Clinical Significance of Incidental Focal Versus Diffuse Thyroid Uptake on FDG-PET Imaging

The number of incidentally detected thyroid lesions found with 18F-fluorodeoxyglucose positron emission tomography is increasing. Malignant cases incidentally found with this technique are mainly primary thyroid cancers, particularly papillary thyroid carcinoma, which tend to harbor a higher rate of unfavorable prognostic features than routinely diagnosed primary thyroid cancers. The significance of standardized uptake values in predicting malignancy of incidental thyroid fluorodeoxyglucose uptake is controversial, and more studies are needed to establish its role in differentiating benign and malignant incidental thyroid fluorodeoxyglucose uptake. In this article, we review recent publications regarding incidental thyroid lesions found on fluorodeoxyglucose positron emission tomography and their differential diagnosis, including the risk for malignancy.