Inclusion Criteria:
1. Posterior circulation acute ischemic stroke within 24-72 hours from symptom onset/last seen well (except for isolated vertigo), where patient is ineligible for IV thrombolytic treatment or the treatment is contraindicated (e.g., patient presents beyond recommended time from symptom onset), or where patient has received IV thrombolytic therapy without recanalization.
2. Occlusion (TIMI 0-1) of the basilar artery or intracranial segments of both vertebral arteries (V4) as evidenced by CTA/MRA/DSA.
3. Age ≥18 and ≤ 80.
4. Baseline NIHSS score obtained prior to randomization must be equal or higher than 6 points.
5. No significant pre-stroke functional disability (mRS ≤ 1).
6. Patient treatable within 72 hours of symptom onset. Symptom onset is defined as the point in time the patient was last seen well (at baseline) if patients are unable to provide a reliable history or the point in time when symptoms have started if patients can provide a reliable history.
7. Informed consent obtained from patient or authorized patient surrogate
Exclusion Criteria:
Clinical criteria
1. Known hemorrhagic diathesis, coagulation factor deficiency, or oral anticoagulant therapy with INR \> 3.0.
2. Baseline platelet count \< 50000/µL.
3. Baseline blood glucose of \< 50mg/dL or \>400mg/dl.
4. Severe, sustained hypertension (SBP \> 220 mm Hg or DBP \> 110 mm Hg) NOTE: If the blood pressure can be successfully reduced and maintained below these levels using commonly used medications in China for these purposes (including iv antihypertensive drips), the patient can be enrolled.
5. Patients in whom baseline NIHSS can not be obtained by a neurologist or emergency physician prior to sedation or intubation.
6. Seizures at stroke onset which would preclude obtaining a baseline NIHSS.
7. Serious, advanced, or terminal illness with anticipated life expectancy of less than one year.
8. History of life threatening allergy (more than rash) to contrast medium.
9. Patients with acute stroke within the first 48 hours after percutaneous cardiac, cerebrovascular interventions and major surgery .
10. Renal insufficiency with creatinine ≥ 3 mg/dl.
11. Woman of childbearing potential who is known to be pregnant or lactating or who has a positive pregnancy test on admission.
12. Subject participating in a study involving an investigational drug or device that would impact this study.
13. Known diagnosis or clinical suspicion of cerebral vasculitis.
14. Patients with a pre-existing neurological or psychiatric disease that would confound the neurological or functional evaluations. This excludes patients who are severely demented, require constant assistance in a nursing home type setting or who live at home but are not fully independent in activities of daily living (toileting, dressing, eating, cooking and preparing meals, etc.).
15. Unlikely to be available for 90 days follow-up (e.g. no fixed home address, visitor from overseas).
16. Any other condition that, in the opinion of the investigator will pose a significant hazard to the subject if participating in the trial.
Neuroimaging criteria
17. Hypodensity with a posterior circulation Acute Stroke Prognosis Early CT score (pc-ASPECTS) \< 6 and Pons-midbrain-index of ≥ 3 on CT angiography source images or MR with diffusion-weighted imaging or non-contrast CT.
18. CT or MR evidence of hemorrhage (the presence of microbleeds on MRI is allowed).
19. Complete cerebellar infarct on CT or MRI with significant mass effect and compression of the fourth ventricle.
20. Complete bilateral thalamic infarction on CT or MRI.
21. Evidence of vertebral occlusion, high grade stenosis or arterial dissection in the extracranial or intracranial segment that cannot be treated or will prevent access to the intracranial clot or excessive tortuosity of cervical vessels precluding device delivery/deployment.
22. Subjects with occlusions in both anterior and posterior circulation.
23. Evidence of intracranial tumor (except small meningioma).
