MRCP shows a 'duct-penetrating sign' — the main pancreatic duct passing through a mass without obstruction. This is most characteristic of:
- A Pancreatic ductal adenocarcinoma
- B Autoimmune pancreatitis (mass-forming type) ✓
- C Serous cystadenoma
- D Mucinous cystic neoplasm
Correct answer: B. Autoimmune pancreatitis (mass-forming type)
Explanation
The duct-penetrating sign on MRCP or ERCP describes the main pancreatic duct traversing through the mass smoothly without obstruction or upstream dilation. This is a key differentiating feature of autoimmune pancreatitis (AIP) from pancreatic ductal adenocarcinoma (PDAC). In PDAC, the duct is typically obstructed or abruptly cut off by the mass. In AIP (mass-forming type), the inflammatory process narrows the duct but does not obstruct it, and the duct 'penetrates' through the mass. This sign has high specificity for AIP and is useful to avoid unnecessary surgery.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.