Resection is not necessary, however, thoracotomy or mediastinoscopy are usually required to confirm the diagnosis. Chemotherapy or radiation are the common modes of treatment. Prognosis varies with the histology. The majority of mediastinal thyroid tissue is a substernal extension of a cervical goiter. On plain film the mass is well defined and homogeneous, causing smooth displacement and often narrowing of the trachea.
Calcification is common.
Although 131I studies are usually diagnostic and should be the first study to evaluate the suspected mass, false negative results occur. In the face of a negative radionuclide study but clinical suspicion of an intrathoracic goiter, a CT exam should be performed. Additionally, as the mass is encapsulated and does not invade, the displaced mediastinal vessels generally are arranged concentrically around the mass. A second, much rarer presentation of intrathoracic goiter is from heterotopic tissue. It is important to make the differentiation between these two types for surgical planning as each has a distinct blood supply.