Management of a large mediastinal cyst of thyroid origin.

Large mediastinal cysts of the thyroid are rare and it is difficult to make a definitive tissue diagnosis prior to surgical removal. Ultrasonography and computed axial tomography are useful in documenting the cystic nature of the lesion and demonstrating its relationship to other mediastinal structures. These studies may also suggest the tissue of origin. We report a case of massive mediastinal thyroid cyst situated in the right posterior mediastinum and causing significant tracheal compression. Because of this unusual location and lack of iodine uptake, preoperative diagnosis was not possible. At surgery, which we performed via right thoracotomy because of the location of the mass, its origin from thyroid tissue was demonstrated. Resection was accomplished with care taken not to injure the recurrent laryngeal nerve. The patient recovered uneventfully.