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Stereotactic breast biopsies have become indispensable and the standard of care for patients in whom screening mammography or tomosynthesis reveals breast lesions suggestive of malignancy. A variety of stereotactic biopsy systems and needle types are now available, which allow more accurate sampling of lesions as well as successful biopsy of lesions in difficult locations in patients of all body habitus. We discuss how to plan, perform, and follow up stereotactic biopsies. Most importantly, we offer suggestions on how to avoid problems and complications and detail how to achieve technical success even in the most challenging cases. Stereotactic biopsy has proven over time to be an accurate and acceptable alternative to surgical biopsy for histopathologic diagnosis of breast abnormalities. Successful performance of this minimally invasive procedure spares women from undergoing potentially deforming and expensive procedures to diagnose breast disease.
A large number of women, mostly 40 years and older, undergo screening mammography, which is a recommended breast cancer screening examination by primary care physicians, the American Cancer Society as well as the government-appointed United States Preventive Services Task Force.
Based on the Breast Cancer Facts and Figures 2013-2014 from the American Cancer Society, in 2012, the percentage of women 40 years and older who obtained screening mammography ranged from 47%-72% depending on the state. More recently, tomosynthesis, a new 3-dimensional mammographic application, has demonstrated to increase the diagnostic accuracy of digital mammography and breast cancer detection rates.
The use of tomosynthesis is likely to continue to increase in the coming years. In women with suspicious breast lesions identified on screening mammography or tomosynthesis, stereotactic breast biopsy is one of the methods for obtaining the tissue necessary for histopathologic diagnosis.
Indications for Stereotactic Breast Biopsy
An abnormal finding detected on screening mammography or tomosynthesis requires additional mammographic, or sonographic imaging to determine its degree of suspicion for malignancy. A final assessment category based on the Breast Imaging Reporting and Data System (BI-RADS) lexicon of the American College of Radiology (ACR), depending on the degree of suspicion for malignancy, is then assigned.
Radiographic studies with an ACR BI-RADS category 4 (suspicious) or category 5 (highly suggestive of malignancy) assignment require biopsy of the lesion in question. Depending on the clinical suspicion and patient or physician preference, a lesion classified radiographically as ACR BI-RADS category 3 (probably benign) may also be referred for biopsy. In patients referred for biopsy for a definitive tissue diagnosis, either surgical biopsy or needle biopsy of the area of suspicious abnormality may be performed. Although the method of biopsy would depend on availability as well as physician or patient preference, the less costly and less invasive needle biopsy is often preferred.
Any suspicious lesion identified on mammography or tomosynthesis and visible under ultrasound is usually biopsied under ultrasound guidance. Ultrasound-guided biopsy is generally more comfortable for the patient (who lies supine), does not expose the patient or breast to additional radiation, is less costly, and is often more readily accessible. Mammographically identified lesions not visible under ultrasound, most commonly calcifications and less commonly masses, asymmetries and architectural distortions, undergo stereotactic biopsy. Lesions only or best visualized on tomosynthesis may now undergo stereotactic biopsy under tomosynthesis guidance.
Preprocedure Patient and Lesion Evaluation
When stereotactic biopsy is planned for a radiographically suspicious abnormality visible on mammography or tomosynthesis, the patient and the lesion must be evaluated to determine whether the stereotactic biopsy is clinically feasible as well as technically possible.
The patient’s medical history, medication list (with special attention to anticoagulation and antiplatelet medications), and allergy history (especially previous adverse reactions to local anesthetics, epinephrine, latex, disinfectant solutions, or tape and adhesives) must be obtained. Any physical limitations should be noted, as should any history of susceptibility to vasovagal reaction. Certain patient physical limitations, including limited range of motion of the neck, or back, and being wheelchair bound, must be taken into consideration when the biopsy unit is selected. Stereotactic biopsy requires that the patient’s breast remain in compression for at least 15-30 minutes, during which time the patient must be immobile. In addition, patient’s breast size, compressed breast thickness, and lesion depth and location must be taken into account when planning target approach and special maneuvers.
