Four-dimensional flow magnetic resonance imaging analysis of long-term blood flow in high-flow extracranial-intracranial bypass surgery with internal carotid artery ligation.

Abstract

High-flow bypass with a radial artery graft (RAG) treats complex internal carotid artery (ICA) aneurysms. We used four-dimensional flow magnetic resonance imaging (4D flow MRI) to quantify long-term cerebral hemodynamics, compare maintained and reduced bypass flow, evaluate differences between ruptured and unruptured aneurysms, and identify predictors of flow decline. We retrospectively studied 21 patients (2010-2024) who underwent ICA ligation with RAG. Serial postoperative 4D flow MRI measured blood flow volume (BFV) in the bypass (BFVbypass), contralateral ICA (BFVcICA), and basilar artery (BFVBA). Total flow (BFVtotal) equaled BFVbypass + BFVcICA + BFVBA. The median follow-up time was 64 months. By last follow-up, 9 patients (43%) demonstrated reduced bypass flow; reduced long-term bypass flow was associated with cerebral infarction within 30 days (p = 0.006). Unruptured aneurysms (n = 15) exhibited transient asymptomatic postoperative hyperperfusion that BFVtotal increased from 13 ± 3 mL/s preoperatively to 15 ± 2 mL/s in the initial postoperative period and decreased to 12 ± 3 mL/s at the last follow-up. Conversely, ruptured cases showed no significant change in BFVtotal between early postoperative and final time points. The bypass contributed approximately 30% of total cerebral inflow at both early and late postoperative stages. The final BFVbypass /BFVtotal ratio inversely correlated with BFVcICA/BFVtotal (r = -0.729, p < 0.001). Long-term 4D flow MRI revealed that high-flow bypass provides durable revascularization with stable graft patency and flow contribution. Postoperative infarction is a potential predictor of decreased bypass flow. Transient hyperperfusion appears specific to unruptured cases.