Horiguchi et al., "A case of annular pancreas with Wirsung's duct
encircling the duodenum: embryological hypothesis based on cholangiopancreatographic and immunohistochemical findings," Clinical Journal of Gastroenterology, vol.
The diagnosis was stated by means of duodenoscopy with biopsy (histology), ultrasound and CT examination of abdomen for finding dilated biliary tract or Wirsung's duct
and also the invasion to adjacent organs (especially pancreas).
Histologic findings were evaluated in a pancreatic polypeptide-rich area, named the ventral pancreas, because ampullary carcinomas are anatomically involved in the outflow of the pancreatic juice from Wirsung's duct
or the main pancreatic duct but not from Santorini's duct or the accessory pancreatic duct.