A 72-year-old woman from Delhi presents with 2 weeks of jaundice, pruritus, and acholic (pale) stools. She denies fever, chills, or abdominal pain. Vitals are stable; temperature 37.2°C. On examination, she is deeply icteric with hepatomegaly but no RUQ tenderness. Laboratory: total bilirubin 9.5 mg/dL (direct 8.1 mg/dL), ALP 410 U/L, GGT 350 U/L, ALT 120 U/L, AST 140 U/L, INR 1.1. Abdominal ultrasound reveals a dilated intrahepatic biliary tree (IHD) and a dilated common bile duct (10 mm), but the extrahepatic bile duct appears normal caliber distally. What is the most likely diagnosis?

Explanation

## Clinical and Radiological Clues **Key Point:** The **selective dilatation of intrahepatic ducts with a normal-caliber distal CBD** is the pathognomonic ultrasound finding of **hilar cholangiocarcinoma (Klatskin tumour)**. ## Differential Diagnosis by Imaging Pattern ```mermaid flowchart TD A[Obstructive jaundice + dilated CBD on US]:::outcome --> B{Ultrasound pattern?}:::decision B -->|Dilated IHD + dilated distal CBD| C[Distal CBD obstruction]:::action C --> C1[Pancreatic head cancer]:::outcome C --> C2[Distal cholangiocarcinoma]:::outcome C --> C3[Choledocholithiasis]:::outcome B -->|Dilated IHD + NORMAL distal CBD| D[Hilar obstruction]:::action D --> D1[Hilar cholangiocarcinoma]:::outcome D --> D2[Hepatic hilar stricture]:::outcome B -->|Dilated IHD + dilated extrahepatic ducts| E[Intrahepatic cholestasis]:::action ``` ## Why This Is Klatskin Tumour ### Imaging Signature | Feature | Klatskin Tumour | Pancreatic Cancer | Choledocholithiasis | |---|---|---|---| | **IHD dilatation** | Marked (>8 mm) | Yes | No (unless stone impacted) | | **Distal CBD caliber** | **Normal or tapered** | Dilated (>8 mm) | Dilated (>8 mm) | | **Gallbladder** | Normal | Normal | Often with stones | | **Hepatomegaly** | Possible | Possible | No | | **Fever/pain** | Absent (unless cholangitis) | Often present | Often with pain | **High-Yield:** Klatskin tumours arise at the **confluence of right and left hepatic ducts**, causing **selective obstruction of the hilum** while the distal CBD remains patent and normal-caliber. This creates the classic "double duct sign" on MRCP (dilated intrahepatic ducts + normal distal CBD). ### Clinical Context - **Age:** 72 years (peak incidence 60–80 years) - **Painless jaundice:** Typical for malignancy - **Afebrile:** Excludes acute cholangitis (though can occur later) - **Hepatomegaly:** Suggests advanced disease or liver involvement - **Normal INR:** Preserved synthetic function (no cirrhosis) - **Markedly elevated ALP/GGT:** Cholestasis pattern, not hepatocellular injury **Clinical Pearl:** Klatskin tumours are **intrahepatic cholangiocarcinomas** arising at the hepatic duct confluence. They account for ~50% of all cholangiocarcinomas and carry a poor prognosis because they are often diagnosed late and involve major vascular and biliary structures. ## Diagnostic Confirmation **Next step:** MRCP will show: - Dilated intrahepatic ducts - Abrupt narrowing at the hilum ("bird's beak" appearance) - Normal distal CBD - Possible involvement of right and/or left hepatic ducts EUS-guided biopsy or percutaneous biopsy may be needed for tissue diagnosis.