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1 Department of Radiology, Breast Imaging Section, Memorial Sloan-Kettering
Cancer Center, 1275 York Ave., New York, NY 10021.
2 Department of Surgery, Memorial Sloan-Kettering Cancer Center, New York, NY
10021.
3 Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, NY
10021.
Received March 18, 2003;
accepted after revision May 28, 2003.
Address correspondence to L. Liberman
(libermal{at}mskcc.org).
Abstract
 Top Abstract IntroductionSubjects and MethodsResultsDiscussionReferences |
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SUBJECTS AND METHODS. Twenty women scheduled for MRI-guided needle localization and surgical biopsy were prospectively entered in the study. MRI-guided biopsy was performed with a vacuum-assisted probe, followed by placement of a localizing clip, and then needle localization for surgical excision. Vacuum-assisted biopsy and surgical histology were correlated.
RESULTS. Vacuum-assisted biopsy was successfully performed in 19 (95%) of the 20 women. The median size of 27 MRI-detected lesions that had biopsy was 1.0 cm (range, 0.4–6.4 cm). Cancer was present in eight (30%) of 27 lesions and in six (32%) of 19 women; among these eight cancers, five were infiltrating and three were ductal carcinoma in situ (DCIS). Among these 27 lesions, histology was benign at vacuum-assisted biopsy and at surgery in 19 (70%), cancer at vacuum-assisted biopsy in six (22%), atypical ductal hyperplasia at vacuum-assisted biopsy and DCIS at surgery in one (4%), and benign at vacuum-assisted biopsy with surgery showing microscopic DCIS that was occult at MRI in one (4%). The median time to perform vacuum-assisted biopsy of a single lesion was 35 min (mean, 35 min; range, 24–48 min). Placement of a localizing clip, attempted in 26 lesions, was successful in 25 (96%) of 26, and the clip was retrieved on specimen radiography in 22 (96%) of 23. One complication occurred: a hematoma that resolved with compression.
CONCLUSION. MRI-guided vacuum-assisted biopsy is a fast, safe, and accurate alternative to surgical biopsy for breast lesions detected on MRI.
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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For MRI-detected lesions that can be seen on sonography, biopsy can be performed under sonographic guidance. However, "second-look" sonography fails to identify a sonographic correlate in up to 77% of MRI-detected lesions referred for biopsy [5–7]. Although the frequency of cancer is higher among MRI-detected lesions that have sonographic correlates as compared with those that do not (43% vs 14%, p = 0.01), suspicious MRI-detected lesions that lack sonographic correlates also warrant biopsy [7]. The utility of breast MRI is dependent on the availability of methods to perform biopsy of lesions detected on MRI only.
MRI-guided breast biopsy is a challenging endeavor because of the requirement for specific MRI-compatible equipment, the need to remove the patient from the magnet to perform the biopsy, limited access to the medial and posterior breast, decreasing lesion conspicuity during the procedure (the "vanishing" target), needle artifact obscuring the lesion site, desirability of placing a localizing clip, and limitations in confirming lesion retrieval [8]. In spite of these challenges, investigators have reported clinical experience with MRI-guided needle localization for surgical excision [4, 9–18] and MRI-guided percutaneous biopsy using a fine needle [11, 15, 19–21], automated core needle [12, 15, 22–24], or vacuum-assisted biopsy probe [25–29]. This study was performed to evaluate a new method for performing MRI-guided vacuum-assisted breast biopsy in a study of lesions that had subsequent surgical excision.
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Patient Selection
Twenty women scheduled for MRI-guided needle localization and surgical
excision were prospectively asked to participate in this study. A woman was
invited to participate in the study if she was scheduled for MRI-guided needle
localization of a nonpalpable mammographically occult lesion, if she had
undergone diagnostic breast MRI at our institution for screening of women who
are at high risk for breast cancer or for extent of disease assessment, if
logistics (staffing, magnet time, and operating room schedules) allowed the
biopsy to be performed on the day of her surgery, and if her surgeon approved
her participation.
Of 98 consecutive women who had MRI-guided needle localization during the study period, 27 were invited to participate in the study, and 20 agreed to be included. The median age of these 20 women was 51 years (range, 19–64 years). The indication for breast MRI in these 20 women was assessment of disease extent in women with known cancer diagnosed within 6 months of breast MRI in 10 and screening of women who are at high-risk for breast cancer in 10. The protocol for this study was approved by our institutional review board.
