A 45-year-old male with a history of chronic alcohol use presents with severe epigastric pain radiating to the back, associated with Grey-Turner sign. CT abdomen performed at day 5 of illness shows the finding marked **A** — a heterogeneous walled collection with non-enhancing necrotic pancreas. Which of the following best describes the pathophysiological mechanism underlying this radiological finding?

Explanation

## Why "Premature intra-acinar trypsinogen activation leading to pancreatic autodigestion and necrosis" is right The structure marked **A** — a heterogeneous walled collection with non-enhancing necrotic pancreas — is the radiological hallmark of walled-off necrosis (WON), which occurs in necrotizing pancreatitis. The pathophysiological mechanism of necrotizing pancreatitis is premature intra-acinar trypsinogen activation, which triggers pancreatic autodigestion, systemic inflammatory response (SIRS), and necrosis of pancreatic and peripancreatic tissue. This patient's clinical presentation (alcohol history, severe epigastric pain radiating to back, Grey-Turner sign indicating retroperitoneal hemorrhage) and imaging findings at day 5 are classic for necrotizing pancreatitis. Per Harrison 21e Ch 348, this mechanism is the fundamental pathophysiology distinguishing necrotizing from interstitial edematous pancreatitis. ## Why each distractor is wrong - **Obstruction of the main pancreatic duct by a gallstone with subsequent parenchymal atrophy**: This describes chronic pancreatitis with ductal obstruction, which presents with calcifications and atrophy (structure **C**), not acute necrosis with a heterogeneous walled collection. Gallstones cause acute pancreatitis via biliary reflux, not ductal obstruction. - **Chronic inflammation with fibrosis and calcification of the pancreatic parenchyma**: This is the pathophysiology of chronic pancreatitis, which would show ductal dilatation and calcifications (structure **C**), not acute necrotic collections. The timeline (day 5) and clinical presentation indicate acute, not chronic, disease. - **Malignant transformation of pancreatic ductal epithelium with infiltration of peripancreatic fat**: This describes pancreatic cancer, which would present with a hypoenhancing mass and double-duct sign (structure **D**), not a heterogeneous necrotic collection. The clinical context of acute pancreatitis does not support malignancy. **High-Yield:** Necrotizing pancreatitis (10–20% of acute pancreatitis) has 15–30% mortality; pathophysiology is premature trypsinogen activation → autodigestion; WON appears after 4 weeks with enhancing wall + non-enhancing necrosis; step-up approach (fluids → ERCP → antibiotics + drainage → endoscopic necrosectomy) improves outcomes. [cite: Harrison 21e Ch 348]