Incidental papillary thyroid carcinoma in a patient presenting with Graves' hyperthyroidism and concomitant obstructive sequestered intrathoracic multinodular goiter

A previously healthy 27-year-old woman presented with a thyroid goiter, symptoms of thyrotoxicosis, and mild respiratory obstruction. The serum thyroid stimulating hormone (TSH) was suppressed, serum T4 was elevated, and 24-hour radioiodine uptake was elevated at 59%. Thyroid scintigraphy showed intense uptake in an enlarged gland, with a cold nodule on the right, and a large isolated mass in the mediastinum, with very mild uptake. Total thyroidectomy and excision of the mediastinal mass revealed multiple pathologies: Graves disease in the thyroid gland with an incidental papillary thyroid carcinoma, and a benign sequestered intrathoracic multinodular goiter. Thyroid carcinoma can develop in a gland affected by Graves disease, however, the presence of concomitant sequestered intrathoracic thyroid tissue unaffected by Graves disease is highly unusual and has not been previously described. We present the scintigraphic findings, and several theories that could help explain these findings.