Role of stereotactic biopsy in diagnosing breast cancer.
Localization techniques that may be used during needle biopsy include clinical guidance, the grid coordinate system, ultrasound guidance and stereotactic guidance. Of these four options, only stereotactic guidance permits localization of a lesion in three dimensions.
This article explains the principles behind stereotactic localization and discusses the equipment and personnel involved in the stereotactic breast biopsy procedure. It also discusses patient positioning techniques and sampling technique during stereotactic breast biopsy, with particular emphasis on the mammographer's role throughout the procedure.
This article is a Directed Reading. See the quiz at conclusion.
In 1996, nearly 1.4 million cases of cancer will be diagnosed in the United States. Of those, 185,700 will be new cases of breast cancer: 184,300 in women and 1,400 in men.
U.S. women have a 1 in 8 chance of developing breast cancer during their lifetime, with the probability of developing the disease increasing steadily with age. (See Table 1.) Women between the ages of 40 and 59 have a 1 in 26 probability of developing breast cancer, while those between 60 and 79 years of age have a 1 in 14 chance of developing the disease.
Table 1 Percentage of Population (Probability) Developing Breast Cancer at Certain Ages (U.S., 1990-1992 Data)(*)
Birth-39 40-59 60-79 Lifetime Years Years Years (Birth-Death) 0.47 3.91 6.93 12.64 (1 in 218) (1 in 26) (1 in 14) (1 in 8)
(*) Information adapted from: Parker SL, Tong T, Bolden S, Wingo PA. Cancer statistics, 1996. CA. 1995;65:5-27.
Unfortunately, despite improved early detection methods,. the mortality rate for breast cancer has remained unchanged. Researchers estimate that as many as 44,300 women and 260 men will die from breast cancer this year, making the disease the second leading cause of cancer deaths in women, after lung cancer. (See Table 2.) In 1996 alone, breast cancer will account for 31% of all new cancers in women and cause 17% of cancer deaths in women.
Table 2 Estimated New Cancer Cases and Deaths, Distribution by Site, U.S. Women, 1996(*)
New Cancer Site Cancer Cases Deaths Melanoma of skin 3% 1% Oral 2% 1% Breast 31% 17% Lung 13% 25% Pancreas 2% 5% Colon and rectum 11% 10% Ovary 4% 6% Urinary 4% 3% Cervix uteri 3% 2% Corpus/unspecified uterus 6% 2% Leukemia/lymphomas 6% 8% All other 15% 20%
(*) Excludes basal and squamous cell skin cancers and carcinoma in situ except bladder. Information adapted from: Parker SL, Tong T, Bolden S, Wingo PA. Cancer statistics, 1996. CA. 1995;65:5-27.
Mortality is directly related to the stage at which breast cancer is detected. Effective diagnosis and treatment requires that breast cancer be detected in its earliest, nonpalpable stages. To date, screening mammography is the only proven method of detecting nonpalpable lesions. However, even careful mammography can produce indeterminate findings, resulting in unnecessary biopsies and surgery. In fact, only 10% to 20% of nonpalpable lesions turn out to be cancerous.
Combining mammographic findings with known risk factors and a thorough knowledge of breast anatomy can help minimize the false-positive interpretation of mammography.[1,2] Still, many women with nonpalpable breast lesions must undergo biopsy. Stereotactic breast biopsy, introduced in Europe in the late 1980s and brought to the United States in the early 1990s, offers an alternative to traditional surgical biopsy. This revolutionary technique is faster, less expensive, less painful and less invasive for women who have nonpalpable breast lesions.
Overview of Breast Anatomy
An accurate diagnosis depends upon a thorough understanding of breast anatomy and physiology. The human breast consists of 20 separate glands or lobes, each with its own duct opening separately onto the surface of the nipple.
The lobes develop by ingrowths from the surface epidermis; during infancy, they consist only of rudimentary branching ducts surrounded by cuffs of connective tissue that are an extension of the papillary dermis. In men, this state persists throughout life. In women, during the 3- to 4-year period before the onset of menstruation, the breasts enlarge and the ducts and the specialized loose periductal stroma proliferate. During adolescence, stromal breast growth continues, and buds form at the end of ducts. These are the lobules, and they are the beginnings of the secretory gland structure that develops later during pregnancy and lactation.
In the female adult, the breast undergoes cyclical changes that parallel those of the endometrium during the menstrual cycle. Influenced by estrogen, there is epithelial proliferation during the first half of the cycle, which continues as progesterone is added during the second half of the cycle. During this second phase there is abortive secretory activity, and the gland enlarges and feels tense. The breast reaches its maximum development during pregnancy and lactation.
In the normal breast, the epithelium constitutes about 15% of the organ. The remainder consists of lobules of fat contained by fibrous septa that stretch from the dermis to the fascia overlying the pectoral muscles. These septa play a large part in giving the female breast its firmness and configuration. The septa also form an avenue for the spread of carcinoma to the skin and pectoral muscles.
Screening mammography is the single most important diagnostic tool in the early detection of breast cancer. The impetus behind breast cancer screening is based on six criteria:
* The disease is important.
