Thyroid lesion incidentally detected by 18F-FDG PET-CT – a two centre retrospective study
Background. Thyroid PET incidentalomas represent a diagnostic challenge. The SUVmax value is one possible parameter that can help in distinguishing between benign and malignant thyroid PET lesions.
Materials and methods. We retrospectively evaluated 5911 18F-FDG PET-CT examinations performed at two different medical centres from 2010 to 2011. If pathologically increased activity was accidentally detected in the thyroid (incidentaloma), the SUVmax value of the thyroid lesion was calculated. Patients with incidentalomas 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. In the first centre the incidence of thyroid incidentalomas was 2.89%. In 5 of 41 patients with focal incidentaloma a malignant lesion was detected. The SUVmax value of benign lesions was 5.6 ± 2.8 and for malignant 15.8 ± 9.2 (p < 0.001). In the second centre the incidence of thyroid incidentalomas was 4.82%. Benign lesions were detected in 20 patients and malignant in 5 patients. The SUVmax value of benign lesions was 3.7 ± 2.2 and 5.1 ± 2.3 for malignant lesions (p = 0.217).
All 29 further investigated diffuse thyroid PET incidentalomas were benign.
Conclusions. Thyroid PET incidentalomas were found on 18F-FDG PET-CT examinations in 2.89% and 4.82% respectively. Only focal thyroid PET incidentalomas represented malignant lesion in 12% (first centre) and in 20% (second centre). The SUVmax value may help in distinguishing between benign and malignant thyroid PET lesions, but it must be used with caution.