Background: The precise intraoperative localization of insulinoma is essential for successful surgical treatment. In addition to various imaging modalities developed recently, arterial stimulation and venous sampling (ASVS) has also been used for tumor localization.
Methods: Preoperative and intraoperative ASVS procedures were performed in 6 patients with insulinoma. Intraoperative ASVS was performed before and after tumor resection. Immunoreactive insulin (IRI) concentrations and the IRI ratio (IRI concentration at each time interval after calcium injection/baseline IRI concentration) were determined by the conventional or a quick IRI method.
Results: The site of the tumor was identified preoperatively in all patients. The peak of the IRI ratio varied widely, but setting the cutoff value at 3.0 clearly differentiated peak IRA ratios in feeding arteries from those of nonfeeding arteries. Intraoperative ASVS showed a similar elevation of IRI levels, but the elevation disappeared after tumor resection in all but 1 patient. In 2 patients, resection of the tumor was confirmed during surgery by measuring IRI levels by the quick IRI method.
Conclusions: A combination of ASVS and conventional imaging modalities is useful for precise localization of insulinoma. Resection of the tumor can be confirmed intraoperatively by comparing IRI levels associated with preoperative and postresective ASVS.