What is the most likely diagnosis for a patient presenting with obstructive jaundice, elevated liver enzymes, and ultrasound findings of dilated bile ducts and a distended gallbladder?

Most Likely Diagnosis: Pancreatic Cancer

Based on the classic presentation of obstructive jaundice with a palpable distended gallbladder (Courvoisier's sign), the most likely diagnosis is pancreatic cancer (Option B).

Clinical Reasoning

Key Diagnostic Feature: Courvoisier's Sign

• A palpable, distended gallbladder in the setting of painless obstructive jaundice strongly suggests malignant distal biliary obstruction, most commonly from pancreatic cancer 1
• This clinical sign is rarely seen with benign causes like common bile duct stones, as chronic gallstone disease typically results in a fibrotic, non-distensible gallbladder 1

Laboratory Pattern Analysis

• The markedly elevated direct bilirubin (122.3 μmol/L, normal 1.5-6.5) and total bilirubin (134.5 μmol/L, normal 3.5-16.5) with elevated alkaline phosphatase (421 IU/L, normal 39-117) demonstrate a classic obstructive cholestatic pattern 1
• This pattern is consistent with extrahepatic biliary obstruction from any cause, but must be interpreted with imaging and clinical findings 1

Ultrasound Findings Interpretation

• Dilated intra- AND extrahepatic bile ducts with hugely distended gallbladder points to distal common bile duct obstruction 1
• This pattern excludes Klatskin tumor (Option A), which characteristically shows dilated intrahepatic ducts with normal-sized extrahepatic ducts 2, 3

Differential Diagnosis Elimination

Why NOT Klatskin Tumor (Option A):

• Klatskin tumors (perihilar cholangiocarcinoma) occur at the confluence of the right and left hepatic ducts 1
• The pathognomonic ultrasound finding for Klatskin tumor is dilated intrahepatic bile ducts with a normal-sized extrahepatic biliary tree 2, 3
• This patient has dilated extrahepatic ducts, which excludes this diagnosis 2

Why NOT Mirizzi's Syndrome (Option C):

• Mirizzi's syndrome involves extrinsic compression of the common hepatic duct by an impacted gallstone in the cystic duct or Hartmann's pouch 4
• This typically does NOT produce a hugely distended gallbladder, as the gallbladder itself is diseased and fibrotic 4
• The 2-month progressive course without acute cholecystitis symptoms makes this unlikely 4

Why NOT Common Bile Duct Stone (Option D):

• While CBD stones can cause obstructive jaundice with dilated ducts, a palpable distended gallbladder is uncommon with benign obstruction 1
• Chronic gallstone disease causes gallbladder fibrosis, preventing distension (negative Courvoisier's sign) 1
• CBD stones more commonly present with acute symptoms, cholangitis, or fluctuating jaundice rather than progressive 2-month history 1

Clinical Pitfalls to Avoid

Common Diagnostic Errors:

• Do not assume all distal biliary obstructions are stones - the presence of Courvoisier's sign mandates investigation for malignancy 1, 5
• Do not rely solely on ultrasound for definitive diagnosis - while US is appropriate for initial evaluation, contrast-enhanced CT or MRI/MRCP is required for complete assessment of pancreatic masses 1
• Do not delay further imaging - this patient requires urgent MDCT or MRI/MRCP to confirm pancreatic mass, assess resectability, and evaluate for metastases 1

Next Steps in Management:

• Obtain contrast-enhanced CT abdomen or MRI with MRCP to visualize pancreatic head mass and assess vascular involvement 1
• Measure CA 19-9 tumor marker (elevated in up to 85% of pancreaticobiliary malignancies, though not specific) 1
• Consider ERCP with biliary stenting for symptomatic relief if unresectable, or proceed to surgical evaluation if resectable 1, 5
• Tissue diagnosis via EUS-guided fine needle aspiration if needed for treatment planning 1