I-131 false positive uptake in a huge parapelvic renal cyst.

A male patient had undergone total thyroidectomy for thyroid papillary carcinoma. He was administered thyroablation activity of radioiodine. Whole body imaging after diagnostic activity of 131-I demonstrated intense radioiodine uptake in the right side of the upper abdominal region. The serum thyroglobulin level was low. Ultrasonography demonstrated a large irregular anechoic structure in the centre of the right kidney--a cyst in the parapelvic region. Renal cysts can lead to erroneous interpretation of radioiodine scintigraphy.