A 52-year-old woman presents to the emergency department with acute onset severe epigastric pain radiating to the back, associated with nausea and vomiting. Serum lipase is 420 U/L (normal <30 U/L). Abdominal ultrasound shows the finding marked **A** in the diagram. Which of the following best explains the pathophysiological mechanism by which this finding leads to acute pancreatitis?

Explanation

## Why option 1 is correct Gallstones are the most common cause of acute pancreatitis worldwide (40–50% of cases), with significantly higher prevalence in women due to the "4 F's" (Female, Fat, Forty, Fertile). The pathophysiological mechanism is well-established: a stone migrates from the gallbladder into the common bile duct, becomes impacted at the ampulla of Vater, and causes transient or persistent obstruction of the pancreatic duct opening. This obstruction leads to increased intraductal pressure, reflux of bile into pancreatic ducts, and crucially, activation of pancreatic enzymes (trypsinogen → trypsin) within the pancreatic parenchyma itself, triggering autodigestion and acute inflammation. This is the textbook mechanism described in Harrison 21e Ch 348 and Bailey & Love 28e. ## Why each distractor is wrong - **Option 2 (Alcohol)**: While alcohol is the second most common cause of acute pancreatitis (30–40%, predominating in men), its mechanism differs fundamentally—it causes direct toxic injury to acinar cells and increases ductal permeability, not mechanical obstruction at the ampulla. This patient's imaging shows gallstones, not a history of heavy alcohol use. - **Option 3 (Hypertriglyceridemia)**: Although severe hypertriglyceridemia (TG > 1000 mg/dL) is a recognized cause of pancreatitis via lipotoxicity and duct obstruction, it accounts for only 1–4% of cases and is not the finding marked **A** on this patient's ultrasound. - **Option 4 (Post-ERCP)**: Post-ERCP pancreatitis occurs in 3–5% of endoscopic procedures due to direct mechanical trauma to the pancreatic duct. However, this patient presented with acute symptoms before any intervention, and the ultrasound finding is gallstones, not a history of recent ERCP. **High-Yield:** Gallstones → ampulla obstruction → ductal hypertension + enzyme activation = gallstone pancreatitis; alcohol → direct acinar toxicity + ductal permeability = alcoholic pancreatitis. Female predominance = think stones first. [cite: Harrison 21e Ch 348; Bailey & Love 28e]