Risk-stratification of thyroid nodules examined by ¹⁸FDG-PET/CT while ensuring congruity between imaging and histopathological localization

Purpose: The risk of malignancy (ROM) in FDG-avid thyroid incidentalomas varies between studies, which may be contributed by discordance between the anatomical localization depicted on ¹⁸FDG-PET/CT and by histopathological examination. The purpose was to ensure anatomical congruity between the index tumour identified by ¹⁸FDG-PET/CT and the histopathological examination, in order to assess the risk of malignancy (ROM) in PET-positive and PET-negative thyroid nodules. Further, preoperative characteristics indicative of thyroid malignancy were identified. Methods: Thirty-two patients referred to thyroid surgery were prospectively included. ¹⁸FDG-PET/CT, fine-needle aspiration biopsy and thyroid ultrasonography examination were performed in all participants. The exact anatomical localization of the index nodule was established by histopathological examination to ensure concordance with the ¹⁸FDG-PET/CT finding. Results: Forty thyroid nodules were included. Malignancy was identified in 10 of 28 PET-positive nodules and in 1 of 12 PET-negative nodules, resulting in a ROM of 36% and 8%, respectively. A Hurtle cell neoplasm was found in 50% of patients with a benign nodule and a PET-positive scan. One PET-negative nodule represented a papillary microcarcinoma. In PET-positive nodules, hypoechogenicity, irregular margins, and pathological lymph nodes on thyroid ultrasonography were characteristics associated with malignancy. Conclusions: In this study—ensuring anatomical congruity between PET-findings and the histopathological examination—the risk of malignancy in PET-positive thyroid nodules was 36%. A low ROM was seen in thyroid nodules without suspicious ultrasonographic findings, independent of the ¹⁸FDG-PET/CT result. Trial registration number: NCT02150772 registered 14th of April 2014.