Clinical Significance of Incidental Pituitary TC-99m MIBI Uptake on Parathyroid Spect and Factors Affecting Uptake Intensity.

OBJECTIVE: (1)To define a quantitative cutoff value for incidental pituitary Technetium-99m methoxyisobutylisonitrile (Tc-99m MIBI) uptake above which is of clinical importance and (2) to investigate possible factors affecting the intensity of uptake in pituitary adenoma.

MATERIALS AND METHODS: A retrospective analysis of 55 patients with a simultaneous parathyroid single-photon emission computed tomography and pituitary magnetic resonance imaging were included. Twenty-four patients with pituitary adenoma were chosen as the study group and 31/55 patients who had no signs of a pituitary adenoma were included in the control group. Mean count values (count/pixel) for pituitary region of interest (ROI)/mean value for normal cortical region ROI (P/C) were calculated in both groups. Median P/C values were compared. A cutoff value for P/C was calculated as a quantitative parameter to indicate pituitary tumors. Possible contributing factors in intensity of pituitary Tc-99m MIBI uptake were investigated.

RESULTS: Median P/C ratios were significantly higher in the study group (p < 0.001). A cutoff value of 7.675 was found for P/C to have a sensitivity, spesificity, positive predictive value, and negative predictive value 100%, 96.8%, 96%, and 100%, respectively. There was no correlation between investigated factors and degree of pituitary Tc-99m MIBI uptake.

CONCLUSIONS: Incidental pituitary Tc-99m MIBI uptake values above 7.675 for P/C are suspicious for pituitary adenoma and can be further investigated clinically and radiologically. Tc-99m MIBI uptake is not affected from the biochemical nature of the adenoma, the therapies received, size, local invasion, or cystic necrotic component of the tumor.