What is the most likely diagnosis for a patient presenting with jaundice, dark urine, pale stool, and a palpable distended gallbladder, with lab results showing elevated alkaline phosphatase, direct bilirubin, and total bilirubin, and ultrasound findings of dilated intra and extrahepatic bile ducts?

Most Likely Diagnosis: Pancreatic Cancer

The most likely diagnosis is B. Pancreatic cancer, based on the classic presentation of Courvoisier's sign—a palpable, distended gallbladder in the setting of painless obstructive jaundice with dilated intra- and extrahepatic bile ducts, which strongly suggests malignant distal biliary obstruction. 1

Clinical Reasoning

Key Diagnostic Features Present

• Courvoisier's sign is pathognomonic for distal malignant obstruction: A palpable, distended gallbladder with painless obstructive jaundice mandates investigation for malignancy, most commonly pancreatic cancer 1

• The imaging pattern is definitive: Dilated intra- AND extrahepatic bile ducts with a hugely distended gallbladder points specifically to distal common bile duct obstruction 1

• The laboratory pattern fits: The markedly elevated direct bilirubin (122.3 μmol/L, normal 1.5-6.5), total bilirubin (134.5 μmol/L, normal 3.5-16.5), and alkaline phosphatase (421 IU/L, normal 39-117) represent a classic obstructive cholestatic pattern consistent with extrahepatic biliary obstruction 1

• The chronicity supports malignancy: The 2-month history of progressive symptoms without acute pain, fever, or fluctuating jaundice is characteristic of malignant rather than benign obstruction 1

Why Other Diagnoses Are Excluded

A. Klatskin Tumor (Perihilar Cholangiocarcinoma) - INCORRECT

• Wrong anatomic location: Klatskin tumors occur at the confluence of the right and left hepatic ducts (hilar region), NOT the distal common bile duct 1, 2

• Opposite imaging pattern: Klatskin tumors characteristically show dilated intrahepatic bile ducts with a NORMAL-SIZED extrahepatic biliary tree and common bile duct 2, 3, 4

• Gallbladder appearance contradicts this: Klatskin tumors are associated with a contracted rather than distended gallbladder (opposite of Courvoisier's law) 5

• The ultrasound findings exclude this: All three studies of Klatskin tumors consistently demonstrated "dilated intrahepatic bile radicles with normal common bile ducts" 3, 4, which is the opposite of this patient's presentation

C. Mirizzi's Syndrome - INCORRECT

• This is a benign inflammatory condition: Mirizzi's syndrome involves external compression of the common hepatic duct by an impacted stone in the gallbladder neck or cystic duct, not a 2-month progressive painless jaundice 1

• Wrong clinical presentation: Mirizzi's typically presents with acute symptoms, cholangitis features (fever, rigors), or fluctuating jaundice, not chronic progressive painless jaundice 1

• Gallbladder would not be distended: In Mirizzi's syndrome, the gallbladder is typically contracted or inflamed around the impacted stone, not hugely distended 1

D. Common Bile Duct Stone - INCORRECT

• Palpable distended gallbladder is uncommon with benign obstruction: CBD stones more commonly present with acute symptoms, cholangitis (fever, rigors), or fluctuating jaundice rather than chronic progressive painless jaundice 1

• Clinical course is wrong: The 2-month progressive history without acute pain episodes or fever is atypical for choledocholithiasis, which usually presents more acutely 1, 6

• Courvoisier's law applies: A palpable gallbladder suggests the gallbladder wall is compliant (not chronically scarred from gallstones), pointing toward malignant rather than stone-related obstruction 1

Critical Next Steps

• Obtain contrast-enhanced CT abdomen or MRI with MRCP to visualize the pancreatic head mass and assess vascular involvement for resectability 1

• Measure CA 19-9 tumor marker, which is elevated in up to 85% of pancreaticobiliary malignancies, though it can also be elevated in benign biliary obstruction 7, 1, 8

• Consider ERCP with biliary stenting for symptomatic relief if the tumor is unresectable, or proceed to surgical evaluation if resectable 1

Common Pitfalls to Avoid

• Don't be misled by the location terminology: "Extrahepatic bile duct dilation" includes the common bile duct—when BOTH intrahepatic AND extrahepatic ducts are dilated, the obstruction is DISTAL (pancreatic head region), not proximal (hilar/Klatskin location) 1, 2

• Don't dismiss Courvoisier's sign: While not 100% sensitive, a truly palpable distended gallbladder in painless jaundice has high specificity for malignant distal obstruction 1

• Don't wait for CA 19-9 results to image: Proceed directly to cross-sectional imaging, as CA 19-9 can be elevated in benign obstruction and is not specific enough for diagnosis 7, 8