Thyroid Incidentaloma identified by 18F-Fluorodeoxyglucose Positron Emission Tomography with CT (FDG-PET/CT): clinical relevance
Loredana Pagano1, MariaTeresa Samà1, Marco Rudoni2, Sara Belcastro1, Arianna Busti1, Marina Caputo1, Eugenio Inglese2 & Gianluca Aimaretti1
Thyroid incidentalomas was defined as newly identified thyroid lesions encountered during imaging study for non-thyroid diseases. In the last years, the use of FDG-PET/CT for staging of metastatic diseases was increased. The aim of this retrospective study was to evaluate the FDG-PET/CT uptake, to identify a SUVmax cut off predictive of malignancy and to determine the FDG-PET/CT prognostic role in patients with thyroid incidentalomas. 42 patients (ptx) with incidental thyroid uptake at FDG-PET/CT were included in the analysis (32 W, mean age 66.74±11.81 years). All ptx performed a thyroid function and an ultrasonography (US) evaluation. 36/42 patients underwent an US-FNAC of the thyroid nodules. Ptx with TIR 3, TIR 4 and TIR 5 FNAC-diagnosis underwent a total thyroidectomy. A diffuse (group A) or focal (group B) 18F-FDG uptake was shown in 26.2 and 73.8% ptx, respectively. Differentiated thyroid cancer was shown in 9% and 41.9% ptx in group A and B, respectively. A statistical correlation was found between focal uptake and euthyroidism (P<0.0001) and between diffuse uptake and thyroid dysfunction (P < 0.0001). A correlation between the SUVmax value > 5 and the presence of thyroid cancer (r=0.377 P<0.01) was found in group B. The FDG-PET/CT sensitivity and specificity was 85.7% and 53.6%, respectively; the PPV was 48% and the NPV was 88.2%. The neck US increased FDG-PET specificity from 53.6% to 75%. In particular hypoechogenicity and the number of US risk factors correlate with the diagnosis of thyroid carcinoma (r=0.338; P<0.02 r=0.287; P=0.065 respectively). Our data suggest that the incidental detection of diffuse thyroid uptake at FDG-PET/CT is related to a benign disease, while focal thyroid uptake evidences an high risk of malignancy, especially with a SUVmax value > 5, euthyroidism and suspicious US features.