Tiny (≤3 mm) Unruptured Intracranial Aneurysms: A 13-Year Contemporary Insight on Treatment Safety From a Multicenter Registry

BACKGROUND AND OBJECTIVES: Tiny or very small unruptured intracranial aneurysms (≤3 mm) carry a very low estimated rupture risk, yet many are electively treated. Although factors influencing procedural risks have the potential to guide treatment selection, they remain poorly characterized in this population. METHODS: A retrospective cohort study was conducted using prospectively collected data from the multicenter Stroke Thrombectomy and Aneurysm Registry, including patients treated for unruptured aneurysms between 2013 and 2025. Tiny aneurysms were defined as ≤3 mm. Primary outcomes were intraprocedural and postprocedural complications. Propensity score matching and multivariable logistic regression were performed. RESULTS: Among 5107 treated aneurysms, 783 (15.3%) were tiny. Patients with tiny aneurysms were younger, more often female, and had higher rates of vascular risk factors, prior subarachnoid hemorrhage, or family history of aneurysms (P < .05). Intraoperative complications (5.2% vs 5.1%, P = .91), postprocedural complications (8.4% vs 8.7%, P = .83), in-hospital mortality, and long-term outcomes were comparable with small (3-5 mm) aneurysms. On multivariable analysis, anterior communicating artery (odds ratio [OR] 4.92; 95% CI, 1.34-18.1; P = .016) and posterior communicating artery locations (OR 4.08; 95% CI, 1.40-11.9; P = .010), as well as stent-assisted coiling (OR 3.98; 95% CI, 1.33-11.9; P = .013) predicted intraoperative complications, while favorable preadmission functional status (modified Rankin Scale 0-1; OR 0.40; 95% CI, 0.21-0.76) predicted lower postprocedural complication risk. CONCLUSION: Treatment of tiny unruptured aneurysms remains common despite very low rupture risk. Procedural risks are low and comparable with slightly larger aneurysms. Treatment decisions should integrate both rupture risk and procedural safety, with anterior communicating artery or posterior communicating artery locations and unfavorable baseline functional status representing higher-risk features. When indicated, stent-assisted coiling was independently associated with higher intraoperative complication risk relative to clipping in this cohort.