Stereotactic biopsy systems offer radiologists the ability to target alesion discovered during mammography, to accurately place a needle into itscenter, and to remove tissue samplings for histologic examination. With suchsystems, images are acquired using conventional mammographic imaging orcomputerized digital image acquisition. Percutaneous breast biopsy offers manyadvantages over surgical biopsy for a suspicious lesion in the breast. Withstereotactic biopsy, the patient has an opportunity for a less costly, lessinvasive, and more cosmetically acceptable procedure than she has withexcisional biopsy.

The two basic designs of stereotactic breast biopsy machines are dedicatedprone units (tables) and upright add-on units. With dedicated tables, thepatient lies prone on the table; the affected breast is suspended through anaperture in the table and is positioned against an image receptor. This type ofbreast biopsy system enables the stereotactic core biopsy team to perform theprocedure beneath the table, out of the patient's view (figure 1). Withupright add-on units, a stereotactic biopsy unit is added to a standardmammographic unit, converting it to a stereotactic biopsy system. Thisequipment allows the biopsy to be performed while the patient is seated orlying in the lateral decubitus position (figure 2).

Similarities

Both types of biopsy units share the unique advantage of giving a largepercentage of women with suspicious mammograms an alternative to a traditionalsurgical or excisional biopsy. Advantages of stereotactic core biopsy includeaccurate tissue sampling from the region of interest1,2 (necessary for adefinitive benign or malignant diagnosis), elimination of the need for generalanesthesia (as is often used in excisional biopsies), and elimination ofoperating room costs associated with traditional biopsy. The procedure providesaesthetically pleasing cosmetic results (dermatotomy of one-eighth toone-fourth inch) with avoidance of surgery when the pathologic findings of abenign lesion and mammographic interpretation are in concordance. Otheradvantages include a time efficient procedure in which the invasive trauma tothe breast is minimized, and little to no appreciable post-procedure change inthe mammographic appearance of the breast.

Both types of biopsy units require daily and/or pre-procedure calibration,with recommendations for strict adherence to the calibration process and itsguidelines (figure 3). Several prone table and upright stereotactic biopsysystems are available with digital acquisition capabilities. These units,equipped with computer acquisition features and digital displays, allow nearlyreal-time visualization of stereotactic images, thereby eliminating the needfor conventional film processing and its associated wait time. Digital systemsoffer image enhancement via a variety of post-processing tools. The mostcommonly used tools ("zoom", "magnification", and"image inversion") (figure 4) enhance the radiologist's abilityto visualize and target microcalcifications.

Regardless of the type of biopsy system used, difficulty in thevisualization of certain ill-defined areas of architectural distortion, lowdensity lesions, masses with ill-defined borders, and vague microcalcificationsmay prevail on some computer-acquired stereotactic images. Therefore,conventional mammographic film processing may be necessary to better definethese types of lesions stereotactically.

Both units are equipped with compression paddles which immobilize the breastfor the duration of the procedure. Each also accepts variations of automatedspring loaded biopsy guns and sampling needles. Most units offer a 360°biopsy access to either breast (depending upon the orientation of the breastand the image receptor), and both types offer percutaneous breast procedureoptions of:

1) wire localization,

2) fine needle aspiration biopsy, and

3) needle core biopsy.

While uniquely similar in the broad advantage of offering an alternativeapproach to surgical breast biopsies for many women, each type of unit iscontrasted with distinct differences in cost, necessity of floor space, lesionvisualization, and variations in the level of patient positioning challenges.

Prone table pros

Because prone tables support the patient above the area in which theradiologist is working, some patients, and radiologists alike, feel that thepatient's anxiety level may be minimized by her inability to observe theprocedure in progress, thus maximizing her tolerance of the procedure. Also,because of the prone position, vasovagal reactions are unlikely to occur. Theamount of working space between the breast and tube is attractive and allowsthe stereotactic biopsy team to work with comfort and ease. The advantage of ac-arm/image receptor located beneath the surface of the table is that itgenerally allows for quick and easy lesion positioning within the imagingaperture without physically moving the patient (figure 5). The basic design ofthe prone tables enables the unaffected breast to be positioned away from theimage receptor, creating little to no interference with imaging during biopsy.

