Occult thyroid carcinoma manifested as a large mediastinal tumor

The authors report a rare case of clinically occult thyroid carcinoma that initially manifested as a metastatic mediastinal tumor with tracheal stenosis. A curative operation was performed by complete removal of the tumor through a median sternotomy approach combined with resection of the tracheal invasion. Histopathological examination revealed transition of a well-differentiated papillary carcinoma into a poorly differentiated component in the lesion invading the trachea, which suggested that this transition might have rendered the tumor more aggressive, leading to tracheal invasion.