Iodine-123-IBZM-SPECT: studies in 15 patients with pituitary tumors

Single photon emission computerized tomography (SPECT) using the Iodine 123 labeled dopamine D2 receptor antagonist S(-)Iodobenzamide [S (-)IBZM] was performed in 15 patients with pituitary tumors. Among them there were five prolactinoma patients with macroadenoma and two acromegalic patients with macroadenoma. Specific binding in the area of the adenoma was only observed in one subject, a macroprolactinoma patient, who was responsive to dopaminergic treatment. None of the other patients, among them one macroprolactinoma patient responsive to dopaminergic treatment showed specific binding in the area of the tumor. IBZM-binding in the striatum was found to be significantly lower in the group of pituitary tumor patients as compared to controls. The results show that D2 receptors in pituitary adenomas can be visualized using SPECT. However, the sensitivity of IBZM-SPECT appears to be too poor to visualize PRL- and GH- secreting macroadenomas in general.