Repeat high-flow bypass surgery for rescue of anastomotic aneurysm formation after external carotid artery-to-middle cerebral artery bypass: illustrative case.

BACKGROUND: Intracranial anastomotic aneurysms (IAAs) are rare and often challenging to treat. While endovascular treatments for IAAs have been documented in the literature, no prior reports exist on the use of high-flow bypass surgery (HFBS) as a rescue treatment for IAAs. Here, the authors present the first successful case of HFBS for IAAs. OBSERVATIONS: A 45-year-old woman presenting with persistent dizziness was diagnosed with a large right middle cerebral artery (MCA) aneurysm. She underwent HFBS using a radial artery (RA) graft through an external carotid artery (ECA)-RA-MCA bypass, combined with aneurysm molding and proximal MCA clipping. One year postoperatively, a de novo aneurysm developed at the anastomotic site. The recurrent aneurysm was successfully treated with clipping and remolding, followed by MCA reconstruction with HFBS using an RA graft via ECA-RA-RA-MCA bypass. The postoperative course remained uneventful, with no evidence of aneurysm recurrence during 1 year of follow-up after the second procedure. LESSONS: IAAs may develop following bypass procedures, underscoring the importance of rigorous postoperative surveillance. The authors demonstrate that HBFS represents a viable alternative approach for this complication, with satisfactory clinical outcomes in their case. These findings suggest that HFBS may potentially emerge as a novel therapeutic option for IAAs. https://thejns.org/doi/10.3171/CASE25656.