* It has a recognizable presymptomatic stage.
* Reliable tests exist that are acceptable in terms of risk, cost and patient discomfort.
* Therapy in presymptomatic stages reduces morbidity and mortality more than therapy initiated after the presence of symptoms.
* Facilities are available for the diagnosis and treatment of patients with positive screening results.
* Screening programs take precedence over other needs competing for the same resource.
The first reported use of mammography dates to 1930, when Stafford Warren, M.D., used in vivo mammography to image breast tissue. Unfortunately, the widespread use of mammography was thwarted by the lack of reproducibility and the poor quality of the images.[4-6]
The reintroduction of mammography in 1960 by Robert Egan was the key in the detection of breast tumors that were too small to be detected upon palpation. Egan's technique relied on the use of high-milliamperage/low-kilovoltage and yielded reproducible results on industrial film. These early attempts at mammography relied on injections of air and contrast materials to intensify the image. However, the first images used dangerously high levels of radiation, long exposure times and produced poor quality images.[4,6]
By the mid-1960s, the first x-ray machines developed exclusively for mammography had been introduced. The use of a molybdenum target substituted for tungsten heightened the contrast between water, fat and calcific densities, and a built-in compression device reduced scattered radiation, diminished motion-related artifacts and separated breast structures. The introduction in 1972 of an image intensifying screen with a single-emulsion film held in place by a vacuum revolutionized mammography.[4,6]
Today's screen-film mammography systems use smaller focal spots, a longer and fixed source-to-image distance to improve the sharpness of the image, and more effective compression devices to eliminate motion and to separate mammary structures. Moving grids also are incorporated to reduce scatter, and automatic exposure control is used to achieve more consistent quality. Other improvements include enhanced positioning capabilities that allow the patient to stand during the procedure for ease of positioning, and an alternate, smaller focal spot for the production of magnified images. Newer equipment permits greater image contrast and detail and requires less radiation than earlier models.[4,6]
Four components are critical to obtaining quality mammographic images: a motivated and competent mammographer, a cooperative patient, dedicated mammography equipment and a knowledgeable radiologist. Of the four, the competent mammographer is key, because without him or her the role of the other three is greatly diminished.
The mammographer is responsible for completing a brief but detailed patient history to discover any risk factors. The patient's history is critical, particularly if suspicious occult lesions are discovered. In addition to being female, risk factors for breast cancer include age, a family history of breast cancer, a history of benign breast disease, obesity, cigarette smoking and an early onset of menarche.[2,4-6]
After obtaining an adequate patient history, the mammographer visually inspects the patient's breast and meticulously identifies any abnormalities or unusual landmarks on a diagram, taking care to accurately mark their positions as well as their relationship to the nipple and chest wall. Biopsy scars, skin lesions and any other unusual findings are carefully noted. In addition, the patient's nipples must be observed carefully and any asymmetry, retraction or discharge must be noted.
The mammographer also may need to perform breast palpation. If a lump is present, the mammographer may have to palpate the area to determine whether routine views will adequately image the area.
Because the quality of mammographic images is directly related to the amount of compression applied, the mammographer must work closely with the patient to determine the degree of compression she can reasonably tolerate. Deciding how much compression she can bear allows the patient to take an active role in the procedure and often results in a more cooperative patient.[2,4-6]
Following the examination, the mammographer must review the mammogram to determine whether it is a quality image or if it has been corrupted by motion, poor positioning, incorrect technique or faulty film-screen contact. In certain cases, the mammographer may decide it is necessary to obtain supplemental views as part of the screening mammogram.
Until recently, the millions of women whose mammograms showed suspicious nonpalpable breast lesions had two options: Either undergo another mammographic examination a few months later to see if its findings are more conclusive, or undergo excisional biopsy for an immediate answer. A majority of women, finding the idea of waiting months for an answer intolerable, chose the surgical biopsy. The procedure, however, entailed at least one day of hospitalization and the administration of general anesthesia. In addition, the possibility existed of extensive scarring and post-procedure complications.
The introduction of needle breast biopsy offered women a third alternative. The technique was developed in an effort to reduce the number of unnecessary surgical biopsies performed on benign lesions.
Overview of Needle Biopsy
The needle biopsy technique permits nonmalignant breast abnormalities to be detected without the need for surgical biopsy. Because as many as 80% to 90% of all breast abnormalities are benign, the avoidance of unnecessary surgery is paramount in terms of morbidity and mortality, as well as for economic reasons.[7,8]
There are two types of breast needle biopsy -- fine-needle aspiration biopsy (FNAB) and core biopsy. Fine-needle aspiration biopsy provides cells (cytologic material), while core biopsy obtains breast tissue (histologic material). Clinicians must take several variables into consideration when selecting a biopsy method and determining which tools they will use.
Fine-needle Aspiration Biopsy
During fine-needle aspiration biopsy, a small sample of cytologic material is excised from an abnormality and preserved on slides for subsequent interpretation by a cytopathologist, who makes a determination whether the material is malignant or benign.
