The CT fish mouth ampulla sign: a highly specific finding in main duct and mixed intraductal papillary mucinous neoplasms

Br J Radiol. 2019 Nov;92(1103):20190461. doi: 10.1259/bjr.20190461. Epub 2019 Aug 28.


Objective: Main duct and mixed intraductal papillary mucinous neoplasms (IPMN) are pre-malignant cystic pancreatic neoplasms associated with pancreatic duct dilatation. Distinguishing these from benign causes of pancreatic duct dilatation is important in order to allow appropriate surveillance or surgery. A patulous duodenal papilla with extrusion of mucus at endoscopic evaluation, the endoscopic fish mouth ampulla (E-FMA) sign, is reported in main duct and mixed IPMN. We aimed to establish whether a CT correlate (CT-FMA) of this sign exists and whether this was associated with the presence of invasion or high-grade dysplasia. We defined the CT-FMA sign as an uninterrupted column of water attenuation material running from the pancreatic duct to the duodenal lumen.

Methods: A retrospective, blinded review of 44 patients with histologically confirmed IPMN and 87 age-matched controls with pancreatic duct dilatation on CT was undertaken. A case-control series matched for the degree of pancreatic duct dilatation was used to compare the rates of invasion or high-grade dysplasia between main duct and mixed IPMN patients, with and without a CT-FMA sign.

Results: The CT-FMA sign could be identified in 18.5% patients with main duct/mixed IPMN with specificity 100%, positive predictive value 100% and negative predictive value 79.8%. A significant association was found between CT-FMA in main duct/mixed IPMN compared to controls, but not with the presence of high-grade dysplasia or invasion.

Conclusions: The CT-FMA sign is a newly reported, highly specific sign of MD and mixed IPMN.

Advances in knowledge: If a fish mouth ampulla is identified at CT, a diagnosis of main duct or mixed IPMN is highly likely.

MeSH terms

  • Adenocarcinoma, Mucinous / diagnostic imaging*
  • Adult
  • Aged
  • Aged, 80 and over
  • Ampulla of Vater / diagnostic imaging
  • Carcinoma, Pancreatic Ductal / diagnostic imaging*
  • Case-Control Studies
  • Humans
  • Middle Aged
  • Pancreatic Neoplasms / diagnostic imaging*
  • Precancerous Conditions / diagnostic imaging
  • Retrospective Studies
  • Tomography, X-Ray Computed