Chapter 43 Image-Guided Breast Biopsy
INTRODUCTION
Increased utilization of mammography screening is believed to have resulted in a relative increase in breast abnormalities of sufficient risk to warrant a biopsy. It is estimated that approximately 1.5 million breast biopsies are performed each year in the United States. Many of these biopsies are for nonpalpable lesions and, therefore, require some type of image guidance. A significant number of these biopsies will be performed for benign disease because the average positive predictive value for mammography is only 20% (range 15%–35%).1–4 If traditional methods for histologic confirmation were utilized, all women with nonpalpable breast lesions would proceed to the operating room after a wire localization procedure was performed in the radiology suite. Percutaneous image-guided breast biopsy has become an effective minimally invasive alternative to open surgical breast biopsy for the diagnosis of both palpable and nonpalpable image-detected abnormalities.5–7 Although the risk of bleeding and infection may be comparable with those of open surgical breast biopsy, some potential difficulties are unique to image-guided breast biopsy.8
With the early introduction by the Karalinski Institute in 1989 of stereotactic-guided fine-needle aspiration cytology of nonpalpable breast abnormalities,9 image-guided percutaneous breast biopsy has been shown to provide a secondary level of screening in a less-invasive, cost-effective manner to obtain a histologic diagnosis without sacrificing accuracy.5–7,10 The evolution of the biopsy tools used with image guidance (stereotaxic, ultrasound, and recently, magnetic resonance imaging [MRI]) has added to the accuracy of minimally invasive image-guided breast biopsy,11,12 keeping a greater portion of women with probably benign disease out of the operating room for a diagnostic procedure. However, advancement in technology has also added to the potential procedural risks.13
INDICATIONS
Almost any palpable or nonpalpable, indeterminate breast abnormality, which is visualized with imaging modalities (ultrasound, mammography, MRI), can be evaluated with image-guided breast biopsy. The lesions will fall into the following categories established by the American College of Radiology (ACR) lexicon14:
• BI-RADS 3 (probably benign, short-interval followup [6 mo], <2% risk of malignancy) abnormalities identified in a patient with a strong family history, difficult clinical and imaging examination, or a high level of anxiety.
• BI-RADS 4 (suspicious abnormality, biopsy should be considered) abnormalities, which require biopsy, may avoid a trip to the operating room for an abnormality with perhaps only a 20% risk of malignancy.
Stereotactic Breast Biopsy
Stereotaxis mammography determines the position of a nonpalpable breast abnormality by utilizing computerized triangulation of the targeted lesion visualized with two stereo images, separated by a 30° arc.5,15 The equipment for performing a stereotactic breast biopsy is either a dedicated prone table or an add-on unit, which utilizes a targeting and biopsy platform attached to a standard upright mammogram system.15,16 Add-on stereotactic breast biopsy units have been traditionally less popular because the upright patient position and patient visualization of the procedure have the potential for producing increased syncopal episodes.5,17 The advantages of the prone position include gravity to assist the technologist with posterior lesions and a greatly enhanced workspace beneath the table.18 Both are important for positioning and access, which limit many of the potential difficulties in achieving a successful biopsy.
OPERATIVE STEPS
Step 1 Evaluate mammogram and lesion as well as patient and choose image approach to breast (craniocaudal [CC], mediolateral [ML], lateromedial [LM])
Step 2 Position patient on stereotactic biopsy table for visualization of image-detected abnormality
Step 5 Anesthetize skin and breast parenchyma and make skin incision after appropriate antiseptic skin preparation
Step 7 Assess appropriate alignment between lesion and biopsy device on prebiopsy and/or postbiopsy alignment stereo digital images
OPERATIVE PROCEDURE
Evaluating the Mammogram and the Patient and Choosing the Approach to the Breast
Choosing an Inappropriate Mammogram Lesion Type for Biopsy
• Consequence
It is important to anticipate that some patients and some lesions will be difficult to biopsy. The characteristics of certain lesions (low-density nodules, faint microcalcifications, and vague asymmetrical densities) make them more difficult to visualize with digital imaging despite postprocessing features. Also, when the field of view of the breast is limited to a 5 × 5-cm area (the size of the biopsy window in the front compression paddle), the abnormality is not visualized in relation to the remainder of the breast as it is on the mammogram. An asymmetrical density may represent only a summation shadow of overlapping fibroglandular tissue. Loosely clustered calcifications may become more diffuse on stereo images and be impossible to target with any certainty because of varying depth.
