Hemodynamics in a Middle Cerebral Artery Aneurysm Before Its Growth and Fatal Rupture: Case Study and Review of the Literature

Background: Hemodynamics plays an important role in the natural history of intracranial aneurysms. However, it is difficult to obtain longitudinal aneurysm image data. In this study, we had a rare chance to follow the process of growth and rupture of a middle cerebral artery (MCA) aneurysm. The aim of this study was to investigate the role of hemodynamics for growth and rupture in this particular aneurysm patient. Methods: A 57-year-old woman presented with 2 unruptured MCA aneurysms and 1 ruptured anterior choroidal artery (AchA) aneurysm. The unruptured left MCA aneurysm grew in 7 months and ruptured at 11 months. The rupture region was confirmed during the clipping treatment. Computational fluid dynamic (CFD) simulations were conducted on the AchA and MCA aneurysms in 3 serial imaging procedures, and calculated hemodynamics was correlated with aneurysm growth and rupture. Results: The ruptured right AchA aneurysm had much lower wall shear stress (WSS) and higher oscillatory shear index (OSI) than the unruptured left MCA aneurysm. Comparison of the aneurysm growth region with the WSS distribution showed that growth occurred in a high WSS area. During the progression of the MCA aneurysm, we observed that the high aneurysmal WSS region grew first and then the growing region changed into a low WSS level; eventually, rupture occurred in a low WSS area. Conclusions: This case suggests that aneurysm rupture might be associated with low WSS and high OSI, whereas aneurysm growth may be related to high WSS in this particular individual MCA aneurysm patient.