Pituitary (18)F-FDG uptake correlates with serum TSH levels in thyroid cancer patients on (18)F-FDG PET/CT

OBJECTIVE: The objective of this study was to evaluate the relationship between fluorine-18-fluorodeoxyglucose ((18)F-FDG) uptake in the pituitary gland and serum thyroid-stimulating hormone (TSH) levels in differentiated thyroid cancer (DTC) patients on (18)F-FDG PET/computed tomography (CT). PATIENTS AND METHODS: A total of 215 DTC patients and 215 age-paired and sex-paired healthy screening participants were included. DTC patients were divided into hypothyroid, euthyroid and subclinical hyperthyroid patients according to their serum TSH levels. The relationship between (18)F-FDG uptake in the pituitary gland and serum TSH levels was evaluated the in DTC patients, and the pituitary (18)F-FDG metabolism was compared in different thyroid status. RESULTS: The standardized uptake value of pituitary (SUV(p)) in all 430 patients was directly correlated with serum TSH levels (r=0.479 and 0.432, all P<0.05). The SUV(p) in DTC patients was higher than that in 215 healthy participants (z=−10.4, P<0.05). No significant difference of SUV(p) was observed between euthyroid patients and healthy participants (P=0.145). CONCLUSION: Our study established the positive correlation between pituitary (18)F-FDG uptake and serum TSH. TSH values should be measured in patients with incidental pituitary uptake during (18)F-FDG PET/CT. L-T4 replacement for DTC patients may well have the same feedback on the thyroid–pituitary axis as the physiologic thyroid status. The diffuse (18)F-FDG uptake with normal CT or MRI appearance of the pituitary in patients with DTC indicates physiologic uptake.