Radioiodine uptake in A Renal CYST in A Patient with Papillary Thyroid Carcinoma

Objective: To present a case of papillary thyroid cancer (PTC) with radioiodine (RAI) uptake in a benign renal cyst on the posttherapy whole-body scan (pT-WBS).Methods: The clinical course and diagnostic findings are described for a patient with PTC postthyroidectomy, who was found to have RAI uptake in a benign renal cyst after thyroid remnant ablation (TRA). In addition, a literature review regarding iodine uptake in nonthyroidal tissues is presented.Results: With a negative diagnostic scan for PTC postthyroidectomy, our patient underwent RAI TRA with subsequent unexpected uptake in the left posterior upper quadrant of the abdomen on the pT-WBS. Single-photon emission computed tomography/computed tomography imaging delineated the area to the left kidney. On further sonographic imaging, a simple cyst was seen in the suspected area, with no evidence of metastatic lesions.Conclusion: RAI has been used diagnostically to recognize, as well as therapeutically treat, thyroid remnants and distant iodine-avid metastases postsurgery. Rarely however, iodine may be taken up by various normal, nonthyroidal tissues, including thymus, breast, liver, and gastrointestinal tract, or under conditions such as the presence of cysts or inflammation. It is worth considering these processes in the evaluation of unanticipated iodine uptake to prevent potential unnecessary evaluation and testing.Abbreviations: PTC papillary thyroid cancer; pT-WBS posttherapy whole-body scan; RAI radioiodine