We aimed to investigate prevalence, clinical significance and malignancy rates of incidentally detected focal increased FDG uptake in thyroid gland on FDG PET/CT imaging in cases without known thyroid malignancy.
Materials and Methods: Of the 7267 patients who underwent FDG PET/CT imaging between May 2014 and September 2016, 193 (2.6%) patients who had incidentally detected focal increased FDG uptake in thyroid gland were enrolled into the study for retrospective evaluation of clinical follow-up and SUVmax values.
Results: The SUVmax values of incidentally detected focal increased FDG foci ranged between 3-71, with an average of 9.13±7.4. Of the 193 patients, 105 (54%) were examined for possible thyroid diseases. A total 39 (20.2%) patients (10 histopathological, 29 cytological) had pathological examination. In cytological examination, two thyroid papillary carcinomas (TPC), one metastasis and 22 benign lesions were reported and four were suspicious for TPC. Five TPC, two primary tumor metastasis and three benign nodular diseases were detected in 10 patients who underwent sugery. In 10 thyroid nodules pathologically confirmed as malignancy, SUVmax values ranged from 3 to 34.9 (mean 12.5±9.1). In our series, incidental thyroid nodules with focal increased FDG uptake were detected in 2.6% of FDG PET/CT examinations. Pathological examination was performed in 20.2% of those patients and malignancy rate was 25.6% (10/39).
Conclusion: Rate of malignancy is high in incidentally detected focal increased FDG uptake on FDG PET/CT imaging. The fact that majority of patients have not undergone further examination may be due to the short survival expectancy due to primary malignancy.