OBJECTIVE AND IMPORTANCEWe present the case of a patient who experienced bilateral middle cerebral artery infarctions after Hunterian ligation and trapping of a ruptured right cavernous aneurysm, despite a high-flow extracranial-intracranial bypass. This is a rare complication, and it highlights the need for further refinements in our understanding of the hemodynamic insufficiency created by major vessel sacrifice.CLINICAL PRESENTATIONThe patient was a 59-year-old woman who experienced multiple episodes of massive epistaxis before undergoing angiography, which revealed left internal carotid artery occlusion and an irregular right cavernous aneurysm. The patient was then transferred to our center for treatment. The patient was neurologically intact at presentation, and her epistaxis was controlled by nasal packing.INTERVENTIONThe patient underwent an extracranial-intracranial bypass from the external carotid artery to the M2 segment of the right middle cerebral artery, followed by trapping of the aneurysm. Despite evidence of graft patency, the patient experienced bilateral middle cerebral artery distribution infarctions after surgery.CONCLUSIONAlthough extracranial-intracranial bypasses protect the majority of patients who undergo carotid artery ligation from ischemic complications, this case demonstrates that hemodynamic insufficiency can occur even with a high-flow saphenous vein graft. Better ways to quantitate the hemodynamic needs of the brain after major vessel sacrifice may facilitate matching of the revascularization strategy to the specific needs of each patient, thus further reducing the likelihood of ischemic complications.