Directed sonography failed to show a sonographic correlate to the MRI findings in 14 of the 20 women. In the remaining six women, directed sonography was not performed at the discretion of the interpreting radiologist and treating clinician. One woman at high risk for breast cancer who was 19 years old did not have a mammogram; in the remaining 19 women, mammographic parenchymal density [30] was class 4 (dense) in one, class 3 (heterogeneously dense) in 14, and class 2 (scattered fibroglandular densities) in four.
Breast MRI Technique and Interpretation
At our institution, diagnostic breast MRI examinations were performed with
the patient prone in a 1.5-T commercially available system (Signa, General
Electric Medical Systems, Milwaukee, WI) using a dedicated surface breast
coil. Our imaging protocol includes a localizing sequence followed by a
sagittal fat-suppressed T2-weighted sequence (TR/TE, 4,000/85). A T1-weighted
3D fat-suppressed fast spoiled gradient-echo sequence (17/2.4; flip angle,
35°; bandwidth, 31.25 MHz) was then performed before and three times after
a rapid bolus injection of 0.1 mmol/L of gadopentetate dimeglumine (Magnevist,
Berlex, Wayne, NJ) per kilogram of body weight, delivered through an
indwelling IV catheter.
Image acquisition started after injection of contrast material and saline bolus. Images were obtained sagittally, for an acquisition time per volumetric acquisition of less than 3 min each. Total imaging time per breast, including three contrast-enhanced acquisitions, was approximately 20 min. Section thickness was between 2 and 3 mm without a gap using a matrix of 256 x 192 and a field of view of 18–22 cm. Frequency was in the anteroposterior direction. After the examination, the unenhanced images were subtracted from the first contrast-enhanced images on a pixel-by-pixel basis.
In our practice, breast MRI examinations were interpreted by breast imaging specialists in conjunction with clinical history and other breast imaging studies, including mammograms and sonograms when available, using previously described criteria [31].
MRI-Guided Vacuum-Assisted Biopsy Technique
Informed consent, preparation before the biopsy, biopsy equipment, and
radiologists.—Informed consent was obtained for all biopsy and
needle localization procedures. Although no anxiolytic medication was
administered IV, patients were pretreated as needed with oral benzodiazepines
such as diazepam (Valium [one or two 5-mg doses], Roche Pharmaceuticals,
Manatí, PR) or lorazepam (Ativan [one or two 0.5-mg doses],
Wyeth-Ayerst Laboratories, Philadelphia, PA) on the morning of the procedure,
as discussed with the referring clinician.
Biopsies were performed with a commercially available 9-gauge vacuum-assisted MRI-compatible biopsy system (ATEC Breast Biopsy System, Suros Surgical Systems, Indianapolis, IN) (Fig. 1A) by one of three attending radiologists specializing in breast imaging. Before participating in this study, these three radiologists had performed an average of 99 MRI-guided needle localization procedures (range, 89–119) and an average of 335 stereotactic 11-gauge vacuum-assisted breast biopsies (range, 311–364).
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Targeting images.—The patient was positioned prone with both breasts in a dedicated surface breast coil (Open Breast Array Coil, model OBC, MRI Devices, Waukesha, WI). The breast undergoing localization was placed in a dedicated biopsy compression device using a commercially available grid-localizing system (Biopsy Positioning Device, model MR-BI-160, MRI Devices) or a slightly modified design of the commercially available model. A vitamin E marker was placed over the expected lesion site (Fig. 1B).
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An axial localizing T1-weighted sequence was performed, and the volume of interest was selected to include the compression device and a vitamin E marker placed over the expected lesion site. Gadopentetate dimeglumine, 0.1 mmol/L per kilogram of body weight, was injected IV as a rapid bolus injection through an indwelling IV catheter, and acquisition of sagittal images (3-mm slice thickness) started immediately after contrast injection. Time of acquisition, usually less than 1 min, varied with breast size and area covered. The patient was then withdrawn from the magnet with her breast remaining in compression.
