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Mediastinal thyroid goiter with no accumulation on scintigraphy.

A 68-year-old woman was indicated to have a mediastinal tumor by chance. The tumor was suspected to be a mediastinal thyroid goiter on enhanced CT (Picture A, arrowheads). Laboratory tests showed subclinical thyrotoxicosis; however, thyroid stimulating hormone (TSH) receptor antibodies were negative. Thyroid scintigraphy with 99m-TcO4 demonstrated accumulation in the cervical thyroid, although no accumulation was observed in the mediastinal tumor (Picture B, arrowheads). The biopsy of the mediastinal tumor on endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) revealed thyroid follicular cells. The patient’s subclinical thyrotoxicosis state was sustained. On an examination of the resected specimen, the mediastinal tumor was found to be continuous with the cervical thyroid. Multiple thyroid nodules were observed, and the tumor was histologically diagnosed as an adenomatous goiter. Although thyroid scintigraphy is useful for the diagnosis of mediastinal thyroid goiters (1), this is an unusual case of a thyrotoxic multinodular goiter with no accumulation in the mediastinal thyroid component. Hemorrhage and cystic degeneration were observed within the nodule in the mediastinal thyroid component. It has been reported that malignant neoplastic or nodular goitrous thyroid tissue exhibits less accumulation of radiopharmaceuticals than adjacent normal thyroid tissue (2).