RESUMO
CONTEXT: Arterial stimulation and venous sampling (ASVS) is the most sensitive diagnostic method for occult insulinoma localization. We present our experience with this method and modifications used that proved to ensure greater safety and sensitivity with this rare pathology. Relationship between tumour size and changes in peak insulin values and release curves were also tested. SUBJECTS AND METHODS: Six consecutive patients with biochemically established diagnosis of endogenous hyperinsulinism underwent preoperative non-invasive diagnostic tests with sensitivities calculated and compared for all methods. Certain modifications were used in ASVS procedure that included hepatic vein catheterization, order of arterial stimulation, time intervals between each stimulation, diagnostic insulin gradient level and the time frame for diagnostic rise of insulin. Peak insulin values and insulin gradients were compared with tumour size in each patient. RESULTS: In all patients, calcium stimulation accurately localized the insulinoma, with higher sensitivity than any other method. A more than 4-fold increase in insulin level was observed in all patients, after injection into the tumour feeding artery, while 2 to 4-fold increase was observed in the tumour neighbouring areas. Tumour size showed an inversely proportional correlation to peak insulin values in each artery that correctly located the tumour. CONCLUSION: ASVS presents the most accurate and safe method for localization of occult insulinomas. A four-fold insulin gradient can be used as a limit for positive preoperative localization in order to secure a higher specificity.
