131I and 124I Accumulation in a Thymic Cyst.

A 65-year-old woman presented with increased human thyroglobulin (3.3 ng/mL) 5 years after resection of a papillary thyroid carcinoma and successful I radioiodine therapy. I whole-body scintigraphy showed a small focus ventrally in the right lower neck, leading to suspicion of a papillary thyroid carcinoma recurrence. I-PET/CT and real-time PET/US fusion matched to a small hypoechoic/anechoic ovoid structure situated between the right sternoclavicular joint and the brachiocephalic trunk. After surgical resection, histology allowed a diagnosis of thymic cyst. A follow-up I whole-body scintigraphy showed no residual iodine accumulation.