BACKGROUND: Malignant infarction of the middle cerebral artery (MCA) is 
associated with an 80% mortality rate. Non-randomised studies have suggested 
that decompressive surgery reduces this mortality without increasing the number 
of severely disabled survivors. To obtain sufficient data as soon as possible to 
reliably estimate the effects of decompressive surgery, results from three 
European randomised controlled trials (DECIMAL, DESTINY, HAMLET) were pooled. 
The trials were ongoing when the pooled analysis was planned.
METHODS: Individual data for patients aged between 18 years and 60 years, with 
space-occupying MCA infarction, included in one of the three trials, and treated 
within 48 h after stroke onset were pooled for analysis. The protocol was 
designed prospectively when the trials were still recruiting patients and 
outcomes were defined without knowledge of the results of the individual trials. 
The primary outcome measure was the score on the modified Rankin scale (mRS) at 
1 year dichotomised between favourable (0-4) and unfavourable (5 and death) 
outcome. Secondary outcome measures included case fatality rate at 1 year and a 
dichotomisation of the mRS between 0-3 and 4 to death. Data analysis was done by 
an independent data monitoring committee.
FINDINGS: 93 patients were included in the pooled analysis. More patients in the 
decompressive-surgery group than in the control group had an mRS<or=4 (75%vs 
24%; pooled absolute risk reduction 51% [95% CI 34-69]), an mRS<or=3 (43%vs 21%; 
23% [5-41]), and survived (78%vs 29%; 50% [33-67]), indicating numbers needed to 
treat of two for survival with mRS<or=4, four for survival with mRS<or=3, and 
two for survival irrespective of functional outcome. The effect of surgery was 
highly consistent across the three trials.
INTERPRETATION: In patients with malignant MCA infarction, decompressive surgery 
undertaken within 48 h of stroke onset reduces mortality and increases the 
number of patients with a favourable functional outcome. The decision to perform 
decompressive surgery should, however, be made on an individual basis in every 
patient.