The goal of this clinical trial is to learn about clinical usefulness of double pigtail plastic stents during endoscopic transmural drainage of post-inflammatory pancreatic and peripancreatic fluid collections with use of lumen-apposing metal stents (LAMS).

The main question it aims to answer is:

Does introduction of double pigtail plastic stents through the LAMS increases efficacy and safety of endoscopic transmural drainage of post-inflammatory pancreatic and peripancreatic fluid collections?

Acute pancreatitis (AP) of moderate-to-severe clinical course is associated with a high risk of local complications and organ failure leading to increased mortality. Pancreatic and peripancreatic fluid collections (PPFCs) that can appear in the late phase of pancreatitis can take the form of pancreatic pseudocysts and walled-off pancreatic necrosis (WOPN). These types of PPFCs are the most common local complications of acute and chronic pancreatitis. For many years, the traditional treatment of post-inflammatory PPFCs in the late phase of pancreatitis relied on surgical methods. However, there has been a recent dynamic development of minimally invasive techniques, including endoscopic transluminal methods. While endoscopic treatment is an established method of managing these complications, some aspects of endotherapy are still a source of much controversy. One of the most debated issues in interventional endoscopy of local complications in pancreatitis is the use of transmural self-expanding metallic stents (SEMSs).

Endoscopic transmural drainage consists of creating a fistula between the lumen of the PPFC and gastrointestinal tract to allow for a free outflow of fluid out of the PPFC and into the gastrointestinal tract. During an endoscopic ultrasound (EUS)-guided procedure of endoscopic transmural drainage of post-inflammatory PPFCs, this can be visualized in the endosonographic image through the wall of the upper gastrointestinal tract. Afterwards, a transmural puncture of the PPFC is performed under EUS guidance and widened with a cystotome to a diameter of 10 Fr using coagulation. This forms a transmural cystostomy, which joins the gastrointestinal tract and the lumen of the PPFC. The next step of the endoscopic procedure is mechanical (with a dilator) or pneumatic (with a high-pressure balloon) dilation of the pancreaticocystogastrostomy or pancreaticocystoduodenostomy. Once dilated, a transmural SEMS or plastic stent(s) is introduced through the cystostomy to facilitate free passive transmural drainage of the collection contents into the gastrointestinal tract. Passive transmural drainage is an effective method of endoscopic treatment of pancreatic pseudocysts, whose contents are entirely liquid. In the case of necrotic PPFCs that contain both liquefied necrotic material and tissue fragments, it is necessary to use active transmural drainage, which consists of inserting an additional nasal drain through the transmural cystostomy to enable flushing of the collection cavity in the postoperative period.

The development of advanced endoscopic techniques has led to rapid advancements in biomedical materials, including polymers for manufacturing endoscopic devices. Currently, there is a wide variety of transmural endoprostheses of different sizes, shapes, and designs for endoscopic treatment of post-inflammatory PPFCs. These endoprostheses were divided into two groups. The first group includes plastic stents, usually made of Teflon or polyethylene. The second group is SEMSs, often referred to as "lumen-apposing metal stents" (LAMSs), that are used in the treatment of post-inflammatory pancreatic local complications. For many years, the only type of endoprosthesis available for use in transmural drainage was plastic double-pigtail stents. However, LAMSs have been attracting increasing interest as a relatively new option in endoscopy. LAMSs are a special type of SEMS used in a variety of gastrointestinal endoscopic procedures. They are made of nitinol wire and are fully covered with a silicone membrane.

However, the role of LAMSs in transmural drainage remains unclear. Many authors believe that use of LAMS during endoscopic transmural drainage increases risk of complications in form of bleeding. Despite the development of advanced endoscopic techniques and devices, the high rates of bleeding into the PPFC lumen remain a major challenge in transmural drainage treatment. This type of complication is often caused by blood vessels adjacent to the fluid collection being damaged by the distal flange of the LAMS. It seems that inserting a plastic double-pigtail stent through the LAMS limits the risk of this kind of complication by moving the back wall of the PPFC away from the distal flange, PPFC cavity bleeding during transmural drainage is still a major complication associated with a high risk of fatal outcomes.

In this trial the participants with post-inflammatory PPFCs will be divided into two arms.

The first arm will consist of participants who underwent traditional transmural drainage procedure with use of LAMS only.

The second arm will consist of participants with PPFCs who underwent endoscopic transmural drainage with use of LAMS and during the procedure double pigtail plastic stents will be introduced through the LAMS in order to prevent bleeding.

Each arm will consist of at least 50 participants with post-inflammatory PPFCs.

Inclusion Criteria:

• participants of both sexes aged above 18 years
• participants, who provided informed consent for such treatment
• eligibility for transmural endoscopic drainage of post-inflammatory pancreatic and peripancreatic fluid collections procedure according to current medical knowledge based on evidence-based medicine.

Exclusion Criteria:

• pregnancy, breastfeeding, or intention to become pregnant during the study
• contraindications to electrosurgical instruments
• allergy to any of the materials used in the study
• participants ineligible for endoscopic treatment
• participants ineligible for general anesthesia