Avoiding Complications and Minimizing Pain and Anxiety
Any needle biopsy procedure may result in bleeding or infection, although the rate of significant hematoma requiring drainage or infection requiring antibiotic treatment is only 0.2%.
Adverse or allergic reactions to medications, latex, disinfectant solutions, and tape or adhesives are also possible.
To minimize bleeding, patients on anticoagulation therapy need to have their treatment stopped or adjusted, in coordination with their treating physician. Patients on warfarin (Coumadin) or longer-acting anticoagulants may be switched temporarily to a shorter-acting medication, such as heparin or enoxaparin (Lovenox). Generally, patients are instructed to stop taking antiplatelet agents, such as aspirin, ibuprofen, or clopidogrel (Plavix), for 5-7 days before biopsy. Laboratory analysis including prothrombin time, partial thromboplastin time, international normalized ratio, hemoglobin, hematocrit, platelet count, and additional platelet function test may be obtained before the biopsy if clinically indicated but is generally not necessary. In patients with a coagulation abnormality, biopsy may be performed after the abnormality is corrected with the transfusion of blood products. This process requires coordination with the patient and patient’s referring physician. Accurate timing of the transfusion to achieve optimal coagulation effect during the biopsy is crucial.
Pain control during the procedure is essential not only for patient comfort but also for technical success, because it helps ensure the patient can remain motionless during the procedure to permit accurate lesion targeting. Commonly, up to 5 mL of lidocaine (1% or 2%) buffered with sodium bicarbonate (9:1 mixture) is used to achieve skin anesthesia, and at least 10 mL of lidocaine or xylocaine 1% or 2% with epinephrine is used to induce deeper breast parenchyma anesthesia (Fig. 1). Epinephrine is generally not used for skin anesthesia because of the potential for skin necrosis, especially in elderly patients. If the patient is allergic to lidocaine, alternate medications may be substituted, such as chloroprocaine (Nesacaine). Antianxiety medication, such as alprazolam (Xanax) or diazepam (Valium), may be given to the patient to take orally before biopsy, if necessary. Intravenous conscious sedation, with midazolam (Versed) and fentanyl, may be given in very rare instances. For patients with previous adverse reactions to latex, disinfectant solutions, or tape or adhesives, now nonlatex gloves, numerous types of skin disinfectants, and a variety of tapes and skin incision closure material are available.
Choices of Stereotactic Biopsy Systems
Stereotactic biopsy can be performed using a traditional prone stereotactic biopsy table or an add-on stereotactic biopsy unit, attachable to the mammography as well as tomosynthesis equipment. Attachable biopsy units allow the conversion of the mammography or tomosynthesis units into a biopsy-guidance system and allow the patient to sit upright or be recumbent, but not prone, during the biopsy.
Prone Biopsy Table (Mammography Guided Only)
To undergo the biopsy on a prone biopsy table (Fig. 2), the patient must be able to get on the table and lie prone for approximately 20-30 minutes with the targeted breast pendant through an aperture in the table. If the patient is wheelchair bound, the patient may be elevated onto a stretcher bed then rolled onto the table. There is also a patient weight limit on the prone table, which is generally between 136 to 158 kilograms. Weight on the table exceeding the limit may cause mechanical failure, which anecdotally may be averted when the biopsy is performed without moving the table. Otherwise, the biopsy must be performed with an attachable biopsy unit. Although biopsy on the prone table has limitations, the prone biopsy table offers several advantages. Because the patient on a prone biopsy table cannot see the biopsy needle, biopsy on the prone table is generally felt to be less anxiety provoking compared with biopsy with an attachable unit. With the patient prone, there is less patient motion to interfere with accurate targeting. In addition, the physician and technologist, working under the table, have more room to maneuver.
