|Patient: 35 year old female|
|History: 35 year old female: with papillary microcarcinoma was treated with 100 mCi I-131 and delayed whole body and spot images were obtained.|
|Findings: I-131 scan: There is a small focus of tracer uptake superior to the thyroid bed most likely residual thyroid tissue in the thyroglossal duct. Additionally, the whole body images demonstrate increased uptake projecting over the breasts bilaterally. The tracer avid foci in the chest are likely in the breasts as the foci rotate as anterior structures on the oblique images. |
Gadolinium enhanced T1WI: Small mass in the right side of the pituitary gland with delayed enhancement as well as minimal deviation of the pituiatary stalk consistent with a microadenoma.
|DDx: Increased breast/anterior chest wall uptake on I-131 study:|
1. Lactating/breast feeding
2. Lung/chest wall thyroid cancer metastases
|General Discussion: This is a 35 year old woman who was found to have a pituitary microadenoma in the workup of headaches prior to the detection of thyroid cancer. The patient had a history of Hashimoto's thyroiditis and a suspicious thyroid nodule was biopsied and found to be papillary thyroid cancer. After breast uptake was seen on the iodine scan, the prolactin level was found to be 79 ng/ml(upper limit normal 29 ng/ml), making the pituitary microadenoma consistent with a prolactinoma.|
Specific Discussion: Radioiodine is taken up in the breast and excreted in breast milk results in 3 main problems: 1) Exposure of the breast feeding infant to radioiodine and the potential for hypothyroidism. 2) Exposure of the naturally cancer prone mammary ductal epithelium to potentially cancer causing radiation and 3) Potentially misdiagnosing a lung/chest wall metastasis if a patient is being evaluated for thyroid cancer metastases.|
When a woman is lactating, a significant amount of ingested iodine is excreted through the breasts. One study estimated that 28% of the ingested radioactivei iodine is excreted into the breast milk. Studies have demonstrated significant breast uptake for iodine given within one week of stopping lactation, mild uptake after 5 weeks, and no uptake 11 weeks after cessation of breast feeding (1). Different standards have been devised to estimate the dose to the infant and to the infant thyroid. Given some basic assumptions, it was calculated that waiting up to 52 days after 4000 MBq of I-131 is necessary to meet the ICRP infant protection guidelines. Resuming breast-feeding after I-131 administration is not practical.
Lactating or otherwise hormonally stimulated breast tissue concentrates drastically more iodine than hormonally quiesent breast tissue. It has been estimated that 4000 MBq to the breasts gives an absorbed dose of 1.6 Gy. Although no large trials are available to demonstrate a cancer causing effect, there has been demonstration of increased breast cancer in thyroid cancer patients. The models would indicate this dose would give a relative risk of breast cancer of 1.67 (2).
Symmetric, regular I-131 physiologic breast uptake is unlikely to be confused with thyroid metastasis. However, unilateral and/or irregular uptake may be confused with lung or chest wall metastasis.
|References: 1. Bakeet SM. et al. Patterns of radioactive uptake by the lactating breast. Eur J Nucl Med. 1994;21: 604-8.|
2. Robinson PS. I-131 in breast milk following therapy for thyroid carcinoma. 1994;35: 1797-1801.
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Case Number: 93956Owner(s): Brandon Peters and Henry RoyalLast Updated: 12-15-2010 The reader is fully responsible for confirming the accuracy of this content.
The reader is fully responsible for confirming the accuracy of this content.