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

Divisions of Endocrinology (F.M.S., P.H.Z., E.K.T., R.Y.A.d.C., M.A.A.P.) and Nuclear Medicine (J.J.C., J.S., L.K.C., M.I., M.C.P.G., J.C.M.), Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, CEP 05403-000 São Paulo, Brazil; and Department of Preventive Medicine (J.E.-N.), Faculdade de Medicina da Universidade de São Paulo, CEP 01246-903 São Paulo, Brazil

Address all correspondence and requests for reprints to: Maria Adelaide Albergaria Pereira, M.D., Division of Endocrinology and Metabolism, Hospital das Clínicas, University of São Paulo Medical School, Avenida Dr Enéas de Carvalho Aguiar, 255, 7th floor, CEP 05403-000 São Paulo (SP), Brazil.

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%.