• Prevention
Recognizing these demanding lesions may avoid unnecessary scheduling and the possibility of procedures being canceled. Complete diagnostic workup, including spot compression views and possibly ultrasound for asymmetrical densities and microfocus magnification for microcalcification, is essential. A true lateral (90°) view may successfully demonstrate “tea cup” calcifications associated with “milk of calcium,” in which benign calcium deposits layer out within microcysts. It is sometimes prudent to send patients with a complete diagnostic evaluation and a persistent but questionable imaging abnormality to the stereotactic suite ahead of time to see whether the lesion can be successfully visualized.
Failure to Recognize Patient Characteristics that Will Result in an Unsuccessful Stereotactic Breast Biopsy
• Consequence
There are also patient characteristics that will interfere with the success of a stereotactic breast biopsy. Patients with neurologic or musculoskeletal conditions may not tolerate positioning on the already-uncomfortable stereotactic biopsy table. Any condition that increases the likelihood of patient movement will cause a greater risk of missing the target lesion. This includes patients with acute or chronic respiratory conditions with associated coughing and patients with a high level of anxiety, especially those suffering from claustrophobia or agoraphobia. A history of bleeding abnormalities or use of anticoagulants, as with any biopsy, creates the potential for bleeding and complications such as hematoma.
• Prevention
When recognizing the kyphotic patient or those who may not tolerate the table positioning, it is helpful to ask the patient to try lying on the floor at home, with her head turned to one side for approximately 20 to 30 minutes. Having cough suppressants available will deal with most respiratory conditions. Although most stereotactic breast biopsies are performed with only local anesthesia, it may be helpful to use a diazepam for sedation in those anxious patients. If time allows, schedule the biopsy after 10 days of restriction from anticoagulants working on platelet function and allow for the reversal of warfarin. However, because the patient facing a possible diagnosis of breast cancer may not want to wait 10 days or if reversal of warfarin is medically inadvisable, most procedures can still be accomplished with only marginal risk. Using a smaller-gauge biopsy device and wrapping the patient with a pressure-style dressing may be helpful.
Not Choosing the Ideal Approach to the Breast
• Consequence
The shortest skin-to-lesion distance and the ability to clearly visualize the imaged abnormality are both factors the technologist and physician consider when working together to choose the correct approach (CC, LM, ML, and with the Hologic Multi-Care Platinum table, caudocranial) to the breast. Once the shortest skin-to-lesion distance is chosen, the lesion must be well visualized. The visibility of the breast abnormality may occasionally take priority over the shortest distance from the skin to the lesion. Although a lesion in the breast at 12 o’clock may suggest a CC approach, if the lesion is seen better on the patient’s mediolateral oblique (MLO) mammogram view, then an ML approach may be preferable. A situation may arise (on the Fischer Mammotest table) in which the abnormality is best seen in the CC view but the lesion appears to be in the inferior aspect of the breast on the MLO mammogram view. Therefore, it may not be possible to insert the biopsy instrument without traversing most of the breast tissue and striking the back of the patient’s breast (negative stroke margin), because in contrast to the Hologic Multicare Platinum table, the Fischer Mammotest table does not provide a caudocranial approach.
• Repair/Prevention
Determining the true position of the lesion within the breast starts with an understanding of the virtual position of the lesion created by the usual 60° MLO mammogram. A lesion that is in the lateral breast appears to be higher on the MLO view than its true position and a medial lesion appears lower on the MLO view than its true position. Therefore, if the patient’s abnormality is visualized best in the CC view, but the lesion is in the medial aspect of the breast, the biopsy using this approach will be successful and may not impale the underside of the breast because the medial lesion is actually more superior in the breast than it is perceived on the MLO mammogram view.
Failure to Recognize the Position of the Lesion in the Breast
• Consequence
The technologist may have difficulty in locating a lesion for biopsy when positioning the patient on the stereotactic table if the correct position of the lesion in the breast is not appreciated.