At present, vacuum-assisted biopsy devices generally are more associatedwith and adaptable to the prone units than the add-on units. Thesevacuum-assisted devices have proven to be particularly successful in thesampling of microcalcifications and in maximizing the quantity of tissuesampled.3 As prone biopsy units are usually accessory units to most mammographydepartments, the confirmation of microcalcifications in the sample is obtainedwith a standard diagnostic mammographic unit or a dedicated specimen imagingunit. This eliminates the need to move the patient from the prone table to usethe machine for imaging of the tissue samples.

Lesions located in the inferior aspect of the breast traditionally have beenconsidered positioning challenges for both wire localization and percutaneousbreast biopsy procedures. However, with the use of the prone table, easy accessto the inferior aspect of the breast is afforded. Because of the relationshipbetween the surface of the breast and the image receptor beneath the table,most lesions in this region can be visualized with quickness and ease. However,one exception is in a very posterior inferior lesion, as it is difficult topull the breast down enough to keep this lesion within the aperture for biopsy.

A medial lesion also can be easily approached from the medial breast surfacewith the patient on the prone biopsy table. There is no need for taping theopposite breast back to keep it out of the x-ray field. Instead, the oppositebreast is beneath the patient as she is lying on the table.

Prone table cons

In comparison with add-on units, the cost of a prone table is greater. Pronetables usually require a dedicated room because of the floor space necessaryfor installation. Some tables are equipped with height adjustments and,subsequently, have manufacturer recommended weight limitations. Theselimitations may be prohibitive in scheduling some patients for stereotacticbreast procedures.

Breast size and body habitus also play an important role in patientpositioning and lesion visualization on the prone units. This is especiallyprevalent in patients with small breasts and/or large, rotund abdomens. Suchconditions often prohibit the technologist from pulling sufficient breasttissue through the aperture of the table and onto the image receptor below.

When using the prone table, the stereotactic core biopsy team is oftenchallenged in their ability to visualize very posterior lesions and lesionsthat are located deep in the axillary tail of the breast. These challengesescalate with small breast size and/or large body habitus. The inability tovisualize and/or maintain the position of these posteriorly located lesionswithin the aperture for the duration of the procedure may result inunsuccessful biopsy and necessary cancellation of the procedure.

Patients with a tracheostomy, those with debilitative conditions (kyphosis,severe arthritis), emphysema, or dyspnea from congestive heart failure, orthose who have undergone recent surgery (joint replacement, abdominal,thoracic, cervical) may experience difficulty in getting onto the table or inlying prone for the biopsy.

As a result of the height of some tables, patients may experience a feelingof isolation from the stereotactic biopsy team and may require frequent visualand/or verbal interactions from a member of the team. It is important tomaintain clear verbal communication with the patient throughout the procedurein order to reduce her anxiety and sense of isolation.

Add-on units pros

Add-on upright biopsy units are attractively priced when compared to proneunits. The add-on units are multi-use and allow for screening/diagnosticmammographic imaging when stereotactic procedures are not in progress. Theseunits are small, require minimal storage space, and are very attractive tofacilities where the limitation of floor space is a factor.

The flexibility of these units increases the possibility of a successfulbiopsy procedure when the stereotactic biopsy team is challenged by breastsize, body habitus, patient condition, and/or lesion location. In addition,patient weight and body habitus are not primary factors when schedulingprocedures on the add-on biopsy units. The versatile design of such unitsallows creativity in positioning patients with debilitative conditions andfacilitates the movement and positioning of those who are wheelchair bound.

