Flow patterns inside the cerebral aneurysms affect aneurysm wall thickness

The wall properties of cerebral aneurysms, whether thin or thick, cannot be determined using conventional imaging techniques. We previously reported that two parameters, wall shear stress vector direction variation (WSSDV) and oscillatory shear index (OSI), may predict the wall-thinning areas of cerebral aneurysm walls in computational fluid dynamics (CFD) analysis. In this study, we evaluated the positive predictive value (PPV) of these parameters in detecting thin-walled regions (TIWRs) and thick-walled regions (TKWRs) by performing preoperative CFD analysis and proposed that distinct flow patterns determine aneurysm wall thinning or thickening. A total of 42 microsurgical clipping surgeries for unruptured intracranial aneurysms (UIAs) were performed at our hospital between January 2019 and August 2022 without any deterioration of the modified Rankin scale in all patients. We identified 39 actual TIWRs (aTIWRs) in the intraoperative photographs of the aneurysms among 46 expected TIWRs (eTIWRs) of the color maps (PPV: 85%; 95% CI 0.72-0.92), 23 actual TKWRs (aTKWRs) among 29 expected TKWRs (eTKWRs, PPV: 79%; 95% CI 0.62-0.90) on the WSSDV color maps, whereas the OSI color map revealed 39 aTIWRs among 46 eTIWRs (PPV: 85%; 95% CI 0.72-0.92) and 30 aTKWRs among 45 eTKWRs (PPV: 67%; 95% CI, 0.52-0.79). Spearman's rank correlation analysis revealed a strong correlation between the WSSDV and OSI (Spearman's ρ = 0.849, 95% CI 0.73-0.92, p < 0.001). These two parameters reflected the degree of wall shear stress vector change during the cardiac cycle. Parallel or divergent flows may cause aneurysm wall thinning, whereas rotational or convergent flows may cause wall thickening.