• Repair
Remember that when positioning a patient on a prone stereotactic table for an LM or ML approach that this is a 90° angle to the breast compared with the 60° angle associated with the traditional MLO mammogram view. Therefore, the lesion in the lateral aspect of the breast will “move” to a more inferior position with the LM stereotactic approach compared with its apparent position on the MLO mammogram. A lesion in the medial aspect of the breast will “move” to a more superior position with an ML (90°) stereotactic approach compared with its apparent position on the MLO mammogram.
Failure to Visualize the Lesion on Both Stereo Images
• Consequence
When a lesion well visualized on the scout image lacks visibility on both stereo images, another difficulty arises, especially when the physician has already considered the shortest skin-to-lesion distance and the clarity of the image on each mammogram view. This is most often due to fibroglandular tissue that superimposes itself over the target lesion in one of the stereo images because of the angle of exposure.
• Repair
A technique known as target on scout can be utilized to resolve the issue of limited clarity of the lesion on one of two stereotactic images. The stereo image, with poor lesion visibility, is replaced by the original scout image in which the lesion is clearly identified. The targeting is then performed on the one remaining stereo image and the scout image. The software is able to recognize the 15° separation between the two targeted images and then calculate the appropriate coordinates. It is important to maintain all followup prefire and postfire images consistent with the targeting images. On the replaced scout image on the Hologic Multi-Care Platinum table, with the biopsy device in position, it is more difficult to visualize the targeted lesion because of the cartesian targeting platform.
Patient Positioning
Failure to Image a Lesion that is Deep against the Pectoral Muscle
• Consequence
The position of certain lesions, including those against the chest wall or in the tail of the breast or axilla, may require innovative positioning by the experienced technologist.
Obtain Scout and Stereo Digital Images
Not Correctly Positioning the Breast Lesion within the Compression Window
• Consequence
Failure to position the breast so that the lesion to be biopsied falls within the 5 × 5 cm opening of the compression paddle such that it appears in the middle third of the scout image will result in the lesion being “thrown” outside the visualization/targeting window on one of the two stereo images (Fig. 43-2).
Failure to Recognize the Depth of a Lesion in the Breast
• Consequence
A lesion that is too superficial may interfere with the successful function of certain biopsy devices that may require the sampling portion of the device to be within the skin. A vacuum-assisted biopsy (VAB) device requires maintaining a suction vacuum to pull tissue toward the sampling portion of the device. If the entire sampling portion is not beneath the skin because the lesion is too superficial, the vacuum is unable to maintain enough suction to pull the tissue in for biopsy (Fig. 43-3). The newer large, intact sampling devices utilize radiofrequency-activated tissue cutting and must, therefore, be a certain distance beneath the skin to avoid any inadvertent burns.
If a lesion is too deep, insertion of the biopsy device without encroaching on the backside of the breast will be difficult, and a stroke margin problem will be encountered. This is especially true for devices that have a spring-loaded mechanism to advance the biopsy portion of the device forward into the breast. A stroke margin is the distance from the device tip after advancing forward to the back of the breast. There is a problem when this distance is less than the stroke (forward motion) of the particular device (negative stroke margin) (Fig. 43-4).
• Repair
The use of skin hooks can retract the skin so the back of the VAB device is covered; thus, there will be adequate suction for biopsy and the skin can be protected from the heat of the radiofrequency-activated large intact sample device (Fig. 43-5). Repositioning the patient for a different approach to the breast may be all that is required (e.g., changing from a CC to an ML or LM approach) to deal with lesions that are determined to be too deep.
• Prevention
The ability to recognize the significance of lesion movement from one stereo image to the next can alert the astute physician to the depth (superficial or deep) of the lesion and further predict a problem of a lesion too close to the skin or too deep against the back of the breast or rear image receptor.
Targeting the Lesion
A Negative Stroke Margin
• Consequence
Once the target information is acquired, whether there will be an adequate stroke margin becomes evident. The stroke margin again is the distance from the postfired position of the biopsy probe to the back of the breast or rear-image receptor. A negative stroke margin is encountered when the breast is very thin or the lesion is in a posterior position in the breast. This situation may result in the biopsy needle striking the rear-image receptor and piercing the back of the patient’s breast skin (see Fig. 43-4).