Attachable Biopsy Unit (Mammography and Tomosynthesis Guided)
An attachable stereotactic biopsy device is attached to the existing mammography or tomosynthesis unit, converting it to a biopsy system. The patient is generally sitting upright for the procedure. However, a stretcher bed or special reclining chair may be used to allow the patient to lie in the lateral decubitus position for the biopsy, with the breast targeted for biopsy located nondependently and “up” (Fig. 3). If the patient is sitting upright and can see the biopsy needle, it may increase patient anxiety and provoke a vasovagal reaction. There is increased chance of patient motion if the patient is sitting upright, although this may be minimized with the use of cushions and pillows for the patient. Because the images acquired with the mammography or tomosynthesis unit are used for diagnostic imaging, the resolution and quality of the images, especially of faint calcifications, are usually superior.
Stereotactic Biopsy Technique and Needle Selection
Before the biopsy, the patient’s mammograms or tomosynthesis images are reviewed to determine the approach that allows the lesion’s best visualization, shortest distance from the skin to the lesion, and avoidance of intervening vessels. The best approach is also determined by the patient’s breast size, compressed breast thickness, and lesion’s depth and location.
A nonangle scout view or tomosynthesis of the targeted lesion is first obtained with the patient’s breast in compression. The lesion’s x (horizontal), y (vertical), z (depth from the skin surface) axes are determined through measurement of the parallax shift of the targeted area from defined angles of view (+15° and −15° from midline and along the x-axis). For tomosynthesis and stereotactic units, dedicated software is available (Hologic Inc) for targeting (Fig. 4). Otherwise, a manual calculation approach is possible, as detailed in the article by Viala et al.
The compressed breast thickness must be 5 mm or greater than the z (depth) calculated by the system to ensure that the needle would not exit the breast and strike the image receptor or breast support.
The ACR recommends targeting just inferior or superior to the lesion, especially if the lesion is small, so that the lesion is visible adjacent to the needle aperture, on the postfire images to permit confirmation of accurate targeting.
Depending on the size of the lesion, biopsy can also be performed successfully when the target calipers are placed right on the lesion (Fig. 5).
Once the lesion coordinates have been calculated and confirmed to be adequate for biopsy, the skin is cleansed. The skin and breast parenchyma are anesthetized, and a skin incision is made. The biopsy needle is then introduced through the skin incision into the breast parenchyma, to the prefire position just proximal to the target. Prefire stereotactic images are obtained to confirm the expected needle trajectory. Retargeting may be performed before “firing,” if necessary. If the lesion is only seen on one of the +15° and −15° stereopair images and on the target scout nonangle image, targeting can be done on the 0° and one of the 15° stereopair images instead. The needle is then fired and postfire stereotactic images are obtained to confirm optimal final needle aperture position. Repositioning can be performed if the probe aperture is not adjacent to the targeted lesion. It is generally not necessary to create another skin incision when repositioning. When the new target has been selected and transmitted to the equipment, simply retract the needle until the tip is just beneath the skin, select the new target, move the needle to the newly targeted prefire position, then “fire” the probe. The repositioning may be also be performed by adjusting the x, y, and z axes of the needle position manually.
After the postfire images confirm accurate targeting, tissue sampling in a 360° fashion may be performed. More accurately, the sampling is performed mainly at the clock positions where the lesion is located, as identified on the postfire images. For example, if the lesion is now located superior to the probe aperture, only the areas from 9- to 3-o’clock position, going through the 12-o’clock position, need to be sampled. Sometimes, selective sampling of the 10-, 12-and 2-o’clock positions may be sufficient, depending on how large the lesion is.
The use of vacuum-assisted biopsy (VAB) needle devices is now the standard of care for stereotactic biopsy. These needles are powered with suction and have a rotating cutter. They can obtain multiple samples in a 360° fashion without the need to remove the needle from the lesion. The vacuum draws the breast tissue into an aperture in the probe, where the tissue is cut; the tissue is then transported to the specimen port for collection. VAB needles have been shown to be more accurate and allow larger volume tissue sampling than automated biopsy needles. In addition, VAB offers a higher calcification retrieval rate and a lower rate of targeting errors with decreased rebiopsy and underestimation rates.
