1095 Mismatch Between CT Hypoperfusion and Bypass Vessel Recipient Territories Predisposes to Perioperative Stroke in STA-MCA Bypass for Symptomatic Atherosclerotic Intracranial Carotid and Middle Cerebral Artery Disease

INTRODUCTION: Direct STA-MCA bypass for symptomatic atherosclerotic intracranial carotid and middle cerebral artery disease (AIMCAD) has failed to show benefit over medical management in previous high quality randomized controlled trials due to high rates of ipsilateral ischemic stroke during the first 48 hours post-operatively. Despite the use of perfusion imaging to guide patient selection in these trials, selection of an appropriate M4 branch was at the neurosurgeon’s discretion and no trials studied perioperative stroke outcomes based on M4 vessel recipient. METHODS: Consecutive STA-MCA bypasses performed for AIMCAD between 2019 and 2024 at a single institution were analyzed for incidence of ipsilateral perioperative ischemic stroke. Dependent variables included region of predominant hypoperfusion (frontal vs temporal) on preoperative CT perfusion maps and M4 bypass recipient vessel territory (frontal vs temporal). A perfusion-bypass mismatch was identified when the predominate hypoperfused vascular region and M4 recipient branch were incongruent. RESULTS: STA-MCA bypass was performed in 24 patients with a 16.7% perioperative stroke rate (n = 4). All strokes occurred in patients harboring predominate frontal MCA territory perfusion deficits who also received bypass to M4 temporal branch recipients (100% perfusion-bypass mismatch). All four strokes occurred in frontal regions with concordant clinical symptomatology. CONCLUSIONS: In patients with predominate frontal cerebral hypoperfusion secondary to AIMCAD, direct low-flow bypass to a M4 temporal branch (i.e. perfusion-bypass mismatch) may predispose to ipsilateral frontal lobe perioperative ischemic stroke. We hypothesize that creation of a de novo frontal watershed region supplied by the low flow temporal bypass may drive perioperative stroke in these tenuously perfused patients. Selection of M4 vessel recipients tailored to pre-operative CT perfusion imaging may lead to lower rates of perioperative stroke.