The role of circle of Willis anomalies in cerebral aneurysm rupture

Background and purpose Limited data exist to guide patient selection for preventive treatment of unruptured cerebral aneurysms. Cerebral aneurysms have been associated with circle of Willis anomalies but whether this association is also related to aneurysmrupture is not known. The occurrence of cerebral aneurysm rupture when a circle of Willis anomaly was present or absent was compared. Methods Patients admitted over a 2 year period with a diagnosis of a cerebral aneurysm and an anterior communicating artery (ACoA) or posterior communicating artery (PCoA) aneurysm were included in the analysis. Brain vascular imaging was reviewed for aneurysm size, morphology and presence of circle of Willis anomaly. Relevant medical history and demographics were obtained from the medical records. Results Of the 113 patients with ACoA or PCoA aneurysms, 85 (75.2%) cases were ruptured. There were 49 (43.4%) PCoA aneurysms and 64 (56.6%) ACoA aneurysms. Mean aneurysm size was 5.65 mm (SD 3.31). A circle of Willis anomaly was identified in 46 (40.7%) of all patients. Circle of Willis anomalies were present in 38 (46.9%) ruptured aneurysm cases and eight (29.6%) unruptured aneurysm cases. Multivariate analysis revealed a higher risk of aneurysm rupture when a circle of Willis anomaly was present (p=0.0245, OR 3.72 (CI 1.18 to 11.66)). Conclusions This series shows that circle of Willis anomalies are more commonly found in ruptured as opposed to unruptured cerebral aneurysms of the anterior and posterior communicating arteries. The presence of a circle of Willis anomaly may be an important characteristic for selecting patients for preventive aneurysm treatment.