The role of preoperative and intraoperative procedures for the localization of
insulinoma has been extensively debated. Transhepatic portal vein sampling before surgery has been recommended when other tests fail to localize the tumour. To determine the role of different investigations, 53 patients with
insulinoma, four with
hyperplasia or
nesidioblastosis and one with
insulin autoimmune syndrome were studied. Patients were operated on in three consecutive periods during each of which a different localization procedure was considered to represent the 'gold standard'. During the first period, of 16 patients (including one with
hyperplasia) investigated by arteriography, 13 underwent successful resection. Tumours in the other three patients with
insulinoma were resected at a second operation, one during the first period and one each during the second and third periods. During the second period, 28 patients underwent exploration after transhepatic portal sampling: the tumour was found in all 26 patients with
insulinoma operated on in this hospital, one patient with
hyperplasia is receiving medical treatment and one patient had unsuccessful surgical exploration elsewhere despite positive findings on arteriography and transhepatic portal sampling performed in this department. During the third period 13 procedures were performed. All were successful using intraoperative ultrasonography without transhepatic portal sampling. In three further patients intraoperative localization failed because of non-adenomatous beta cell disease. Left-sided resection successfully cured symptoms in two patients with
hyperplasia and prompted the diagnosis of
insulin autoimmune syndrome. High success rates for surgical treatment of
insulinoma can be achieved with transhepatic portal vein sampling or intraoperative ultrasonography. Transhepatic portal sampling is therefore unnecessary before a first operation on the pancreas for
insulinoma. In the rare failures of intraoperative localization of an
insulinoma, a small left pancreatic resection can help to distinguish
insulinoma from
hyperplasia without precluding further segmental resection.