Predicting the onset of middle cerebral artery aneurysms: Influence of bifurcation angle

Aneurysms are abnormal bulges in arteries caused by vessel wall weakening. The rupture risk associated with an aneurysm can result in life-threatening complications, such as subarachnoid hemorrhage. The rupture of smaller bifurcation aneurysms is difficult to predict, as well as risky to operate on, as the bifurcation angle plays a dominant role. Patient management and treatment modalities for smaller aneurysms require an understanding of their growth propensity due to hemodynamic forces and their interaction with the vessel wall. The main objective of the present study is to analyze the factors resulting in the onset of an aneurysm and hemodynamic interactions facilitating its formative growth, in particular in the middle cerebral artery. To start with, the original anatomical state of the healthy bifurcation blood vessel is retrospectively constructed to facilitate computational fluid dynamics simulations. Numerical simulations are performed on a larger cohort of 42 patient-specific aneurysms, and four representative small aneurysms are exemplified in this study. Hemodynamic parameters, such as wall shear stress, time-averaged wall shear stress, wall shear stress gradient, wall shear stress divergence, relative residence time, aneurysm formation index, pressure distribution, and energy loss, are analyzed between aneurysmal and pre-aneurysmal healthy stages. In particular, the effect of asymmetry on aneurysm formation was investigated. Aneurysm formation has altered the hemodynamic conditions, indicating low wall shear stress, higher residence time, and recirculating flow conditions. Both pressure and wall shear stress divergence decreased after aneurysm formation. Greater hemodynamic stresses are observed in the daughter vessels with larger bifurcation angles. Aneurysms with larger bifurcation angle was observed to have greater energy losses compared to smaller bifurcation angles.