Endocrine Abstracts

The use of ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG–PET) has increased the detection of thyroid incidentalomas (TI). These are associated with a risk of malignancy between 25 and 50%. Some studies show an association between SUVmax uptake and malignancy.

The objective of this study was to determine the prevalence of malignancy on ¹⁸F-FDG–PET positive thyroid nodules and to evaluate the relationship between SUVmax uptake and malignancy in a population of patients followed in a central hospital.

We evaluated retrospectively all ¹⁸F-FDG–PET exams performed between 2008 and 2013. The inclusion criterion was focal thyroid uptake in patients studied for non-thyroid purposes.

From the 1810 ¹⁸F-FDG–PET exams (1384 patients), 3.2% (43) fulfilled the inclusion criteria, 60.5% were females (28), mean age was 68 years. Thyroid ultrasound was done in 39.5% (17) with an average nodule size of 20.5 mm. FNAC was performed in 37.2% (16) with 50% (8) benign, 31% (5) non-diagnostic, 6.5% (1) suspicious for papillary carcinoma and 12.5% (2) papillary carcinoma.

Surgery was performed in the latter two categories, with a histological classification of papillary carcinoma in all three procedures (one with distant metastasis). The median SUVmax was five for the benign cases and 7.95 for the malignant ones (P=0.38).

Focal ¹⁸F-FDG–PET thyroid uptake had a prevalence of 3.2%. The prevalence of malignancy was 19% on ¹⁸F-FDG–PET positive exams. Only 37.2% were evaluated by FNAC. Two possible explanations are the end of life status of these patients but also the lack of knowledge, on non-endocrine services, regarding the risk of malignancy of TI patients. A trend towards a higher risk of malignancy with higher SUVmax was found although it was not statistically significant. The limitations of the current work reflect an undervaluation of patients at risk and the rather high number of non-diagnostic FNAC.