Choledocholithiasis (Answer: C)
The most likely diagnosis is choledocholithiasis (common bile duct stones), given the combination of right upper quadrant pain, jaundice, elevated conjugated bilirubin (30 μmol/L), markedly elevated alkaline phosphatase (280 IU/L), and most importantly, a dilated common bile duct measuring 1 cm on ultrasound with multiple gallstones. 1, 2
Clinical Reasoning
This patient presents with a classic cholestatic pattern that points directly to biliary obstruction:
The dilated common bile duct (1 cm) is the key diagnostic finding that confirms mechanical biliary obstruction, as ultrasound has 71-97% specificity for detecting obstructive jaundice by demonstrating bile duct dilatation 1, 2
The cholestatic liver enzyme pattern (elevated alkaline phosphatase 280 IU/L with elevated bilirubin 30 μmol/L) indicates biliary obstruction rather than hepatocellular injury 1, 3
Multiple gallstones visualized on ultrasound combined with CBD dilatation strongly suggests stone migration into the common bile duct, which occurs in 10-20% of patients with cholelithiasis 3
Why Not the Other Diagnoses?
Acute cholecystitis (B) is excluded because:
- No pericholecystic fluid is present on ultrasound 1
- The absence of gallbladder wall thickening or pericholecystic inflammation makes acute cholecystitis unlikely 1, 2
- The dilated CBD points to a more distal obstruction beyond the gallbladder 1
Ascending cholangitis (D) is less likely because:
- The patient lacks the complete Charcot's triad (fever, jaundice, RUQ pain) - no fever is mentioned 3
- While leukocytosis (WBC 15) is present, ascending cholangitis is a life-threatening condition that typically presents with more severe systemic toxicity 3
- Choledocholithiasis is the underlying cause that can lead to cholangitis if untreated, but this patient appears to have uncomplicated biliary obstruction 3
Acute pancreatitis (A) is unlikely because:
- The enzyme pattern is cholestatic (high alkaline phosphatase) rather than showing elevated amylase/lipase 4
- The dilated CBD with stones is the primary pathology, though gallstone pancreatitis could develop as a complication 3
Important Clinical Caveats
Normal liver enzymes do not exclude choledocholithiasis - a small case series demonstrated that CBD stones can exist with repeatedly normal bilirubin and liver enzymes, particularly when marked CBD dilatation serves as a "pressure sump" 5
The absence of intrahepatic duct dilatation does not rule out obstruction - early or intermittent obstruction may not show upstream dilatation 5, 6
This patient requires MRCP as the next diagnostic step to comprehensively evaluate the biliary tree, as MRCP has 85-100% sensitivity and 90% specificity for detecting choledocholithiasis 7, 2
Therapeutic ERCP should follow confirmatory imaging rather than being performed empirically, as ERCP carries risks of pancreatitis and perforation 7, 8