Mediastinal Thyroid Carcinoma and Graves' Disease: A Rare Presentation

BACKGROUND: Mediastinal thyroid carcinoma is extremely rare, with few cases reported in the literature. Case Report. A 73-year-old man presented with weight loss for 6 months. Imaging by computed tomography (CT) documented a large mediastinal mass below the thyroid gland and pulmonary metastases. Neck ultrasound found two spongiform nodules in the right thyroid lobe, and fine-needle aspiration citology (FNAC) of these nodules revealed they are benign. Endobronchial ultrasound-guided needle biopsy of the mediastinal mass was compatible with papillary thyroid cancer. A few weeks later, the patient developed overt hyperthyroidism due to Graves' disease, which was treated with antithyroid drugs. (99m)Pertechnetate scintigraphy showed increased diffuse uptake in the thyroid parenchyma but the absence of uptake in the paratracheal mass and in the lung nodules. The patient was not considered eligible for surgical intervention or therapy with tyrosine kinase inhibitor due to tracheal and mediastinal vessel invasion and was treated with palliative radiotherapy. Two months later, restaging PET-FDG showed an intense uptake in the right lobe of the thyroid gland, lymph nodes, lungs, bone, muscle, myocardial, kidney, and adrenal gland. CONCLUSION: In this case, thyroid carcinoma presented as a mediastinal mass with concurrent hyperthyroidism due to Graves' disease. Although uncommon, the clinicians should be aware of these situations. Obtaining a prompt histological examination of an intrathoracic mass is crucial to ensure an early diagnosis and treatment.