A False Positive I-131 Metastatic Survey Caused by Radioactive Iodine Uptake by a Benign Thymic Cyst

Figure 1

An initial diagnostic SPECT/CT scan was performed 24 hours after administration of 5.3 mCi of Iodine-123. There is uptake in the left, posterior thyroid bed and anteriorly at the level of the hyoid bone. Physiologic uptake was noted in the salivary glands, nasopharyngeal mucosa, and gastrointestinal tract. A large (8 cm × 9 cm × 8 cm) heterogeneous left anterior mediastinal mass with mixed solid and cystic architecture was noted. This mass did not demonstrate uptake of the Iodine-123 tracer ((a), (b)). Posttreatment SPECT/CT one week later showed uptake of radioactive iodine by the mediastinal mass ((c), (d)).

(a)

(b)

(c)

(d)