PATTERNS OF RADIOIODINE UPTAKE BY THE LACTATING BREAST

Breast uptake of radioiodine, if not suspected, may be misinterpreted as thyroid cancer metastasis to the lung. To characterize the patterns of radioiodine breast uptake, we retrospectively studied 20 radioiodi ne scans that were performed within 1 week of cessation of breast feed ing. Four patterns of uptake were identified: ''full'', ''focal'', ''c rescent'' and ''irregular''. The uptake was asymmetric in 60% (left>ri ght in 45%, right>left in 15%), symmetric in 25% and unilateral in 15% of cases. A characteristic full bilateral uptake was present in 40% o f cases. In three cases with the irregular pattern, caused in part by external contamination with radioactive milk, the uptake closely mimic ked lung metastases. Delayed images, obtained in one case, showed an a pparent radioiodine shift from the breast to the thyroid, suggesting t hat the presence of breast uptake can modulate radioiodine uptake by t hyroid tissue. In a case of unilateral breast uptake, a history of mas titis was obtained, which to our knowledge has not been previously rep orted. Breast uptake of radioiodine may take several scintigraphic pat terns that are not always characteristic of the lactating breast and m ay affect the apparent extent of thyroid remnant/metastasis.