Among patients presenting with jaundice and a dilated common bile duct on ultrasound, what is the most common cause of biliary obstruction worldwide?

Explanation

## Epidemiology of Obstructive Jaundice When imaging reveals a dilated common bile duct (CBD), the differential diagnosis narrows to mechanical obstruction. Among all causes of biliary obstruction, gallstones are overwhelmingly the most common. ## Why Choledocholithiasis is the Answer **Key Point:** Gallstones account for 80–90% of all cases of obstructive jaundice worldwide. Choledocholithiasis occurs when a stone migrates from the gallbladder into the common bile duct, causing acute or chronic obstruction. **High-Yield:** The classic triad of obstructive jaundice from choledocholithiasis is: 1. Jaundice (conjugated hyperbilirubinemia) 2. Pale/clay-colored stools (reduced bile reaching intestine) 3. Dark urine (conjugated bilirubin in urine) **Mnemonic — Causes of Obstructive Jaundice (in order of frequency):** **SCAB** - **S**tones (choledocholithiasis) — 80–90% - **C**ancer (pancreatic head, cholangiocarcinoma) — 10–15% - **A**bscess, strictures, parasites - **B**iliary atresia (neonates) **Clinical Pearl:** Choledocholithiasis is more common in patients with a history of biliary colic, female sex, family history of gallstones, or rapid weight loss. In India, parasitic causes (ascariasis, echinostomiasis) are more common than in Western populations, but stones remain the leading cause overall. ## Comparison Table | Cause | Frequency | Onset | Imaging | Bilirubin Pattern | | --- | --- | --- | --- | --- | | **Choledocholithiasis** | 80–90% | Acute (hours–days) | Stone in CBD on US/CT | Conjugated ↑↑ | | **Pancreatic cancer** | 5–10% | Insidious (weeks–months) | Mass at head; CBD dilated | Conjugated ↑↑ | | **Cholangiocarcinoma** | 2–5% | Insidious | Stricture; "double duct sign" | Conjugated ↑↑ | | **Strictures** | 1–3% | Variable | Narrowing on ERCP | Conjugated ↑↑ | [cite:Harrison 21e Ch 297; Robbins 10e Ch 18]