Determining lesion location and desired depth of probe insertion.—After images were reviewed at the console, a cursor was placed over the lesion on the monitor. The horizontal (x-axis) and vertical (y-axis) coordinates of the lesion were determined on the basis of the spatial relationship between the lesion, vitamin E marker, and grid lines. The depth (z-axis) coordinate of the lesion was determined on the basis of the relationship between the lesion and the skin surface.
The skin surface was identified as the slice on which the indentations from the grid were evident as low-signal-intensity lines. The depth of the lesion from the skin surface in millimeters (z) was calculated by determining the number of sagittal slices between the skin and the lesion and multiplying by 3 (to account for the 3-mm slice thickness). The depth of the skin surface from the outer aspect of the needle guide was 20 mm (because the needle guide was 2-cm thick). Therefore, the desired depth of insertion of the center of the collecting area (the "mouth") of the vacuum-assisted biopsy probe from the outer aspect of the needle guide (in millimeters) was 20 plus z, where z was the calculated depth of the lesion (in millimeters) from the skin surface.
Preparing the probe.—The clear obturator was placed inside the white introducer, and the depth stop was set so that it was the appropriate distance from the tip of the clear obturator. For example, if the lesion was 30 mm deep in relation to the skin, the desired distance from the tip of the obturator to the depth stop was 50 mm (30 + 20 = 50 mm). The obturator was not placed inside the patient at this point, but rather measured to determine where to set the depth stop (Fig. 1C). The clear obturator was then removed from the white introducer, and the sharp stylet was placed inside the white introducer as far as it could go (Fig. 1D).
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Placing the device and imaging to confirm its location.—A mark was made on the skin overlying the lesion, and the skin was cleansed with alcohol and anesthetized with 3–8 mL of 1% lidocaine hydrochloride (Xylocaine [10 mg/mL], AstraZeneca, Wilmington, DE). Deep anesthesia was provided by injecting 10–20 mL of 1% lidocaine hydrochloride (Xylocaine [10 mg/mL], AstraZeneca) with epinephrine 1:100,000. A skin nick was made with a scalpel. The stylet was placed in the incision until the white plastic introducer entered the skin (to create the tract) and was then removed.
The needle guide was oriented so that one of the holes would be in the appropriate location. The stylet was then placed through the needle guide in the appropriate orientation with the tip protruding only slightly from the far side of the needle guide, and the tip of the stylet was placed in the skin at the site of the scalpel incision before attaching the needle guide to the grid. This procedure helped to ensure that the biopsy device entered through the incision site, even when that site was later obscured by the needle guide. A twisting motion was helpful when advancing the stylet. The stylet was advanced to the depth stop (Fig. 1E).
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The stylet was removed, and the clear obturator was placed inside the white plastic introducer to assist in MRI confirmation of location. The tray with the stylet was removed from the room before MRI was performed. A sagittal T1-weighted MRI study (3-mm slice thickness) was then performed to document the location of the obturator, with the ideal location of the tip of the obturator being at the site of the lesion.
If the obturator was superficial in relation to the lesion, the obturator was removed, leaving the introducer in place. The stylet was placed inside the introducer, advanced to the appropriate depth, and then removed, with the introducer remaining in position. Alternatively, if the obturator was deep in relation to the lesion, the obturator and introducer were simply pulled back to the appropriate depth.
Performing the biopsy, obtaining postexamination images, and collecting the specimens.—After appropriate positioning was confirmed on MRI, the obturator was removed and the biopsy device was inserted (Fig. 1F). When the biopsy device was fully inserted into the white introducer, the center of the mouth was positioned where the tip of the obturator had been. The control module was outside the MRI scanner; only the foot pedal and biopsy device came into the room with the magnet. The direction of tissue acquisition was chosen on the basis of the location of the introducer with respect to the lesion. The protocol was to obtain at least six specimens. Tissue was acquired by stepping on the foot pedal. A beep was heard each time a specimen was acquired. The direction of tissue acquisition was determined by the radiologist performing the biopsy by turning the arrow on the biopsy probe in the desired direction.
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After tissue acquisition was complete, the biopsy device was removed, the obturator was reinserted, and sagittal T1-weighted images (3-mm slice thickness), the postexamination images, were obtained to assess the completeness of tissue acquisition. While the postexamination images were being acquired, the technologist retrieved the samples from the collecting chamber and placed them in formalin.
