Anatomical localization of insulinomas: still a need to combine a set of diagnostic procedures

The diagnosis of insulinoma is based on universally defined clinical and laboratory parameters (Whipple triad and fasting test). Pre-operative tumor localization is the main challenge in the diagnostic management of insulinomas. The pre-operative and/or intra-operative localization of the tumor is required for the optimal surgical approach. We describe two cases of insulinoma characterized by a typical clinical presentation, a positive diagnosis on fasting test, and computerized tomography failure in localizing the tumor. In the first patient, angiography with hepatic venous sampling after calcium stimulation correctly localized pre-operatively the region of the pancreas where the tumor was and, following intra-operative investigations, the lesion was successfully enucleated. In the second patient, angiography with hepatic venous sampling after calcium stimulation failed to identify the region of the insulinoma, which was detected by intra-operative ultrasound and successfully enucleated. Invasive pre-operative procedures for tumor regionalization and/or localization (angiography with hepatic venous sampling after calcium stimulation, endoscopic ultrasound) should be performed in cases where the tumor cannot be localized with enough certainty by non-invasive imaging. However, a careful intra-operative study should be performed in all patients undergoing surgery to complete the information obtained pre-operatively and to exclude the presence of other smaller lesions.