Safety of coil embolisation in small (smaller than 5 mm) unruptured intracranial aneurysms: A retrospective multicentre analysis

Background: Risk-benefit analysis results for the treatment of unruptured aneurysms smaller than 5 mm are controversial. This study aimed to identify the outcomes and complication associated with treating such unruptured aneurysms.Methods: This was a retrospective study of 165 consecutive patients who underwent endovascular procedures for unruptured cerebral aneurysms of a maximum diameter 5 mm between January 2018 and March 2021. Patient background, aneurysm characteristics, adjuvant technique, volume embolization rate (VER), symptomatic complications, and modified Rankin Scale (mRS) scores were examined.Results: Sixty patients with sufficient data were included in the study. The mean age was 62.1 +/- 14.6 years, and the median follow-up period was 12 months. The mean maximum diameter was 4.16 +/- 0.63 mm, the neck diameter was 2.73 +/- 0.82 mm, and 90% of patients had anterior circulation. Complete occlusion was achieved in 34 cases (57.6%). Although there were no intraoperative ruptures, complications were observed in four patients (6.7%), and one patient (1.7%) had worsened mRS score. Only one patient (1.7%) required retreatment. The first coil VER was independently associated with complete occlusion after endovascular treatment. Univariate anal-ysis of complications showed an association between hypertension, hyperlipidaemia, and the estimated glomerular filtration rate.Conclusions: No patient experienced mRS score deterioration, and only one patient developed permanent disability due to ischemic complications; hence, we could safely treat small unruptured aneurysms. Complica-tions are not related to procedural factors such as coiling adjuvant technique. However, lifestyle-related diseases are related to complications, and we suggest that physicians should remain vigilant of the indication for coiling when treating patients with underlying diseases.