Stereotactic breast biopsy
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Stereotactic breast biopsy refers to percutaneous sampling of breast tissue using mammographic guidance for targeting.
It is the biopsy method of choice when the finding of interest is best seen on mammography, such as microcalcifications (most common), architectural distortion, or an asymmetry or mass without a sonographic correlate 6. Biopsy is generally undertaken for lesions that are assessed as BI-RADS 4 (suspicious for malignancy) or BI-RADS 5 (highly suggestive of malignancy).
Stereotactic devices differ by imaging modality (analog vs digital), calculation of coordinates (manual or digital), and type of needle (fine-needle aspiration biopsy or vacuum-assisted core needle biopsy).
Patient position depends on the equipment. In the prone position, the patient lies face down on a special bed with the breast protruding through a hole in bed surface. However, in the sitting upright position, the patient is in front of the equipment and can see the needle.
The breast is placed in compression using special paddle with a central window and a mammogram is performed.
Once the lesion is highlighted in the first mammogram, additional views are needed to triangulate the lesion in three-dimensional space. Traditionally, two additional projections are performed at +15 and -15 degrees. In the era of digital breast tomosynthesis, the lesion is located on a tomosynthesis slice obtained as part of the initial mammogram.
The spatial coordinates of the lesion target are then calculated. With the breast still in compression, the cutaneous entry point is identified.
Vacuum-assisted core biopsy
First, local anesthesia (1% lidocaine) is applied. The needle is then pushed to the target previously determined. The distance is confirmed through an additional acquisition and corrected if necessary.
Vacuum-assisted biopsy involves obtaining multiple tissue cores via a rotating 10-14 gauge needle while the machine applies suction (23-25 mmHg). Due to the vacuum, breast tissue is first drawn into the tray at the tip of the needle, cut by a high speed rotating blade and then suctioned into a receptacle. The number of withdrawn samples can vary from 5 to 20. With multiple rotations of the needle in one position, tissue can be sampled from a region 1-2 cm in diameter.
All withdrawn samples are x-rayed (specimen radiography) in order to verify the presence of microcalcifications if that was part of the target lesion 6.
At the end of the procedure, a radiopaque, non-magnetic clip is placed through the needle into the biopsy site to identify the area on future imaging.
The needle is withdrawn, compression is applied, and the wound dressed.