Intravenous Tumor Thrombus From Papillary Carcinoma of Thyroid Demonstrated by F-18-FDG PET/CT

A 24-year-old man with papillary thyroid carcinoma underwent 131I ablation after thyroidectomy. On posttherapy whole-body scintigraphy, only the remnant thyroid was visualized. In view of elevated unstimulated thyroglobulin level 7 months after 131I ablation, 18F-FDG PET/CT scan was ordered for further evaluation. On PET/CT images, a large filling defect from the dilated left brachiocephalic vein to superior vena cava was noted corresponding with high FDG uptake. It was considered as a malignant thrombus.