Mammography, ultrasound, and breast MRI examinations are classified using the American College of Radiology Breast Imaging Reporting and Data System (BI-RADS), which gives a final assessment category indicating the level of suspicion for malignancy for each study (6).

BI-RADS 3 lesions have imaging features that suggest a less than 2% chance of malignancy. The criteria of a BI-RADS 3 mammographic lesion are largely based on two studies that collectively include over 80,000 mammograms (7, 8). In these studies, a 6-month follow-up mammogram identified interval progression of those few BI-RADS 3 lesions that were actually malignant and diagnosed these cancers early enough to maintain a favorable prognosis (9). At the same time, close follow-up of BI-RADS 3 lesions reduces the false negative rate of biopsy and decreases health care costs. Examples of BI-RADS 3 mammographic lesions include a nonpalpable low-density solid mass with a round or oval shape and predominantly circumscribed margins on a baseline mammogram or clustered microcalcifications with a punctate morphology on a baseline study. New or enlarging solid masses should not be categorized as BI-RADS 3 lesions but should undergo biopsy.

The BI-RADS lexicon for lesions detected on ultrasound and MRI are less widely validated than for mammography. Stavros et al. initially developed a classification scheme to differentiate benign from malignant lesions on ultrasound with a 98.4% sensitivity and a 99.5% negative predictive value for malignancy (10). Subsequent studies have confirmed the low rate of subsequent malignancy in BI-RADS 3 masses (11, 12). An incidental homogeneously hypoechoic oval mass with circumscribed margins and parallel orientation is an example of an ultrasound BI-RADS 3 lesion.

The specific morphologic and/or kinetic features of lesions appropriate for a BI-RADS 3 recommendation on MRI have not been well established but are generally based on the principles used to characterize BI-RADS 3 lesions on mammography. The cancer yield of BI-RADS 3 lesions on MRI has varied between 0% and10% (13, 14). Eby et al. evaluated the characteristics of probably benign MRI lesions and found that foci, defined as lesions less than 5 mm in size that are too small to further characterize, comprise 46% of BI-RADS 3 lesions (14). Liberman et al. also found a 3% malignancy rate in suspicious lesions less than 5 mm in size (15). Studies have suggested that unique foci with a high T2 signal intensity correlate may safely be followed on a 6-month follow-up MRI given the low rate of malignancy of these lesions.

BI-RADS 4 lesions have between a 2% and 95% chance of representing malignancy and can be further subdivided
into BI-RADS 4a (low suspicion of malignancy), 4b (moderate suspicion), and 4c (high suspicion) categories. BI-RADS 5 lesions are highly suspicious with a greater than 95% chance of malignancy. Percutaneous biopsy is recommended for all examinations with BI-RADS 4 or 5 recommendations. Percutaneous biopsy is most useful for BI-RADS 4 lesions because surgery can be avoided in 70% to 80% of cases where biopsy yields benign and concordant pathology. Percutaneous biopsy of BI-RADS 5 lesions is recommended due to improved surgical outcomes at lumpectomy, including decreased positive margin rates (16).

Patients are asked to discontinue aspirin, warfarin, nonsteroidal anti-inflammatory agents, vitamin E, or other anticoagulation or antiplatelet drugs for at least 5 days prior to the procedure. However, patients who are anticoagulated for a medical reason are advised to consult their ordering physician to determine whether the medication can be safely discontinued. Studies have demonstrated that core biopsy can safely be performed without clinically significant complications if anticoagulants cannot be discontinued or if urgent results are required (17). Premedication with antibiotics in patients with prosthetic valves or joint replacements is generally not necessary.

Stereotactic biopsy may be performed on either dedicated prone tables or an upright add-on unit. Add-on units convert a standard diagnostic mammography unit, and the biopsy is performed with the patient in a sitting or decubitus position. Add-on units require less space, are less expensive, and allow the room to be used for routine mammography when a biopsy is not being performed, but they are associated with an increased risk of vasovagal reactions. Advantages of prone tables include that the biopsy is performed out of the patient’s view, that vasovagal reactions are uncommon, and that more working space between the biopsy gun and the patient is permitted (1). The cost and space requirement for a dedicated room make prone tables impractical for centers that perform a low volume of stereotactic biopsies, and both types of units are considered acceptable and commonly used.

The technique for performing stereotactic biopsy is similar regardless of the type of unit used. The direction of approach is selected based on lesion location and/or visibility. A scout image is taken with the target centered in a cutout compression plate. A stereotactic pair in which images are taken at +15 and -15 degrees from a center line is obtained. Stereotactic biopsy is based on the concept that a lesion can be localized in three dimensions—the x, y, and z axes—based on the apparent change in position on the stereotactic pair (parallax). Once the target is selected, the housing unit is moved to the x and y coordinates. The skin is cleansed and anesthetized, and the biopsy needle inserted into the breast to the predetermined depth. Another stereotactic pair is obtained with the needle in the prefire position to confirm accurate targeting, and then the needle is typically fired (Fig. 15-2). A postfire stereotactic pair may be obtained to confirm needle position prior to sampling. If the target is calcifications, a specimen radiograph is taken to confirm retrieval of some of the targeted calcifications. If the target is a mass or asymmetry, a postfire image should be obtained to confirm that the needle trough is within the mammographic abnormality. Finally, a localizing clip is placed at the biopsy site and an image obtained to confirm clip deployment. After completion of the biopsy, a 2-view mammogram is performed to confirm clip placement and position relative to the biopsy site. This postbiopsy mammogram is also useful to confirm sampling of a mammographic mass or asymmetry, although these may be obscured by postbiopsy change.

Several factors may complicate successful stereotactic biopsy, including the following: