[False positive scintigraphic images in the surveillance of differentiated thyroid cancers]

Iodine-131 whole body imaging and serum thyroglobulin are used in the follow-up evaluation of differentiated thyroid carcinomas. Iodine 131 is used to detect and treat functioning lesions. Iodine 131 activity detected outside the normal thyroid bed is usually attributed to metastatic disease. False-positive localization of radioiodine has been described, and may be a potential pitfall. We report here six personal cases of false-positive localisations of radioiodine du to body secretions, pathologic exudate, activity in nonlactating breast, salivary gland inflammation, ovarian teratoma. Some of these false-positive can be ruled out easily by removing of clothes, removing of nozzle in patients with tracheostomy, or by ingestion of water in subjects with abnormal mediastinal hyperfixation. Recognition of false-positive radioiodine images is very important to prevent costly additional investigation and possibly inappropriate therapy.