• Repair
Several methods are available for eliminating the negative stroke margin. Taking a different approach to the breast lesions (e.g., changing from a lateral approach to a medial approach) may actually provide the necessary amount of tissue behind the lesion. Using a biopsy device that has a shorter-throw (forward movement of an automated device) or a biopsy tool that has a shorter sample notch can reduce the required breast thickness. Manual insertion of the biopsy instrument (avoiding the automated firing) allows a controlled forward motion of the sampling notch into appropriate position. Use of the lateral arm allows insertion of the biopsy device through the side of the compressed breast, parallel to the compression paddles. Also, use of the double-paddle technique adds an additional buffer between the back of the breast and the back compression paddle.
• Prevention
Small or ptotic breasts create one of the most common difficulties in stereotactic breast biopsy. A minimal compression thickness is required to avoid stroke margin problems. This minimal compression thickness varies between biopsy devices. It is important to recognize the patient with these characteristics. Once again, the ability to accurately access the position of the lesion and appropriately position the patient for the correct approach will limit these difficulties.
Prepare the Breast: Skin Preparation, Local Anesthesia, and Skin Incision
Using Local Anesthetic with Epinephrine in the Skin
• Consequence
The skin wheal is raised, usually with 1% lidocaine. For stereotactic biopsy, it is important to avoid the use of local anesthesia combined with epinephrine. The constant pressure of the 5 × 5 cm biopsy window (in the compression paddle) on the breast for the entire length of the procedure (sometimes >30–45 min) will cause a decrease in blood flow and result in skin necrosis at the entrance site. Local anesthesia with epinephrine (1 : 100,000) is commonly used with the deeper injection into the breast parenchyma.
Injecting Too Much Local Anesthetic
• Consequence
Too much local anesthetic injected into the biopsy site can also pose potential problems. The injection is not performed in real time as is done with ultrasound-guided procedures and, therefore, can cause inadvertent lesion movement, and faint, noncalcified lesions can become difficult if not impossible to see on additional imaging.
• Repair
If the injection is too large, a quantity of local anesthetic results in the movement of the lesion such that adequate sampling may be altered; in this situation, it will be necessary to remove the biopsy device from the breast and retarget the lesion. If the lesion is faint and/or noncalcified, correction is more difficult. Occasionally, waiting a few minutes for reabsorption or dilution of the local anesthetic is sufficient. Sometimes, a review of the stereo digital images taken for initial targeting can help judge the correct position of the lesion by comparing the surrounding breast architecture. A last resort would be postponing the procedure and rescheduling.
• Prevention
Physicians have employed different techniques for providing the patient with adequate anesthesia and avoiding the difficulties outlined. One technique utilizes a skin wheal followed by injection of deep local anesthetic at the four quarters of the clock (12, 3, 6, 9 o’clock positions) positioned at the lateral aspect of the skin wheal. The 1½ inch needle is inserted to the hub and the local anesthetic is injected gently as the needle is withdrawn. This technique disperses the local anesthetic evenly and provides a region of anesthesia where tissue sampling will occur. Another technique involves placing local anesthetic directly at the biopsy site only after a skin wheal has been raised. A spinal needle can be directed with stereotactic guidance to the correct x-, y-, and z-axis (depth) coordinates, and 1 or 2 ml of local anesthetic is directed in a limited fashion to the biopsy site. However, the most accurate prevention starts with recognition of which lesions will be difficult to visualize when larger amounts of local anesthetic are injected (faint asymmetrical densities and microcalcifications). Prior to injecting larger quantities of local anesthetic, deploying a metallic clip in the lesion will eliminate nonvisualization. In addition, allowing injection of deep local anesthesia only after the biopsy device is in position and visually aligned with the target lesion will usually accomplish the goal.
Insertion of the Biopsy Device
Failure to Recognize Specific Insertion Depths for Different Devices
• Consequence
Certain devices require placement at a depth less than that calculated by the system software. The “pullback” is calculated by the individual manufacturers because of the device mechanics such as the forward motion or throw with the amount of “dead space” at the front of the needle along with the length of the sampling portion of the needle. If the required pullback in depth is ignored for a particular device, the device may be too deep or not aligned correctly with the lesion and adequate tissue sampling will not occur.
