False-positive radioiodine whole body scan due to a renal cyst.

We report a case of 75-year-old woman with follicular thyroid cancer, who underwent ablative radioiodine treatment. On post-therapy whole body scan, abnormal uptake in the left upper abdomen was found, although stimulated thyroglobulin level was not suggestive for distant metastases of differentiated thyroid carcinoma. Additional SPECT/CT acquisition revealed focal 131I uptake located at the posterolateral wall of the left kidney corresponding to a round lesion of 47 mm in maximal diameter. In order to verify this finding abdominal ultrasound and abdominal contrast-enhanced CT were performed, confirming multiple renal cysts in the left kidney, the biggest one was the site of abnormal radioiodine accumulation. Despite the high incidence of renal cysts, especially in the elderly, radioiodine uptake in renal cysts is extremely rare. Different hypotheses on the mechanism of radioiodine uptake in the cyst were proposed, among them active secretion by sodium-iodide symporter or other transporting proteins. We conclude that abnormal radioiodine uptake in renal cysts can be an exceptional finding mimicking a metastasis. PMID: 30306537 [PubMed - as supplied by publisher]
Source: Endokrynologia Polska - Category: Endocrinology Authors: Tags: Endokrynol Pol Source Type: research