Endovascular Management of Moyamoya Type II Endoleak Utilizing a CO ₂ -Assisted Protection Strategy: A Case Report

An 84-year-old woman developed progressive aneurysm enlargement due to a refractory Moyamoya T2EL 5 years after EVAR with an AFX II stent graft. Angiography demonstrated persistent retrograde perfusion through the inferior mesenteric artery via complex vasa vasorum-dominant collaterals. Because of unfavorable flow dynamics for embolization, CO₂ was intentionally injected to transiently suppress antegrade flow from the sigmoid artery, generating a controlled "to-and-fro" pattern. Under these hemodynamic conditions, NBCA was carefully administered, resulting in complete occlusion of the endoleak without reflux or non-target embolization. Follow-up computed tomography (CT) at 1 year confirmed stable sac size with no re-dilation.Clinical ImpactMoyamoya type II ELs are associated with microcollateral networks that complicate embolization and increase the risk of sac enlargement. Although NBCA can penetrate complex channels, reflux poses a significant hazard. In this case, targeted CO₂ injection effectively displaced competing flow, enabling safe, selective NBCA deposition. This CO₂-assisted strategy represents a feasible option for treating anatomically complex, refractory type II endoleaks.