Pre-specified futility boundary was reached.

The purpose of this study is to determine if extracranial-intracranial bypass surgery when added to best medical therapy can reduce the subsequent risk of ipsilateral stroke in high-risk patients with recently symptomatic carotid occlusion and increased cerebral oxygen extraction fraction measured by positron emission tomography (PET).

The overall purpose of this research is to determine if a surgical operation called "Extracranial-Intracranial Bypass" can reduce the chance of a subsequent stroke in someone who has complete blockage in one main artery in the neck (the carotid artery) that supplies blood to the brain and has already suffered a small stroke. This surgery involves taking an artery from the scalp outside the skull, making a small hole in the skull and then connecting the scalp artery to a brain artery inside the skull. In this way the blockage of the carotid artery in the neck is bypassed and more blood can flow to the brain. In some people natural bypass arteries develop and the brain is already getting plenty of blood. These people have a low risk of stroke if they take medicine. In other people, no natural bypass arteries develop so less blood flows to their brains. This second group has a much higher risk of stroke while taking medicine, as high as 25-50% within the next two years. It is this second group of people who may benefit from having the bypass operation and who are the candidates for this study.

This bypass surgery is considered experimental because it is not generally performed for this condition and it is unknown whether it leads to a decrease, an increase or no change in the risk of stroke. In order to determine if people fit into this second group of people who may benefit from the bypass operation they need to have a test called a PET scan. The PET scan measures the amount of blood that is getting to the brain and the amount of oxygen that the brain is using. The PET scan uses radioactive oxygen and water and is experimental (not approved by the United States Food and Drug Administration). If the PET scan shows that less blood is getting to the brain, there will be a 50-50 chance (like a coin toss) of receiving the bypass surgery or not. There will then be follow-up visits to the clinic one month later and then every three months for two years to check on the appropriate medical treatment that everyone will receive and to determine who has had a stroke.

The study hypothesis is that extracranial-intracranial bypass surgery when added to best medical therapy can reduce by 40 percent subsequent stroke within two years in participants with recent TIA ('ministroke") or stroke (\

Inclusion Criteria:

• Vascular imaging demonstrating occlusion of one or both internal carotid arteries.
• Transient ischemic attack (TIA) or ischemic stroke in the hemispheric carotid territory of one occluded carotid artery.
• Most recent qualifying TIA or stroke occurring within 120 days prior to projected performance date of PET.
• Modified Barthel Index > 12/20 (60/100).
• Language comprehension intact, motor aphasia mild or absent.
• Age 18-85 inclusive.
• Competent to give informed consent.
• Legally an adult.
• Geographically accessible and reliable for follow-up.

Exclusion Criteria:

• Non-atherosclerotic carotid vascular disease. Blood dyscrasias: Polycythemia vera ,essential thrombocytosis, sickle cell disease (SS or SC).
• Known heart disease likely to cause cerebral ischemia (echocardiography not required). This includes the following conditions ONLY: Prosthetic valve, Infective endocarditis, Left atrial or ventricular thrombus, Sick sinus syndrome, Myxoma, Cardiomyopathy with ejection fraction <25%. This is an all-inclusive list. The following conditions are NOT EXCLUSIONS: Atrial fibrillation, patent foramen ovale, atrial septal aneurysm.
• Other non-atherosclerotic condition likely to cause focal cerebral ischemia.
• Any condition likely to lead to death within 2 years.
• Other neurological disease that would confound follow-up assessment.
• Pregnancy.
• Subsequent cerebrovascular surgery planned which might alter cerebral hemodynamics.
• Any condition which in the participating surgeon's judgment makes the subject an unsuitable surgical candidate.
• Participation in any other experimental treatment trial.
• Participation within the previous 12 months in any experimental study that included exposure to ionizing radiation.
• Acute, progressing or unstable neurological deficit. Neurological deficit must be stable for 72 hours prior to the performance of PET.
• If supplemental arteriography is required, allergy to iodine or x-ray contrast media, serum creatinine > 3.0 mg/dl or other contraindication to arteriography.
• If aspirin is to be used as antithrombotic therapy in the perioperative period, those with allergy or contraindication to aspirin are ineligible.
• Medical indication for treatment with anticoagulant drugs, ticlopidine, clopidogrel or other antithrombotic medications such that these medications cannot be replaced with aspirin in the perioperative period as deemed necessary by the COSS neurosurgeon if the participant is randomized to surgical treatment.
• Remediable medical conditions. Patients with the following conditions can become eligible if the exclusion criterion no longer applies within 120 days of onset of the most recent qualifying event: Uncontrolled diabetes mellitus (FBS > 300 mg%/16.7 mmol/L), Uncontrolled hypertension (systolic BP>180, diastolic BP >110), Unstable angina, Uncontrolled hypotension (diastolic BP < 65).

Surgical group: Within 30 days after surgery for 93 operated and within 30 days after randomization for 4 not operated Non-surgical group: Within 30 days after randomization

Only serious adverse events were assessed