Applied Radiology

Diagnosis

Invasive lobular carcinoma

Findings

Originally, magnetic resonance imaging (MRI) was requested for preoperative planning (see http://www.appliedradiology.com/Issues/2010/10/Articles/AR_10-10_Argus/Clinical-indications-for-breast-MRI.aspx for a review of clinical indications for breast MRI). Unfortunately, the patient was unable to tolerate the exam due to peripheral neuropathy. As an alternative, breast-specific gamma imaging (BSGI) was performed. The BSGI study demonstrated increased radiotracer uptake within the upper outer left breast, extending from the anterior to posterior third of the breast. At this point, the mass had been biopsied and was a known malignancy, BI-RADS 6.

Discussion

BSGI relies on Tc-99m Sestamibi as the radiotracer. Using a breast-specific gamma camera, the sensitivity of BSGI has been estimated to be 84% to 96%, which is comparable to MRI and mammography (with the exception of dense breast tissue, in which the sensitivity of mammography decreases to <68%).^{1, 2} The specificity for BSGI using breast-specific gamma cameras has been reported as anywhere from 59% to 93%, which is at least equal to that of MRI and mammography.^{2, 3} However, researchers currently studying BSGI believe one of its strengths to be a higher specificity and typically quote specificity in the range of 87% to 89%.

Several additional benefits of using BSGI have been identified.³ The images are acquired with the patient in a seated position, providing improved comfort. Images are obtained in the craniocaudaul and mediolateral projections, allowing direct comparison with mammography. The smaller, more portable camera/detector and low radiation exposure eliminates the need for a dedicated room.

At this point, BSGI is a relatively young field with the need for further studies. However, BSGI is already FDA cleared and in the appropriate clinical settings may be reimbursed by Medicare and most third party payors.

The clinical indications for BSGI are:

1. Breast MRI is clinically indicated, but not possible (i.e., pacemakers, body habitus, severe claustrophobia, etc.);
2. Patients with indeterminate breast abnormalities (i.e., as an alternative to follow up for BI-RADS 3 findings or mammographically occult palpable masses);
3. Patients with technically difficult breast imaging (i.e., dense breast tissue with concerning risk factors, though not sufficient to warrant MRI).

References

1. Killelea BK, Gillego A, Kirstein LJ, et al. George Peters Award: How does breast-specific gamma imaging affect management of patients with newly diagnosed breast cancer? Am J Surg. 2009;198:470-474.
2. Brem RF, Floerke AC, Rapelyea JA, et al. Breast-specific gamma imaging as an adjunct imaging modality for the diagnosis of breast cancer. Radiology. 2008;247:651-657.
3. Brem RF, Petrovitch I, Rapelyea JA, et al. Breast-specific gamma imaging with 99mTc-Sestamibi and magnetic resonance imaging in the diagnosis of breast cancer – A comparative study. Breast J. 2007;13:465-469.