A thyroglossal duct cyst of the anterior mediastinum.

Thyroglossal duct cysts (TGDCs) are developmental anomalies arising from the embryonic thyroglossal duct. They are commonly midline cervical structures associated with the hyoid bone. We report a 3.5-cm diameter isolated TGDC of the anterior mediastinum in a 65-year-old European woman who was treated by transcervical excision. The mass was limited to the mediastinum with a normal neck on computed tomographic scan and clinical examination. This is the second case of mediastinal TGDC known to be reported, and the oldest known age at presentation. The TGDC should be considered as an uncommon differential diagnosis of an anterior mediastinal mass.