Hydrogel coils in intracranial aneurysm treatment: a multicenter, prospective, randomized open-label trial

Studies have demonstrated the effectiveness of hydrogel-coated coils (HGCs) to achieve the composite endpoint of decreased recanalization rates and greater safety. Herein, the authors aimed to assess the true ability of second-generation HGCs to prevent recanalization.

This randomized controlled study, the HYBRID (Hydrocoil Versus Bare Platinum Coil in Recanalization Imaging Data) trial, comparing HGCs with bare platinum coils (BPCs), was conducted in 43 Japanese institutions. The aneurysm diameter range was 7-20 mm. HGCs were used in 4 patients in the BPC arm, and at least one HGC was used in each patient in the HGC arm, excluding 3 patients. Additionally, an HGC length ≥ 50% of the length of all the coils used was strongly recommended. The primary endpoint was recanalization 1 year after embolization, according to core laboratory evaluation. Angiographic change was also classified as further thrombosis, unchanged, or recanalization. Changes in cases with both initial and 1-year posttreatment angiographic images were compared. In the post hoc analysis, major recanalization was defined as any change, from complete occlusion or a neck remnant at the end of the procedure to body filling (BF) on the 1-year posttreatment angiogram or any increase in the size of BF in patients with BF at the end of the procedure, and its rate was compared between the two treatment arms.

Recruitment ended when 432 patients were randomized; 217 and 215 patients were allocated to the HGC and BPC arms, respectively. The recanalization rates in the HGC and BPC arms were 3.3% and 7.1%, respectively (risk difference -3.8%, 95% CI -8.6 to 0.5), with no statistically significant difference (p = 0.083). Regarding aneurysm occlusion within 1 year, there was significantly more thrombosis and less recanalization in the HGC group (p = 0.043). The major recanalization rates were 2.3% and 6.6% in the HGC and BPC arms, respectively, with a significant difference between the two (p = 0.036).

The study results did not confirm the effectiveness of second-generation HGCs using recanalization imaging data. However, these coils may induce more thrombosis and less recanalization for medium-sized cerebral aneurysms. Clinical trial registration no.: UMIN000006748 (www.umin.ac.jp/ctr/).