Thymic Uptake of 18F-FDG Following Radioiodine Ablation Therapy

We report the case of a 47-year-old woman with a history of non-Hodgkin's lymphoma. During the course of her disease, we performed various ¹⁸F-FDG PET/CT that identified several significant incidental findings. First, we incidentally identified a hypermetabolic nodule in the left thyroid lobe, whose final diagnosis showed differentiated thyroid carcinoma. Second, metabolic activity was visualized in the thymus secondary to ablative treatment with radioiodine. This uptake disappeared in subsequent studies. Several papers have reported thymic rebound following chemotherapy but we have found only one case report of ¹⁸F-FDG uptake after radioiodine treatment. On the other hand, this case is of interest because it supports the benefit of studying the hypermetabolic thyroid nodules incidentally detected on the PET/CT performed for other reasons.