High-Flow Bypass Combined with Proximal Parent Artery Occlusion for Giant Basilar Artery Aneurysms: Long-Term Outcomes of a 5-Year Follow-up Cohort

Background: Giant basilar artery aneurysms represent a formidable challenge in neurovascular surgery. Despite advances in flow diverters and bypass techniques, optimal management remains controversial, particularly in the posterior circulation where treatment-related morbidity is high. Objective: This study aimed to evaluate the feasibility, safety, and long-term clinical outcomes of high-flow extracranial–intracranial (EC-IC) bypass combined with aneurysm isolation for giant basilar artery aneurysms treated at a single high-volume neurosurgical center. Methods: We retrospectively analyzed 21 consecutive patients with giant basilar artery aneurysms treated between 2010 and 2019. All patients underwent an external carotid artery–radial artery–posterior cerebral artery (ECA–RA–P2) high-flow bypass, followed by either immediate or staged aneurysm isolation. Aneurysm isolation consisted of proximal basilar artery occlusion achieved by endovascular coil embolization or microsurgical clipping. To ensure procedural consistency and minimize bias, all operations were performed by the same neurosurgeon. Clinical outcomes, complications, and bypass patency were evaluated, with a minimum follow-up of 5 years using DSA or CTA. Results: Among the 21 patients, 6 presented with acute subarachnoid hemorrhage (SAH). None had a posterior communicating artery. All underwent successful ECA–RA–P2 bypass. Group 1 ( n = 12) underwent simultaneous bypass and aneurysm isolation. Of these, 4 patients had endovascular coil occlusion of the basilar artery without branch vessels, and 8 patients underwent proximal basilar artery microsurgical clipping, including all 6 emergent SAH cases. Group 2 ( n = 9) underwent staged aneurysm isolation, performed 3–7 days after bypass (5 coil occlusions, 4 clippings). Angiography confirmed good graft patency in all patients, and no major complications occurred intraoperatively. In Group 1, 3 patients developed brainstem infarction, 2 had minor complications with full recovery within 3 months, and 1 died. All 6 SAH patients treated with proximal clipping recovered well without severe complications. In Group 2, no major complications occurred. At 5-year follow-up, all bypass grafts remained patent on DSA or CTA. Two patients developed recanalization of the proximal basilar artery, which were successfully re-occluded endovascularly without complications. Conclusion: High-flow bypass combined with proximal basilar artery occlusion is a feasible and effective option for treating giant basilar artery aneurysms. Importantly, staged occlusion performed after hemodynamic stabilization of the bypass graft may reduce perioperative morbidity and appears safer than simultaneous occlusion. These findings support the role of tailored bypass strategies in the management of complex posterior circulation aneurysms. Publication History Article published online: 27 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany