Risk of malignancy in thyroid incidentalomas detected by 18F-fluorodeoxyglucose positron emission tomography. A systematic review
K. Soelberg, S. Bonnema, T. Brix & L. Hegedüs
Background: The expanding use of 18F-fluoro-deoxy-glucose positron emission tomography (18F-FDG PET) has led to the identification of increasing numbers of patients with an incidentaloma in the thyroid gland. The aim of this study was to review the proportion of incidental thyroid cancers found by 18F-FDG PET or PET/CT imaging.
Methods: Studies evaluating thyroid carcinomas discovered incidentally in patients or healthy volunteers by 18F-FDG PET were systematically searched in the PubMed database from 2000 up to 2011. The main exclusion criteria were known thyroid disease, lack of assigned diagnoses, investigation of diffuse uptake only, or investigation of patients with head and neck cancer, or cancer in the upper part of the thorax.
Results: Twenty-two studies met our criteria comprising a total of 125754 subjects. 1994 (1.6%) had an unexpected focal hypermetabolic activity, while 999 of 48 644 individuals (2.1%) had an unexpected diffuse hypermetabolic activity in the thyroid gland. A diagnosis was assigned in 1051 (271 had surgical confirmation) of the 1994 patients with a focal uptake (366, corresponding to 34.8%, were malignant), and in 168 of 999 patients with diffuse uptake (7, corresponding to 4.4%, were malignant). In the eight studies reporting individual maximum standard uptake values (SUVmax), the mean SUVmax value was 4.8 (SD 3.1) and 6.9 (SD 4.7) in benign and malignant lesions, respectively, (P< 0.001).
Conclusions: Incidentally found thyroid nodules, using 18F-FDG PET, are at high risk of harboring malignancy if uptake is focal. SUV-values are significantly higher in malignant than in benign nodules. The pronounced inhomogeneity and other shortcomings of the studies are discussed.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.