Extracranial-intracranial Bypass Surgery for Symptomatic Chronic Middle Cerebral Artery Occlusion: the CMOSS-2 Trial

Inclusion Criteria: 1. Age of 18-65 years; 2. Confirmed as chronic occlusion of unilateral middle cerebral artery (MCA) by digital subtraction angiography (DSA) or computed tomography angiography (CTA). Other cerebral artery stenosis should be less than 50%. 3. CT perfusion demonstrates severe hemodynamic insufficiency in the territory of the qualifying MCA with MTT (symptomatic side) ≥ 6s or rCBF (symptomatic side/contralateral side) ≤ 0.8; 4. mRS score is 0-2 points; 5. A history of ischemic events (including\<1/2 cerebral infarction in the middle cerebral artery supply area, or transient ischemic attack \[TIA\]) related to the qualifying artery within 12 months ; 6. The onset of acute stroke should be more than 1 month; 7. CT or MRI excludes large cerebral infarction (infarction\>1/2 of the territory of the qualifying middle cerebral artery); 8. Patients or their guardians voluntarily participate of the study and sign the consent form. Exclusion Criteria: 1. History of intracranial hemorrhage, subarachnoid hemorrhage, subdural hemorrhage, or extradural hemorrhage within 6 weeks; 2. Unstable angina pectoris or myocardial infarction, congestive heart failure within 6 months; 3. Women who are pregnant or lactating; 4. Coagulation dysfunction or hemorrhagic tendency (e.g. INR \> 1.5 and/or platelet count \< 100,000 mcL); 5. Other diseases with a life expectancy of less than 2 years 6. Previous treatment with EC-IC bypass surgery 7. Known allergy or contraindication to aspirin or clopidogrel or other antiplatelet drugs. 8. Known cardiac conditions that may lead to cardiogenic embolism: including prosthetic valves, infective endocarditis, left atrial or left ventricular thrombosis, atrial fibrillation, sick sinus node syndrome, atrial mucinous tumor or cardiomyopathy, ejection fraction \<25%; 9. Allergy to iodine or x-ray contrast, blood creatinine \> 3.0 mg/dl or other contraindications to arteriography 10. Uncontrolled diabetes mellitus with fasting blood sugar (FBS) \>16.7 mmol/L 11. Uncontrolled hypertension with a sitting systolic blood pressure \>180 mmHg or a sitting diastolic blood pressure \>110 mmHg; 12. Persistent worsening of neurological symptoms within 72 hours; 13. Severe liver dysfunction, defined as serum alanine transaminase (ALT) and/or glutamic oxalacetic transaminase (AST) \> 3 times the upper limit of normal range; 14. Active peptic ulcer disease; 15. Having received a clinical trial drug or device within 30 days prior to screening, or being enrolled in another clinical trial; 16. Other diseases or medical history that, in the judgment of the investigator, may affect the efficacy or safety evaluation of this study.