Substernal thyroid carcinoma detected by 67Ga scan in a patient with normal 131I scan

A patient with a superior mediastinal mass on an admission chest radiograph was initially evaluated by an 131I thyroid scan which failed to demonstrate a substernal thyroid. However, the tomographic 67Ga scan clearly showed an abnormal uptake in the area corresponding to the mass lesion on radiographic examination. Subsequent resection and biopsy of the substernal mass revealed a poorly differentiated follicular carcinoma with foci of anaplastic carcinoma. The differential diagnosis of the anterior mediastinal mass and the usefullness of the tomographic gallium scan are briefly discussed.