The technique relies on the use of a 20- to 23-gauge needle that may be attached directly to a syringe or via connective tubing. The biopsy needle is inserted into the abnormality, with negative pressure applied by pulling back on the syringe to permit aspiration of material for sampling. Needle length is contingent upon the size of the breast and the depth of the abnormality. The small gauge needle and the relatively small sample size can make it difficult to obtain an adequate sample, making careful preparation essential.
The cornerstone of the FNAB technique calls for meticulous localization of the abnormality. Also essential is a well-trained biopsy team, generally consisting of a nurse, a mammographer, a cytopathologist and a clinician (a radiologist and/or a surgeon). Fine-needle aspiration biopsy can be performed in as few as 3 to 30 minutes.
Core biopsy is used to obtain a larger tissue sample and is performed with a specially designed 14- to 18-gauge needle (the 14-gauge needle is the most popular size). The needle is placed in a "rapid-fire" automated biopsy gun. Once the needle has been inserted to the appropriate depth, a spring-loaded, double-action gun quickly advances the two-stage needle, removing a core of the abnormality during its operation. Histological samples obtained with core biopsy are preserved in formalin and transported to the histopathologist for interpretation.
In general, because of the larger volume of specimen obtained, core biopsy is considered by some clinicians to offer a more definitive diagnosis. Core biopsy is a lengthier procedure than FNAB, requiring from 20 minutes to 1 hour.[7-14]
Localization Techniques In Needle Breast Biopsy
Needle biopsy of a suspicious area in the breast can be performed under clinical guidance or with one of three imaging techniques -- a grid coordinate system, ultrasound guidance or stereotactic guidance. Each localization method has advantages and disadvantages, and each provides a different degree of accuracy.
Palpable abnormalities in the breast may or may not be mammographically and sonographically occult. Under the clinical guidance localization technique, the clinician inserts the biopsy needle into the abnormality by hand, relying on palpation of the abnormality to determine accurate placement of the needle. Because the breast is not in a fixed position during this technique, the abnormality is subject to movement, which may increase the difficulty of this approach.
Although clinically guided biopsy primarily is used in conjunction with FNAB, the technique also can be used with core biopsy. However, the clinically guided core biopsy requires greater skill on the part of the clinician due to the difficulty in managing the heavier biopsy instrument and the need for speed when biopsying an unsecured breast. Care must be taken to keep the biopsy needle parallel to the chest wall, which can be difficult when working with an unfixed breast. These factors can compromise accuracy, sterility and safety during the biopsy procedure.
The primary disadvantage of clinically guided breast needle biopsy is that there is no systematic method available to accurately document needle placement. Therefore, negative biopsy results obtained under clinical guidance may be considered suspicious and may necessitate surgical biopsy of the abnormality or follow-up interval mammography to confirm the biopsy results. However, if the biopsy results are positive, excisional biopsy can be avoided and a definitive treatment plan can begin.
Grid Coordinate System
A grid coordinate system uses dedicated mammography equipment and a needle localization grid to localize the abnormality in two dimensions. Although relatively inexpensive and a proven method for needle localization, this method is unable to determine the exact depth of an abnormality. Depth can only be estimated. In addition, this method relies on freehand guidance of the biopsy needle, which may result in inaccurate placement of the needle.
Ultrasound-guided biopsy is used for both palpable and nonpalpable lesions. Unlike clinically guided biopsy, real-time ultrasound combined with fine-needle biopsy permits monitoring of needle movement and can yield extremely accurate results in the hands of a skilled clinician. However, when used in combination with large core biopsy, excursion of the needle is not as easily monitored due to the speed at which the needle moves.[8,15]
In addition, a recent study comparing ultrasound-guided biopsy with stereotactic biopsy reported that 50% of all abnormalities and more than 60% of carcinomas were not visualized with sonography. In particular, calcifications, architectural abnormalities and small masses measuring 6 mm or less in size posed imaging difficulties under sonography.[16,17]
Although traditionally used in conjunction with core biopsy, stereotactic guidance is increasingly being used with FNAB. It is accomplished with specially designed equipment that localizes an abnormality by using two angled radiographs taken approximately 30[degrees] apart (+15[degrees] and -15[degrees] from center) and a computerized coordinate system. (See Fig. 1.)
[Figure 1 ILLUSTRATION OMITTED]
Stereotactic imaging is based on stereoscopy, the principle used by the human eyes and brain to create 3-D images. Each eye provides the brain with a different perspective of an object, and the brain fuses those images together to perceive the distance, or the depth, of the object.
Although traditional radiography provides accurate horizontal and vertical measures of anatomical structures, depth perception is more difficult. Stereotactic localization resolves the issue of depth perception. Studies have shown that stereotactic imaging permits accurate localization of an abnormality in three dimensions to within 1 mm tolerances.[18-20]
The stereotactic method of localization is less dependent on the clinician's skill than the clinically guided or ultrasound methods because the breast is immobilized by a compression device, making a lesion less likely to move during the procedure.
In addition, stereotactic biopsy equipment is not hand-held or manually guided. A computerized guidance system holds the equipment as the needle is directed into the breast to take a specimen of the lesion. Parallel orientation of the needle eliminates excursion of the needle through the breast into the chest wall or thorax.