The needle size ranges from 11 gauge to 7 gauge. Depending on the type of lesion and size of the biopsy needle, on average, 6-12 samples are obtained. For a small cluster of calcifications, a small number of samples may be sufficient for accurate diagnosis. However, an area of architectural distortion generally requires a larger number of core samples to avoid missing any underlying malignancy and to ensure accurate diagnosis of a radial scar.
Overcoming Technical Challenges
Stereotactic biopsy is challenging in patients with a small or thin breast, superficial lesion close to the skin, deep lesion adjacent to the chest wall, or lesion located in the very superior portion of the breast (inner or outer quadrants). Dedicated maneuvers generally allow any lesion visible under mammography or tomosynthesis to be successfully biopsied.
In all cases, it is important to remember that the lesion does not need to be at the center of the needle aperture for successful sampling. With VAB probes, as long as the lesion is at the edge of the needle aperture, successful tissue retrieval can generally be achieved.
Small or Thin Breast
Image quality of the small breast or anterior breast may be poor if the breast does not fill the opening of the compression paddle. A malleable putty or aluminum foil may be placed adjacent to the breast to decrease any “air gap” and to improve image quality.
When the patient’s compressed breast thickness is less than 3 cm on mammography, special maneuvers may be needed to permit stereotactic biopsy. First, the breast tissue may be manually pushed inward on both sides and up from the nipple, while slow compression of the breast is applied with the paddle, so that more breast tissue gathers centrally and bulges anteriorly through the biopsy rectangular aperture (Fig. 6). Then the breast may be subsequently taped in place with aid of additional sponge, gauze, or saline bag to ensure the breast tissue maintains this thickness during biopsy. If this maneuver is not sufficient to achieve adequate breast thickness for biopsy, a “double-paddle” approach may be taken (Fig. 7). With this approach, another biopsy paddle may be placed in front of the image plate, to allow the breast tissue to bulge both anteriorly and posteriorly.
In addition, local anesthetic or sterile saline may be injected into the breast parenchyma to increase its thickness, before the biopsy probe being fired. Firing the probe into the breast just short of the targeted site or outside of the breast and subsequently manually inserting the probe into or adjacent to the targeted spot is helpful to avoid contact of the needle tip with the receptor or support plate.
For superficial lesions, “petite” biopsy needles with a smaller biopsy aperture may be used to avoid cutting the skin. There are also plastic aperture sleeves that partially cover the probe aperture and prevent inadvertent skin sampling. The subcutaneous tissue may also be expanded with additional injection of local anesthetic or sterile saline to push the lesion deeper and away from the skin. Some superficial breast calcifications may demonstrate to be dermal calcifications on stereotactic localization. Dermal calcifications may be confirmed while the patient is on the stereotactic biopsy table by placing a small metallic marker (a “BB”) at the skin site targeted by the tip of the needle and performing a 90° tangential view.
Deep or Very Superior Lesion
For deep lesions close to the chest wall or lesions very high in the breast, in either the upper or the inner quadrants, proper patient positioning is key to technical success. When the prone biopsy table is used, the patient’s arm in addition to the targeted breast may be placed through the table aperture. This so-called “arm-through-the-hole” technique enables full access to the posterior or upper breast. The affected arm needs to be supported with a sling or resting on a stand. The affected hand may also hold on to the handrail of a stepstool to keep the breast motionless (Fig. 8). Unlike for diagnostic breast imaging, the breast does not have to be imaged with the conventional craniocaudal or caudocranial or 90° lateral views during the stereotactic biopsy. To optimize the accessibility of posterior breast tissue and lesions, the receptor plate can be positioned at an oblique angle to allow the compression paddle to be placed as close as possible up against the rib cage or sternum.