When stereotactic procedures are performed on the upright unit, optimalpatient/lesion positioning can be achieved when a "chair/bed" is used(because of the design of these units, the traditional stretcher is notacceptable). The chair/bed should be medium sized, comfortable, and be equippedwith height adjustments. These features optimize patient comfort and maximizemaneuverability in patient positioning and lesion capture. With the utilizationof this type of patient support device, 360° access to either breast can beobtained by having the patient seated or lying in a lateral decubitus position;patients with sensitive areas (due to recent joint replacement, abdominaland/or thoracic surgery, etc.) are often more comfortable when placed in thelateral decubitus position (figure 6).

The versatility of the add-on unit, the availability of flexibility inpatient-to-machine orientation, and the use of the chair/bed enhances thestereotactic biopsy team's ability to visualize and maintain lesionposition. Posterior lateral and posterior medial lesions are best visualizedwith the patient lying in the lateral decubitus position.

In the laterally approached lesion, especially those located deep in theaxillary tail of the breast, a slight rolling of the patient forward from thelateral decubitus position aids in bringing the lesion into the field of viewand maintaining its position during biopsy.

Positioning of the breast in patients with breast implants is more easilyaccomplished with the add-on units. This is mostly because of thetechnologist's ability to position the breast for the implant displacedview4 in the same manner in which the breast is imaged during mammographicexamination (figure 7). The patient may experience less discomfort and stressto the opposite breast by sitting erect or lying in the lateral decubitusposition.

Add-on unit cons

Some patients and radiologists feel the most apparent disadvantages of theupright biopsy unit are that the patient is subjected to viewing the procedurewhen she is in the sitting position, and the possibility of vasovagal episodesassociated with patient anxiety. Another disadvantage is the limited workingspace between the biopsy gun and the patient's head when the superiorapproach is used. There is also less working space between the aperture and thetube than there is with the prone table; however, this is usually notproblematic unless the patient's breast is very thick. Due to thenecessary angling of the head and neck for the biopsy from the superior aspectof the breast, the patient may be unable to remain still for the duration ofthe procedure when the lesion is located very posteriorly. An alternateapproach should be considered during the pre-procedure case review whensuperior access is planned for biopsy of such a lesion.

Visualization of the medially approached lesion is more challenging than thesuperior or lateral lesions and may require taping the unaffected breast awayfrom the field of view and placing the patient's opposite arm by her side.The use of tape eliminates the need for the patient's assistance inholding the unaffected breast away from the field of view during biopsy.Inferior lesions may prove more challenging to position with the add-on units,but usually can be biopsied. With the patient lying on a decubitus board, or asimulation thereof, inferior lesion capture can be achieved with minimal medialor lateral exaggeration of the breast tissue. This patient clevation alsoallows adequate space for the stereotactic movement of the cassette holder andx-ray tube.

Patient considerations for biopsy

Both types of biopsy units share a unique similarity in their need forcareful patient and lesion selection. With each type of unit, thepatient's tolerance of the procedure due to possible physical discomfortand anxiety must be considered. In a prospective randomized study of 103 womenwho had biopsies performed in either the prone or sitting position, Helbich etal5 found no difference in overall tolerance of the procedure using eithermethod. However, significantly more of those patients biopsied in the proneposition indicated a preference for premedication for repeat biopsy. Of thetotal patient group, one patient fainted in the prone position and two faintedin the upright position.5

If a suspicious lesion persists after a complete mammographic work-up (toinclude ultrasound, if indicated), the lesion still may not be ideally suitedto core biopsy. These lesions include those that are difficult to visualize andthose that are problematic for diagnosis. Examples of such lesions are faintmicrocalcifications, poorly defined low densities, and areas of architecturaldistortion.

