Preoperative localization of a vasoactive intestinal peptide-secreting tumor by transhepatic portal venous sampling

A 35-yr-old woman presented with episodic secretory diarrhea. Plasma vasoactive intestinal peptide (VIP) and pancreatic polypeptide (PP) venous levels were elevated. An abdominal computerized tomographic scan showed an enlarged head of the pancreas but no discrete mass. Superselective abdominal arteriography also failed to localize the tumor. Transhepatic portal vein sampling for VIP and PP showed a large increase in VIP and PP in the veins draining the head of the pancreas, with the highest levels being found at the union of the posterior superior pancreaticoduodenal vein with the portal vein. Surgical exploration confirmed this tumor location and a 2 x 3 cm encapsulated benign tumor was enucleated from the posterior surface of the head of the pancreas. Postoperatively, VIP and PP levels decreased to normal and the diarrheal episodes ceased. This case report demonstrates the usefulness of transhepatic portal vein sampling in localization of VIPomas if other radiological modalities are not helpful.