Background: The management of unruptured aneurysms is controversial, with the decision to treat influenced by aneurysm characteristics including size and morphology. Aneurysmal bleb formation is thought to be associated with an increased risk of rupture.
Objective: To correlate computational fluid dynamic (CFD) indices with bleb formation.
Methods: Anatomical models were constructed from three-dimensional rotational angiogram (3DRA) data in 27 patients with cerebral aneurysms harbouring single blebs. Additional models representing the aneurysm before bleb formation were constructed by digitally removing the bleb. We characterized haemodynamic features of models both with and without the bleb using CFDs. Flow structure, wall shear stress (WSS), pressure, and oscillatory shear index (OSI) were analyzed.
Results: There was a statistically significant association between bleb location at or adjacent to the point of maximal WSS (74%, p=0.019), irrespective of rupture status. Aneurysmal blebs were related to the inflow or outflow jet in 89% of cases (p<0.001), while 11% were unrelated. Maximal wall pressure and OSI were not significantly related to bleb location. The bleb region attained a lower WSS following its formation in 96% of cases (p<0.001) and was also lower than the average aneurysm WSS in 86% of cases (p<0.001).
Conclusion: Cerebral aneurysm blebs generally form at or adjacent to the point of maximal WSS and are aligned with major flow structures. Wall pressure and OSI do not contribute to determining bleb location. The measurement of WSS using CFD models may potentially predict bleb formation and thus improve the assessment of rupture risk in unruptured aneurysms.
From: Computational Fluid Dynamic Analysis of Intracranial Aneurysmal Bleb Formation by Russell et al.