Hemodynamic Differences Between Ruptured and Unruptured Cerebral Aneurysms Simultaneously Existing in the Same Location: 2 Case Reports and Proposal of a Novel Parameter Oscillatory Velocity Index

Studies have demonstrated certain hemodynamic characteristics featuring the rupture status of cerebral aneurysms using computational fluid dynamics. These studies were conducted based on the comparison of a large number of ruptured and unruptured aneurysms. However, not only aneurysm size and location but also perianeurysm environment, such as hemorrhage and intracranial pressure, affect hemodynamic changes. We hypothesized that a case in which ruptured and unruptured cerebral aneurysms simultaneously exist in the same location would be an ideal model to demonstrate hemodynamic characteristics of the rupture status. We report 2 rare cases with subarachnoid hemorrhage, each of which involved 2 aneurysms at the common parent artery. One patient had 2 anterior communicating artery aneurysms, and the other patient had 2 middle cerebral artery aneurysms. Preoperative morphologic and hemodynamic examinations were performed to diagnose the rupture status of the 2 aneurysms, and each ruptured aneurysm was then confirmed during surgical clipping. Morphologic evaluation revealed higher shape indexes in both ruptured aneurysms. Lower wall shear stress, wall shear stress gradient, and aneurysm formation indicator were observed in both ruptured aneurysms. In contrast, ruptured aneurysms had a higher oscillatory shear index and oscillatory velocity index, which was the novel hemodynamic parameter to quantify the fluctuation of flow velocity vector. Quantitative characterization of the hemodynamic environment can distinguish the rupture status by using appropriate models minimizing certain bias caused by subarachnoid hemorrhage and aneurysm location.