The core biopsy specimens retrieved from the stereotactic biopsy device are laid out in a Petri dish and imaged (Fig. 9). The specimen radiography serves to document the tissue retrieval and the presence of the targeted lesion within the specimen cores, especially the calcifications. Calcifications or lesional tissue within the cores may be marked with ink to aid the pathologist in tissue analysis (Fig. 10). Selected cores may also be separated from the other core samples for more detailed analysis. The specimen cores are then immersed in formalin, labeled appropriately, and sent to the pathology department for analysis.
Postbiopsy Clip Placement and Mammography
Once the specimen retrieval is completed, a localizing postbiopsy marker clip, usually a 3-mm titanium clip, is placed at the biopsy site. This clip facilitates future mammographic monitoring of the area and serves to guide future surgical excision. To ensure that the clip is deployed at the biopsy site, an image of the biopsied area is obtained, while the breast is still under compression on the biopsy unit. Because clip migration has been reported in up to 20% of cases,
2-view mammography, including a craniocaudal and a mediolateral or lateromedial view, should be performed after the breast is decompressed to assess the final position of the deployed clip. Clip migration should be documented in the biopsy report.
Postprocedure Patient Treatment and Follow-Up
Immediately after the biopsy needle is withdrawn from the breast, focal compression of the biopsy site is performed to achieve hemostasis. If persistent bleeding is noted, it is helpful to keep the breast under the compression paddle, adding focal compression at the biopsy site. When hemostasis is achieved, the skin incision is closed generally with Steri-Strips (thin adhesive strips). It is rarely necessary to close the skin incision with sutures, as the skin incision is generally 5 mm. After the postprocedure mammography is performed, a compression bandage may also be applied across the breast for a few hours or overnight to ensure continued hemostasis. It is also helpful to place an ice pack at the biopsy site. If pathology results are benign, mammographic follow-up at 6-12 months after the biopsy is recommended.
After stereotactic biopsy, it is imperative to compare the results of imaging and pathologic analysis to determine radiologic-pathologic concordance and to determine whether surgical excision or additional intervention is necessary. An addendum to the biopsy report should be issued describing radiologic-pathologic concordance or discordance, along with a final follow-up recommendation for the referring physician and patient. Surgical excision or rebiopsy should be recommended in cases of radiologic-pathologic discordance. If the calcifications are not described by the pathologist to be within the samples of targeted calcifications, evaluation of additional tissue blocks and the tissue with polarized light may be required. Consultation with the pathologist is essential. Calcifications within the cores may get dissolved during processing or fall out of the tissue and be lost during cutting. Therefore, it is important to document the presence of the calcifications within the sampled cores with a specimen radiograph at the time of the procedure.
Management of high-risk breast lesions such as flat epithelial atypia, atypical ductal hyperplasia, papillary lesions, lobular neoplasia, radial scar, and mucocelelike lesions is challenging. There is significant subjectivity in the pathologic interpretation of such lesions and lack of consensus regarding their treatment. For patients with such high-risk lesions, a multidisciplinary team approach, including pathologists, radiologists, and surgeons, would lead to an individualized treatment plan.
The ACR and the American College of Surgeons have established accreditation programs for facilities that perform stereotactic biopsies. These programs outline specific quality-control tests that must be performed by the medical physicist and radiologic technologist to ensure proper functioning of the imaging system, the mechanical safety of the equipment, and the localization accuracy. In addition, physicians who perform these procedures must meet initial and continuing training requirements and must perform a minimum number of procedures annually. The facility must also have a quality-control program in place to monitor the outcome data from the procedures.
Percutaneous image-guided biopsy has proven over time to be an accurate and acceptable alternative to surgical biopsy for obtaining histopathology diagnosis of breast abnormalities. Percutaneous image-guided biopsy is an outpatient procedure that does not necessitate general anesthesia, is readily available, is less invasive, and carries very low risks. Given the large number of women undergoing screening mammography, and increasingly tomosynthesis, a significant number of breast biopsies are likely to be recommended. The majority of the lesions biopsied are expected to be benign, and minimally invasive biopsy spares women from undergoing potentially deforming and expensive procedures for diagnosing breast disease.
Survival experience in the breast cancer detection demonstration project.