18F-Fluorodeoxyglucose Positron Emission Tomography Does Not Predict Malignancy in Thyroid Nodules Cytologically Diagnosed as Follicular Neoplasm

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Abstract
Objective: The objective of this study was 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 two each with Hürthle cell and follicular variants of papillary cancer. Twenty-one patients had benign nodules: 11 follicular adenomas, eight adenomatous hyperplasias, and two 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.