Unilateral breast uptake of tc-99m pertechnetate in a patient with cold nodule of the thyroid.

Common causes of unilateral breast uptake of Tc-99m pertechnetate are predominant breast-feeding on one side, mastitis, and breast cancer. Uptake of Tc-99m pertechnetate in the epithelial cells of the breast, like that of iodide, depends on the transmembrane sodium/iodide symporter (NIS), the expression of which is known to be greatly enhanced during lactation and in breast cancer. The authors present an interesting case of predominant left breast uptake of Tc-99m pertechnetate detected incidentally during thyroid scintigraphy, for the evaluation of a nodule in the left lobe of thyroid.

Introduction

Uptake of Tc-99m pertechnetate in the epithelial cells of the breast depends on the transmembrane sodium/iodide symporter (NIS). Uptake of this tracer in one breast may be due to predominant breast feeding on one side, mastitis, or carcinoma of the breast. We present a case of left-sided breast uptake of Tc-99m pertechnetate detected incidentally during thyroid scintigraphy.

Case Report

A 26-year-old female was referred for thyroid scintigraphy for the evaluation of swelling in the neck for 7 months with no thyrotoxicosis symptoms. She was breast feeding her 8-month-old child. Thyroid function tests showed mildly increased serum T3 and T4 levels, with normal serum thyroid stimulating hormone (TSH). No thyroid stimulating immunoglobulins were detected. Fine-needle aspiration cytology of the thyroid nodule was performed and a final diagnosis of colloid goiter with cystic degeneration was made. Tc-99m pertechnetate thyroid scintigraphy revealed a cold nodule in the lower half of the left lobe of the thyroid. Incidentally, significant radiotracer accumulation was also detected in the left breast [Figure 1], while the right breast appeared unremarkable.

Figure 1

Tc-99m pertechnetate scan of the neck and chest (anterior views). Scans obtained at 20 min after intravenous injection of Tc-99m pertechnetate show a “cold” nodule in the lower half of the left lobe of the thyroid (arrow). Intense and diffusely increased radiotracer uptake is noted in the left breast

Discussion

The NIS is present in normal mammary tissue during gestation and lactation. In vitro and in vivo studies have confirmed that lactogenic hormones, such as prolactin, estrogen, and oxytocin, are able to stimulate functional NIS expression in mammary tissue.[1] Uptake of Tc-99m pertechnetate in the epithelial cells of the breast, like that of iodide, depends on the transmembrane NIS, the expression of which is known to be greatly enhanced during lactation and in breast cancer. Unilateral uptake of I-131 has also been documented in a patient during follow-up of papillary thyroid carcinoma, who had been breastfeeding for 3 years with only one breast.[2] In a series of 20 I-123 scans performed within 1 week of cessation of breast feeding, radiotracer uptake was found to be asymmetric in 12 and unilateral in 3 patients. In one of the three patients with unilateral uptake, a history of mastitis was obtained, with consequent inability to produce milk from the involved breast. It was also noted that 70% of the cases with asymmetric uptake (45% of all cases) showed higher uptake in the left breast.[3] This may, possibly, be attributed to infants’ preference to selective breast feeding from one side. Unilateral breast uptake of Tc-99m pertechnetate due to unilateral feeding has been previously reported in a euthyroid patient with a multinodular goiter.[4] Bilateral breast uptake has also been reported in a lactating patient with hyperthyroidism, who showed only faint thyroid uptake, despite being diagnosed with Graves’ disease.[5] In our patient also, a history of feeding predominantly from the left breast was obtained.