While the majority of patients with acute pancreatitis suffer a mild and uncomplicated course of disease, up to 20% develop a more severe course with development of pancreatic and/or peripancreatic necroses. With time, these necroses become encapsulated with a well-defined inflammatory wall, so called walled-off necroses (WON). Up to 30% of WONs become infected, which prolongs the length of hospital stay, increases morbidity and mortality significantly, and generally requires an invasive intervention. During the last decade, minimally invasive therapies consisting of percutaneous and endoscopic, transluminal drainage followed, if necessary, by percutaneous or endoscopic necrosectomy, have replaced open surgery as the standard treatment resulting in better patient outcomes. The investigators have for nearly two decades been practicing an endoscopic step-up approach as standard treatment for infected WON.

Recently, lumen apposing metal stents (LAMS) have been introduced for the treatment of pancreatic fluid collections. The stent is fully-covered and shaped with two bilateral anchor flanges with a saddle in between. A dedicated through-the-scope delivery system, where the tip serves as an electro cautery device enables extra-luminal access and deployment of the stent. Initial results from primarily retrospective case series were promising. However, a recent randomized controlled trial failed to demonstrate superiority in terms of number of necrosectomies needed, treatment success, clinical adverse events, readmissions, length of hospital stay (LOS), and overall treatment costs. Furthermore, a number of serious adverse events with development of pseudoaneurisms probably due to collapse of the cavity have led to alterations in treatment with sequential computed tomography (CT) scans and insertion of double pigtail stents within the metal stent. In that trial, the mean diameter of the treated necroses was limited and in addition, the study was launched before the introduction of a novel 20 mm in diameter LAMS. The investigators hypothesize, that use of a 20 mm LAMS in large caliber WON is superior to the standard double pigtail technique.

Aim To compare the use of a novel 20 mm lumen apposing metal stent (LAMS) (Hot Axios, Boston Scientific) with a conventional double pigtail technique for endoscopic transluminal drainage of large (> 15 cm) pancreatic and/or peripancreatic walled-of necrosis (WON).

Inclusion Criteria:

Inclusion criteria (all criteria must be fulfilled):

1. Patients with acute, necrotizing pancreatitis and

   1. WON exceeding a diameter of 15 cm (measured on contrast-enhanced CT (CECT); see details on imaging tests below). WON is defined based on the revised Atlanta criteria as a mature, encapsulated pancreatic or peripancreatic necrosis with a well-defined inflammatory wall[12].
   2. Imaging test(s) must be done within 1 week before the index drainage procedure.
   3. Debut of pancreatitis must be within 3 months before the index drainage procedure.

2. One or more indication(s) for endoscopic, transmural drainage must be established:

1. Confirmed or suspected infection.1 2. Severe intraabdominal hypertension or abdominal compartment syndrome. 3. Persisting abdominal pain, early satiety, or general discomfort. 4. Obstruction of the GI or biliary tract. 5. Leakage of pancreatic juice, e.g. ascites or pleural effusion.

3. Preoperatively, the WON must be considered eligible for endoscopic, transgastric drainage with both conventional double pigtail and LAMS technique. Distance between the gastric wall and WON must not exceed one cm and there must be no major interposed vessels.

Infection in WON:

1. Confirmed infected necrosis is defined as a) positive culture from WON obtained by fine- needle aspiration prior to or at the first drainage procedure or b) presence of gas in WON on CECT prior to drainage with no earlier puncture/drainage and no signs of perforation to the GI tract.
2. Infected necrosis is suspected when a patient with WON present with clinical signs of persistent sepsis without other causes of infection.

Exclusion Criteria:

1. Patients under the age of 18.
2. Pregnancy.
3. Known or suspected malignant disease.
4. Pancreatitis secondary to trauma or surgical intervention.
5. Chronic pancreatitis.
6. Collections that may only be drained from the duodenum.
7. Previous surgical or endoscopic drainage or necrosectomy.