Selective Intra-Arterial Calcium Stimulation with Hepatic Venous Sampling for Preoperative Localization of Insulinomas

OBJECTIVE: To determine the value of selective intra-arterial calcium stimulation with hepatic venous sampling using serum insulin and C-peptide gradients for the preoperative localization of insulinomas. MATERIALS AND METHODS: Seven consecutive patients [three men and four women aged 15-77 (mean, 42.7) years] with hypoglycemia underwent selective intra-arterial calcium stimulation in conjunction with hepatic venous sampling. Insulin gradients were calculated by an individual blinded to all other preoperative imaging studies and operative findings. In all patients except one, C-peptide gradients were also analyzed. The results were compared with the preoperative findings of ultrasonography, computed tomography, arteriography and endoscopic ultrasonography, as well as with the intraoperative findings of ultrasonography and palpation at surgery. RESULTS: Eight insulinomas (mean diameter, 12.5 mm) were diagnosed after surgery. In six patients, the calcium stimulation test with insulin gradients allowed accurate localization of the pathologic source of insulin secretion. Both C-peptide and insulin gradients substantially increased diagnostic accuracy. In one patient, C-peptide gradients were more helpful than insulin gradients for tumor localization. CONCLUSION: Selective intra-arterial calcium stimulation with hepatic venous sampling is a highly accurate and safe method for the preoperative localization of insulinomas. Additional C-peptide gradients seem to be helpful in assessing tumor location, but further study is needed.