Background Aneurysmal recanalization is a problem with endovascular coiling and one of its risk factors is the low volume embolization ratio (VER). The first coil VER (1st VER) is believed to be critical for obtaining a high VER. The main objective of this study was to evaluate factors potentially useful for selecting the optimal 1st VER for endovascular coiling.

Methods 609 initial saccular aneurysmal treatments performed between January 2010 and December 2014 at our institution were included in this retrospective study. Attempted procedures, retreatment cases, intraoperative rupture cases, and stent-assisted coiling cases were excluded. Age, sex, aneurysm location, ruptured aneurysm, aneurysm shape, neck size, maximum aneurysm size, dome-to-neck ratio, aneurysm volume, procedure, immediate Raymond scale score, 1st VER, and VER between the recanalization groups and non-recanalization groups were compared.

Results The factors related to recanalization were ruptured aneurysms, neck width, maximum aneurysm size, aneurysm volume, procedure, 1st VER, and VER. The cut-off values for aneurysm recanalization were a 1st VER of 10.0% and a VER of 33.0%. The maximum average VER of normal size aneurysms was found in the groups with a 1st VER of 17.5–20.0%.

Conclusions 1st VER was found to be a helpful index for estimating aneurysmal recanalization after coil embolization. The target 1st VER was 17.5–20.0% for obtaining a higher VER and avoiding recanalization.