False-positive radioiodine whole-body scan in thyroid cancer patients due to unrelated pathology.

Radioiodine whole-body scanning is the imaging modality of the highest accuracy in diagnosing metastases from differentiated thyroid cancer. However, unrelated pathology in one of several nonthyroidal tissues that normally take-up/secrete radioiodine may result in a false positive scan. The authors report cases of an ectopic kidney, chronic sinusitis, dacryocystitis, and an artificial eye, complicating differentiated thyroid cancer, that on radioiodine scanning mimicked lumbar, frontal, and left and right orbital bone metastases, respectively. The nature of the radioiodine uptake was suspected from the results of a bone scan and proven by ultrasound (ectopic kidney), by reimaging after specific treatment (chronic sinusitis, and dacryocystitis), or by postwashing reimaging (artificial eye). To our knowledge, this is the first report of such cases. Nonthyroidal pathology should be excluded before exposing patients with apparent thyroid cancer metastases that have atypical characteristics on radioiodine whole body imaging.