Atherosclerotic changes of the parent artery associated with ruptures in small (<7 mm) anterior communicating artery aneurysms

Background Small unruptured aneurysms are usually considered low-risk lesions and are typically managed conservatively. However, recent evidence indicates that small aneurysms account for a substantial proportion of ruptured intracranial aneurysms. Objective To determine which morphology- and hemodynamics-related parameters are associated with the rupture status of small (<7 mm) anterior communicating artery (ACoA) aneurysms. Methods We retrospectively reviewed 332 consecutive patients with ACoA aneurysms who were treated at our institute. Clinical data, imaging data, and intraoperative video recordings were reviewed and analyzed. Results In total, 317 patients with small (<7 mm) ACoA aneurysms were included in the study, among whom 220 (69.4%) presented with ruptured aneurysms and 97 (30.6%) with unruptured aneurysms. The ruptured aneurysms showed a significantly higher height-to-width ratio, aspect ratio, and size ratio than the unruptured aneurysms ( p < 0.05), and were more often irregular in shape or accompanied by a daughter sac. Among the 317 aneurysms, 53 aneurysms were analyzed for intracranial atherosclerosis and 47 aneurysms were evaluated to assess the hemodynamic parameters. Moderate-to-severe parent-artery atherosclerosis was also more significantly found in the ruptured aneurysms group ( p < 0.01). Fluid–structure interaction analysis showed that, compared with the unruptured aneurysms, the ruptured aneurysms were associated with a lower time-averaged wall shear stress, higher oscillatory shear index, and higher von Mises stress in the parent artery. Conclusion Our study demonstrated that the rupture of small (<7 mm) ACoA aneurysms may be associated with the parent artery and aneurysmal neck atherosclerosis, the hemodynamic environment, and adverse morphological characteristics.