Placing the clip.—The localizing clip (MammoMark Biopsy Site
Marker, Artemis Medical, Hayward, CA) was a titanium clip attached to a
resorbable collagen pledget. In preparation for clip placement, the blue
tubing was peeled off the biopsy handpiece, and the front end of the probe
(the portion with the mouth) was separated from the hand-piece portion. The
front end of the probe was placed back into the introducer. The clip was then
placed inside the probe as far as it would go
(Fig. 1G). Resistance was felt
when the clip touched the end of the "mouth," indicating that it
had reached the appropriate depth. The clip introducer was then pulled back
slightly (
2 mm), and the clip was deployed by pushing down on the handle.
The clip introducer was turned 180° and removed, the biopsy handpiece was
removed and inspected to make sure that the clip had not been retained in the
mouth, and the introducer was removed. A sagittal T1-weighted MRI study (3-mm
slice thickness) was then performed.
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MRI-guided needle localization.—After MRI-guided vacuum-assisted biopsy and clip placement had been completed, MRI-guided needle localization was performed using previously described methods [17] with an MRI-compatible hookwire (MReye Modified Kopans Spring Hook Localization Needle [20-gauge], Cook, Bloomington, IN). The protocol called for a two-view mammogram after localization to document the location of the localizing wire and clip, which was sent with the patient for use during surgery, and for specimen radiography to confirm retrieval of the clip.
Data Collection and Analysis
The time of the biopsy, in minutes, was determined by calculating the
interval between the beginning of the MRI localizing sequence and the end of
the final MRI sequence performed after clip deployment. After the biopsy
device was placed, the time of each round of tissue acquisition was
determined, in seconds, by calculating the interval between stepping on the
foot pedal to begin to acquire tissue and releasing the foot pedal at the
completion of tissue acquisition, including any interval injection of
anesthesia.
The radiologist performing the biopsy reviewed MRIs obtained during and after biopsy to determine the presence and extent of postbiopsy changes (e.g., hematoma or air); to assess whether the MRI target was sampled or possibly excised; and to evaluate whether the localizing clip was visible, noting any problems with visualization of the clip. The radiologist reviewed the postbiopsy mammogram to assess for air, hematoma, or both; to assess whether the clip was identified; and to calculate the maximum distance between the clip and the localizing wire. The radiologist also reviewed the specimen radiograph to determine whether the clip was retrieved at surgery.
Histologic results of vacuum-assisted biopsy and surgical excision were reviewed and correlated. A lesion was considered to be cancer if cancer was found at vacuum-assisted biopsy, surgical excision, or both. A false-negative finding was defined as a lesion yielding benign results without atypia at vacuum-assisted biopsy and cancer at surgery. Data were entered into a computerized spreadsheet (Excel, Microsoft, Redmond, WA) for analysis.
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Lesions
Twenty-seven lesions underwent biopsy in 19 women having a median age of 51
years (range, 19–64 years). Single lesions in 11 women underwent biopsy
and two lesions in eight women underwent biopsy. The median size of these 27
lesions was 1.0 cm (range, 0.4–6.4 cm). Seventeen were mass lesions and
10 were non–mass lesions. Among these 27 lesions, quadrant location was
upper outer quadrant in 11, lower outer quadrant in 11, upper inner quadrant
in four, and lower inner quadrant in one. Two lesions were posterior to the
biopsy compression grid.
A separate skin incision was made for each lesion that underwent biopsy. For 26 (96%) of the 27 lesions, a single skin incision was made; for one lesion, a second incision was required for repositioning the stylet before biopsy. For the two lesions that were posterior to the grid, the skin incisions were made as close to the lesions as possible, posteriorly within the grid, and suction was applied in the posterior direction to acquire tissue.
Biopsy Specimens
The median number of specimens obtained per lesion was eight (range,
6–14). In 23 lesions, only a single round of tissue acquisition was
necessary; in four lesions, MRI after the first round of tissue acquisition
did not ensure lesion sampling, and a second round of tissue acquisition was
performed.
Clip Deployment
Clip placement was attempted in 26 lesions and was successful in 25 (96%)
of 26. One woman declined placement of a clip. The initial attempt at clip
placement was successful in 20 (77%) of 26 lesions, and a second attempt was
successful in five (19%) of 26 lesions; in one lesion (4%), clip placement
failed in spite of two attempts. In all instances of unsuccessful clip
deployment, the collagen pledget was visible in the mouth of the biopsy
handpiece after its removal; therefore, failure of clip deployment was
immediately apparent to the radiologist performing the biopsy.
