Pancreatic fluid collection is a late complication of severe acute pancreatitis. According to the revised Atlanta classification, walled-off necrosis (WON) is defined as an encapsulated collection of necrotic tissue that is observed after four weeks of the onset of acute pancreatitis. Infected WON is associated with high morbidity and mortality; therefore, an appropriate treatment, including antibiotics and drainage, is mandatory. With the development of endoscopic equipment, endoscopic ultrasonography (EUS)-guided drainage has become a first-line treatment modality for infected WON. For patients who are refractory to EUS-guided drainage, endoscopic necrosectomy (EN) is a treatment option to facilitate direct removal of infected necrotic tissue within the WON. However, due to potentially lethal adverse events of EN, such as bleeding, perforation, and peritonitis, EN is usually withheld for several days after EUS-guided drainage. This strategy is known as "the step-up approach." Recently, with the accumulated evidence supporting the safety of EN, especially with the use of a dedicated lumen-apposing metal stent, it has been reported that EN immediately after EUS-guided drainage can shorten the treatment duration without increasing adverse events. Given these lines of evidence, the investigators hypothesized that immediate EN following EUS-guided drainage of WON might shorten time to clinical success compared to the step-up approach. To examine this hypothesis, the investigators planned to conduct a multicenter randomized controlled trial comparing treatment duration between EN immediately after EUS-guided drainage versus the step-up approach in patients with symptomatic WON.
