Objectives: To evaluate the usefulness of ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) in predicting malignancy in thyroid nodules cytologically diagnosed as follicular neoplasm.

Patients and Methods: A total of 46 patients with thyroid nodules larger than 1 cm in diameter cytologically diagnosed as follicular neoplasm at Asan Medical Center, Seoul, Korea, were included. FDG-PET images were taken in all patients before surgical resection, and the maximum standardized uptake value (SUVmax) of each nodule was measured.

Results: FDG-PET showed hypermetabolic activity of all nodules compared with normal thyroid tissue. Thirty-six patients underwent surgery, whereas 10 refused immediate operation. Fifteen patients had cancer: 11 with follicular, and 2 each with Hürthle cell and follicular variants of papillary cancer. Twenty-one patients had benign nodules: 11 follicular adenomas, 8 adenomatous hyperplasias, and 2 Hürthle cell adenomas. SUVmax did not differ significantly between malignant and benign nodules (3.6 ± 3.5 vs. 3.4 ± 3.2; P = 0.83) or among subtypes of benign nodules (P = 0.23). However, SUVmax differed significantly among subtypes of malignant nodules (P = 0.02).

Conclusions: On FDG-PET, the glucose metabolic activities of benign thyroid follicular nodules were as high as those of malignant nodules. These findings suggest that FDG-PET has limited value for selecting candidates for surgery among patients cytologically diagnosed as follicular neoplasm.