A 48-year-old woman who had undergone subtotal thyroidectomy with right modified neck dissection underwent F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) for assessing the extent of disease postoperatively (restaging). Biopsy was reported as follicular carcinoma thyroid. Abnormal linear FDG uptake was seen extending along the entire extent from the superior vena cava into the right brachiocephalic vein (RBCV), and up to the right internal jugular vein in the neck. An FDG-avid metastatic lymph node mass was seen in the right paratracheal location, which was infiltrating into the RBCV. CT angiography further confirmed invasion of this mass into the RBCV with extension of tumor thrombus into the superior vena cava not reaching the right atrium. This case shows that it is possible for metastatic follicular carcinoma thyroid to invade into great veins, which can be well depicted on FDG PET-CT.