Unusual false-positive results of whole-body 131I scintigraphy: Four different case scenarios

Post-treatment or diagnostic whole-body radioiodine scintigraphy is widely used to assess the residual, recurrence, or metastases of differentiated thyroid carcinoma because of the high sensitivity and accuracy that this assessment provides. While bearing in mind all the diagnostic potential of this test, we have to consider its’ potential pitfalls, as well. Herein, we present 4 patients with differentiated thyroid carcinoma, who received 131I for ablation therapy after having undergone total thyroidectomy. On post-treatment radioiodine scintigraphy, foci of unusual 131I uptake were noted in facial, axillary, inguinal, and renal regions, which were finally either histologically or anatomically diagnosed as papillary oncocytic cystadenoma, ectopic axillary breast tissue, epidydimal cyst, and simple renal cyst, respectively. Such 131I uptake patterns underscore the value of recognizing where and why false-positive uptakes take place and should appreciate the potential causes of false-positive results in whole-body 131I scintigraphy.