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J Nucl Med. 2018 May;59(5):749-755. doi: 10.2967/jnumed.117.198085. Epub 2017 Oct 12.

18F-FDG-Avid Thyroid Incidentalomas: The Importance of Contextual Interpretation.

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Centre for Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Australia
Department of Nuclear Medicine and Specialised PET Services, Royal Brisbane and Women's Hospital, Brisbane, Australia.
Department of Surgical Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia.
Department of Surgery, University of Melbourne, Melbourne, Australia.
Melbourne EpiCentre, Royal Melbourne Hospital, Melbourne, Australia.
Department of Medicine, University of Melbourne, Melbourne, Australia; and.
Centre for Cancer Imaging, Peter MacCallum Cancer Centre, Melbourne, Australia.
Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, Australia.


18F-FDG-avid thyroid incidentaloma (TI) is seen in approximately 2.5% of patients imaged for staging or response assessment of malignancy and represents thyroid cancer in approximately 35% of cases. Consequently, the 2015 American Thyroid Association guidelines strongly recommend investigation of all 18F-FDG-avid nodules 1 cm or larger with ultrasound and fine-needle aspiration cytology (FNA). This study aimed to assess the overall and thyroid cancer-specific survival in a large cohort of patients with 18F-FDG-avid TI with long-term follow-up to assess the validity of this approach. Methods: Retrospective review of 45,680 PET/CT scans performed at a comprehensive cancer center from January 2007 to January 2015 identified 2,588 18F-FDG PET/CT reports referring to the thyroid. After exclusion of nonavid thyroid nodules, diffuse 18F-FDG uptake, known thyroid cancer, abnormalities adjacent to the thyroid, and repeat studies, 500 patients (1.1%) with TI were identified, of whom 362 had confirmed death or more than 12 mo of clinical follow-up. Variables including age, sex, primary malignancy, overall survival, thyroid cancer-specific survival, FNA, and histopathology were collected until January 2016. Multivariate logistic regression and survival analysis were performed. Results: The 362 analyzed patients (65% female) had a median age of 65 y (range, 19-96 y) and follow-up of 24 mo (range, 1-103 mo). Lymphoid, lung, and colorectal malignancy were the most common staging indications. Median overall survival was 20 mo (interquartile range, 9.5-39 mo). Most of the 180 observed deaths were due to the primary malignancy under investigation (92.2%) or to causes not related to cancer (7.2%); one patient (0.6%) died from incidentally detected medullary thyroid cancer. 18F-FDG avidity in the index malignancy, an advanced stage for that malignancy, and a clinician decision not to investigate 18F-FDG-avid TI were all predictors of mortality, with hazard ratios of 8.5, 3.0, and 3.3, respectively, and 95% confidence intervals of 4.6-15.8, 2.3-3.9, and 2.0-5.0, respectively (P < 0.001). Of 131 patients suitable for cytologic or histopathologic evaluation, 47 (36%) had incidental thyroid cancer (24 papillary, 11 malignant FNA, 5 oncocytic/Hürthle cell, 2 medullary, 1 follicular, and 4 metastases from underlying malignancy). Conclusion: Overall survival with 18F-FDG-avid TI was poor because of the prognosis associated with underlying malignancy, which must be considered before investigation of 18F-FDG-avid TI and certainly before aggressive treatment. Active surveillance should be considered in this group of patients.


FDG; PET/CT; incidentaloma; oncology; thyroid

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