SPURIOUS THYROID-CANCER BONE METASTASES ON RADIOIODINE SCAN DUE TO EXTERNAL CONTAMINATION

In patients with differentiated thyroid cancer, bone uptake on radioio dine whole body scan indicates functional metastasis and is usually fo llowed by treatment with a high dose of I-131. However, apparent radio iodine uptake in the bone may be due to other causes. We describe 19 r adioiodine artifacts that mimicked bone metastases and were proven to be due to external contamination as they disappeared on reimaging afte r 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 extrem ity. Thirteen artifacts were focal and six were smeared. The prevalenc e of scans showing such artifacts was 0.5% of the total number of radi oiodine scans performed over a 3-year period. Distinguishing contamina tion artifacts from real bone metastases based on scintigraphic appear ance is rather difficult. Repeat post-cleaning images should be obtain ed in all newly identified cases of apparent bone metastasis.