Nuclear Medicine Breast Imaging with Tc-99m Sestamibi
Written by Tatiana S. Kain, M.D.
Case
A 56 year-old female presented with a palpable mass in the left axilla. The patient reported general good health and no significant past medical history. All of her mammograms were reportedly stable and unremarkable, demonstrating dense fibroglandular appearance (Figure 1). Also, physical examination failed to reveal any palpable mass in her breast. A nuclear medicine Tc-99m sestamibi scan was then performed, demonstrating markedly abnormal, increased activity in the left breast, the left axilla, and substernal area, indicative of neoplastic process in the breast with metastasis to the axillary and substernal nodes (Figure 2) . Based on this information a breast biopsy was performed, demonstrating a high grade infiltrating ductal carcinoma.
Discussion
Overview
Technetium (Tc)-99m sestamibi scintimammography, also known as Miraluma, is gaining recognition among radiologists and breast surgeons as an important tool in the detection of breast cancer. Tc-99m sestamibi was approved by the FDA in 1990 for use in cardiac imaging and in 1997 for use in breast imaging. Today, Tc-99m sestamibi scintimammography is being used for detection of breast cancer in conjunction with physical examination and mammography. Unlike mammography and ultrasound, which offer anatomic evaluation, Tc-99m sestamibi scan provides information regarding the metabolic activity of the tissue [1]. The accumulation of the radiopharmaceutical in the breast is linearly dependent on the blood supply [2], desmoplastic activity, and the quantity of the mitochondria [1]. Both myocardial and neoplastic cells exhibit large concentrations of mitochondria and are rich in blood supply, and therefore demonstrate increased activity relative to the surrounding tissue.
Technique
The Miraluma study is performed by intravenous injection of 25-30 mCi of Tc-99m sestamibi into a vein contralateral to the side of the lesion. Injection of the ipsilateral arm should be avoided due to possible uptake of the radiopharmaceutical on the injected side due to the dose infiltration, which can mimic metastatic adenopathy. If bilateral breast lesions are present, the patient should be injected in the dorsum of the foot. Three views are obtained: Prone, lateral views of each breast are taken first, starting with the side with a possible lesion; the patient is then positioned supine and an anterior view is performed. Each image is acquired/ for 10 minutes.
Clinical implications
Due to the fundamental difference between an anatomical and a metabolic study, scintimammography images, unlike mammograms, are not affected by dense fibroglandular breast tissue [3]. Thus, scintimammography may provide additional and important information and help to detect breast cancer in younger patients who often present with dense mammograms. This technique can also help to distinguish between scar tissue and recurrent tumor in patients who underwent lumpectomy and/or radiation therapy, and might be helpful in preoperative planning for patients with diagnosed breast carcinoma, as it shows the extent of tumor in the breast and the presence of synchronous lesions. Furthermore, scintimammography may provide additional information regarding the axillary lymph node status.
Conclusions
While scintimammography cannot replace mammography as a screening tool, it can play a major role as a complimentary imaging modality in young patients with dense mammograms, in patients who are at a high risk for breast cancer, and in patients with indeterminate findings on mammography or ultrasonography.
References
1. Maublant JC, Zhang Z, Rapp M et al. In vitro uptake of technetium 99m-teboroxime in carcinoma cell lines and normal cells; Comparison with technetium 99m-sestamibi and thallium-201. J Nucl Med. 1993;34:1949- 1952.
2. Taillefer R, Robidoux A, Lambert R et al. Technetium 99m- sestamibi prone scintimammography to detect primary breast cancer and axillary lymph node involvement.
J Nucl Med. 1995;36:1758- 1765.
3. Palmedo H, Biersack HJ, Lastoria S et al. Scintimammography with technetium 99m- methoxyisobutylisonitrile: results of a prospective European multicentre trial. Eur. J Nucl Med. 1998;25 (4).
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