A gastrinoma is a tumor in the pancreas or duodenum that secretes excess of gastrin leading to ulceration in the duodenum, stomach and the small intestine. There is hypersecretion of the HCl acid into the duodenum, which causes the ulcers. Excessive HCl acid production also causes hyperperistalsis, and inhibits the activity of lipase, causing severe diarrhea.
It is most commonly found in the duodenum (50-70%) and less commonly in the pancreas (20-40%). Those occurring in the pancreas have a greater potential for malignancy. Most gastrinomas are found in the gastrinoma triangle; this is bound by the junction of cystic and common bile ducts, junction of the second and third parts of the duodenum, and the junction of the neck and body of the pancreas.