Solitary Asymptomatic Thyroid Metastasis from Hepatocellular Carcinoma Detected by FDG-PET/CT

Thyroid metastases from hepatocellular carcinoma (HCC) seldom occur and are often difficult to diagnose because of their asymptomatic clinical course. We evaluated a very rare case of solitary thyroid metastasis from HCC that showed high uptake of fluorine-18 fluorodeoxyglucose (FDG), when imaged using fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT). The patient was a 74-year-old man and presented with a remarkably elevated des-gamma-carboxy prothrombin level of 1,157 mAU/ml 22 months after hepatic lobectomy. FDG-PET/CT imaging revealed a hypodense tumor with high FDG uptake, with a maximum standardized uptake value of 5.2 in the thyroid left lobe. Solitary thyroid metastasis from HCC was suspected and subsequent fine needle aspiration did indeed reveal HCC. The patient received left thyroidectomy with left regional lymph node dissection. Two months after left thyroidectomy, contrast-enhanced computed tomography showed local recurrence, and the patient received ongoing radiotherapy treatment. To our knowledge, the present study is the first to demonstrate the feasibility of FDG-PET/CT in the diagnosis and management of clinically diagnosed, asymptomatic, solitary thyroid metastasis from HCC.