Evaluation of Incidental Thyroid Findings Detected by Positron Emission Tomography/Computed Tomography

Abstract
Background: Thyroid incidenteloma detected on 18F-FDG PET/CT carries a high risk of malignancy. This high risk of malignancy supports the performance of a further diagnostic procedure, such as ultrasonography and fine needle aspiration biopsy.
Aim of Study: To determine the role of PET/CT in evalu-ation of incidental thyroid lesions detected in patients being studied for lymphomas and/or cancers other than of thyroid.
Material and Methods: This study included thirty four patients with incidental abnormal increased FDG uptake. All patients were subjected to ultrasound examination and patients with focal increased tracer uptake were subjected to fine needle aspiration biopsy.
Results: This study included a total of 1263 consecutive patients who underwent a FDG PET/CT study for staging of an advanced cancer of any site of the body other than the thyroid gland during the period. An incidental abnormal increase in FDG uptake in the thyroid gland was observed in 39 (3.08%) patients. Out of these patients, 26/39 (66.6%) presented with a focal and 13/39 (33.4%) with a diffuse thyroid uptake giving a prevalence of 2.06% for focal uptake and 1.03% for diffuse uptake. Six patients out of 23 patients with focal abnormal thyroid uptake were proven to have thyroid malignancy (Four patients with papillary thyroid carcinoma, one patient with follicular thyroid carcinoma and the remaining patient with atypical Hurthle cells). Thus the malignancy rate in patients with thyroid incidentalomas which proceeded to tissue biopsy was about 26%.
Conclusion: An incidental focal uptake of 18F-FDG in the thyroid gland is of significant risk of malignancy. A high value of SUVmax increases the risk of malignancy and SUVmax does not correlated with the diameter of malignant lesions, so FDG-PET/CT can detect malignancy in small thyroid lesions.