Because approximately 50% of insulinomas and a similar proportion of gastrinomas are not evident on preoperative imaging studies, precise intraoperative localization of these small tumors is imperative. Recently the use of high-resolution real-time B-mode ultrasonography has dramatically facilitated the operative detection of pancreatic islet cell tumors. The tumor appears sonolucent compared to the more echo-dense surrounding pancreas. This operative technique has been especially useful in patients with insulinoma because these tumors are generally located within the pancreas. In fact, it is so helpful during explorations for insulinoma some suggest that extensive preoperative localization studies are no longer indicated-that the patient can simply be explored with intraoperative ultrasonography (IOUS). It has not been as useful for gastrinomas because of their common extrapancreatic location. Accumulating evidence suggests that IOUS is an effective tool to aid in the operative localization and resection of pancreatic islet cell tumors. Not only can it precisely localize the tumor, it can accurately document the relation of the tumor to other vital pancreatic structures including ducts, veins, and arteries.
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