Walled‑Off Necrosis (WON): Definition, Diagnosis, and Evidence‑Based Management

Definition

• WON is a mature, encapsulated collection of pancreatic and/or peripancreatic necrotic tissue that develops ≥ 4 weeks after the onset of acute necrotizing pancreatitis and is surrounded by a well‑defined, enhancing inflammatory wall. – International Society for Pancreatic Surgery (World Journal of Emergency Surgery 2019) 1

Distinguishing Features

• Timing: WON appears after ≥ 4 weeks, whereas acute necrotic collections occur within the first 4 weeks of pancreatitis. – International Society for Pancreatic Surgery (World Journal of Emergency Surgery 2019) & American College of Radiology (Journal of the American College of Radiology 2020) 1, 2
• Composition: WON contains heterogeneous liquid and solid necrotic debris, in contrast to simple pseudocysts that contain only fluid. – American Gastroenterological Association (Gastroenterology 2007) 3
• Encapsulation: A mature inflammatory wall formed by granulation tissue characterizes WON as a chronic collection. – International Society for Pancreatic Surgery (World Journal of Emergency Surgery 2019) 1

Imaging for Diagnosis

• Characterizing solid debris: Magnetic resonance imaging (MRI) and endoscopic ultrasound (EUS) are superior to CT for evaluating the internal consistency and amount of solid necrotic material. – American Gastroenterological Association (Gastroenterology 2007) 3
• Maturation assessment: Imaging performed at ≈ 4 weeks confirms encapsulation and wall formation. – International Society for Pancreatic Surgery (World Journal of Emergency Surgery 2019) 1
• Optimal endoscopic approach: EUS‑guided cystogastrostomy is the preferred technique for centrally located collections abutting the stomach. – American College of Radiology (Journal of the American College of Radiology 2020) 2

Confirming Infection

• Clinical suspicion: Infection should be suspected in patients with previously sterile necrosis who develop persistent or worsening symptoms/signs of infection. – American Gastroenterological Association (Gastroenterology 2007) 3
• Diagnostic aspiration: When infection is suspected, perform CT‑guided fine‑needle aspiration with Gram stain and culture to document infection. – American Gastroenterological Association (Gastroenterology 2007) 3
• Targeted antibiotics: Antibiotic therapy must be tailored to the results of the aspiration culture. – American Gastroenterological Association (Gastroenterology 2007) 3

Management Strategies

Endoscopic Drainage (First Step)

• Indication: Endoscopic drainage is the initial preferred minimally invasive intervention for WON, especially when the collection is adjacent to the gastric wall. – American College of Radiology (Journal of the American College of Radiology 2020) 2

Percutaneous Catheter Drainage (Second Step)

• Higher re‑intervention: Percutaneous catheter drainage (PCD) is associated with higher re‑intervention rates compared with endoscopic approaches. – American College of Radiology (Journal of the American College of Radiology 2020) 2
• Limited cure rates: When used alone, PCD achieves cure in only ≈ 14–32 % of cases. – American College of Radiology (Journal of the American College of Radiology 2020) 2
• Failure with duct occlusion: PCD may fail if a complete pancreatic duct occlusion lies centrally to the collection. – American College of Radiology (Journal of the American College of Radiology 2020) 2

Antibiotic Prophylaxis

*Evidence for prophylactic antibiotics to prevent conversion of sterile to infected necrosis is mixed; use should be limited to the above high‑risk group. – American Gastroenterological Association (Gastroenterology 2007) 3

Specialized Care for Infected WON

• Center expertise: Management of infected WON should be performed at centers with multidisciplinary expertise in endoscopic, radiologic, and surgical techniques. – American Gastroenterological Association (Gastroenterology 2007) 3

Critical Pitfalls (Evidence‑Based)

• Do not mistake WON for a simple pseudocyst; misclassification leads to inappropriate treatment. – American Gastroenterological Association (Gastroenterology 2007) 3

All facts are derived from peer‑reviewed guidelines or consensus statements; specific levels of evidence were not provided in the source articles.

Management of Peripancreatic Walled Off Necrotic Pseudocyst

Understanding Pancreatic Collections

• Pancreatic collections are classified according to the revised Atlanta classification based on the presence of necrosis and time since onset of pancreatitis 4
• Walled-off necrosis (WON) refers to a mature, encapsulated collection of pancreatic and/or peripancreatic necrosis that has developed a well-defined inflammatory wall, typically occurring >4 weeks after onset of pancreatitis 5
• Infected pancreatic collections are associated with high mortality rates and require prompt intervention 6

Indications for Intervention

• Clinical deterioration with signs or strong suspicion of infected necrotizing pancreatitis 7
• Ongoing organ failure without signs of infected necrosis (after 4 weeks) 8
• Gastric outlet, biliary, or intestinal obstruction due to large walled-off necrotic collection 8
• Disconnected pancreatic duct syndrome 8
• Symptomatic or growing pseudocyst 8
• Ongoing pain and/or discomfort (after 8 weeks) 8

Step-Up Approach to Management

• Endoscopic ultrasound (EUS)-guided cystogastrostomy is the preferred initial approach 9
• Advantages of endoscopic drainage include shorter hospital stays compared to surgical approaches 9 and better patient-reported mental and physical outcomes 9
• Endoscopic drainage is optimal for central collections abutting the stomach 9
• Percutaneous Catheter Drainage (PCD) may be considered for large, complex collections involving the pancreatic tail 10, collections not in direct communication with the pancreas 10, or patients who are poor surgical candidates 10
• PCD has limitations, including typically requiring prolonged drainage period 10, higher rates of reintervention compared to endoscopic approaches 10, and lower cure rates (14-32%) when used alone 10

Surgical Intervention

• Surgical intervention is reserved for cases where less invasive approaches fail 7
• Indications for surgical intervention include failure of percutaneous/endoscopic procedures 7, abdominal compartment syndrome 7, acute ongoing bleeding when endovascular approach fails 7, and bowel complications or fistula extending into collection 7
• Surgical approaches include laparoscopic or open cystogastrostomy 6
• Reported pseudocyst recurrence rates of 2.5-5% 6
• Surgical intervention should be postponed for >4 weeks after disease onset to reduce mortality 7

Special Considerations

• Main pancreatic duct status should be evaluated, as complete occlusion central to the pseudocyst may lead to failure of PCD 10
• Conservative management may be appropriate for small (<5cm), stable, and sterile pseudocysts 6
• Infected collections should be managed at centers with specialist expertise in endoscopic, radiologic, and surgical management 11

Pitfalls to Avoid

• Avoid early surgical intervention (<4 weeks after disease onset) as it results in higher mortality 7
• Don't rely solely on size as the criterion for intervention; under revised criteria, size alone does not warrant treatment 6
• Needle aspiration should be used primarily as a diagnostic tool, not for therapeutic purposes 6
• Recognize that percutaneous drainage alone has limited success for definitive treatment of necrotic collections 10

Management of Pancreatic Pseudocyst

Diagnostic Considerations

• CT scanning confirms the diagnosis and helps evaluate the maturity of the collection, according to the Gut guideline society 12

Treatment Outcomes

• EUS-guided cystogastrostomy has high success rates, with 48-67% definitive control and low complication rates, as reported by the Gastroenterology guideline society 13
• Endoscopic treatment has an appreciable morbidity rate, with bleeding occurring in approximately 14% of cases, as noted by the Gastroenterology guideline society 13
• Surgical drainage has no significant morbidity when performed appropriately, with no pseudocyst recurrence reported in well-selected cases and recurrence rates of 2.5-5% in larger series, according to the Gastroenterology guideline society 13