Possible hemodynamic mechanisms in the size change of cerebral aneurysms: an exploratory study

Background: In asymptomatic small unruptured intracranial aneurysms (IAs), growth is one of the important factors determining treatment to prevent rupture and hemorrhage. Hemodynamic factors play a crucial role in the growth and regression of aneurysms, although the mechanisms involved are not yet clear. The aim of this study was to investigate the hemodynamic mechanisms underlying size changes in small unruptured IAs (<7 mm) during follow-up.

Methods: This retrospective cohort study analyzed 63 patients with unruptured IAs (<7 mm) who underwent computed tomography angiography (CTA) imaging follow-up for more than 6 months. Aneurysm hemodynamic and morphological parameters were measured by software AneuFlow. Statistical comparisons were performed between enlarging aneurysms and stable aneurysms.

Results: Enlarging aneurysms (43/63, 68%) exhibited a significantly higher baseline wall shear stress (WSS) (7.98 vs. 5.76 Pa, P=0.04) and a borderline higher WSS gradient (WSSG) (9.83 vs. 5.62 Pa/mm, P=0.05) compared to stable aneurysms. During enlargement, WSSG decreased (P=0.04), while parent vessel diameter increased (P<0.01), accompanied by reduced parent vessel WSS (P<0.01). In 30% of growing cases, parent vessel expansion was correlated with marked WSS and WSSG reduction in the aneurysm, suggesting adaptive remodeling. Low normalized WSS (NWSS) was correlated with decrease in diameter of the parent vessel (D_vessel) (r=0.30, P=0.02) and aneurysm surface area (r=0.36, P<0.01)

Conclusions: This study analyzed the effect of hemodynamics on the size change of aneurysms. High WSS and high WSSG may be inducing factors for aneurysm enlargement, while high WSS may lead to expansion of the parent vessel. In the early stages of aneurysm development, low WSS may contribute to size reduction.