Selective uptake of 75Se-selenomethionine by thymoma with pre red cell aplasia.

Red cell aplasia and an enlarging anterior mediastinal mass developed in a patient being followed for thyroid carcinoma. Differential diagnosis included thymoma and metastatic thyroid carcinoma. Preoperative scanning demonstrated significant uptake of 75Se-selenomethionine whereas 67Ga-galiium citrate failed to visualize the mass. Subsequent thoracotomy revealed a lymphocytic thymoma which was resected, resulting in reversal of the red cell aplasia. The use of 75Se-selenomethionine scanning maybe a useful adjunct in the preoperative evaluation of suspected thymomas.