Morphologic and Hemodynamic Risk Factors in Ruptured Aneurysms Imaged before and after Rupture

BACKGROUND AND PURPOSE:Due to limited information about aneurysm natural history, choosing the appropriate management strategy for an unruptured aneurysm is challenging. By comparing unruptured and ruptured cases, studies have identified a variety of aneurysm morphologic and hemodynamic properties as risk factors for rupture. In this study, we investigated changes in 4 ruptured aneurysms before and after rupture and tested whether previously published risk factors identified a risk before rupture.MATERIALS AND METHODS:A retrospective review of ruptured aneurysms based on the inclusion criteria of documenting angiographic images before and after rupture was performed. Such cases are extremely rare. To minimize hemodynamic influence due to location, we selected 4 cases at the posterior communicating artery. 3D morphologic and hemodynamic analyses were applied to examine qualitative and quantitative risk factors in aneurysms before and after rupture.RESULTS:When we compared aneurysms before and after rupture, all increased in size. Volume, surface area, and morphology changed in both high and low wall shear stress areas. Aneurysm surface ratio, nonsphericity index, and pulsatility index were the only risk factors to consistently identify risk before and after aneurysm rupture for all aneurysms.CONCLUSIONS:Although changes in shape and flow properties were found before and after aneurysm rupture, in this small study, we found that some risk factors were evident as early as 2 years before rupture.

Due to limited information about aneurysm natural history, one of the biggest challenges in clinical aneurysm management is determining the risk of rupture for incidentally found aneurysms. Currently, size guidelines identified by the International Study of Unruptured Intracranial Aneurysms are the dominant criteria guiding treatment decisions.¹ Studies have suggested that the mechanisms underlying aneurysm rupture are multifactorial, and they have likewise identified different types of risk factors. For example, researchers have found that certain aneurysm shapes are risk factors that may associate aneurysm morphology with rupture.^2–4 By analyzing blood flow properties in groups of ruptured and unruptured aneurysms, reports have also shown that certain hemodynamic factors may play an important role in aneurysm rupture.^5–9 However, the morphologic and hemodynamic risk factors analyzed in these studies have generally been identified by analyzing ruptured aneurysms after rupture. Because clinical reports also suggest that aneurysms change due to rupture, how well these risk factors can actually help predict rupture has been controversial.^10–12In general, it is expected that the predictive ability of any aneurysm rupture risk factor will be higher as an aneurysm is closer to rupture. The fundamental rationale in aneurysm risk analysis based on comparing ruptured and unruptured aneurysm groups is that aneurysms that rupture have the same risk characteristics in the unruptured and ruptured states.^5–9,13 In that case, the results obtained by comparing ruptured with unruptured aneurysms can help assess the risk of rupture in as-yet-unruptured aneurysms. However, there are limited studies testing this hypothesis.In this study, we re-examined morphologic and hemodynamic risk factors that have been reported in the literature by using a unique dataset of aneurysms imaged in both their unruptured and ruptured states.^{4,6–8,14–17} Our objective was to investigate morphology and flow properties of aneurysms before and after rupture and find whether previously identified risk factors were present in aneurysms before rupture. We sought to identify risk factors that consistently existed in ruptured aneurysms in both unruptured and ruptured states to guide early determination of aneurysm rupture risk.