Clinical Significance of Diffuse $^{18}F$-FDG Uptake in Residual Thyroid Gland after Unilateral Thyroid Lobectomy

다국어 초록 (Multilingual Abstract)

Purpose We investigated the clinical significance of diffuse uptake in remaining thyroid after unilateral lobectomy for thyroid cancer. Methods A total of 144 thyroid cancer patients who underwent $^{18}F$-FDG PET/CT after lobectomy were enrolled in the present study. The PET/CT images were evaluated for the presence of diffuse $^{18}F$-FDG uptake with maximum SUV (SUVmax) >2.0 in the residual thyroid and placed into one of two groups: with diffuse uptake and without diffuse uptake group. Clinical, laboratory, and PET/CT parameters in both groups were compared. Correlations between SUVmax of thyroid and available parameters were analyzed. Results Forty-two of 144 patients (29.2%) had diffuse thyroid uptake (mean SUVmax: $3.2{\pm}1.1$). All patients with diffuse uptake and 96 (94.1%) without diffuse uptake were receiving thyroxine therapy (P=0.09). Thyroid function tests showed that most patients were euthyroid status (78.6 vs. 85.3%, P=0.36). TgAb levels were significantly higher in patients with diffuse uptake ($338.0{\pm}664.6$ vs. $57.3{\pm}46.4$, P<0.0001). Mean attenuation values in the diffuse uptake group were significantly lower ($72.2{\pm}15$. vs. $97.0{\pm}16.0$, P<0.0001). An inverse correlation was found between SUVmax and mean attenuation values of residual thyroid in all patients (r=-0.57, P<0.0001) and subgroup with diffuse uptake (r=-0.31, P<0.05). Conclusion In this study, diffuse $^{18}F$-FDG uptake in the residual thyroid after unilateral lobectomy was a relatively frequent finding and may be associated with chronic thyroiditis. This uptake is not influenced by thyroid status or thyroxine therapy. The $^{18}F$-FDG uptake is inversely correlated with mean attenuation value of thyroid.