Analysis of aneurysm rupture in relation to the geometric indices: aspect ratio, volume, and volume-to-neck ratio

Introduction Geometric indices of cerebral aneurysms have been widely studied to determine rupture risk. However, most of these parameters were evaluated based on two-dimensional (2D) images and could have a measurement bias. We propose a new three-dimensional geometric index, an aneurysm volume-to-neck area ratio (VNR). To determine whether the VNR of ruptured aneurysms is different from that of unruptured aneurysms, we compared VNR with other 2D geometric indices in discriminative capacity for aneurysm rupture status. Methods Two hundred fourteen aneurysms in 195 patients (mean age, 57.44 ± 11.21 years; males, 69; females, 126) were retrospectively evaluated. There were 105 ruptured and 109 unruptured aneurysms. The five geometric indices [aspect ratio (AR), bottleneck ratio (BR), height-width ratio (HWR), volume, and VNR] were calculated from angiographic data and assessed to determine correlation with aneurysm rupture ( t test). Receiver operating characteristic (ROC) curve analysis was used for comparison of discriminative capacity between different indices. Results AR, BR, HWR, and VNR were correlated with rupture status. Areas under the ROC curve of the aspect ratio and VNR were significantly larger than that of the HWR, BR, and volume. However, AR and VNR did not show a significant difference. Conclusion A larger aneurysm volume in proportion to the neck could be one of the geometric indices of aneurysms that indicate a higher rupture risk. This characteristic is represented by the aspect ratio.