In a 35-year-old woman presenting with jaundice, the most common site of biliary obstruction causing extrahepatic cholestasis is which of the following?

Explanation

## Most Common Site of Biliary Obstruction **Key Point:** The common bile duct (CBD) is the most common site of biliary obstruction in extrahepatic cholestasis, accounting for >80% of obstructive jaundice cases. ### Anatomical Basis for CBD Obstruction ```mermaid flowchart TD A[Biliary System]:::outcome --> B[Intrahepatic ducts]:::outcome A --> C[Extrahepatic ducts]:::outcome C --> D[Right hepatic duct]:::outcome C --> E[Left hepatic duct]:::outcome D --> F[Common hepatic duct]:::outcome E --> F F --> G[Common bile duct]:::action G --> H[Ampulla of Vater]:::outcome G --> I[Most common obstruction site]:::urgent ``` **High-Yield:** The CBD is the narrowest and longest segment of the biliary tree, making it the most vulnerable to obstruction by stones, strictures, and tumors. ### Common Causes of CBD Obstruction | Cause | Frequency | Clinical Feature | |-------|-----------|------------------| | Choledocholithiasis | 70–80% | Intermittent jaundice, pain | | Pancreatic cancer | 10–15% | Painless progressive jaundice | | CBD stricture | 5–10% | Post-surgical, post-inflammatory | | Cholangiocarcinoma | 3–5% | Insidious onset | **Clinical Pearl:** Painless progressive jaundice suggests malignant obstruction (pancreatic head cancer, cholangiocarcinoma), while colicky pain with jaundice suggests choledocholithiasis. **Mnemonic: CHOPS** — Choledocholithiasis, Hepatic duct (less common), Obstruction (CBD most common), Pancreatic cancer, Strictures. ### Why Other Sites Are Less Common - **Hepatic duct:** Rare obstruction site; usually involved in hilar cholangiocarcinoma (Klatskin tumor) - **Cystic duct:** Obstruction causes acute cholecystitis, not jaundice (unless Mirizzi syndrome) - **Intrahepatic ducts:** Obstruction is rare; seen in primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) [cite:Harrison 21e Ch 298]