Unruptured Intracranial Aneurysm Risk Scores Underperform in Predicting Subsequent Rupture: A Retrospective Single-Center Study

<b>Background/Objectives:</b> Risk-stratification tools, including the PHASES, UIATS, and ELAPSS, are commonly used to guide management of incidentally detected unruptured intracranial aneurysms (UIAs), but their predictive accuracy in real-world settings remains unclear. This study evaluated how these scores would have advised treatment in patients who subsequently presented with aneurysmal subarachnoid hemorrhage (aSAH). <b>Methods:</b> We retrospectively analyzed adults treated for aSAH at Copernicus Memorial Hospital (Łódź, Poland) between January 2022 and June 2024. For each ruptured aneurysm, we calculated PHASES (5-year rupture risk), UIATS recommendation, and ELAPSS (5-year growth risk) as if the lesion had been detected incidentally. Identical assessments were performed for UIAs that remained unruptured. Discrimination for rupture was evaluated using receiver-operating characteristic analysis (AUC). <b>Results:</b> Of 180 aneurysms (mean age 66.9 ± 11.3 years), 103 (57%) were ruptured. Patients with ruptured aneurysms were significantly older (69.9 vs. 64.0 years; <i>p</i> = 0.003), while sex, hypertension, smoking, and aneurysm morphology did not differ significantly. UIATS more frequently favored conservative management in ruptured aneurysms (56.3% vs. 39.0%; <i>p</i> = 0.046). PHASES (1.6% vs. 1.6%) and ELAPSS (3-year: 14.5% vs. 12.6%; 5-year: 22.6% vs. 20.0%) showed no significant differences between groups. Age was the only independent predictor of rupture (OR = 1.05/year; <i>p</i> < 0.001). The model's cross-validated AUC was 0.731. <b>Conclusions:</b> Most ruptured aneurysms would not have been recommended for treatment based on UIATS. PHASES, ELAPSS, and UIATS did not reliably discriminate between ruptured and unruptured aneurysms, emphasizing the need for more precise and individualized risk assessment tools.