Hemodynamic changes after intracranial aneurysm growth

Transition of intracranial aneurysmal wall enhancement from high to low wall shear stress mediation with size increase: A hemodynamic study based on 7T magnetic resonance imaging

Background

Wall shear stress (WSS) has been proved to be related to the formation, development and rupture of intracranial aneurysms. Aneurysm wall enhancement (AWE) on magnetic resonance imaging (MRI) can be caused by inflammation and have confirmed its relationship with low WSS. High WSS can also result in inflammation but the research of its correlation with AWE is lack because of the focus on large aneurysms limited by 3T MRI in most previous studies.This study aimed to assess the potential association between high or low WSS and AWE in different aneuryms. Especially the relationship between high WSS and AWE in small aneurysm.

Methods

Forty-three unruptured intracranial aneurysms in 42 patients were prospectively included for analysis. 7.0 T MRI was used for imaging. Aneurysm size was measured on three-dimensional time-of-flight (TOF) images. Aneurysm-to-pituitary stalk contrast ratio (CRstalk) was calculated on post-contrast black-blood T1-weighted fast spin echo sequence images. Hemodynamics were assessed by four-dimensional flow MRI.

Results

The small aneurysms group had more positive WSS-CRstalk correlation coefficient distribution (dome: 78.6 %, p = 0.009; body: 50.0 %, p = 0.025), and large group had more negative coefficient distribution (dome: 44.8 %, p = 0.001; body: 69.0 %, p = 0.002). Aneurysm size was positively correlated with the significant OSI-CRstalk correlation coefficient at the dome (p = 0.012) and body (p = 0.010) but negatively correlated with the significant WSS-CRstalk correlation coefficient at the dome (p < 0.001) and body (p = 0.017).

Conclusion

AWE can be mediated by both high and low WSS, and translate from high WSS- to low WSS-mediated pathways as size increase. Additionally, AWE may serve as an indicator of the stage of aneurysm development via different correlations with hemodynamic factors.

Nomogram-based geometric and hemodynamic parameters for predicting the growth of small untreated intracranial aneurysms

Previous studies have shown that the growth status of intracranial aneurysms (IAs) predisposes to rupture. This study aimed to construct a nomogram for predicting the growth of small IAs based on geometric and hemodynamic parameters. We retrospectively collected the baseline and follow-up angiographic images (CTA/ MRA) of 96 small untreated saccular IAs, created patient-specific vascular models and performed computational fluid dynamics (CFD) simulations. Geometric and hemodynamic parameters were calculated. A stepwise Cox proportional hazards regression analysis was employed to construct a nomogram. IAs were stratified into low-, intermediate-, and high-risk groups based on the total points from the nomogram. Receiver operating characteristic (ROC) analysis, calibration curves, decision curve analysis (DCA) and Kaplan-Meier curves were evaluated for internal validation. In total, 30 untreated saccular IAs were grown (31.3%; 95%CI 21.8%-40.7%). The PHASES, ELAPSS, and UIATS performed poorly in distinguishing growth status. Hypertension (hazard ratio [HR] 4.26, 95%CI 1.61-11.28; P = 0.004), nonsphericity index (95%CI 4.10-25.26; P = 0.003), max relative residence time (HR 1.01, 95%CI 1.00-1.01; P = 0.032) were independently related to the growth status. A nomogram was constructed with the above predictors and achieved a satisfactory prediction in the validation cohort. The log-rank test showed significant discrimination among the Kaplan-Meier curves of different risk groups in the training and validation cohorts. A nomogram consisting of geometric and hemodynamic parameters presented an accurate prediction for the growth status of small IAs and achieved risk stratification. It showed higher predictive efficacy than the assessment tools.

Hemodynamic study on the therapeutic effects of varying diameter embolic coils in the treatment of intracranial aneurysms

Endovascular coiling is the predominant method for treating cerebral aneurysms. Extensive reports on selecting coil length, hardness, and material are available. However, the impact of coil diameter on postoperative outcomes remains unclear. This study enrolled six personalized geometric models of intracranial aneurysms: three bifurcation aneurysms and three sidewall aneurysms. Four coil models were constructed by changing the coil diameter. Coil embolization was simulated using the finite element method. Computational fluid dynamics was used to characterize hemodynamics in the aneurysms after embolization. Evaluation parameters included velocity reduction, wall shear stress (WSS), low WSS (LWSS), oscillatory shear index (OSI), relative residence time (RRT), and residual flow volume in the aneurysms. At the peak time (t = 0.17 s), the proportion of LWSS area in bifurcation aneurysms increase with the rise in coil diameter: 0.8D, 71.28 ± 12.62% versus 1D, 74.97 ± 19.17% versus 1.2D, 78.88 ± 18.56% versus 1.4D, 84.00 ± 11.53% (mean ± SD). The proportion of high OSI area decreases as the coil diameter increases: 0.8D, 4.41% ± 2.82% versus 1.0D, 3.78 ± 3.33% versus 1.2D, 2.28% ± 1.77% versus 1.4D, 1.58% ± 1.11% (mean ± SD). The proportion of high RRT area increases as the coil diameter rises: 0.8D, 3.40% ± 1.68% versus 1.0D, 7.67 ± 4.12% versus 1.2D, 9.84% ± 9.50% versus 1.4D, 22.29% ± 14.28% (mean ± SD). Side wall aneurysms do not exhibit the aforementioned trend. Bifurcation aneurysms plugged with a coil of 1.4 times the diameter have the largest RFVs (<10 mm/s) within the group. Aforementioned patterns are not found in sidewall aneurysms. In the treatment of aneurysms with coiling, varying coil diameters can result in different hemodynamic environments within the aneurysm. Larger coil diameters have improved hemodynamic performance for bifurcation aneurysms. However, coil diameter and embolization effectiveness have no significant relationship for sidewall aneurysms.