Clinical Features of Ruptured Very Small Intracranial Aneurysms (<3 mm) in Patients with Subarachnoid Hemorrhage

Although small unruptured aneurysms rarely rupture, many patients with subarachnoid hemorrhage (SAH) have ruptured small, especially very small intracranial aneurysms (VSIAs; <3 mm) in clinical practice. We aimed to clarify the proportion and clinical features of patients with SAH with ruptured VSIAs.609 patients with ruptured intracranial aneurysms diagnosed at our institution from January 2012 to December 2018 were retrospectively analyzed. We classified patients into 2 groups based on ruptured aneurysm size: VSIAs or non-VSIAs (≥3 mm). We analyzed age, sex, location of aneurysms, World Federation of Neurological Surgeons grade on admission, treatment modality, and outcome at discharge.Among 609 patients, 103 had ruptured VSIAs. The proportion of young patients (age <40 years) was greater in the VSIA group than the non-VSIA group (10.7% vs. 3.6%, P = 0.002). The proportions of VSIAs located in the middle cerebral and vertebrobasilar arteries were relatively low and high, respectively (P = 0.002, 0.005). Significantly more patients with VSIAs than those with non-VSIAs were classified under World Federation of Neurological Surgeons grade I-III (70.9% vs. 56.3%, P = 0.006). Coil embolization was preferred for VSIAs (68.0% vs. 32.0%, P = 0.006). Outcomes were more favorable in the VSIA group than in the non-VSIA group.Small unruptured aneurysms rarely rupture; however, many patients with SAH have ruptured VSIAs in clinical practice. We observed that VSIA rates among ruptured aneurysms were fairly high. Age, posterior circulation location, and preferable outcome may be important clinical characteristics of ruptured VSIAs.