The stereotactic breast biopsy (SBB) procedure was pioneered at the Karolinska Institute in Sweden, recognized worldwide for its high success rate in the detection of occult breast cancer.
At the Karolinska Institute, mammograms are coded with a classification label ranging from 1 to 5, where 0 = no breast present, 1 = a normal mammogram, 2 = an abnormality with no suspicion of cancer, 3 = uncertainty and some suspicion regarding cancer, 4 = probable malignancy and 5 = definite malignancy. All mammograms are coded according to this scale and read twice for accuracy. Patients whose mammograms receive a code of 3 undergo stereotactic fine-needle aspiration biopsy at the site of the abnormality, providing immediate clarification of suspicious findings. Only patients who mammograms receive a code of 4 or 5 receive a traditional surgical biopsy.
Since the introduction of routine SBB in Sweden, there has been a decrease in the number of surgical biopsies performed in favor of stereotactic breast biopsies, resulting in a quicker, less expensive, less invasive and more humane system of early breast cancer detection.
It also is interesting to note that the false-positive detection rate for breast cancer screening in the United States is four times the false-positive rate in Sweden, where there also has been no increase in false-negative findings.
Overview Of Stereotactic Biopsy Systems
Two types of stereotactic units are available: an upright, add-on unit and a prone table. Add-on units are attached to a free-standing mammography unit and require that the patient sit upright during the procedure. Prone tables permit the patient to remain recumbent, abdomen down, during the procedure. (See Figs. 2A and 2B.)
[Figure 2 ILLUSTRATION OMITTED]
Stereotactic imaging produces a quantitative 3-D image of a breast lesion based on a "stereo pair" of images taken from two perspectives, horizontal and vertical. Two images are acquired using x-ray mammography and two different positions are projected side by side on film or on a computer monitor to form the stereo pair. The clinician targets the abnormality and the computer determines its location based on the abnormality's shift from a reference point or points. The computer also provides a coordinate system for translating the results for practical application.
After coordinates have been determined, a needle is placed in the breast for sampling and a confirmation (prefire) stereo pair is acquired. If the second stereo pair demonstrates actual needle placement, then sampling is completed. Subsequent samples can be taken with or without other stereo pair images. (See Fig. 3.)
[Figure 3 ILLUSTRATION OMITTED]
The coordinate system is used to identify a unique visual point in the breast that will be used as the target for the needle biopsy. As such, the coordinate system localizes the lesion in three dimensions. The horizontal plane is expressed by X or H, the vertical plane by Y or V, and depth by Z or D.
Two types of coordinate systems are available: Cartesian and Polar. The Cartesian system defines a point by distances from three axes (horizontal, vertical and depth) that intersect at right angles. (See Fig. 4.) For example, the location of an abnormality may be expressed from a fixed point as:
* X = + 4mm.
* Y = + 10mm.
* Z = + 22 mm.
[Figure 4 ILLUSTRATION OMITTED]
The primary advantage of the Cartesian system relates to the user's familiarity with the coordinate system. In addition, its simplicity allows users to easily adjust the needle position. The Cartesian system also allows easier correlation with aspects such as scale and reference points.
The Polar coordinate system defines a target by distances from a fixed point and angular distances from a reference line; coordinates are given as H, V and D. (See Fig. 5.) Horizontal and vertical coordinates are given in angles rather than in millimeters. Although the Polar coordinate system is more accurate than the Cartesian system, it is more difficult for the user to recognize errors unless they are gross in nature. Fixing errors requires complex trigonometric calculations that are too complex to be adjusted during a procedure. It is best to begin again if an error is detected. Furthermore, because the needle travels in an arc, a correction of H,V and D coordinates may change the accuracy of other coordinates.
[Figure 5 ILLUSTRATION OMITTED]
Accurate targeting during SBB is essential for precise localization. The cornerstone of stereotactic localization involves targeting the same point in space on two planar imaging. A unique point within an abnormality also must be pinpointed on the scout image and both planes, which may be difficult with odd-shaped masses, diffuse areas of distortion or microcalcifications. (See Fig. 6.) The physical principles of shift and display play important roles in targeting. The biopsy should not proceed if the abnormality cannot be identified in both stereo images. Alternative views may be required to achieve this.
[Figure 6 ILLUSTRATION OMITTED]
In general, equipment manufacturers usually recommend a specific targeting sequence that involves:
* Identifying reference points with a cursor.
* Maintaining the same vertical axis and indication of target(s) on both planar images.
* Checking the scout image for superimposed blood vessels that may be punctured during biopsy.
* Verifying both stereo images for localization of the abnormality and rechecking against the scout image for proper centering.
* Checking stereo images for direction of abnormality shift.
* Verifying coordinates.
* Checking the scout image for position of the abnormality in the biopsy window.
* Comparing the depth coordinate with mammographic information. With most SBB units, the depth coordinate should be a positive number; a negative depth coordinate indicates an error in positioning.
This sequence is designed to detect targeting errors. Prefire images also permit the clinician to correct unnoticed targeting errors. Prefire stereo images with the needle at the exact depth coordinate or at the prefire position help verify correct placement of the biopsy needle. Faulty targeting, movement of the patient or the abnormality and calculation errors have the same visual appearance. Verification of correct placement of the biopsy needle is made when no errors are detected and the stereo images concur with the scout images.