Typically, indistinct densities, lesions with ill-defined borders, and thosewith very fine, scattered microcalcifications may be difficult to visualizestereotactically. Areas of architectural distortion, which may represent aradial scar, can be problematic when trying to obtain correct histologicdiagnosis by needle biopsy.6 Needle localization and excisional biopsy is thepreferred management method for these types of lesions. Posterior lesions,lesions deep in the axillary tail of the breast, and lesions near the areolamay be difficult to capture and maintain in the aperture for stereotacticbiopsy. Superficial lesions may not provide enough skin-to-lesion distance forthe sampling notch of the needle. In these cases, ultrasound guidance may bepreferable. A breast that compresses to less than 2.5 to 3.0 cm may not provideadequate distance to accommodate the throw of the needle. In this case, needlelocalization and excisional biopsy may be necessary for diagnosis.

Regardless of the type of unit used, sampling errors can occur. The mostcommon of sampling errors may result from 1) inadequate calibration of thebiopsy unit, 2) patient motion during the procedure, 3) improper lesiontargeting, 4) lesion movement at the sampling attempt, and 5) malfunction ofthe sampling apparatus (needle and/or gun).

Certain pathologic findings prompt excision following core biopsy. In theevent of pathological findings of atypical hyperplasia, possible phylloidestumor, or a diagnosis of cancer, surgical excision should be performed.7,8Also, if the specimen is insufficient (i.e. fat only or no microcalcificationswhen calcifications were biopsied) or if mammographic and histologic findingsare non-concordant, excision should be performed.

Conclusion

Both types of stereotactic units, namely add-on devices to mammographicunits and prone tables, demonstrate many similarities regarding percutaneousbiopsy procedures. Many of these similarities relate to the types of lesionsbiopsied and the outcomes of the pathologic findings. Differences are mostevident in the equipment choices based on the location of the lesion andspecial patient factors. There are advantages and disadvantages to each type ofunit, and the opportunity to use both types allows for greater flexibility inlesion and patient selection for stereotaxis. AR

Acknowledgement

The authors gratefully acknowledge the assistance of Ms. LouiseLogan and Ms. Susan Ross in the preparation of the manuscript.

References

1. Parker SH, Burbank F, Jackman RJ, et al: Percutaneous large-core breastbiopsy: a multi-institutional study. Radiology 183:359-364, 1994.

2. Elvecrog EL, Lechner MC, Nelson MT: Nonpalpable breast lesions:Correlations of stereotactic large-core needle biopsy and surgical biopsyresults. Radiology 188:453-455, 1993.

3. Burbank F: Stereotactic breast biopsy of atypical ductal hyperplasia andductal carcinoma in situ lesions: Improved accuracy with directional, vacuumassisted biopsy. Radiology 202:843-847, 1997.

4. Eklund GW, Busby RC, Miller SH, Job TS: Improved imaging of the augmentedbreasts. AJR 151:469-473, 1988.

5. Helbich TH, Dantendorfer K, Mostbeck GH, et al: Randomized comparison ofsitting and prone positions for stereotactic fine-needle aspiration breastbiopsy. Br J Surg 83:1252-1255, 1996.

6. Frouge C, Tristant H, Guinebretiere J-M, et al: Percutaneous large-corebreast biopsy: a multi-institutional study. Radiology 183:359-364, 1994.

7. Liberman L, Cohen MA, Dershaw DD, et al: Atypical ductal hyperplasiadiagnosed at stereotactic core biopsy of breast lesions: an indication forsurgical biopsy. AJR 164:1111-1113, 1995.

8. Jackman RJ, Nowels KW, Shepard MJ, et al: Stereotaxic large-core needlebiopsy of 450 nonpalpable breast lesions with surgical correlation in lesionswith cancer or atypical hyperplasia. Radiology 193:91-95, 1994.

Ms. Cousins and Ms. Wayland are mammography specialists at theMedical College of Virginia of Virginia Commonwealth University in Richmond,where Dr. deParedes is Professor of Radiology and Director of Breast Imaging;she is also a member of the editorial advisory board of this journal.