The first coil embolization ratio is the key factor for retreatment for unruptured cerebral aneurysms

BACKGROUND: In coil embolization, a high volume embolization ratio prevents recanalization that may require retreatment. However, patients with a high volume embolization ratio may also require retreatment. Patients with inadequate framing with the first coil may experience recanalization of the aneurysm. We analyzed the relationship between embolization ratio of the first coil and recanalization requiring retreatment. METHODS: We reviewed data from 181 patients with unruptured cerebral aneurysms who underwent initial coil embolization between 2011 and 2021. We retrospectively analyzed the correlation between neck width, maximum aneurysm size, width, aneurysm volume, volume embolization ratio of the framing coil (first volume embolization ratio [1(st) VER]), and final volume embolization ratio (final VER) of cerebral aneurysms in patients and their retreatment. RESULTS: Recanalization requiring retreatment was observed in 13 patients (7.2%). The factors related to recanalization were neck width, maximum aneurysm size, width, aneurysm volume, and 1(st) VER, but not the final VER. Multivariate analysis of the five factors showed a significant difference in the 1(st) VER (P = 0.002). The cutoff value for recanalization was a 1(st) VER of 5.8%. There were 162 cases with a VER ≥ 20% or higher, and the same analysis yielded similar results. CONCLUSION: The 1(st) VER was significantly correlated with recanalization of cerebral aneurysms requiring retreatment. In coil embolization of unruptured cerebral aneurysms, it is important to achieve an embolization rate of at least 5.8% using a framing coil to prevent recanalization.