False-positive thyroid cancer metastasis on whole-body radioiodine scanning due to retained radioactivity in the oesophagus.

In patients with differentiated thyroid cancer, radioiodine uptake in the mediastinal area most often indicates thyroid cancer metastasis. We review 15 radioiodine whole-body scans showing 19 mediastinal artefacts that mimicked lymph node or spinal metastasis. The artefacts disappeared on delayed images after eating and drinking (17) or on studies repeated within 1 week (2), suggesting their oesophageal origin. No patient had clinical oesophageal or gastric disease. Only two artefacts were linear; 12 were focal and five were diffuse. Twelve artefacts were better seen on anterior views (nine in the upper, two in the middle and one in the lower mediastinal area), whereas seven were better seen on posterior views (two in the upper, two in the middle, and three in the lower mediastinal area). The 15 scans were identified from about 1000 scans performed over 24 months in our centre. We conclude that the transient presence of radioiodine in an apparently normal oesophagus may not uncommonly mimic mediastinal lymph node or spinal metastases from thyroid cancer and that its scintigraphic presentation is variable.