Intraoperative ultrasound and preoperative localization detects all occult insulinomas

Hypothesis: Preoperative invasive localization procedures with intraoperative ultrasound (IOUS) can result in successful surgical treatment of occult insulinomas when noninvasive imaging study results are equivocal or negative. Design: Prospective study. Setting: Tertiary care university hospital. Patients: Thirty-seven consecutive patients with a biochemical diagnosis of insulinoma without multiple endocrine neoplasia (MEN). Intervention: All patients underwent portal venous sampling (PVS) (n = 22) or calcium angiogram (n = 15) followed by surgery with palpation and IOUS (n=37). Main Outcome Measure: Portal venous sampling, calcium angiogram, palpation, and IOUS were compared for accurate localization of insulinoma. Results: All patients were cured of hypoglycemia after surgery. Portal venous sampling correctly localized tumors in 17 (77%) of 22 patients. Calcium angiogram was correct in 13 (87%) of 15 patients. Palliation identified 24 (65%) of 37 tumors, and IOUS found 35 (95%) of 37 tumors. The 2 tumors missed by IOUS were located in the tail of the pancreas and were resected based on regional localization alone, Conclusions: Intraoperative ultrasound is the single best localization study, but it will miss some tumors that regional localization can identify. Combining both modalities allowed surgical cure of all insulinomas in our study. Therefore, we recommend both IOUS and regional localization for insulinoma when preoperative imaging studies are equivocal.