Rupture-related Characteristics Of Intracranial Aneurysms Based On Vessel Wall Imaging And Hemodynamic Analysis

Part Ⅰ: Risk Facors for Aneurysmal Wall Enhancement in Unruptured Intracranial AneurysmsObjective: The rupture risk assessment of unruptured intracranial aneurysms(IAs)is still challenging.Aneurysm wall enhancement(AWE)on vessel wall MRI(VW-MRI)is suggested as a potential marker for wall inflammation,but the risk factors for its presence and its relationship with rupture risk of unruptured IAs have not been well described.This study aims to review the clinical and imaging characteristics of unruptured IAs and investigate the correlation between AWE and aneurysmal rupture risk.Methods: The patients with unruptured IAs from January 2015 to December 2016 in our center were retrospectively recruited.Clinical and aneurysm-related characteristics were collected,including age,sex,smoking,medical history of hypertension,diabetes mellitus,subarachnoid hemorrhage(SAH),size,location and multiplicity of the aneurysm.The presence of AWE on VW-MRI images was determined by comparing the post-contrast VW-MRI images with the pre-contrast ones and differentiated as no(NAWE),partial(PAWE)and circumferential(CAWE)wall enhancement.The rupture risk based on the PHASES score was calculated for each case.Univariate and multivariate analysis were performed to investigate the association of AWE with rupture risk and other conventional risk factors.Results: Finally,110 patients(40 males and 70 females;mean age = 57.2 ± 10.7)harboring 140 unruptured IAs(sized from 1.7 to 36.0 mm with a mean size of 9.4±6.4 mm)were included.NAWE was presented in 69(49.3%)lesions,PAWE in 39(27.9%)lesions and CAWE in 32(22.9%)lesions.Univariate analysis revealed that aneurysmal size(P < 0.001),location(P < 0.001),multiplicity(P = 0.016)and irregular shape(P = 0.006)were significantly distributed among different groups.Aneurysm size(odds ratio = 6.910,95% confidential interval = 4.175-11.439,P < 0.001)and location(odds ratio = 2.689,95% confidential interval = 1.642-4.406;P < 0.001)were independently related with the degree of AWE in multivariate analysis.The rupture risk score based on PHASES system increased significantly as the degree of AWE elevated(P < 0.001).Conclusions: VW-MRI is a feasible imaging method to detect characteristics of IA wall.The pattern of AWE was highly associated with conventional rupture risk factors,especially aneurysmal size and location.AWE was also correlated with rupture risk of unruptured IAs based on PHASES score,which might suggest AWE as a valuable radiological parameter for aneurysmal risk assessment.Part Ⅱ: The Correlation of Wall Enhancement and Hemodynamics in Intracranial Aneurysms with High Rupture RiskObjective: The inflammation reaction triggered by hemodynamic changes was thought to be a key mechanism in intracranial aneurysm(IA)rupture.The feasibility of vessel wall magnetic resonance imaging(VW-MRI)in detecting aneurysm wall enhancement(AWE)has been proved in Part I.Meanwhile,computational fluid dynamics(CFD)has been an effective tool in hemodynamic analysis of IAs.This study aims to investigate the relationship between morphology,hemodynamics and AWE on vessel wall MRI,and their potential role in rupture of intracranial aneurysms by using VW-MRI and CFD comprehensively.Methods: The patients with unruptured IAs from January 2015 to December 2016 in our center were retrospectively recruited.Clinical and aneurysm-related characteristics were collected,including age,sex,smoking,medical history of hypertension,diabetes mellitus,subarachnoid hemorrhage(SAH),size,location and multiplicity of the aneurysm.Vessel wall MRI images were reviewed and differentiated as no(NAWE),partial(PAWE)and circumferential(CAWE)wall enhancement.Computational geometry and CFD were used to calculate morphological and hemodynamic parameters.The PHASES score was calculated for each case to estimate its rupture risk.Univariate and multivariate logistic regression analysis was performed to investigate the relationship between morphological-hemodynamic pattern and AWE as well as their association with rupture risk.Results: Fifty-seven patients(22 males and 35 females;mean age of 58.4)harboring 65 unruptured IAs(sized from 2.6 to 19.6 mm with a mean size of 7.1 ± 3.0 mm)were retrospectively recruited.AWE was present in 39(60.0%)lesions,including 14(21.5%)PAWE and 12(18.5%)CAWE.In univariate analysis,hemodynamic parameters,including wall shear stress(P = 0.001),low wall shear stress area(P =0.003)and relative residence time(P = 0.022),and morphological parameters,including aneurysmal size(P < 0.001),aspect ratio(P = 0.011),size ratio(P < 0.001),bottleneck factor(P = 0.013)and dome-to-neck ratio(P = 0.007),were significantly different among groups with different degree of AWE.Further multivariate analysis revealed that size ratio(odds ratio = 2.575,95% confidential interval = 1.197-5.540,P = 0.016)and wall shear stress(odds ratio = 0.182,95% confidential interval = 0.035-0.939,P = 0.042)were independently associated with the degree of AWE.With increasing PHASES score,size-related parameters and the frequency of irregular shape increased significantly and a hemodynamic pattern of lower and oscillating wall shear stress was observed.Simultaneously,the proportion of NAWE aneurysms decreased,and PAWE and CAWE aneurysms increased significantly(P < 0.001).Conclusions: The presence of AWE was significantly correlated with hemodynamics and morphology of unruptured IAs.IAs with higher rupture risk presented with a significant larger and irregular shape,lower and oscillating wall shear stress and more intense AWE,which supported the interaction between morphology,hemodynamics and inflammation and their potential role in aneurysm rupture mechanism.