Low PHASES-Estimated Rupture Risk Among Patients Presenting with Ruptured Intracranial Aneurysms: A Retrospective Single-Centre Observational Study

Background/Objectives: The PHASES score is widely used to estimate the 5-year rupture risk of unruptured intracranial aneurysms, yet many patients present with aneurysmal subarachnoid haemorrhage despite low calculated risk. This study aimed to characterise the demographic and aneurysm-related profile of patients with ruptured aneurysms classified as low risk by PHASES. Methods: This retrospective single-centre observational study included 243 consecutive patients with radiologically confirmed ruptured intracranial aneurysms treated between 2013 and 2021. PHASES scores and estimated 5-year rupture risks were calculated retrospectively. Age, sex, arterial hypertension, aneurysm size, location, and multiplicity were analysed using non-parametric statistical methods. Results: The mean PHASES score was 5.16 ± 3.43 points. An estimated 5-year rupture risk below 1% was assigned to 125 patients (51.44%), and 54 patients (22.22%) had PHASES scores of 0–2. Ruptured aneurysms measuring ≤7 mm occurred in 147 patients (60.49%), and 210 patients (86.42%) were younger than 70 years. Internal carotid artery aneurysms were the most frequent overall, whereas anterior communicating artery aneurysms had the smallest median diameter while remaining among the most common rupture sites. Arterial hypertension was associated with larger aneurysm diameter. Conclusions: Low PHASES-estimated risks were common in this cohort of patients presenting with aneurysm rupture. Because the study included no comparison group with unruptured aneurysms, it cannot assess PHASES calibration or predictive performance. PHASES should therefore be used as a population-based decision-support tool rather than a stand-alone predictor of individual rupture risk, with morphology, imaging findings, documented growth, and patient-specific factors incorporated into clinical assessment.