Bleeding rates of concomitant unruptured intracranial aneurysms in patients with subarachnoid hemorrhage during hospitalization.

Multiple aneurysms are a risk factor for intracranial aneurysm rupture; however, data on the rupture of concomitant unruptured aneurysms during hospitalization in patients with aneurysmal subarachnoid hemorrhage (aSAH) remain limited. This study assessed the bleeding rates and characteristics of concomitant unruptured aneurysms during hospitalization. Clinical data from patients with aSAH and multiple aneurysms enrolled in the Nagasaki subarachnoid hemorrhages (SAH) Registry Study (2003-2022) were retrospectively analyzed. Patients without residual aneurysms after initial treatment, those with infectious endocarditis, or those lacking sufficient information on concomitant unruptured aneurysm bleeding or discharge date were excluded. The bleeding rate during hospitalization was calculated, and cumulative rupture rates were estimated using Kaplan-Meier analysis to examine associations between aneurysm size, location, and bleeding risk. Among 1,016 patients with aSAH, 661 (133 men, mean age 66 years) harboring 814 concomitant unruptured aneurysms met the inclusion criteria. Bleeding occurred in 12 of 814 (1.5%) concomitant unruptured aneurysms in 11 (1.7%) patients. The mean time to bleeding onset was 15.7 days (range: 4-50). The bleeding rate was higher in posterior-circulation concomitant unruptured aneurysms than in anterior-circulation ones (5.7% vs. 0.85%, respectively). These findings highlight an elevated bleeding risk during the acute and subacute phases after aSAH, emphasizing the need for close monitoring and timely intervention for posterior-circulation concomitant unruptured aneurysms during this period.