diverter deployment was simulated, and preoperative and postoperative hemodynamics were analyzed using computational fluid dynamics. The preoperative and postoperative hemodynamics of the actual surgical plan were simulated using finite element analysis and computational fluid dynamics. The correlation between morphology, hemodynamics, and incomplete occlusion was evaluated by calculating the hemodynamics of aneurysm models with different heights and neck widths, adjusted according to the original geometry.

Results: Simulation of the actual surgical plan showed that the incompletely occluded aneurysm had a larger postoperative velocity at the sac and neck region (v_a and v_neck) and residual flow volume than the occluded aneurysm in both cases. The inflow rate (Q_inflow), inflow concentration index (ICI), v_a, and residual flow volume increased when the aneurysm neck width was expanded; with the increase in height, Q_inflow and ICI increased up to a certain point, while v_a and residual flow volume showed a decreasing trend. Aneurysms located on the superior wall of the internal carotid artery ophthalmic segment had a larger v_neck than those on the inferior wall.

Conclusion: Aneurysms located on the superior wall of the internal carotid artery ophthalmic segment or with a larger neck or height present a more severe hemodynamic environment, requiring careful consideration when planning surgery. This study provides hemodynamic evidence demonstrating how morphology affects aneurysm progression.