Intraoperative biochemical localization of insulinomas by quick radioimmunoassay

In patients with organic hyperinsulinism, intraoperative determination of insulin concentrations in veins draining the pancreas might help localize the tumor. We have developed a radioimmunoassay measuring insulin within 30 minutes. At operation, blood samples are taken at various sites in the splenic, superior mesenteric and portal veins for insulin determinations. In all six patients, the highest insulin concentrations correlated with the site of the tumor. Also, small insulinomas less than 1 cm in diameter could be found. In one patient the tumor appeared to secrete mainly proinsulin. By this procedure we hope to avoid blind distal resection of the pancreas and possibly invasive preoperative diagnostic procedures.