The VIPoma syndrome

INTRODUCTION

VIPomas are rare neuroendocrine tumors that secrete vasoactive intestinal polypeptide (VIP). They are detected in 1 in 10 million people per year [1]. The majority of VIPomas arise within the pancreas, although other VIP-secreting tumors have been reported. These include bronchogenic carcinoma, colon carcinoma, ganglioneuroblastoma, pheochromocytoma, hepatoma, and adrenal tumors. In children, VIPomas occur in sympathetic ganglia and in the adrenal glands [1].

Symptomatic pancreatic VIPomas are usually solitary, more than 3 cm in diameter, and occur in the tail of pancreas in 75 percent of patients. Approximately 60 to 80 percent of VIPomas have metastasized by the time of diagnosis [2,3].

VIPomas usually occur as isolated tumors, but are part of the multiple endocrine neoplasia syndrome type 1 (MEN1) in 5 percent of patients. The latter patients may also have primary hyperparathyroidism, pituitary tumors, gastrinoma, and other tumors. (See "Clinical manifestations and diagnosis of multiple endocrine neoplasia type 1".) In one report of 580 patients with the MEN-1 syndrome, only 2 (0.65 percent) harbored a VIPoma [4].

PATHOPHYSIOLOGY

VIP is a 28 amino acid polypeptide that binds to high affinity receptors on intestinal epithelial cells, leading to activation of cellular adenylate cyclase and cAMP production. This results in net fluid and electrolyte secretion into the lumen [5,6]. VIP also has other actions that may be clinically important in patients with a VIPoma (table 1). (See "Vasoactive intestinal polypeptide".)

The VIPoma syndrome is caused by excessive, unregulated secretion of VIP by the tumor. However, other substances, such as prostaglandin E2, may occasionally be secreted by the tumors [5].