Two-year clinical follow-up of the Multicenter Randomized Clinical Trial of Endovascular Treatment for Acute Ischemic Stroke in The Netherlands (MR CLEAN): design and statistical analysis plan of the extended follow-up study. - van den Berg LA; Dijkgraaf MG; Berkhemer OA; Fransen PS; Beumer D; Lingsma H; Majoie CB; Dippel DW; van der Lugt AJ; van Oostenbrugge RJ; van Zwam WH; Roos YB (Trials, 2016)