Medical Student University of Cincinnati College of Medicine
Introduction: Ruptured intracranial aneurysms carry high morbidity and mortality, so it is important to understand the factors shaping their natural history. The effects of some hemodynamic phenomena, like wall shear stress (WSS), have been studied extensively. Others, such as momentum loss, have been given less attention. Axial momentum loss (AML) at a bifurcation can be calculated as the difference between the momentum vector of blood flow in the parent vessel and the vector components in the daughter vessels parallel to it. To the authors’ knowledge, the effects of AML on aneurysm initiation have not been studied.
Methods: Physics-based models were derived to calculate parameters proportional to AML and WSS at aneurysmal and non-aneurysmal bifurcations of the middle cerebral artery (MCA), internal carotid artery (ICA), and basilar tip (BT). Dimensional measurements were made on 3D models of these bifurcations acquired from radiologic imaging. Comparisons of AML and WSS between aneurysmal and non-aneurysmal bifurcations, stratified by location, were made using t-tests with a critical value of α=0.05. Binary logistic regression models were then built to predict aneurysm presence.
Results: Aneurysmal bifurcations numbered 18/6/11 (MCA/ICA/BT). Non-aneurysmal bifurcations numbered 41/32/13 (MCA/ICA/BT). WSS was significantly greater at aneurysmal bifurcations at all three sites (P=0.020/0.001/0.030 at MCA/ICA/BT). AML was significantly greater at aneurysmal bifurcations of only the ICA and BT (P=0.078/0.003/0.005 at MCA/ICA/BT). The ratios of AML:WSS regression coefficients were 4.41 and 29.5 at the ICA and BT, respectively.
Conclusion : Although limited by its retrospective nature, this study suggests that WSS contributes significantly to aneurysm initiation at the MCA, ICA, and BT, but AML does so only at the ICA and BT. The ratios of AML:WSS regression coefficients suggest that AML contributes more to aneurysm initiation at the BT than at the ICA. Future studies may investigate how the relative contributions of these mechanisms to aneurysm initiation affect rupture risk.
