False-positive iodine-131 whole body scan due to pectus excavatum

A 44-year-old woman with follicular cell carcinoma of the thyroid was treated with 150 mCi of radioactive I-131 6 weeks after a subtotal thyroidectomy. A whole body scan performed 5 days after therapy demonstrated diffuse uptake in the left lung field, but no other evidence of distant metastases. A review of her recent chest X-ray showed a prominant pectus excavatum with a shift of the heart shadow into the left lung field. A Tc-99m labeled red blood cel scan confirmed that the I-131 uptake in the left lung field represented heart blood pool.