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Background: The white-collar sign (WCS) is represented by the formation of neointimal tissue at the level of the aneurysm neck as the successful outcome on follow-up angiography after coil embolization. WCS has been reported only in aneurysms treated with Matrix® coils. This is the first study to report WCS emergence in aneurysms treated with bare platinum coils, and potential factors associated with WCS emergence were evaluated. Method: Total 130 unruptured (female: male ratio, 100: 30; mean age, 60 years) cerebral aneurysms were treated with coil embolization. Embolization status was assessed immediately and 1 year after treatment, and emergence of WCS in follow-up angiography was assessed. We evaluated the association between WCS emergence and aneurysm location, dome diameter, neck diameter, dome-neck ratio, and type of coil used (bare platinum or bioactive). Results: WCS appeared in nine aneurysms (6.9 %), of which six were treated only with bare platinum coils. Neck diameter was significantly smaller in the WCS-positive group than in the WCS-negative group. The proportion of aneurysms treated with bioactive coils was not significantly different between the groups. Immediate embolization status in the WCS-positive group tended to be slightly better than that in the WCS-negative group. No aneurysmal morphological characteristics other than small neck diameter were associated with WCS emergence. Conclusions: WCS is not specific to bioactive coil usage. Small neck diameter was significantly associated with WCS emergence in our series. Further investigations to clarify the predictors of WCS will contribute to progress of aneurysmal embolization. [ABSTRACT FROM AUTHOR]