PREVALENCE OF MALIGNANCY IN PATIENTS WITH THYROID INCIDENTALOMAS DETECTED BY 18 F-FLUORODEOXYGLUCOSE POSITRON EMISSION TOMOGRAPHY

Abstract

Background: Thyroid incidentalomas detected by 18 F-Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) have been reported in 1.1 to 2.9% of scans performed. Previous studies have determined the prevalence of thyroid malignancy in these patients to be 14-72%. Objective: We undertook a retrospective study to determine the prevalence of thyroid incidentalomas in our center, and evaluated the corresponding prevalence for malignancy in these patients. Results: A total of 2,912 FDG-PET scans were performed on 1,855 patients, of which 56 (3.0%) presented with a thyroid incidentaloma (40 focal and 16 diffuse). Among the 22 patients who had an ultrasound, 15 presented with solid nodules (10 focal and 5 diffuse), while 5 were negative for any lesions (4 focal and 1 diffuse). Of 13 patients who had a subsequent FDGPET scan, 8 had resolution of the hypermetabolic foci (61.5%), of which 5 were focal and 3 diffuse. Only 1 of 6 incidentalomas whose histological diagnoses were available showed malignancy (papillary carcinoma). Other cytologic diagnoses include colloid goiter and lymphocytic thyroiditis. Conclusion: The prevalence of thyroid malignancy in focal incidentalomas is 1 in 12 (8.3%) and 1 in 17 in all incidentalomas (5.9%). Our experience indicates that the prevalence rates are much lower than that previously reported. Nevertheless, the prevalence rates are significantly elevated to warrant further evaluation, including an imaging procedure and fine needle aspiration biopsy.