How do gallstones cause pancreatitis?

Mechanism of Gallstone-Induced Pancreatitis

Gallstone pancreatitis is primarily caused by transient obstruction of the ampulla of Vater by a migrating gallstone, leading to pancreatic duct blockage and subsequent intraglandular activation of pancreatic enzymes. 1

Pathophysiological Mechanism

Obstruction Phase

• Gallstones migrate from the gallbladder through the cystic duct into the common bile duct
• The stone then causes temporary blockage at the ampulla of Vater (the junction where pancreatic and bile ducts meet)
• This obstruction prevents normal pancreatic enzyme drainage into the duodenum 1

Enzyme Activation

• The blockage causes pancreatic secretions to back up into the pancreas
• Pancreatic enzymes (normally inactive until reaching the duodenum) become prematurely activated within the pancreas itself
• These activated digestive enzymes (including trypsin, chymotrypsin, lipase, and amylase) begin autodigestion of pancreatic tissue 1

Inflammatory Response

• Autodigestion triggers an intense inflammatory response
• Inflammatory mediators are released into circulation
• This leads to both local pancreatic inflammation and potential systemic inflammatory effects
• In severe cases, this can progress to pancreatic necrosis and multi-organ failure 2

Clinical Considerations

Risk Factors

• Small gallstones (< 5mm) are more likely to cause pancreatitis than larger stones
• Multiple small stones present higher risk than single stones
• The risk of gallstone pancreatitis is increased in Crohn's disease but not in ulcerative colitis 2

Diagnostic Approach

• Diagnosis is based on clinical presentation, elevated pancreatic enzymes (amylase/lipase), and imaging
• Ultrasound and CT scans can identify gallstones and assess pancreatic inflammation
• Endoscopic retrograde cholangiopancreatography (ERCP) may be used in uncertain cases to confirm common bile duct stones 1

Complications

• Persistent obstruction can lead to more severe disease including:
  • Pancreatic necrosis
  • Pseudocyst formation
  • Abscess development
  • Systemic inflammatory response syndrome
  • Multi-organ failure 3

Management Implications

Acute Management

• The primary goal is to remove the obstructing stone and prevent further obstruction
• For mild cases, supportive care with monitoring for resolution
• For severe cases with persistent obstruction or cholangitis, urgent ERCP with sphincterotomy is indicated 4

Definitive Treatment

• Cholecystectomy is crucial for preventing recurrent episodes of biliary pancreatitis
• In mild cases, cholecystectomy can be performed during the same hospitalization once symptoms resolve
• In severe cases, cholecystectomy should be delayed until inflammation subsides 5, 4

Prevention

• Cholecystectomy remains the definitive preventive measure for recurrent gallstone pancreatitis
• Early cholecystectomy (within 48 hours) for mild cases is supported by clinical trials
• For severe cases, the optimal timing remains unclear but should be performed once the patient stabilizes 4

Rare Presentations

In rare cases, gallstones can directly enter and obstruct the pancreatic duct itself rather than just the ampulla, which has been documented through ERCP imaging 6. This direct pancreatic duct obstruction represents an uncommon but important variant of the pathophysiological mechanism.