Insulinoma- how to localize the tumor?

Arterial stimulation with calcium and venous sampling (ASVS) enables us to reach the goal of avoiding that any patient with insulinoma undergoes a blind surgical exploration. Since ASVS is both a functional and morphological localization procedure, its sensitivity is not influenced by factors that are causing the insensitivity of usual anatomical and morphological procedures. This results in all ASVS sensitivity data being the same, regardless of where the procedure was performed. The practical meaning of this is that when ASVS is done after other morphological procedures there are no falsely positive or negative results, and that every patient is sent to surgery with enough insulinoma localization data. Aim: Based on our own experience in preoperative localization of insulinoma we indented to show why we believe that ASVS should be performed to all patients regardless of data collected from other preoperative localization methods. Method: Retrospectively we have analyzed the accuracy of preoperative localization methods. First anatomical and morphological procedures like transabdominal ultrasoundUS, endoscopic ultrasoundEUS, computerized tomography-CT and magnetic resonance imaging-MRI were done. Then we analyzed the data collected during a functional procedure which at the same time allows regionalization ASVS. To estimate the accuracy, the results of every single method were correlated with the operative findings in all sixteen cases. Results: Prior to ASVS fourteen patients underwent US, fifteen had CT, MRI was performed in eight patients and EUS in thirteen. Using only one of these methods enabled identification of tumors in five patients, using two methods in six patients while three and four in one patient each. For three patients none of these methods was successful. ASVS revealed that all seen tumors were functional except three of the six visualized with two methods (US and EUS). In two of these three cases US and EUS localized tumors in pancreatic tail/body whilst ASVS accurately identified tumors in pancreatic head. For these patients US and EUS showed falsely positive results. In the third of these patients EUS showed tumor localized in pancreatic head, while US and ASVS accurately pointed to tail. This too was a falsely positive result of EUS. ASVS successfully provided regionalization data in three patients where other visualization methods failed. Operative and later histological findings confirmed the accuracy of ASVS in all sixteen patients including two patients that previously underwent distal pancreatectomy based on falsely positive EUS findings.