Introduction Many studies have suggested that packing density and recurrence are close relation for coil embolization in unruptured intracranial aneurysms (UIA). Furthermore, various coils have been produced recently. There are a lot of choices in coil embolization. However, it is not easy to measure the utility of these various coil. Aim of this study is to evaluate relationship between coil types, packing density and recurrence in coil embolization of UIA.

Methods Aneurysms were measured its volume by semiautomatic cerebral aneurysm measurement software, NeuroVision (Cybernet Systems, Tokyo, Japan) and explored the value of volume embolization ratio (VER). During this period in more than 95% procedures, we used 3 types of coils; GDC, Matrix2, Target coil (Stryker Neurovascular, Fremont, CA, USA). In 1st period (from July 2008 to Sep 2011), we used Matrix2 and GDC. In 2nd period (from Oct 2011 to Dec 2012), we used Matrix2, Target I and GDC. In 3rd period (from Jan 2013 to Dec 2013), we used Matrix2, Target I, II (Longer length), III (OD ≦ 1.5mm) and GDC. Aneurysms, which were coiled with other products, were excluded from this study. According to the volume of the aneurysm, the aneurysms were divided into four groups. Group A, B, C and D are small size aneurysm less than 4.9 mm, Medium size (5 mm to 9.9 mm), Large size (10 mm to 14.9 mm) and Giant size (more than 15 mm). We compared VER (%) and retreatment ratio in that period according to the aneurysm volume.

Results From July 2008 to December 2013, 431 unruptured intracranial aneurysms were treated with endovascular surgery in our institution. Seven aneurysms were excluded for some reasons. 4 aneurysms did not measured VER and 3 aneurysms were treated with other coils. VER in each period were 24.5% in 1st period, 23.7% in 2nd period and 24.2% in 3rd period. In Group A, VER in 3rd period (27.1%) was higher than that of other period (24.9% in 1st period, 25.1% in 2nd period). In all groups, retreatment ratios after more than 1-year follow-up were 10% in 1st period, 6% in 2nd period and 3% in 3rd period. Also in Group B aneurysms, retreatment ratios after more than 1-year follow-up were 12% in 1st period, 6% in 2nd period and 3% in 3rd period.

Discussion Retreatment ratio was getting improved in 3rd periods compared with other period. VER of small size aneurysm in 3rd period is remarkably higher than that of other periods. Although, VER did not so different among in each group, retreatment ratio was remarkably lower in 3rd period. Evolution of coil may lead good clinical outcome of coil embolization for UIA.

Disclosures T. Ishibashi: 1; C; Stryker Japan. 2; C; Stryker Japan. Y. Murayama: 1; C; Stryker Japan, Siemens, NTT docomo. I. Yuki: 1; C; Siemens. M. Ebara: None. H. Arakawa:  None. K. Irie: None. H. Takao: None. S. Kaku: None. I. Kan: None. K. Nishimura: None. T. Suzuki: None. M. Watanabe: None. H. Sakamoto: None.