During a laparoscopic cholecystectomy for symptomatic cholelithiasis, the surgeon encounters a stone impacted in the biliary tree. What is the most common site of impaction of gallstones within the biliary system?

Explanation

## Most Common Site of Gallstone Impaction ### Anatomy and Frequency of Impaction Sites | Site | Frequency | Clinical Significance | |------|-----------|----------------------| | **Ampulla of Vater (Oddi's sphincter)** | 60–70% | Causes choledocholithiasis; risk of pancreatitis | | Hartmann's pouch | 20–30% | Cystic duct obstruction; acute cholecystitis | | Common bile duct (proximal/mid) | 5–10% | Obstructive jaundice | | Hepatic ducts | <5% | Rare; intrahepatic stones | **Key Point:** When a stone escapes the gallbladder and enters the common bile duct (choledocholithiasis), it most commonly impacts at the ampulla of Vater (the narrowest and most dependent part of the biliary tree), where it meets the duodenum. ### Why the Ampulla of Vater? 1. **Anatomical narrowing:** Sphincter of Oddi creates the tightest point in the biliary tree 2. **Dependent position:** Gravity favors stone migration to the lowest point 3. **Angle of entry:** The common bile duct enters the duodenum at an acute angle, creating a natural "trap" 4. **Peristalsis:** Duodenal contractions can push stones backward into the ampulla ### Clinical Consequences of Ampullary Impaction - **Obstructive jaundice:** Elevated conjugated bilirubin, dark urine, pale stools - **Acute pancreatitis:** Stone transiently obstructs pancreatic duct orifice (most common cause of gallstone pancreatitis) - **Cholangitis:** If infection supervenes (fever, jaundice, RUQ pain = Charcot's triad) **High-Yield:** Ampullary impaction is the most common site of choledocholithiasis and is the most frequent cause of gallstone-induced acute pancreatitis. This is heavily tested in NEET PG. **Clinical Pearl:** ERCP with sphincterotomy is the gold standard for removal of stones impacted at the ampulla of Vater.