title: Thyroid lesions incidentally detected by (18)F-FDG PET-CT - a two centre retrospective study.
abstract: BACKGROUND
  Incidental (18)F-FDG uptake in the thyroid on PET-CT examinations represents a diagnostic challenge. The maximal standardized uptake value (SUVmax) is one possible parameter that can help in distinguishing between benign and malignant thyroid PET lesions.
  
  
  METHODS
  We retrospectively evaluated (18)F-FDG PET-CT examinations of 5,911 patients performed at two different medical centres from 2010 to 2011. If pathologically increased activity was accidentally detected in the thyroid, the SUVmax of the thyroid lesion was calculated. Patients with incidental (18)F-FDG uptake in the thyroid were instructed to visit a thyroidologist, who performed further investigation including fine needle aspiration cytology (FNAC) if needed. Lesions deemed suspicious after FNAC were referred for surgery.
  
  
  RESULTS
  Incidental (18)F-FDG uptake in the thyroid was found in 3.89% - in 230 out of 5,911 patients investigated on PET-CT. Malignant thyroid lesions (represented with focal thyroid uptake) were detected in 10 of 66 patients (in 15.2%). In the first medical centre the SUVmax of 36 benign lesions was 5.6 ± 2.8 compared to 15.8 ± 9.2 of 5 malignant lesions (p < 0.001). In the second centre the SUVmax of 20 benign lesions was 3.7 ± 2.2 compared to 5.1 ± 2.3 of 5 malignant lesions (p = 0.217). All 29 further investigated diffuse thyroid lesions were benign.
  
  
  CONCLUSIONS
  Incidental (18)F-FDG uptake in the thyroid was found in 3.89% of patients who had a PET-CT examination. Only focal thyroid uptake represented a malignant lesion in our study - in 15.2% of all focal thyroid lesions. SUVmax should only serve as one of several parameters that alert the clinician on the possibility of thyroid malignancy.
authors.affiliation: Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia.
authors.forename: Jan
authors.initials: J
authors.lastname: Jamsek
authors.affiliation: Department for Nuclear Medicine, Institute of Oncology Ljubljana, Ljubljana, Slovenia.
authors.forename: Ivana
authors.initials: I
authors.lastname: Zagar
authors.affiliation: Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia ; Department for Nuclear Medicine, University Medical Centre Ljubljana, Ljubljana, Slovenia.
authors.forename: Simona
authors.initials: S
authors.lastname: Gaberscek
authors.affiliation: Department for Nuclear Medicine, University Medical Centre Ljubljana, Ljubljana, Slovenia.
authors.forename: Marko
authors.initials: M
authors.lastname: Grmek
keywords: 18F-FDG; PET incidentaloma; PET-CT; thyroid; thyroid cancer