Pituitary 18F-FDG uptake correlates with serum TSH levels in subjects with diffuse thyroid 18F-FDG uptake

Abstract

Purpose: The aim of this study was to evaluate the relationship among FDG uptake in the pituitary gland (FDGp), FDG uptake in the thyroid gland (FDGt), and serum thyroid-stimulating hormone (TSH) levels in patients with diffuse FDGt incidentally noted on positron emission tomography/computed tomography (PET/CT) scan.Materials and Methods: This retrospective study was approved by our institutional review board. We retrospectively reviewed FDG PET/CT scans of 2,945 subjects who underwent health screening. Of these, 44 subjects had diffuse FDGt and available thyroid function tests. FDGt and FDGp were correlated with serum TSH. FDGp in 44 paired control subjects without FDGt and 15 thyroid cancer patients undergoing thyroid hormone withdrawal were additionally measured, and compared with FDGp in the 44 subjects with FDGt divided into three groups according to serum TSH levels.Results: In the 44 subjects, there was a statistically significant (p=0.034) but weak correlation(r=0.320) between FDGt and TSH. On the other hand, a strong correlation was found between FDGp and TSH (p<0.001, r=0.618). As well, there were statistically significant differences in FDGp between the low, normal, and high TSH groups (p<0.001). FDGp in the paired control subjects was not different from that in the normal TSH group (p=0.384), and FDGp in the TSH-stimulated thyroid cancerpatients was not different from that in the high TSH group (p=0.463).Conclusion: In this study, we found a strong positive correlation between the degree of pituitary FDG uptake and serum TSH. It appears that FDG uptake in the pituitary gland holds an important clue to the functional status of the thyroid in subjects with diffuse thyroid FDG uptake.