Background and Aims:
Little is known about the occurence and implications of multivessel occlusions (MVO) in patients who present with an intracranial large vessel occlusion and are candidate for endovascular treatment (EVT). 
Methods:
We report data from the MR CLEAN Registry, a prospective, observational study on all EVT patients in the Netherlands. MVO was defined as an MCA occlusion (M1/M2) or intracranial ICA/ICA-T occlusion, with a concurrent second occlusion in the ACA or PCA territory on initial DSA and confirmed on baseline CTA, as assessed by a core laboratory. Scores on the mRS at 90days were compared between MVO and single vessel occlusion patients with ordinal logistic regression after 1:1 propensity score matching based on age, occlusion location, baseline NIHSS and pre-stroke mRS. 
Results:
Of 1526 patients with proximal occlusions of the anterior circulation, 35 (2.3%) had an MVO. Thirty out of thirty-five (86%) a concurrent ACA occlusion. After matching with 35 single vessel occlusion patients, baseline characteristics were well-balanced. However, worse collateral grades were observed in MVO patients (23% vs 3% absent collaterals, p=0.02). Six percent of MVO patients regained functional independence (mRS 0-2) at 90 days, compared to 31% of single vessel occlusion patients (p<0.01). Mortality at 90 days was 58% vs 44% for MVO and single vessel occlusion patients, respectively (p=0.27). A similar, though non-significant association of MVO and worse outcome was observed in mRS shift analysis (cOR 0.42, 95%CI 0.16-1.10).
Conclusions:
MVO in EVT patients on baseline imaging may be associated with worse functional outcome.

4 - PREVALENCE AND OUTCOME OF PATIENTS WITH MULTIVESSEL OCCLUSIONS IN THE MR CLEAN REGISTRY