Incidental thyroid lesions detected by FDG PET scanning

As FDG PET scanning has become more popular in recent years, it has also become more frequent means of detecting incidental thyroid lesions. The aim of this study is to investigate to prevalance of incidentally found thyroid lesions in patients undergoing FDG PET and determine the risk for thyroid cancer.FDG PET was performed on 5758 patients for eveluation of suspected or known cancer without any history of thyroid disease between January 2006 and May 2012 in our clinic. Patients with incidental thyroid abnormalities were identified. Medical records related to the FDG PET findings including SUVmax and pattern of FDG uptake, FNA diagnosis and histopathology after thyroid surgery were reviewed retrospectively.One hundred twenty three patients (2.1%) were identified to have focal incidental thyroid lesions and 52 patients (0.9%) were identified diffuse incidental thyroid lesions on FDG PET. Twenty four patients with focal and 5 patients with diffuse incidental thyroid lesion underwent FNA. The malignant diagnosis was detected 41.6% of focal lesions. In diffuse lesions, malignant diagnosis was not observed. There was a significiant difference in the SUVmax between the benign and malignant lesions (5.7±2.2 and 10.1±5.3). Malignant diagnosis was noted in 57.1% of male patients and 20% of female patients who underwent FNA.The results of this study suggest that focal FDG uptake, high SUV and male gender have high risks for thyroid malignancy in incidentally found thyroid lesions by FDG PET. Further diagnostic work-up is needed in patients with these findings.Key Words: FDG PET scan, Incidental thyroid lesions, Risk of malignancy.