Radar des Essais Cliniques

1. Premorbid mRS ≤1;
2. Time from symptom onset to puncture ≤24 hours; including wake-up stroke and unwitnessed stroke. The time at which symptoms began was defined as the "Last Known Well" (LKW).

3.18 to 75 years of age; 4.Internal carotid artery (ICA) or middle cerebral artery (MCA)-M1 occlusion confirmed by computed tomographic angiography (CTA)/ magnetic resonance angiography (MRA)/ digital subtraction angiography (DSA). Patients with involvement of ipsilateral anterior cerebral artery (ACA), MCA or embryonal posterior cerebral artery (PCA) are eligible for inclusion.

5.NIHSS1a ≥ 1 (with the clarification that changes in alertness cannot be attributable to cerebral edema); 6.Meeting any of the following criteria:

1. ASPECTS 3-5 and NIHSS ≥ 30;
2. ASPECTS 0-2; 7.Signs on CT/MRI of an infarct of at least 50% of the middle cerebral artery territory; 8.No midline shift or midline shift <5mm; 9.Mechanical Thrombectomy and successful recanalization (defined as eTICI ≥2b50); 10.Ability to initiate decompressive hemicraniectomy within 6 hours after completion of mechanical thrombectomy and within 4 hours after randomization; 11.Informed consent obtained from the patient or his/her legal representative.

Clinical Exclusion Criteria

1. Any symptoms and signs of brain herniation before randomization, such as pupil anisocoria and unstable vital signs.
2. In the judgment of the investigator, the subject is likely to have supportive care withdrawn in the first day.
3. Commitment to decompressive hemicraniectomy (DHC) prior to enrollment.
4. Severe, sustained hypertension (systolic blood pressure > 220 mm Hg or diastolic blood pressure > 110 mm Hg);
5. Baseline blood glucose <50 mg/dl (2.8 mmol/L) or >400 mg/dl (22.2 mmol/L);
6. Baseline platelet count <100 x10^9/L;
7. Known hemorrhagic diathesis, coagulation factor deficiency, or oral anticoagulant therapy with international normalized ratio > 1.7;
8. Severe renal insufficiency, defined as serum creatinine > 3.0 mg/dl (or 265.2 μmol/l) or glomerular filtration rate \[GFR\] < 30 ml/min, or patients requiring hemodialysis or peritoneal dialysis;
9. Patients that cannot complete 90-day follow-up (such as no fixed residence, overseas patients, etc.);
10. Suspected vasculitis or septic embolism;
11. Neurological diseases or mental disorders before onset that affect the assessment of the condition;
12. Females who are pregnant or in lactation;
13. Participating in other clinical trials that could confound the evaluation of the study;
14. Subjects who, in the opinion of the investigator, have a life expectancy <3 months due to conditions not related to current LHI or are unlikely to comply with follow-up requirements. Other conditions that the investigators believe are not suitable for participation or may pose a significant risk to the patient.

Neuroimaging Exclusion Criteria

1. Evidence of other brain diseases such as cerebral trauma, intracranial tumor (except small meningioma), cerebral aneurysm, etc.
2. Evidence of acute ischemic infarction in bilateral anterior circulation territory or involvement of posterior circulation territories (other than in patients with a fetal or near-fetal PCA configuration);
3. Vascular perforation during thrombectomy;
4. The pre-randomization CT findings exhibits evidence of parenchymal hemorrhage 2 intracranial hemorrhage, diffuse severe subarachnoid hemorrhage, or intraventricular hemorrhage. Patients with localized mild subarachnoid hemorrhage, hemorrhagic infarction type1 or 2, and small parenchymal hematoma type 1 without midline shift may be included;