Unexpected Uptake by the Gallbladder in Post-Ablative I-131 Scan

A 47-year-old woman was diagnosed as papillary thyroid carcinoma. I-131 ablation therapy was applied following total thyroidectomy, and the whole-body scan revealed a focus of increased uptake in the right upper quadrant. Lateral view images of the uptake site showed that the focus was located near the right liver lobe. The patient was referred to radiology department for correlative abdominal Computed Tomography (CT) and Ultrasonography (US) to rule out a possible liver metastasis. CT images detected a gallstone in the corresponding area, which was verified by US. These methods did not reveal any metastatic disease in the liver or in other abdominal organs. This is the first published case report documents a rare false-positive finding of I-131 scan that was associated with an asymptomatic gallstone, and emphasizes the importance of correlative imaging in gallbladder related I-131 uptake.