Endocrine Abstracts

Introduction: Positive radiotracer uptake by the thyroid gland can occur in PET-CT. It’s meaning has led to conflicting results mainly resulting from small studies.

Objective: We aim to present a large single institution consecutive case series.

Material and methods: Observational, descriptive and retrospective study of the PET-CT scans performed between the years 2000–2017. We searched the word thyroid in the computer imaging system and created an Excel database with the epidemiological records and the characterization of the findings in respect to the type of radiotracer and the type of uptake. The results were matched with the list of thyroid cythologies and then the histological results. SUVmax and SUVpeak were calculated with respect to the probability of malignancy.

Results: In brief, we characterized 30470 Nuclear Medicine exams corresponding to 20432 patients: 28499 ¹⁸F-FDG-PET/CT (93.53%), 1654 ⁶⁸Ga-DOTANOC-PET/CT (5.43%), 235 ⁶⁸Ga-PSMA-PET/CT (0.77%) and 82 ¹⁸F-Flurocolina-PET/CT (0.27%). Thyroid uptake occurred in 4.96% patients. Fine needle aspiration (FNA) was performed in 443 cases: age average 60.99±13.54; 150 male sex (33.9%), 293 female sex (66.1%); 405 ¹⁸F-FDG-PET/CT (91.4%) and 38 ⁶⁸Ga-DOTANOC-PET/CT (8.6%). Thyroid uptake occurred in 153 ¹⁸F-FDG-PET/CT (37.8%), 78 in the right lobe (51%), 53 in the left lobe (34.6%), 4 in the isthmus (2.6%), 13 bilateral (8.5%) and 5 with diffuse uptake (3.3%). Malignant disease was diagnosed in 15.1% of ¹⁸F-FDG-PET/CT – FNA cases: 23.5% of those with uptake and 9.9% of those without uptake. SUVmax malignant vs benign: 9.181±4.93 vs 6.447±3.26, P: 0.014551 (<0.05); ROC: 0.668; Youden SUVmáx 6.9 (sensitivity (SN) 55.06; specificity (SP) 69.76). SUVpeak malignant vs benign: 6.17±3.47 vs 4.13±1.6; P: 0.007618 (<0.05); ROC: 0.708; Youden SUVpeak 4.8 (SN 57.5; SP 74.05). Malignant disease was found in 69.1% of cases in histology.

Conclusions: We present one of the largest and most complete consecutive case series. The incidence of focal thyroid FDG uptake is clinically relevant. It represents an increased probability of malignancy therefore justifying the continuation of the investigation of those cases throught the correlation with other imaging, cythological and molecular biology exams. Despite overlap, an increased SUVmax heightens that suspicion.