The Biopsy Instrument
Biopsy instruments are available as reusable or disposable units. Each biopsy gun consists of a spring-loaded system with a cocking mechanism and firing mechanism. (See Fig. 7.)
[Figure 7 ILLUSTRATION OMITTED]
The anterior and posterior carrier blocks of the gun hold the hubs of each part of the biopsy needle. This design facilitates high velocity firing. The distance that the gun moves the needle from the starting (cocked) position to the home (fired) position is known as the "stroke" of the instrument.
Stroke varies from 11 mm to 23 mm, depending on the manufacturer and model. Strokes of 22 mm to 23 mm are the most popular. In instruments with a shorter stroke, less of the sample notch is available for obtaining specimens. Some biopsy guns have multiple stroke movements that are useful for breasts of thinner compression widths.
Spring force and velocity determine the efficiency of a biopsy instrument in obtaining an adequate core of tissue. These factors are particularly important with firm abnormalities. Deflection is less likely to occur with more force and velocity.
Other characteristics that are important in a good biopsy instrument include:
* Maintenance of spring force. The spring force of a biopsy gun can weaken with continued use. Regular quality checks by the gun's manufacturer will help assure consistency.
* Weight. Heavy guns may be difficult to hold steady during the procedure.
* Cocking mechanism. A double cocking mechanism allows the needle to remain in place for successive samples. Safety features. An automatic or manual safety feature should be standard to prevent premature or accidental firing.
Firing of the biopsy instrument occurs in two stages. The posterior carrier block fires first, causing the anterior block to drive the cutting cannula forward over the styles and obtain the core of tissue.
The biopsy needle consists of two parts: an inner styles used for cutting a notch in the skin for specimen acquisition and an outer cutting cannula. The core of tissue is obtained during excursion of the cutting cannula.[8,22,23]
Typically, needles have a beveled tip; however, a new pencil-point needle called the Harper needle may offer some advantage. Whatever its shape, the biopsy needle must be compatible with the biopsy instrument. Although needle hubs may fit perfectly into the carrier blocks, alignment of the styles and cannula may be incorrect. Misalignment can result in difficulties during needle excursion, such as fragmented core samples or drag on the biopsy needle, resulting in tearing of breast tissue and hematoma.
Biopsy needles used during stereotactic core biopsy procedures range in size from 14- to 18-gauge, with 14-gauge needles the most popular. The larger the gauge, the smaller the size of the needle. Needle gauge affects the size of the biopsy specimen and is directly correlated with the effectiveness of histologic interpretation.[22,23]
Needles range in length from 10 cm to 16 cm, and length is an important consideration prior to biopsy. For example, shorter needles may limit the depth that can be achieved, e.g., a 16-cm needle will reach deeper into the breast tissue than a 10-cm needle.
Needle length also can cause superimposition of the biopsy instrument in the biopsy window. With shorter needles, more of the biopsy gun will impinge on the radiographic image, possibly obscuring the location of the abnormality or perhaps interfering with imaging of the abnormality during pre- and postfire images.
Physical constraints of upright systems may dictate needle length; for example, some upright units may not be able to accommodate longer needles.[8,24,25]
The breast must be thick enough when compressed to tolerate the motion of the needle from the prefire position to the home (fired) position without exiting the breast and striking the breast support. The distance from the home position to the breast support, with an allowance of 4 mm built in for safety measures, is called the stroke margin. (See Figs. 8 and 9.)
[Figure 8 to 9 ILLUSTRATION OMITTED]
The stroke margin is a critical measurement. A positive stroke means that there is enough thickness in the compressed breast to tolerate firing of the needle without exiting the breast. A negative stroke margin indicates that the needle will pass through the breast and strike the breast support.
When the needle hits the breast support, it can damage the underside of the breast. Also, the needle may bend from the impact and cause damage to the breast upon removal, much like a fishhook. To remove the damaged needle, the breast may have to be decompressed and the needle removed from the other side if it is not possible to remove it from the point of entry.[8,24,25]
Stroke margin may be calculated manually or by computer. However, visual indicators are equally important and should be in agreement with any calculations. For example, if the computer calculates a positive stroke margin but visual clues suggest otherwise, verification of the calculations is essential. All biopsy team members must know the correct stroke margin.
If the depth calculation is made from the proximal aspect of the compressed breast,
stroke margin = (compression thickness - 4 mm) - prefire depth + stroke.
If depth is determined from the distal aspect of the compressed breast,
stroke margin = (prefire depth - stroke) - 4 mm.[8,22]
Several options are available to counter a negative stroke margin. A shorter biopsy needle may be used, the prefire position of the needle may have to be altered or the breast may have to be repositioned. However, the actual programming of appropriate needle length and stroke must be determined on a case-by-case basis. Determining the prefire position and calibration of the stereotactic system should be verified daily or more often if necessary to achieve maximum accuracy.
