This is what I found online:
Periampullary tumours are those that arise within 2 cm of the ampulla of Vater in the duodenum
Tumours that fall under this group includes four main types of tumours 1,4
• pancreatic head / uncinate process tumours - includes pancreatic ductal adenocarcinoma involving head and uncinate process of the pancreas
•lower common bile duct tumours - includes types of cholangiocarcinoma involving the intra-pancreatic distal bile duct
• ampullary tumours - those originating from the ampulla of Vater itself
•periampullary duodenal carcinoma
Although patients with periampullary tumors have similar symptoms at presentation, they exhibit different clinical outcomes according to the origin of these tumours.