Purpose: Hemodynamic factors may play an important role in the initiation and growth of intracranial aneurysms (IA). In this study we sought to characterize the hemodynamic flow characteristics of evolving aneurysms and compare them against a cohort of patients with stable aneurysms using 4D-flow MRI.
Methods: From our institution registry of untreated IA, 10 patients who had evolving aneurysm (defined as interval change in size or morphometry i.e. new lobulation, daughter sac, irregular wall) and 10 patients whose aneurysms remained completely stable during their sequential surveillance imaging were identified. These patients prospectively underwent a dedicated MR imaging protocol encompassing MRA, vessel wall imaging and 4D-flow using a 3T MR scanner (GE MR750). 4D-flow data was processed using Arterys software (San Francisco, CA) and hemodynamic parameters including flow velocity, peak wall-shear stress (WSS), flow eccentricity and flow-jet angle in each aneurysm were obtained. The associations of flow parameters and commonly used clinical variables and risk factors, size and morphometric features were assessed using univariate and multivariate analyses in evolving vs. stable IAs.
Results: There was no significant difference between two groups in regards to age, sex, IA-size, aspect-ratio and size-ratio. The mean, IQR of aneurysm size were 5.4, 3.7-6.7mm in stable and 4.9, 3.5-6 mm in evolving IAs. The mean follow-up time was comparable (43 months in stable and 51 months in evolving IAs, p=0.58). The frequency of IA wall enhancement was higher in evolving IAs (70%) than stable IAs (30%), without statistical significance (p=0.09). The mean ± SD of flow parameters in evolving vs. stable IAs were: peak-WSS: 68.1 ± 18.3 cPa vs. 49.2 ± 17.2 cPa, p=0.04; flow eccentricity: 0.27 ± 0.13 vs. 0.15 ± 0.05, p=0.03; and flow-jet angle: 76.9 ±13.4° vs. 61 ±17.5°, p=0.05. After controlling for clinical and morphometric variables, multivariate logistic regression analysis identified Peak-WSS and flow eccentricity as independent predictors of evolving IAs.
Conclusion: 4D-flow MRI-derived peak WSS and flow eccentricity may help distinguish evolving from stable IAs independent of commonly used size and morphometric features.