Walled-Off Pancreatic Necrosis Mimicking a Pancreatic Pseudocyst: A Diagnostic Pitfall With Therapeutic Implications.

Pancreatic pseudocysts and walled-off pancreatic necrosis are distinct late complications of acute pancreatitis, each requiring different therapeutic approaches. Accurate characterization of pancreatic fluid collections before intervention is essential to minimize treatment failure and procedure-related complications. We present a case of a female patient with a history of severe necrotizing biliary pancreatitis who underwent surgical cystogastrostomy for a presumed pancreatic pseudocyst. During surgery, a retrogastric collection was accessed through the anterior gastric wall, yielding 2,600 mL of fluid with macroscopically apparent debris, followed by cystogastrostomy using an endoscopic linear stapler and laparoscopic cholecystectomy. The initial postoperative course was favorable; however, five days later, the patient developed severe upper gastrointestinal bleeding with a hemoglobin level of 6 g/dL. Urgent endoscopy demonstrated Forrest Ib bleeding at the cystogastrostomy site without successful endoscopic hemostasis, requiring emergency laparotomy, gastrostomy, and surgical hemostasis. The subsequent course was complicated by persistent gastric fistula, tissue lysis, and complete anastomotic dehiscence, requiring multiple surgical interventions, including closure of the posterior gastric defect with an omental patch, diverting jejunostomy, and feeding jejunostomy. After clinical stabilization and enteral nutritional support, delayed intestinal reconstruction was successfully performed. This case highlights the importance of distinguishing pancreatic pseudocysts from walled-off pancreatic necrosis, particularly in patients with a previous episode of extensive pancreatic necrosis. Although delayed imaging may demonstrate a predominantly fluid-filled collection, residual necrotic material may persist and influence treatment outcomes. Current management of walled-off pancreatic necrosis favors a delayed, minimally invasive step-up approach, with endoscopic transmural drainage, followed by necrosectomy when clinically indicated. Careful assessment of the nature and maturity of pancreatic collections before intervention may reduce the risk of severe complications, including bleeding, fistula formation, and anastomotic failure.