Background Although it is generally believed that blebs represent weaker spots in the walls of intracranial aneurysms (IAs), it is largely unknown which aneurysm characteristics favor their development.
Objective To investigate possible associations between aneurysm hemodynamic and geometric characteristics and the development of blebs in intracranial aneurysms.
Methods A total of 270 IAs in 199 patients selected for surgical clipping were studied. Blebs were visually identified and interactively marked on patient-specific vascular models constructed from presurgical images. Blebs were then deleted from the vascular reconstruction to approximate the aneurysm before bleb formation. Computational fluid dynamics studies were performed in these models and in cases without blebs. Hemodynamic and geometric characteristics of aneurysms with and without blebs were compared.
Results A total of 173 aneurysms had no blebs, while 97 aneurysms had a total of 122 blebs. Aneurysms favoring bleb formation had stronger (p<0.0001) and more concentrated inflow jets (p<0.0001), higher flow velocity (p=0.0061), more complex (p<0.0001) and unstable (p=0.0157) flow patterns, larger maximum wall shear stress (WSS; p<0.0001), more concentrated (p=0.0005) and oscillatory (p=0.0004) WSS distribution, and a more heterogeneous WSS field (p<0.0001), than aneurysms without blebs. They were also larger (p<0.0001), more elongated (p<0.0001), had wider necks (p=0.0002), and more distorted and irregular shapes (p<0.0001).
Conclusions Strong and concentrated inflow jets, high-speed, complex, and unstable flow patterns, and concentrated, oscillatory, and heterogeneous WSS patterns favor the formation of blebs in IAs. Blebs are more likely to form in large, elongated, and irregularly shaped aneurysms. These adverse characteristics could be considered signs of aneurysm instability when evaluating aneurysms for conservative observation or treatment.
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Contributors SFSA, AMR, and JRC designed the study. FM contributed to development of the methodology. FM and JRC designed the software tools. BJC simulated vascular reconstructions. SFSA curated the data. SFSA and JRC performed the data analysis. SFSA, FM, AMR, and JRC contributed to interpretation of the results. AMR and JRC aquired funding, supervised students and coordinated the project.SFSA and JRC drafted the manuscript. All authors contributed to manuscript edition and approved the final manuscript.
Funding This work was supported by NIH grant R01NS097457.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval The protocols for patient consent, handling of patient data and analysis were approved by the institutional review board (IRB) at the University of Pittsburgh (Protocol # STUDY20020015), University of Illinois at Chicago (Protocol # 2015-0322), Allegheny General Hospital (Protocol # RC-5141), and Helsinki University Hospital. The whole study's IRB is overseen by the University of Pittsburgh's IRB.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available upon reasonable request. The data that support the findings of this study are available from the corresponding author, upon request.