Normal thymic uptake of 2-deoxy-2[F-18]fluoro-D-glucose

Whole-body 5-deoxy-2-[F-18]fluoro-D-glucose (FDG) positron emission tomography (PET) of a 54-year-old woman with a history of recurrent thyroid follicular cancer and an elevated thyroglobulin level showed significant FDG uptake in the thyroid bed and anterior mediastinum. A previous scan after high-dose I-131 therapy also showed iodine uptake in these regions. Because of a lack of response to iodine therapy, the patient had surgery. Recurrent thyroid cancer was found in the neck, but the mediastinal lesion was shown to consist of normal thymus tissue. In repeated examinations performed after surgery, there was no uptake of FDG or I-131 in the anterior mediastinum. Previous treatment with a high dose of radioiodine may have contributed to visualization of a normal adult thymus with FDG PET.