What is a pancreatic pseudocyst, including its pathophysiology, clinical presentation, diagnosis, and management?

Pancreatic Pseudocyst: Comprehensive Overview

Definition and Pathophysiology

A pancreatic pseudocyst is a collection of pancreatic juice enclosed by a wall of fibrous or granulation tissue that develops following acute pancreatitis, requiring at least 4 weeks from disease onset to form. 1, 2 This time requirement is critical—collections appearing earlier are classified as acute fluid collections, which lack the organized fibrous wall and have different natural histories. 1, 2

The pseudocyst wall consists of fibrous or granulation tissue but is not lined by epithelium, distinguishing it from true cysts. 1, 3 This organized wall formation takes time to develop, explaining the 4-week threshold. 2

Critical distinction: All localized collections following necrotizing pancreatitis should be considered localized necrosis (walled-off necrosis) until proven otherwise with definite imaging evidence showing fluid rather than necrotic tissue. 2 This is a common diagnostic pitfall—mistaking walled-off necrosis for simple pseudocyst leads to inappropriate management and worse outcomes. 4

Clinical Presentation

The clinical presentation is often nonspecific, with abdominal pain being the most common symptom. 5 Key presentations include:

• Epigastric mass with vomiting suggests a persistent fluid collection that may have formed a pseudocyst, potentially causing gastric outlet obstruction. 2, 6
• Persistent epigastric discomfort, bloating, and loss of appetite indicate symptomatic pseudocyst requiring intervention consideration. 4
• Sudden high fever suggests infection, though unremitting low-grade fever is common in necrotizing pancreatitis without necessarily indicating infection. 2
• Jaundice may indicate biliary obstruction from mass effect. 4

Diagnostic Approach

Initial Imaging

CT scanning is the most common and first-line diagnostic tool for pseudocyst evaluation. 2, 7, 5 However, CT alone cannot reliably distinguish pseudocyst from other peripancreatic collections. 2

Ultrasound or MRI must be obtained to confirm fluid content (as opposed to necrotic tissue) before definitively diagnosing pseudocyst. 2, 4 This step is essential to avoid the critical error of mistaking walled-off necrosis for pseudocyst. 4

Advanced Imaging

• Endoscopic ultrasound (EUS) with fine needle aspiration has become the preferred test to distinguish pseudocyst from other cystic lesions when diagnostic uncertainty exists. 8
• MRI or MRCP is preferred for pregnant females and can document communication between the cyst and main pancreatic duct. 1
• Dynamic CT scanning between 3-10 days after admission delineates the extent of pancreatic and peripancreatic necrosis in severe cases. 1, 6

Monitoring Protocol

In severe cases, repeat CT scanning every 2 weeks monitors for complications. 2 Patients with three or more fluid collections have greater risk of complications and death. 6

Natural History and Conservative Management

More than half of acute fluid collections resolve spontaneously, and in otherwise stable patients they do not require treatment. 2 The size and duration of pseudocyst are poor predictors of resolution potential or complications, though larger cysts are more likely to be symptomatic. 8

Most pseudocysts resolve with supportive care alone. 8 This conservative approach is appropriate for asymptomatic patients without complications.

Indications for Intervention

Intervention is indicated when:

• Clinical deterioration with signs of infected necrotizing pancreatitis 4
• Gastric outlet, biliary, or intestinal obstruction 4, 5
• Symptomatic or growing pseudocyst causing persistent epigastric discomfort, bloating, or loss of appetite 4
• Hemorrhage: CT attenuation values >50 HU suggest blood content 2
• Infection: indicated by sudden high fever 2
• Rupture: free gas in retroperitoneum on plain films is a late sign of infection with gas-forming organisms 2, 6

Management Algorithm

Step-Up Treatment Approach

The American College of Gastroenterology recommends a step-up treatment approach, starting with EUS-guided cystogastrostomy for central collections abutting the stomach, with success rates of 48-67% and low complication rates. 4

Treatment Options by Priority

1. Endoscopic drainage (first-line):

   • Transpapillary or transmural drainage provides high success and low complication rates 7, 9
   • EUS-guided cystogastrostomy for central collections 4
   • Less invasive than surgery, avoids external drain, high long-term success rate 8
   • Feasibility highly dependent on anatomy and topography 7, 9

2. Percutaneous catheter drainage (second-line):

   • Recommended for large, complex collections involving the tail 4
   • Used for infected pseudocysts 7, 9
   • Requires prolonged drainage period with higher reintervention rates 4
   • Usefulness in chronic pancreatitis-associated pseudocysts is questionable 7, 9

3. Surgical intervention (reserved for failures):

   • Reserved for failed endoscopic/percutaneous approaches 4
   • Must be postponed >4 weeks after disease onset to reduce mortality 4
   • Internal drainage and pseudocyst resection have good overall outcome but somewhat higher morbidity and mortality compared with endoscopic intervention 7, 9

Specialist Referral Criteria

Management in, or referral to, a specialist unit is necessary for patients with extensive necrotizing pancreatitis or complications who may require ITU care and/or interventional radiological, endoscopic, or surgical procedures. 1, 4

A specialist unit must have:

• Full intensive care facilities 1, 2
• Emergency ERCP capability available at any time 1, 2
• Expert radiological support for dynamic scanning, percutaneous procedures, and angiography 1, 2
• Surgeon with pancreatico-biliary expertise supervising management 1

Transfer criteria include:

• Extensive necrotizing pancreatitis 1, 4
• Infected collections 4
• Organ failure 4
• Failed initial interventions 4

Complications

The most frequent complication following nonoperative management is pseudocyst formation itself. 1 Other complications include:

• Hemorrhage (CT attenuation >50 HU suggests blood) 2
• Infection (7-25% of pancreatic injuries develop abscess or intra-abdominal sepsis) 1
• Pancreatic fistula (10-35% of major injuries after operative drainage or resection) 1
• Post-traumatic pancreatitis (17% incidence) 1
• Biliary or gastric outlet obstruction 4

Common Pitfalls

• Do not mistake walled-off necrosis for simple pseudocyst—internal consistency must be determined by EUS or MRI before treatment planning. 4
• Do not rely on CT alone for diagnosis—confirm fluid content with ultrasound or MRI. 2, 4
• Do not perform surgical intervention before 4 weeks from disease onset—premature surgery increases mortality. 4
• Do not assume size or duration predicts outcome—clinical symptoms and complications drive management decisions. 8
• Consider recurrence even years later—late recurrent pseudocysts can occur up to 9 years after initial treatment, requiring evaluation to rule out cystic neoplasm. 3