Unusual false-positive radioiodine whole-body scans in patients with differentiated thyroid carcinoma.

Radioiodine whole-body imaging is the most accurate method in the diagnosis of metastases from differentiated thyroid cancer. However, false-positive images rarely occur. The authors report unusual cases of thymic hyperplasia and post-traumatic skull changes mimicking mediastinal, skull, or cerebral metastases. Nonthyroidal causes were diagnosed by other radionuclide studies (bone and brain scintigraphy) and CT scans. Follow-up and undetectable thyroglobulin levels helped confirm the benign cause.