Endocrine Implications of Thyroid Incidentalomas Detected During Lymphoma Staging With 18F-Fluorodeoxyglucose Positron Emission Tomography.

OBJECTIVE

This study investigated the prevalence, characteristics, and endocrine implications of thyroid incidentalomas detected during lymphoma staging using FDG-PET/CT.

DESIGN

Retrospective cohort study.

PATIENTS: A total of 795 adult patients with lymphoma who underwent FDG-PET/CT for staging at a tertiary oncology centre were included.

MEASUREMENTS: Thyroid uptake was classified as focal, diffuse, or absent. Additional data included demographic features, lymphoma subtype, thyroid function, autoantibodies, ultrasound (US), fine-needle aspiration cytology (FNAC), and histopathology when available.

RESULTS

Thyroid abnormalities were detected in 139 patients (17.5%). Focal FDG uptake was observed in 33 patients (4.2%) and was associated with a malignancy rate of 18.2% (28.6% among those who underwent FNAC). Diffuse uptake was observed in 20 patients (2.5%) and was significantly associated with positive thyroid autoantibodies (58.3%, p < 0.01). Older age and female gender were independent predictors of thyroid uptake. ROC analysis identified optimal age thresholds of 68.6 years for females and 59.8 years for males (AUC = 0.72). SUVmax, Hounsfield units, and ACR TI-RADS classification were not significantly associated with malignancy. All malignant cases occurred in nodules classified as TI-RADS 4 or 5. Volume on CT was inversely associated with malignancy (ρ = -0.50, p = 0.046). No significant impact on overall survival was observed.

CONCLUSIONS

Thyroid incidentalomas are frequent during lymphoma staging by FDG-PET/CT and should be appropriately evaluated. Focal uptake carries a relevant malignancy risk, even in nodules with low SUVmax. Diffuse uptake often reflects autoimmune thyroiditis. A multimodal diagnostic approach is essential to guide management and avoid unnecessary delays in cancer care.