FALSE-POSITIVE RADIOIODINE UPTAKE IN THE ABDOMEN AND THE PELVIS - RADIOIODINE RETENTION IN THE KIDNEYS AND REVIEW OF THE LITERATURE

Because the kidneys are usually not visualized on radioiodine whore-bo dy scans, the renal uptake can be mistaken for a thyroid cancer metast asis. The authors report the prevalence and characteristics of radioio dine retention in the kidneys and review the reported causes of false- positive radioiodine uptake in the abdomen and pelvic areas. Radioiodi ne uptake in the renal bed was noted on 9 of 400 (2.2%) I-123 diagnost ic whole-body scans performed over a 7-month period in our center. The uptake was noted more clearly on posterior views, cleared on delayed images after further hydration, and was not consistently present on fo llow-up scans. It was unilateral and mimicked a renal or adrenal metas tasis in 44% of the scans. In three cases, the uptake was associated w ith a dilated calyx, an extrarenal pelvis, or a voluminous pelvis. Fal se-positive radioiodine uptake in the abdomen and pelvis has been prev iously reported in association with 14 different conditions. However, renal retention may represent the most common cause of false-positive radioiodine uptake in the abdomen pelvis. Delayed imaging after additi onal hydration is usually sufficient to clarify its origin.