Spurious thyroid cancer bone metastases on radioiodine scan due to external contamination

In patients with differentiated thyroid cancer, bone uptake on radioiodine whole body scan indicates functional metastasis and is usually followed by treatment with a high dose of 131I. However, apparent radioiodine uptake in the bone may be due to other causes. We describe 19 radioiodine artifacts that mimicked bone metastases and were proven to be due to external contamination as they disappeared on reimaging after skin cleaning and garment change (15 artifacts) or on a repeat study (four artifacts). All artifacts were noted only on anterior views; 12 in the skull, five in the shoulder girdle and two in the upper extremity. Thirteen artifacts were focal and six were smeared. The prevalence of scans showing such artifacts was 0.5% of the total number of radioiodine scans performed over a 3-year period. Distinguishing contamination artifacts from real bone metastases based on scintigraphic appearance is rather difficult. Repeat post-cleaning images should be obtained in all newly identified cases of apparent bone metastasis.