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Shedding light on tiny intracranial aneurysms: a retrospective risk assessment. OBJECTIVE: Tiny intracranial aneurysms (tiAs) pose challenges in detection and management. Recent advances in neuroimaging have improved the detection rates of these diminutive lesions, yet the decision-making process regarding their treatment remains controversial. While larger aneurysm size is a relevant risk factor for a possible rupture in common risk scores, the rupture of tiAs leading to subarachnoid hemorrhage (SAH) is also reported frequently. However, a heterogeneity in practice exists, and clear guidelines for the treatment of incidental tiAs are lacking. The aim of this study was to investigate clinical decision-making for aneurysm repair by investigating the risk factors for rupture in tiny aneurysms. METHODS: This retrospective analysis utilized data from patients admitted to the University Medical Center Hamburg-Eppendorf for aneurysmal SAH (n = 427) between 2010 and 2020 and patients with unruptured intracranial aneurysm (UIAs) discussed by the medical center's aneurysm board (n = 743) between 2012 and 2022. Patients with single tiAs, defined as a maximum diameter of 3 mm, were selected for further analysis. Patient demographics, aneurysm characteristics, and risk factors were compared between the SAH and UIA groups. A modified UIA treatment score (UIATS*) and the PHASES (population, hypertension, age, size of aneurysm, earlier SAH from another aneurysm, site of aneurysm) score were collected in UIA patients and applied retrospectively in SAH patients for the time of admission. RESULTS: The authors identified 79 tiAs in the SAH cohort and 109 tiAs in the UIA cohort. Irregular morphology (OR 4.53, 95% CI 1.84-11.16; p < 0.001) and a high size ratio/aspect ratio (> 3/1.6; OR 14.73, 95% CI 3.55-61.17; p < 0.001) were significantly associated with rupture when comparing tiAs of the SAH and UIA groups. When applying the UIATS* to tiny aneurysms retrospectively, intervention would have been recommended in 20.3% of SAH cases compared with 0.9% of UIA cases (p < 0.001). Comparatively, for nontiny aneurysms, intervention would have been recommended in 33.9% of SAH cases compared with 15.6% of UIA cases (p < 0.001). CONCLUSIONS: In the present collective, several ruptured tiAs could be identified. Nevertheless, only a few would have been recommended for treatment. Especially tiAs with irregular morphology and abnormal configurations should be critically evaluated for rupture risk. Current scoring systems provide valuable guidance but should be used in conjunction with individualized, multidisciplinary treatment approaches.