“Hybrid” Bypasses for Cerebral Revascularization: Indications, Techniques and Long-Term Outcomes

Introduction: We describe novel hybrid bypass constructs that can help augment cerebral revascularization while obviating the need for more than 1 extracranial-to-intracranial (EC-IC) bypass. Hybrid constructs may be useful as a primary bypass technique while treating complex aneurysms or as a salvage technique for malfunctioning bypass grafts.

Methods: All bypasses performed between 2005-2022 were retrospectively reviewed to identify hybrid constructs and classified into: 1. Lambda-λ-Bypass: Two extracranial donor grafts converging into a single intracranial anastomosis 2. Upsilon-Ƴ-Bypass: Single extracranial donor graft dividing midway into two separate intracranial anastomoses. 3. Bamboo-shoot-bypass: conjoined vein plus artery graft with tapering graft caliber. Demographic, clinical, and radiographic data was collected to investigate the indications, operative techniques, and long-term outcomes [modified Rankin scores (mRS) and angiographic graft patency].

Results: Sixteen “hybrid” bypasses were identified out of 371 bypasses performed between 2005-2022. The mean age at presentation was 49years (range 17-72) and 56% (9/16) patients were female. The median duration of clinical and radiological follow-up was 27 months (range 1-84) with 75% patients followed over the long-term (>12 months). The most common pathology was aneurysms in 69% (11/16) cases. Upsilon and Bamboo-shoot bypasses were the most common hybrid constructs performed in six patients each using the combination of radial artery graft and saphenous vein graft. Majority of hybrid bypasses [88% (14/16)] were performed to rescue a malfunctioning EC-IC graft. One bamboo-shoot bypass was used to overcome short graft length and one upsilon-bypass was used to revascularize two M2-MCA branches. At last follow-up, 81% patients (13/16) were mRS 0-2 and long-term graft patency was 92% (11/12).

Conclusion : Hybrid bypasses reduce the need for long bypass grafts in select cases and can be utilized to overcome technical constraints when performing traditional EC-IC bypasses. They are also valuable as a rescue strategy for malfunctioning grafts from prior EC-IC bypasses.