The Mammographer's Role As a Member of the Biopsy Team
Successful stereotactic breast biopsy relies heavily on a cohesive team-approach. Most SBB teams are small, consisting of a clinician, a mammographer, a nurse and possibly an additional mammographer.
The primary responsibilities of the clinician are to target and sample the abnormality. To successfully perform SBB, the clinician must be able to visualize the abnormality in three dimensions in terms of its size, shape and distribution within the breast. Correct visualization is essential to avoid incorrect sampling, faulty positioning and procedural difficulties.
Although SBB relies on the use of a computer program to calculate lesion position, computations are based on the information provided by biopsy team members. If any of the input information is incorrect, an error in localization will result. In fact, errors in localization rarely are the result of computer errors and usually are the result of human errors.
The mammographer's responsibilities as a member of the biopsy team may vary from institution to institution, but they usually include positioning the patient, helping position the abnormality by obtaining scout images and stereo images, communicating with the patient throughout the procedure, obtaining post-study images and providing follow-up care and comfort. The flow chart shown in Fig. 10 outlines the entire SBB procedure.
[Figure 10 ILLUSTRATION OMITTED]
Positioning the Patient
Patient positioning is the first step in targeting an abnormality, and proper positioning is essential if an accurate sample is to be obtained.
When using a prone SBB unit, the mammographer should ask the patient to get into a comfortable position on the table before the procedure begins so that any awkward positions can be identified and alleviated. Points of pressure commonly involve the shoulder opposite the affected breast, the ribs and the neck. A thin sponge or towel can help alleviate some of the pressure in these areas. A small pillow placed under the patient's abdomen also can help relieve pressure on the lower back and related discomfort. It is important, however, not to place anything under the patient's head, because this can cause additional stress and strain on the neck. A small towel placed between the neck and table can provide ample support. (See Fig. 11.)
[Figure 11 ILLUSTRATION OMITTED]
When using an upright SBB unit, back support is essential to keep the patient in position and minimize discomfort and fatigue. Support for the feet and legs also helps keep the patient comfortable. It is particularly important with upright units that the patient's view of the biopsy instrument be shielded to minimize the possibility of a vaso-vagal response.
The mammographer also is responsible for ensuring that the patient does not move during the procedure. Patient motion during SBB can increase the amount of radiation required and lengthen the duration of the procedure, as well as complicate the biopsy.
A simple but effective technique in monitoring patient movement is to mark the breast in the biopsy window. (See Fig. 12.) If patient motion causes the abnormality to move, the original coordinates are no longer valid. Patient motion can require that the breast be repositioned in the biopsy window, as well as require new stereo images and retargeting of the abnormality. A second skin incision may even be necessary in some patients. Furthermore, additional prefire images will be required to confirm accurate placement of the needle. Repeat stereo images may not be necessary with a Cartesian coordinate system, in which a new measurement and adjustment is possible. However, additional prefire images still are necessary to verify needle placement.
[Figure 12 ILLUSTRATION OMITTED]
Obviously, patient cooperation is paramount for successful patient positioning. Positioning often takes longer than the biopsy procedure itself, and it is essential that the patient understand the need for remaining motionless during the entire procedure, from imaging through the actual biopsy. The mammographer plays a vital role in patient communication, and it is important that the mammographer gain the patient's trust.
Not surprisingly, many patients are anxious not only about the threat of carcinoma, but about the biopsy procedure itself. The mammographer should communicate with the patient in an effort to reduce anxiety and minimize discomfort. It is important that the entire procedure be explained to the patient in terms that the patient can comprehend. It may be helpful to recommend that the patient use the lavatory before the procedure and remove any clothing or jewelry that might interfere with her comfort during the procedure.[24,25]
Advise the patient that pain usually is limited to the sting of the needle for local anesthesia. Inform the patient that although she may feel a thumping sensation during the procedure, pain related to the biopsy should be absent or minimal. Reassure her that additional anesthesia can be administered during the procedure, if required.
Because the sound of the biopsy instrument may startle the patient and cause undesirable movement, the mammographer should explain, in advance, that the biopsy instrument will make a noise when firing. Placing a reassuring hand on the patient's shoulder immediately before firing also can help eliminate a startled response.
Positioning the Abnormality And Obtaining Images
Once the patient has been properly positioned, the mammographer must ensure adequate centering and visualization of the abnormality in the biopsy window. This is accomplished by obtaining scout images.
The scout image is generally acquired with the c-arm perpendicular to the image receptor.[8,25] The mammographer must locate the abnormality on the scout image as well as on the stereo images. The mammographer also should use the scout image to identify any blood vessels that overlie the abnormality. Blood vessels that project over the abnormality may be at risk for puncture.
After an adequate scout image is obtained, the mammographer must acquire two images to form the stereo pair. This is accomplished by following the manufacturer's specific instructions for the imaging unit. If the abnormality is not identifiable on either image, the mammographer will need to reposition the patient, redo the scout image and repeat the stereo images until the abnormality is visible in the biopsy window for all images.
The next step is to use the manufacturer's specifications to determine the abnormality's coordinates. Once the coordinates have been determined in two planes, they are electronically translated into three coordinates reflecting the horizontal position, vertical position and depth of the abnormality. It is important to note that although the scout image is required for positioning of the patient, it is not a part of the localization computation to pinpoint the abnormality in three dimensions.
