Active_comparator: Endoscopic step-up approach

After endoscopic drainage of WON, patients will be reassessed 72 hours after the procedure. If there is no clinical improvement 72 hours after drain placement, a CECT is performed to check the adequacy of the drainage. Irrigation of the WON via a nasocystic drain or endoscopic irrigation (step 1) is performed in case of inadequate drainage. If a nasocystic drain is inserted, 500ml of normal saline, twice a day will be used to irrigate the WON. If endoscopic irrigation is performed, only irrigation with normal saline without necrosectomy is allowed.~Patients are again evaluated 72 hours after step 1. In case of improvement, treatment is conservative; otherwise step 2 will be initiated, which is endoscopic necrosectomy. Further endoscopic necrosectomy will be performed until there is clinical improvement.

Active_comparator: Direct endoscopic necrosectomy approach

Patients in the DEN group will undergo an immediate endoscopic necrosectomy after LAMS placement and balloon dilatation. A 10Fr 5cm double pigtail plastic stent will be inserted within the LAMS after necrosectomy. Patients will be assessed in 72 hours after the procedure. If there is no clinical improvement, a CECT is performed to check the adequacy of the drainage. DEN will be repeated in case of inadequate drainage. Patients will be reassessed every 72 hours and DEN repeated until there is clinical improvement. Subsequently, necrosectomy is performed weekly until a reassessment CECT at 3 weeks.