title: Clinical Significance of Diffuse (18)F-FDG Uptake in Residual Thyroid Gland after Unilateral Thyroid Lobectomy.
abstract: OBJECTIVE
  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 ± 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 ± 664.6 vs. 57.3 ± 46.4, P < 0.0001). Mean attenuation values in the diffuse uptake group were significantly lower (72.2 ± 15. vs. 97.0 ± 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Nuclear Medicine, Ajou University School of Medicine, San 5, Woncheon-dong, Yeongtong-gu, Suwon, Korea.
authors.forename: Hee-Sung
authors.initials: HS
authors.lastname: Song
authors.affiliation: Department of Nuclear Medicine, Ajou University School of Medicine, San 5, Woncheon-dong, Yeongtong-gu, Suwon, Korea.
authors.forename: Su Jin
authors.initials: SJ
authors.lastname: Lee
authors.affiliation: Department of Nuclear Medicine, Ajou University School of Medicine, San 5, Woncheon-dong, Yeongtong-gu, Suwon, Korea.
authors.forename: Seok-Ho
authors.initials: SH
authors.lastname: Yoon
authors.affiliation: Department of Surgery, Ajou University School of Medicine, San 5, Woncheon-dong, Yeongtong-gu, Suwon, Korea.
authors.forename: Jandee
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Surgery, Ajou University School of Medicine, San 5, Woncheon-dong, Yeongtong-gu, Suwon, Korea.
authors.forename: Euy-Young
authors.initials: EY
authors.lastname: Soh
authors.affiliation: Department of Nuclear Medicine, Ajou University School of Medicine, San 5, Woncheon-dong, Yeongtong-gu, Suwon, Korea.
authors.forename: Young-Sil
authors.initials: YS
authors.lastname: An
authors.affiliation: Department of Nuclear Medicine, Ajou University School of Medicine, San 5, Woncheon-dong, Yeongtong-gu, Suwon, Korea.
authors.forename: Joon-Kee
authors.initials: JK
authors.lastname: Yoon
keywords: Diffuse thyroid uptake; FDG PET/CT; Thyroid lobectomy; Thyroiditis