Renal cyst uptake following I-131 treatment for thyroid cancer

A 69-YEAR-OLD FEMALE with papillary thyroid carcinoma was treated with 1-131 for post-surgical thyroid remnant, which was seen on a pre-therapy 1-123 scan. The post-therapy scans showed two large, rounded foci of 1-131 uptake in the upper abdomen. This is of uncertain significance due to the patient's lack of clinical history to explain the findings. These foci were thought to represent a normal variant of bowel uptake. However, they were found to correlate to large renal cysts bilaterally on a follow-up CT scan. Although renal cyst uptake with 1-131 has been reported in literature, this dramatic illustration with single photon emission computed tomography (SPECT) imaging demonstrates that this physiologic uptake of 1-131 could potentially lead to a false positive interpretation.