Ectopic mediastinal thyroid tissue: cervical or mediastinum originated?

A 22-year-old female patient was admitted to our clinic after both clinical and laboratory findings suggested hyperthyroidism. At pre-operative magnetic resonance imaging (MRI), we detected a substernal goitre with lobulated outlines at the inferior of the right lobe that extended 5 cm inferior to the carina. The thyroid mass extended to the mediastinum and was totally extracted by cervical incision. Postoperatively, a residual thyroid mass of 8.5×9×10 cm in size, was detected on MRI at the median part of the anterior mediastinum. The isolated mediastinal thyroid mass was then extracted by sternotomy. We believe that, because of the close anatomical relationship between the thyroid tissue extending cervically and the mass detected in the mediastinum, the mediastinal mass might have developed from the cervical thyroid tissue residues by pushing the cervical thyroid or it might have mechanically entered the mediastinum.