Introduction Potentially fatal unruptured intracranial aneurysms are often incidentally discovered from the occurrence of subarachnoid hemorrhage. Unfortunately, there is a paucity of research on early indicators of rupture risks. Procedural intervention by aneurysmal clipping or endovascular coiling is based on 1998 ISUIA trial results which suggest that aneurysm diameters < 7 mm have a low risk of rupture. Recent studies indicate that rupture risk is multifaceted and observed trends in clinical practice are different from the outlines described in published literature. This Chicago-based study aims to provide insight into unruptured intracranial aneurysm risk assessment accuracy by focusing on the influence of anatomic location on ruptured aneurysm size with a subgroup analysis of patients self-reporting as African-American.

Methods In this IRB-approved retrospective cohort study, consecutive adult patients presenting to Rush University Medical Center with subarachnoid hemorrhage were evaluated for cerebral aneurysm anatomic location and dome diameter. They were classified into groups of 3 mm, > 3 mm and 7 mm, and > 7 mm and data was further stratified by self-identified African American race. Classifications of anatomic location were based on currently known areas of common aneurysm growth and rupture-likelihood. All calculated group percentages were compared to evaluate the relationship between ruptured aneurysm size, anatomic location, and race.

Results From Aug 2012 - Aug 2015, Jan - Apr 2019, and Dec 2021 - Apr 2022, 293 of 475 patients had ruptured aneurysms leading to subarachnoid hemorrhage. For all patients, anatomic distribution varied based on size with smaller ruptured aneurysms ( 3 mm; > 3 mm and 7 mm) located at ACOM (32.4%; 31.5%) and MCA (14.9%; 16.9%) and larger ruptured aneurysms (> 7 mm) at PCOM (33.3%) and ACOM (20.4%) (p-value: 0.002). When separating by race, a strong ruptured aneurysm size and location relationship in 3 mm (30.3%) and > 3 mm and 7 mm (30.3%) at ACOM as well as > 3 mm and 7 mm (28.8%) and > 7 mm (50%) at PCOM was found in self-identifying African-Americans (p-value: 0.005). A weaker correlation between mean aneurysm size and race as well as anatomic location and race was identified (p-values: 0.1 and 0.25 respectively).

Conclusion The average size of ruptured aneurysms varies based on location. This may be helpful in calibrating dome size thresholds used to determine future rupture risk and treatment decision-making based on anatomic location. Cerebral aneurysms among self-identifying African Americans do not rupture at different dome diameters and locations than non-African Americans suggesting a strong possibility for a universal standard of treatment regardless of race. This retrospective cohort study is limited in defining a causal relationship between intracranial size and location; therefore, more data must be collected and assessed from 2015-2022 for the determination of a stronger size, anatomic location, and race relationship significance.

Disclosures S. Pathak: None. Y. Radaideh: None. M. Chen: None.