In conclusion, the mammographer is responsible for many duties during stereotactic breast biopsy. He or she is not only responsible for proper positioning of the patient and positioning of the abnormality in the biopsy window, but also for more complex issues such as assessing breast composition, identifying the abnormality on the scout image, maintaining clarity on the stereo projections and determining a positive stroke margin.
The mammographer can enhance his or her SBB techniques by:
* Becoming familiar with the stereotactic biopsy unit.
* Mastering a basic understanding of SBB, including the concept of stroke and the calculations needed to determine stroke margin.
* Practicing with a phantom to enhance technical experience.
* Becoming proficient at locating the abnormality within the patient's breast based on the two-view mammogram.
In addition, the mammographer often is responsible for discussing follow-up care with the patient during the postbiopsy compression. Many institutions provide these instructions in a printed format so that the patient may take them home with her for further clarification.
After the patient has been positioned, the scout image and stereo pair have been acquired and the abnormality's coordinates have been determined, the biopsy procedure itself can begin. The following is an overview of the steps that occur during SBB sampling:
* Draping. Equipment and the patient are draped to prevent blood spatter. This is particularly important with upright units.
* Application of antiseptic. The biopsy unit is wiped down with antiseptic. The area within the biopsy window should be lightly cleansed with alcohol or a povidone-iodine solution, and any excess solution should be removed with a sterile sponge.
* Needle placement. A sterile needle is placed on the needle guidance system according to manufacturer's instructions.
* Secure biopsy instrument. A loaded biopsy gun is secured in the holder. Programming of biopsy unit. The biopsy unit is programmed for needle length and the stroke of the biopsy gun. Needle guidance. The biopsy team may use automated or manual controls to match the needle guidance device with target coordinates for X and Y axes of the target lesion.
* Administration of anesthesia. The needle is brought forward, indicating the site for anesthesia. Local anesthesia can be administered to the skin and subcutaneous tissues. Too much anesthesia can interfere with visualization of the abnormality on subsequent images, since anesthetic volume can displace the abnormality. To minimize possible displacement, 2% lidocaine hydrochloride can be used instead of a 1% formulation.
* Mark the skin for incision. Bring the needle forward just enough to make a mark on the skin.
* Skin incision. The clinician moves the needle forward to accurately indicate the site for incision. For a core biopsy, a 3 mm to 4 mm skin incision will facilitate entry of the biopsy needle, reducing skin drag on the outer cannula when the biopsy gun is fired. In some cases, a small skin incision made with a smaller gauge needle may facilitate smooth passage of the biopsy needle through the skin.
* Placement of the biopsy needle. The clinician guides the biopsy needle into the breast, advancing it to the desired depth.
* Prefire stereo pair images. Stereo pair images must be acquired before the biopsy gun is fired to ensure correct needle placement and to check for any movement of the abnormality. Retracting the anterior needle guide for prefire images may prevent superimposition of the needle over the abnormality.
* First sample. The clinician should check for proper seating of the biopsy instrument, making sure that the anterior needle guide is forward to ensure accurate needle placement. A positive stroke margin must be verified. Once a positive stroke margin is ensured, the clinician fires the biopsy instrument to obtain the first sample.
* Postfire images. The mammographer acquires postfire images immediately after firing the biopsy instrument to verify that the needle has transversed the abnormality. Movement of the lesion and needle deflection are two possible problems that may be seen on postfire images. Multiple samples may be obtained if necessary. Removal of the specimen(s). The core specimen is removed from the needle and preserved.
Problem Solving in SBB
Several errors are common to SBB -- errors in patient selection, stereotactic errors, sampling errors, insufficient sampling errors and errors in analysis. Fortunately, with planning and communication between all members of the biopsy team, most of these errors can be avoided.
Patient selection is critical to the success or failure of SBB, and errors in patient selection can adversely alter the results of the procedure.
The first step in determining whether a patient is a viable candidate for SBB is assessing whether she can remain prone or sit upright for the duration of the procedure, depending on whether the SBB unit is a prone or upright unit. Extremely large patients may not fit on a prone table and, therefore, may require another form of biopsy of the abnormality. Likewise, patients with paralysis may be unable to sit upright for SBB with a freestanding, add-on stereotactic mammography unit,[25,26]
In addition, patients who are unable to remain motionless for the duration of the procedure are not good candidates; this includes patients with severe arthritis, heart failure and other conditions. Cognitively impaired patients generally are not good candidates for SBB, since they are often unable to comprehend and comply with the need to remain motionless during the procedure.[17,24]
Certain pre-existing conditions or traits may alter the approach required or may entirely rule out the possibility of SBB. For example, patients who are taking anticoagulants generally are not good candidates for core biopsy with SBB, and a fine-needle aspiration biopsy that uses another localization method may be the preferred methodology for these patients. Should the nature of an abnormality in a patient taking anticoagulants require a large-sample core biopsy, the patient may be required to alter her medication schedule as well as receive prophylactic antibiotics before, during and after biopsy.