• Prevention
It is crucial not only to be familiar with the biopsy mechanism of the device but also to know the specifications from the manufacturers for stereotactic targeting, including the pullback depth. The Fischer MammoTest table allows the specifications for all the biopsy devices physicians will use to be programmed into the system. The Lorad Multi-Care table requires calibration of each device to the system on each patient (z-axis = zero), and the physician manually sets the depth.
Inability to Avoid a Negative Stroke Margin
• Consequence
If a negative stroke margin cannot be prevented by changing the positioning or approach to the breast or utilizing any of the other previously discussed options, the negative stroke margin must be recognized and manipulated to prevent injury to the patient or the equipment.
• Repair
The most commonly employed correction method is pulling back the prefire position of the biopsy needle a determined number of millimeters until the calculated stroke margin is adequate. Care must be taken not to pull back the biopsy device to a distance that places the sampling notch or biopsy mechanism too far in front of the lesion such that the lesion will be missed.
Assess Appropriate Alignment between the Lesion and the Biopsy Device on Prebiopsy and/or Postbiopsy Alignment Stereo Digital Images
Failure to Recognize Targeting Errors
• Consequence
Interpretation of the stereotactic digital images allows the physician to determine whether the breast-imaged abnormality is within the range required by the device for adequate sampling. Correct targeting demonstrates symmetrical alignment of the lesion and the biopsy portion of the device in each stereo image. There are three types of targeting errors that can occur: x-, y-, and z-axis targeting errors. X-axis deviation occurs when the lesion is pushed to the right or the left of the biopsy needle. Y-axis errors represent movement of the lesion above or below the needle/probe. Z-axis error occurs when the sampling notch or biopsy mechanism is too proximal or too distal to the depth of the breast abnormality.
• Repair
Fortunately, most x- and y-axis targeting errors that present a problem with stereotactic needle-core biopsy have a limited effect on the success of a stereotactic biopsy performed with either a VAB or a large-intake sample device because these devices can be directed for specific sampling (Fig. 43-6). However, if the deviation from the target is significant enough to risk a poor biopsy, the lesion must be retargeted. After the device is removed from the breast, it is redirected and inserted with new coordinates.
• Prevention
To avoid missing a lesion because of an incorrect depth (z-axis) coordinate caused by forward motion of the lesion because of the “plowing” effect as the biopsy device is inserted; targets can be placed on the lesion in each of the new stereo images and the resultant z-axis depth compared with the original z-axis depth. The position of the target in each stereo image can also be helpful in preventing lesion movement and improve the probability of being able to easily visualize a very small lesion once the biopsy needle/probe is fully inserted into the breast. By targeting beneath the lesion, some of the plowing effect is dispersed, and because the lesion will be elevated above the device, even a very small lesion will not be hidden and its position will be easily assessed.
Adequately Sample the Lesion for Diagnosis and/or Potential Therapeutic Removal
Failure to Choose the Correct Biopsy Device
• Consequence
The tools for specimen acquisition have evolved from fine-needle aspiration, automated Tru-Cut core needle, VAB devices to large-intact sampling instruments, and the technologic advancements have closely paralleled the acceptance of image-guided breast biopsy.19 Fine-needle aspiration has long been recognized to have several potential pitfalls. This includes insufficient sampling, as high as 38% in some series, with sensitivity ranges between 68% and 93% and specificity between 88% and 100%.18,19 Cytology rarely provides a specific benign diagnosis and cannot distinguish between invasive and in situ carcinoma. The automated Tru-Cut core needle has a lower false-negative rate compared with that of fine-needle aspiration.5–7 Standard use of the 14-gauge needle essentially eliminated the issue of insufficient sampling.
Several different gauge needles have been evaluated for Tru-Cut biopsy. The lower rate of insufficient sampling and increased sensitivity, without increased complications, has led to a minimum size of 14-gauge as a standard.5,19 The issue of how many cores are needed was addressed by Dr. Laura Lieberman from Sloan-Kettering in New York.20 In this study, 145 lesions were biopsied: 92 were nodular densities, and 53 were microcalcifications. Five cores with a 14-gauge automated Tru-Cut needle yielded a diagnosis in 99% of biopsies for breast masses. Five cores yielded a diagnosis in only 87% of the microcalcification cases, and more than six cores yielded a diagnosis in 92% of the cases.
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