Role of 18F-Fluorodeoxyglucose Positron Emission Tomography in Preoperative Assessment of Cytologically Indeterminate Thyroid Nodules

Objective: The objective of the study was to determine the diagnostic accuracy of 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) in the preoperative diagnosis of thyroid nodules with indeterminate fine-needle aspiration biopsy results. Methods: Forty-two consecutive patients with thyroid nodules with indeterminate cytological results participated in this study. Abnormal 18F-FDG PET uptake was assessed visually and by measuring the maximum standardized uptake value (SUVmax) in thyroid topography. All these results were compared with the final pathological results. Results: The presence of focal uptake correlated with a greater risk of malignancy (P = 0.018). All 11 malignant nodules had focal uptake (sensitivity of 100%). Of the 31 patients with benign nodules, there were 19 with positive uptake (specificity of 38.7%). The pre-PET probability of cancer was 26.2% (11 of 42), and this probability increased to 36.7% after PET for those patients whose exam showed focal uptake (11 of 30). The preoperative use of 18F-FDG PET would result in a significant reduction (39%, 12 of 31) in the number of thyroidectomies performed in patients with benign lesions. SUVmax could not improve this degree of accuracy. There was no correlation between thyroid nodule size and SUVmax value (P = 0.96). Patients with carcinomas were younger than patients with benign lesions (P = 0.048). There was no other clinical, laboratory, or ultrasonographic variable related to malignancy. Conclusions:18F-FDG PET provides high sensitivity to malignant lesions and may be a potentially useful tool in the evaluation of thyroid nodules with indeterminate cytological findings. For these nodules the number of unnecessary thyroidectomies in a hypothetical algorithm using 18F-FDG PET would be reduced by 39%.