Superficial abnormalities also may contraindicate the use of SBB. Typically, the needle should be placed 5 mm before the center of an abnormality. Superficial lesions very close to the skin surface may not provide enough room for the needle and may be better suited for surgical biopsy. Diffuse abnormalities also may be difficult to biopsy using SBB. A diffuse, asymmetric abnormality or microcalcifications can be difficult to pinpoint on two planes; in these cases, surgical biopsy may be the method of choice.
Lastly, the compressed thickness of the breast is also a consideration. The compressed breast must be able to accommodate the full stroke of the biopsy needle. Stereotactic breast biopsy may not be possible for patients with a small compressed breast thickness, due to a negative stroke margin. For a typical 23-mm stroke gun, the compressed breast should measure at least 42 mm. Certain abnormalities in smaller breasts may be biopsied with shorter guns; however, the specimens obtained can be small, resulting in an insufficient sample.
Problems of localization related to calculation errors often are detected upon review of the pre- or postfire stereoimages. Errors can be the result of calibration mistakes or improper seating of the biopsy gun in the SBB unit. Patient motion also is a factor; subtle displacement can be difficult to detect and must be considered. Some SBB centers have reported good results with premedication to reduce patient anxiety in an attempt to eliminate movement. Errors related to motion can be reduced if the procedure is done as quickly and safely as possible.
Also, the administration of local anesthesia immediately adjacent to the target abnormality can result in displacement of the lesion. When required, it is recommended that local anesthesia be administered subcutaneously to avoid displacement.
Most malignancies are heterogeneous in pathology. Surgical biopsy generally is effective in identifying the full range of histology. Core biopsy samples, however, preserve only the specimen sampled and provide no clues to histology of adjacent areas of the degree of heterogeneity in an abnormality. For this reason, multiple core biopsies generally are obtained for each abnormality, including peripheral areas.
Multiple samples are obtained by varying the position of the biopsy needle. As many as five samples can be taken of a suspicious area with the same needle, unless the needle should become contaminated during the procedure. Because peripheral cores often contain the most aggressive cellular elements, multiple passes help to paint a more comprehensive picture of the abnormality. Five passes seems to counteract sampling errors.
Insufficient Number of Passes
In some cases the patient may not be able to tolerate the entire stereotactic biopsy procedure, resulting in the retrieval of an insufficient number of samples.
Specimen Removal and Radiography
Delicate handling is necessary to preserve the specimen retrieved through needle biopsy. It generally is preserved in sterile water with formalin at the conclusion of the procedure. When microcalcifications are involved, specimen radiography can help ensure adequate sampling. Reviewing radiographic images before releasing the patient from compression will permit further sampling, if necessary. In general, a mammography unit with magnification capabilities is used to obtain specimen images. It is recommended that two images be taken, using separate cassettes to distinguish artifacts such as dirt or dust from calcifications in the sample.
A poststudy image with the x-ray tube perpendicular to the breast support can document successful sampling of the abnormality. A recognizable reduction in the number of calcifications in comparison to the scout image can verify sampling. In addition, lucencies resulting from removal of tissue can confirm access to the abnormality.
Following the Procedure
It is important to establish contact with the pathology lab to ensure careful handling and processing of specimens. It also is critical to observe standard precautions regarding the handling of blood-borne pathogens.
Compression should be applied over the biopsy site until bleeding has stopped, followed by the application of an antibiotic ointment and closure of the mammotomy site with steristrips. Placement of a pressure dressing over the biopsy site to prevent hematoma is optional. The application of ice packs may be helpful in reducing pain and swelling. In general, it is recommended that a member of the biopsy team contact the patient 24 hours after the procedure to inquire about possible complications and to encourage the patient to follow postbiopsy instructions.
For many women, needle breast biopsy offers many advantages over surgical biopsy of a suspicious lesion in the breast. Needle biopsy is less traumatic, less expensive and better tolerated. This is especially significant considering that between 80% and 90% of suspicious nonpalpable breast lesions are benign.
The recent addition of stereotactic technology further enhances the needle biopsy procedure. Because it permits clinicians to identify a lesion in three dimensions, stereotactic guidance increases the possibility that the abnormality will be accurately located and sampled.
As a member of the SBB team, the mammographer plays an important role in positioning the patient, determining the abnormality's coordinates within the breast, imaging the abnormality prior to and following the biopsy procedure, and communicating with the patient throughout the procedure. A solid understanding of all aspects of the stereotactic biopsy procedure makes the mammographer a more valuable member of the SBB team.
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Julliana Newman, B.A., ELS, is a certified editor of the life sciences and a medical writer for the American Society of Radiologic Technologists. She has more than 14 years of experience as a medical writer/editor. She has served as managing editor and editorial director for several national medical journals and is the founder of the Journal of Outcomes Management.
Reprint requests may be sent to the American Society of Radiologic Technologists, Publications Department, 15000 Central Ave. SE, Albuquerque, NM 87123-3917. [C] 1996 by the American Society of Radiologic Technologists.
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|Title Annotation:||includes continuing education quiz|
|Date:||Nov 1, 1996|
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