Fluorine-18-fluorodeoxyglucose positron emission tomography in thyroid nodules with indeterminate cytology: a prospective study.

Background: Up to 20% of thyroid nodules subjected to fine-needle aspiration exhibit indeterminate cytology. The rate of malignancy in these nodules ranges from 10 to 40%. The objective of this prospective study was to evaluate the utility of fluorine-18-fluorodeoxyglucose (F-FDG) PET in nonautonomous thyroid nodules of more than 1 cm whose cytology is indeterminate (Bethesda categories III or IV) and that are not highly suspicious on ultrasonography.

Methods: Fifty-nine patients with 63 nodules were studied.

Results: F-FDG PET result was positive in 31 nodules. Of these, 22.6% were malignant, 25.8% were noninvasive follicular thyroid neoplasm with papillary-like nuclear features, 6.5% were tumors of uncertain malignant potential, and 45.1% were benign. F-FDG PET result was negative in 32 nodules. Of these, 3.1% were neoplasm with papillary-like nuclear features, 3.1% were tumors of uncertain malignant potential, and 93.8% were benign.

Conclusions: This study suggests a high negative predictive value of F-FDG PET in thyroid nodules of more than 1 cm whose cytology is indeterminate and that are not highly suspicious on ultrasonography.