Thyroid Incidentalomas disclosed by 18F-Fluorodeoxyglucose Positron Emission Tomography: prevalence and clinical relevance

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: MON 471-496-Thyroid Neoplasia & Case Reports
Monday, June 17, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board MON-474
Pedro Marques*1, Ângelo Silva2, Pedro Ratão2, Teresa C. Ferreira2, Lucília Salgado2, Leone Duarte3, Valeriano Leite1 and Maria João Bugalho1
1Portuguese Institute of Oncology, Lisbon, Portugal, 2Portuguese Institute of Oncology, Lisbon, 3Luz Hospital, Lisbon, Portugal
Introduction: The expanding use of 18F-Fluorodeoxyglucose Positron Emission Tomography (18F-FDG-PET) has contributed to an increasing number of thyroid incidentalomas. The present study was designed aiming to estimate the prevalence of thyroid incidentalomas diagnosed by 18F-FDG-PET and to evaluate the risk and potential of malignancy.

Methods: Retrospective analysis of 9372 18F-FDG-PET exams, performed in Nuclear Medicine Department of Portuguese Institute of Oncology, Lisbon, within 2007 and 2012. The inclusion criteria were focal thyroid uptake in patients studied for nonthyroid purpose. Exclusion criteria were diffuse uptake and known thyroid pathology.

Results: Abnormal uptake (diffuse and focal) was identified in 88 cases. Focal uptake, herein meaning incidentaloma, was seen in 58 cases (prevalence of 0,62%). Cytological diagnosis was available in 21 patients corresponding to: papillary thyroid carcinoma (PTC) in 12, nodular hyperplasia in 6, indeterminate follicular lesions in 2 (follicular adenomas confirmed by histology) and lung cancer metastasis in 1.

Based on cytological criteria, the risk of thyroid malignancy was estimated in 57,1% (12/21). Patients were mostly females (female-to-male=5:1) and the majority was in fifth decade (mean of 56,5±15,7 years). The mean value of the maximum standardized uptake value (SUVmax) was 7,5(±5,2), higher than the observed in benign conditions 5,3(±1,8) (p=0,3).

Ten out of 12 patients with cytology compatible with PTC were submitted to surgery. The diagnosis was confirmed in all, classical variant in 7, follicular variant in 3. Three were multifocal; 6 had extrathyroidal extension; 4 angioinvasion. Two presented cervical lymph nodes metastases; 1 had pulmonary metastases. All patients had radioiodine therapy and 2 patients had second surgery due to locorregional recurrence. At the last observation, 3 patients (30%) had persistence or recurrence of disease. Mean follow-up was 32,7 months.

Conclusion: Focal 18F-FDG-PET thyroid incidentalomas have a considerable risk of malignancy, especially for higher SUVmax. Aggressive histological criteria are found in a considerable number of malignant cases. Therefore, thyroid incidentalomas identified by 18F-FDG-PET should be investigated.

Nothing to Disclose: PM, S, PR, TCF, LS, LD, VL, MJB

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