Altered Flow Territories after Extracranial-Intracranial Bypass Surgery

Abstract

To prevent stroke after carotid sacrifice and to augment cerebral perfusion in patients with internal carotid artery (ICA) occlusion, high-flow extracranial-intracranial (EC-IC) bypass operations are performed. Although the function and efficacy of the bypass is monitored during surgery, the postoperative flow through the bypass is significantly lower than the flow in the contralateral ICA. Thus far, it is unknown whether decreased bypass flow is caused by a low tissue perfusion or by a relatively small flow territory. Seven patients, four with an atherosclerotic ICA occlusion and three with a giant aneurysm of the ICA, were investigated; each underwent a high-flow EC-IC bypass and permanent occlusion of the ICA. Cerebral blood flow was measured with arterial spin labeling perfusion magnetic resonance imaging. Separate flow territory mapping of the EC-IC bypass, contralateral ICA, and posterior circulation was performed with selective arterial spin labeling magnetic resonance imaging. No significant difference was found in cerebral blood flow between the hemisphere ipsilateral to the EC-IC bypass (70.9 +/- 11.3 ml/min/100 g tissue), contralateral to the EC-IC bypass (71.9 +/- 14.3 ml/min/100 g tissue), and comparable findings in 50 healthy control participants (69.1 +/- 17.5 ml/min/100 g tissue). Paired analysis of the individual flow territories demonstrated a 15% volume reduction (P = 0.018) in flow territory of the EC-IC bypass compared with the contralateral side. In the present study, we demonstrate the feasibility of selective arterial spin labeling magnetic resonance imaging for clinical follow-up of patients after high-flow EC/IC bypass surgery, providing both information on flow territories and the level of regional cerebral blood flow.