What is walled‑off necrosis, its clinical presentation, and recommended management?

Walled-Off Necrosis: Definition and Clinical Management

Definition

Walled-off necrosis (WON) is a mature, encapsulated collection of pancreatic and/or peripancreatic necrotic tissue that develops at least 4 weeks after the onset of acute necrotizing pancreatitis, characterized by a well-defined, enhancing inflammatory wall. 1

Key Distinguishing Features

• Timing: WON develops after 4 weeks from pancreatitis onset, distinguishing it from acute necrotic collections (ANC) which occur within the first 4 weeks 1, 2
• Composition: Contains heterogeneous material with both liquid and solid necrotic debris, unlike simple pseudocysts which contain only fluid 1, 3
• Encapsulation: Possesses a mature inflammatory wall formed by granulation tissue, making it a chronic collection 1, 4

Critical Distinction from Other Collections

Clinicians must not mistake WON for simple pseudocysts—the internal consistency is best determined by endoscopic ultrasound (EUS) or magnetic resonance imaging (MRI) 1. The revised Atlanta classification discourages use of the term "pancreatic abscess"; instead, any pancreatic collection can become infected 1.

Clinical Presentation

Symptomatic Presentations (50% of cases)

• Pain: Persistent or worsening abdominal pain after initial pancreatitis episode 3, 2
• Fever: Suggesting possible infection of the necrotic collection 3
• Obstructive symptoms: Gastric outlet obstruction, biliary obstruction, or intestinal obstruction from mass effect 4, 3
• Jaundice: From biliary compression 3

Asymptomatic Presentations (50% of cases)

Approximately half of WON cases remain asymptomatic and the majority resolve spontaneously without intervention 3.

Infection Risk

• Infection occurs in 20-40% of patients with severe acute pancreatitis, typically after 7-10 days of illness 5
• Infected necrosis with persistent organ failure carries 35.2% mortality, while infected necrosis without organ failure has only 1.4% mortality 5
• Suspect infection in patients with preexisting sterile necrosis who develop persistent/worsening symptoms or signs of infection 1

Diagnostic Approach

Imaging Modalities

• Initial assessment: Contrast-enhanced CT 72-96 hours after symptom onset to assess for necrosis development 5
• Best for characterizing solid debris: MRI and EUS are superior for evaluating the internal consistency and amount of solid necrotic material 1, 3
• Maturation assessment: Imaging at 4 weeks to confirm encapsulation and wall formation 1, 4

Confirming Infection

When infection is suspected, perform CT-guided fine-needle aspiration with Gram stain and culture to document infection 1. Tailor antibiotic therapy based on aspiration results 1.

Management Algorithm

Conservative Management (First-Line for Asymptomatic WON)

Small (<5 cm), stable, and sterile WON can be managed conservatively as most resolve spontaneously 4, 3.

• Early enteral nutrition via nasogastric or nasojejunal tube to prevent gut failure and infectious complications 6
• Supportive care with fluid resuscitation and organ support 5
• Serial imaging to monitor for complications 5

Indications for Intervention

Intervention is required for:

• Clinical deterioration with signs or strong suspicion of infected WON 4
• Ongoing organ failure without infection signs (after 4 weeks) 4
• Gastric outlet, biliary, or intestinal obstruction 4
• Disconnected pancreatic duct syndrome 4
• Symptomatic or growing collections 4
• Ongoing pain/discomfort (after 8 weeks) 4

Step-Up Approach to Intervention

The step-up approach prioritizes less invasive techniques before surgery, with endoscopic drainage as the preferred initial method 4, 7.

First Step: Endoscopic Drainage

• EUS-guided cystogastrostomy is the preferred initial approach 4
• Advantages include shorter hospital stays, better patient-reported outcomes, and high success rates (48-67% definitive control) 4, 3
• Optimal for central collections abutting the stomach 1, 4
• Lumen-apposing metal stents (LAMS) with cautery-enhanced delivery systems are currently preferred, but should be removed at 3 weeks if WON is resolved to avoid stent-related complications 7
• Bleeding occurs in approximately 14% of cases 4

Second Step: Percutaneous Catheter Drainage (PCD)

• Consider for collections involving the pancreatic tail, those not in direct communication with the pancreas, or poor surgical candidates 4
• Requires prolonged drainage period and has higher reintervention rates than endoscopic approaches 1, 4
• Cure rates when used alone are only 14-32% 4
• May fail if complete pancreatic duct occlusion exists central to the collection 1, 4

Third Step: Surgical Intervention

Reserved for failure of less invasive approaches 4:

• Failure of percutaneous/endoscopic procedures 4
• Abdominal compartment syndrome unresponsive to conservative management 5, 4
• Acute ongoing bleeding when endovascular approach fails 5, 4
• Bowel complications or fistula extending into collection 4

Surgery should be postponed until >4 weeks after disease onset to reduce mortality 5, 4. Surgical options include laparoscopic or open cystogastrostomy with pseudocyst recurrence rates of 2.5-5% 4.

Special Considerations for Infected WON

• Manage at centers with specialist expertise in endoscopic, radiologic, and surgical management 1, 4
• Antibiotic therapy tailored to culture results 1
• Delayed intervention (after 4 weeks) results in lower mortality 5, 8

Antibiotic Prophylaxis

Evidence for antibiotic prophylaxis to prevent conversion of sterile to infected necrosis is mixed 1. If used, restrict to patients with substantial necrosis (≥30% of gland by CT) and continue for no more than 14 days 1.

Critical Pitfalls to Avoid

• Never intervene before 4 weeks unless absolute indications exist (abdominal compartment syndrome, acute bleeding unresponsive to endovascular approach, or bowel ischemia) 5, 4
• Do not rely on size alone as criterion for intervention; under revised criteria, size does not warrant treatment by itself 4
• Do not mistake WON for simple pseudocyst—this leads to inappropriate treatment selection 1
• Avoid early surgical intervention (<4 weeks) as it results in higher mortality 4, 8
• Do not use needle aspiration therapeutically—it is primarily a diagnostic tool 4
• Remove LAMS early (at 3 weeks) if WON is resolved to prevent stent-related complications 7