Flow reversal bypass surgery for giant intracranial aneurysms: illustrative cases.

backgroundGiant intracranial aneurysms (GIAs) have no definitive treatment paradigm. Flow reversal bypass (FRB) through high- or low-flow extracranial-to-intracranial bypass may facilitate aneurysm thrombosis while maintaining perforator patency, yet predicting when FRB will be successful remains challenging. The authors compared 2 patients with GIAs after FRB surgery to illustrate the successes and possible pitfalls. OBSERVATIONS: The first patient was a 13-year-old boy with giant, partially thrombosed, unruptured aneurysms of the internal carotid artery and upper basilar artery. The second patient was a 38-year-old man with a giant unruptured proximal middle cerebral artery (MCA) M1 aneurysm. Both underwent FRB. The child's upper basilar aneurysm resolved completely without complication. The adult experienced progressive aneurysm recanalization after initial thrombosis and associated MCA territory infarct requiring a subsequent trapping procedure with clipping of distal outflow, which has not been described previously. LESSONS: For select patients with GIAs, proximal occlusion paired with flow reversal is a promising surgical technique that may balance aneurysm thrombosis with maintenance of distal and perforator perfusion. The significant procedural risks of FRB surgery must be balanced with the aggressive natural history of GIAs. Future directions include aneurysm and perforator vessel flow analysis and careful documentation of aneurysm filling following high-flow bypass. https://thejns.org/doi/10.3171/CASE2583.