Clinical benefit of thrombectomy in stroke patients with low ASPECTS is mediated by oedema reduction. 
The impact of endovascular vessel recanalization on patients with a low initial Alberta Stroke Program Early Computer Tomography Score (ASPECTS) is still uncertain.  We hypothesized that vessel recanalization leads to an improvement in mortality and degree of disability by reducing brain oedema and malignant mass effect.  In this multicentre observational study, patients with acute ischaemic stroke due to large vessel occlusion in the anterior circulation and an ASPECTS of ≤ 5 were analysed.  Patients were assembled into two groups: successful vessel recanalization (thrombolysis in cerebral infarctions, TICI scale 2b/3) or persistent vessel occlusion (no endovascular procedure or TICI scale 0-2a).  Observers were blinded to clinical data.  Net water uptake within brain infarct, a quantitative biomarker based on CT densitometry, was used to quantify oedema in admission and follow-up CT and Δ-water uptake was calculated as difference between water uptake at both time points.  Occurrence of malignant infarctions and secondary parenchymal haemorrhage was documented.  Furthermore, modified Rankin scale score at 90 days was used for functional outcome.  We included 117 patients admitted between March 2015 and August 2017 in three German stroke centres: 71 with persistent vessel occlusion and 46 with successful recanalization.  The mean water uptake in the admission imaging was not different between both groups: 10.0% (±4.8) in patients with persistent vessel occlusion and 9.0% (±4.8) in patients with vessel recanalization (P = 0.4).  After follow-up CT, the mean Δ-water uptake was 16.0% (±7.5) in patients with persistent vessel occlusion and 8.0% (±5.7) in patients with vessel recanalization (P < 0.001).  Successful reperfusion was independently associated with a lowered Δ-water uptake of 8.0% (95% confidence interval, CI: -10.5 to -5.3%; P < 0.001) and lowered modifed Rankin scale score after 90 days of 1.5 (95% CI: -2.2 to -0.8; P < 0.001).  The prevalence of malignant infarctions was 44.3% in patients with persistent vessel occlusion and 26.1% in patients with vessel recanalization.  There was no significant difference for secondary haemorrhage in both groups (P = 0.7).  In conclusion, successful recanalization in patients with low initial ASPECTS resulted in a significant reduction of oedema formation and was associated with a decreased prevalence of malignant infarctions and an improvement of clinical outcome.