Endocrinologia e Síndrome Metabólica
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The Role of 18F-Fluorodeoxyglucose Positron Emission Tomography in the Diagnosis of Incidental Thyroid Lesions

O Schillaci, M Guazzaroni, A Lacanfora, D Di Biagio, M Antonicoli, M Mataloni and G Simonetti

Objective: The aim of this study was to determine the diagnostic accuracy of incidental FDG-PET/CT uptake in the thyroid in patients with cancers of nonthyroidal origin, in order to reduce the number of thyroidectomies performed on nodules that subsequently proved to be benign.

Material and methods: From January to September 2011 a total of 2510 patients were evaluated at our institution with whole-body FDG-PET. The studies were done for a variety of diagnoses including metastatic work-up for lymphoma, head and neck cancer, and other nonthyroidal malignant nodules. 30 patients were identified with incidental focal or diffuse uptake in thyroid bed. All patients underwent measurement of serum level of thyroid hormones and ultrasonography (US). While the patients with focal uptake underwent fine needle aspiration biopsy, FNAB.

Results: PET incidentaloma was observed in 30 patients (0.12% of the whole population) with normal thyroid functions and there weren’t known clinical manifestations of thyroid disease. FDG PET uptake pattern was diffuse in 8 patients (26.7%) and focal in 22 patients (73.3%). SUVmax was included between 2.5 and 20. The patients with focal uptake underwent FNAB which demonstrated 4 patients with TIR1 (18.2%), 3 patients with TIR2 (13.6%), 11 patients with TIR3 (50%), 2 patients with TIR4 (9.1%), 1 patient with TIR5 (4.5) and 1 patient with TIR6 (4.5%). All 4 patients
with TIR4, TIR5 and TIR6 underwent to thyroidectomy and the final diagnosis was papillary carcinoma.

Conclusions: The results of this study suggest that incidentally found thyroid lesions by FDG-PET/CT, especially a focal FDG uptake and a high SUV, have a high probability of thyroid malignancy.