The recently published Carotid Occlusion Surgery Study (COSS) failed to show a benefit of extracranial-intracranial (EC-IC) bypass surgery over medical therapy in patients with symptomatic hemodynamically significant carotid occlusion. Since then on, different controversies have been raised on several aspects including the study population, qualifications of surgeons and hemodynamic evaluation.

In COSS protocol, the primary inclusion population is the patient demonstrating occlusion of unilateral ICA while the contralateral ICA less than 50% stenosis. Because of the enrollment problems, in the final result report, 18% patients suffered from contralateral ICA stenosis more than 50%. As we known, COSS utilized oxygen extraction fraction (OEF) ratio by PET as the criterion of hemodynamic evaluation. Bilateral ICAs lesion will disturbed the ratio even the identifying the subgroup of patients with hemodynamic insufficiency.

As an interventional trial, the COSS should ensure the certification for the experienced surgeons. While for expanding the number of centers and enhancing recruitment, COSS made some concessions on the surgeons training and certification. The 15% postoperative event rate is not the best that can be achieved according to recent surgical technical development.

The cerebral hemodynamic insufficiency has been considered as the primary pathophysiological factor for patients with ICA or MCA occlusion. For these patients, antiplatelet therapy is not likely to prevent hemodynamic stroke.EC-IC bypass surgery probably will be the possible effective therapy.

These underlying assumptions deserved further exploration and more strict research.So the CMOSS study in China is designed to compare the efficacy and safety of EC-IC bypass surgery with medical therapy in patients with symptomatic hemodynamically significant carotid occlusion.

Patients with symptoms of cerebral or retinal ischemia associated with ipsilateral internal carotid artery (ICA) occlusion have an annual risk of 5-8% of recurrent ischemic stroke. While in China, the incidence of middle cerebral artery (MCA) occlusion is higher than in western countries. The annual risk of recurrent ischemic stroke in patients with symptomatic ICA or MCA occlusion has not improved over the years. The proportion of recurrence that was minor disabling was rather high.

Inclusion Criteria:

• Age ranging between 18 and 65 years;
• Digital subtraction angiography imaging studies demonstrating occlusion of unilateral ICA or MCA;
• Digital subtraction angiography imaging studies demonstrating less than 50% stenosis of any other vessels especially contralateral ICA and MCA;
• Modified Rankin Scales (mRS) 0-2;
• Qualifying TIA or ischemic stroke in the territory of the occluded ICA or MCA must have occurred within the past 12 months;
• The most recent stoke attacked more than 3 weeks ago;
• The neurological deficit must be stable for more than 1 month;
• No massive cerebral infarction (>50% of the MCA territory) in CT or MRI study;
• CT Perfusion demonstrates "misery perfusion" ;
• Competent to give informed consent;
• Legally an adult;
• Geographically accessible and reliable for follow-up;

Exclusion Criteria:

• Other neurovascular disease (such as cerebral aneurysm or arteriovenous malformation) conditions likely to cause focal cerebral ischemia;
• Known unstable angina or myocardial infarction within recent 6 months;
• Pregnant or perinatal stage women;
• Blood coagulation dysfunction;
• Any diseases likely to death within 2 years;
• Past history of EC-IC bypass surgery;
• Any contraindications or allergy to aspirin or clopidogrel;
• Any heart disease likely to cause cerebral ischemia including prosthetic valves, infective endocarditis, atrial fibrillation, sick sinus syndrome, myxoma and cardiomyopathy with ejection fraction less than 25%;
• Allergy to iodine or radiographic contrast media;
• Serum creatinine > 3mg/dl;
• Uncontrolled diabetes mellitus (fasting blood glucose >16.7mmol/l);
• Uncontrolled hypertension (systolic BP >180 mmHg, diastolic BP>110 mmHg);
• Severe liver dysfunction [alanine transaminase (ALT) and/or aspartate aminotransferase (AST) > 3 times of normal level];
• Concurrent participation in any other experimental treatment trial;
• Any condition that in the surgeon's judgment suggests the patient an unsuitable surgical candidate;