MRCP (magnetic resonance cholangiopancreatography) is performed in a 60-year-old man with obstructive jaundice. It shows an abrupt stricture at the common bile duct with a 'rat-tail' narrowing above the ampulla. The pancreatic duct is not dilated. The MOST likely diagnosis is:

• A Carcinoma head of pancreas
• B Ampullary carcinoma
• C Primary sclerosing cholangitis
• D Cholangiocarcinoma (distal) ✓

Explanation

Distal cholangiocarcinoma (extrahepatic, distal CBD) presents with obstructive jaundice and on MRCP shows an abrupt smooth or irregular narrowing of the distal common bile duct — classically described as 'rat-tail' narrowing — with proximal biliary dilatation but a non-dilated pancreatic duct (since the tumour is in the CBD wall, not compressing the pancreatic duct). Carcinoma of the head of pancreas causes the 'double-duct sign' (simultaneous dilatation of both CBD and PD). Ampullary carcinoma causes dilatation of both ducts. PSC shows multifocal strictures and bead-on-string appearance.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.