Objective—To determine whether the presence, number, and distribution of cerebral microbleeds (CMBs) on pretreatment MRI scans are associated with an increased risk of intracerebral hemorrhage (ICH) or poor functional outcome following endovascular thrombectomy (EVT) for acute ischemic stroke (AIS).

Methods—We analyzed prospectively collected data of consecutive patients treated by EVT for AIS, in a comprehensive stroke center where MRI is the first-line pretreatment imaging. Neuroradiologists blinded to clinical data rated CMBs on T2* sequence using a validated scale. We investigated associations of pre-treatment CMB presence, burden (1, 2–4, and ≥5), and presumed pathogenesis with ICH and poor 3-month functional outcome (modified Rankin score >2).

Results—Among 513 patients, 281 (54.8%) had a poor outcome and 89 (17.3%) had ≥1 CMBs. A total of 190 (37%) patients experienced ICH, in which 66 (12.9%) were symptomatic. CMB burden was associated with worse outcome in a univariable analysis (odds ratio [OR], 1.18; 95% confidence interval [CI], 1.03–1.36 per 1-CMB increase; P=0.02), but significance was lost after adjustment for age, sex, baseline stroke severity, hypertension, diabetes mellitus, atrial fibrillation, prior antithrombotic medication, intravenous thrombolysis, and reperfusion status (OR, 1.05; 95% CI, 0.92–1.20 per 1-CMB increase; P=0.50). Results remained nonsignificant when taking into account CMB location or presumed underlying vasculopathy. CMB presence, burden, location, nor presumed underlying vasculopathy was independently associated with ICH.

Conclusions—Poor outcome or ICH was not associated with CMB presence or burden on pre–EVT MRI after adjustment for confounding factors. Excluding such patients from reperfusion therapies is unwarranted.