Prevalence and Risk of Cancer of Focal Thyroid Incidentaloma Identified by18F-Fluorodeoxyglucose Positron Emission Tomography for Metastasis Evaluation and Cancer Screening in Healthy Subjects

Abstract

We performed a retrospective review of 18F-fluorodeoxyglu- cose positron emission tomography (FDG-PET) examination to determine the prevalence of thyroid FDG-PET incidenta- loma in a patient group evaluated for metastasis of cancer and in a group of healthy subjects who underwent voluntary can- cer screening. We also evaluated the risk of malignancy in focal thyroid FDG-PET incidentaloma and its association with standard uptake values (SUVs) (maximum and greater than 0.75 threshold). A total of 1330 subjects underwent FDG-PET for metastasis evaluation (n 999) and cancer screening (n 331). Twenty-nine of 1330 subjects (2.2%) showed focal (n 21) or diffuse (n 8) thyroid FDG-PET incidentaloma. There was no significant difference in the prevalence of thyroid FDG- PET incidentaloma between the two groups (19 of 999 vs. 10 of 331; P > 0.05). Four of 15 focal incidentalomas (26.7%) whose histological diagnoses were available showed papillary thy- roid cancer. The maximum SUV (16.5 4.70) and greater than 0.75 threshold SUV (14.2 5.3) of malignant lesions were sig- nificantly higher than those of benign tumors (6.5 3.8 and 4.9 3.0; P < 0.05). In conclusion, thyroid FDG-PET inciden- taloma has prevalence of 2.2%, and its prevalence was not different according to the purpose of the FDG-PET. The focal thyroid FDG-PET incidentaloma carries a high risk of malig- nancy, especially in cases with high SUVs. Therefore, focal thyroid FDG-PET incidentaloma with high SUVs warrants a pathological diagnostic procedure if it changes a patient's treatment plan or prognosis. (J Clin Endocrinol Metab 88: 4100 - 4104, 2003)