Time to Perform Biopsy
The median time to perform MRI-guided vacuum-assisted biopsy, from the
original axial localizing images to the final images obtained after clip
deployment, was 35 min (mean, 35 min; range, 24–48 min) for a single
lesion and 65 min (mean, 69 min; range, 62–86 min) for two lesions. The
median time for a round of tissue acquisition was 38 sec (mean, 41 sec; range,
29–87 sec).
MRI Review
The obturator was identified on MRI as a low-signal focus measuring a
median of 0.3 cm (range, 0.2–0.6 cm) in width. MRI sequences performed
after completion of tissue acquisition were reviewed for 26 lesions; in one
lesion these images were not available because of magnet malfunction.
Postbiopsy collections of air (n = 5), fluid (n = 5), or
both (n = 16) measuring a median of 1.9 cm (range, 0.6–3.2 cm)
were observed on MRI in all lesions. The imaging target was sampled in 14
(54%) and possibly was excised in 12 (46%); none of the targets was
missed.
MRI was performed after clip deployment in 24 lesions; in one woman with two lesions, MRI was not performed after clip deployment because of magnet malfunction. The clip was evident as a low-signal focus measuring a median of 0.6 mm (range, 0.4–0.6 mm). In four (17%) of 24 lesions the radiologist noted that differentiating the clip from low-signal foci representing air was difficult, but could be accomplished by comparing images before and after clip placement.
Review of Mammograms Obtained After Biopsy
Mammograms obtained after biopsy in 26 lesions showed hematoma and air in
14 lesions (54%) and air without hematoma in 10 lesions (38%); in two lesions
(8%), change due to biopsy was not visible on the mammogram. Among the 14
hematomas, eight were mammographic masses measuring a median of 2.3 cm (range,
1.5–3.0 cm), and six were more subtle increased density at the biopsy
site.
The median maximal distance from the clip to the localizing wire was 0.6 cm (range, 0.1–4.1 cm). The distance from the clip to the localizing wire was 1 cm or less in 19 (76%) of 25 lesions, 1.1 cm in three lesions (12%), and greater than 3 cm in three lesions (12%). In the latter three lesions, the distances from the clip to the wire were 3.4, 4.0, and 4.1 cm, respectively; all three clips were deep (medial) in relation to the localizing wires. In two of these three lesions, MRI review indicated that the clip had deployed deep in relation to the biopsy site; in the third, the clip was at the biopsy site, but the wire had migrated superficially, perhaps because it was not firmly anchored in the biopsy cavity.
Specimen Radiography
Specimen radiography, performed in 23 lesions in which the clip was placed,
confirmed retrieval of the localizing clip in 22 (96%). In one smooth mass
that yielded fibroadenoma at vacuum-assisted biopsy, a mammogram obtained
after biopsy showed that the clip was 4.0 cm deep (medial) in relation to the
lesion. Specimen radiography showed retrieval of the localizing wire, but the
clip was not identified. Surgical histologic analysis showed fibroadenoma,
other benign findings, and biopsy site changes.
Complications
A complication was encountered in one (4%) of 27 lesions and in one (5%) of
19 patients. The complication was a clinical hematoma, evident as swelling
with bluish discoloration immediately after biopsy. The mammogram obtained
after biopsy confirmed a 3-cm soft-tissue mass with air, consistent with the
clinically evident hematoma. The hematoma resolved with compression and did
not delay subsequent surgery.
Final Histology: Cancer
Cancer was found in eight (30%) of 27 lesions and in six (32%) of 19 women,
based on review of vacuum-assisted biopsy and surgical histology. The median
size of the MRI lesions in these eight cancers was 1.1 cm (range,
0.6–6.5 cm). Among these eight cancers, five were infiltrating cancer
(infiltrating ductal in two, infiltrating ductal and lobular in two, and
infiltrating lobular in one) and three were ductal carcinoma in situ (DCIS).
MRI review suggested that the MRI target may have been excised at
vacuum-assisted biopsy in three of these cancers (two DCIS and one
infiltrating lobular carcinoma) and was sampled at vacuum-assisted biopsy in
five.
Four of eight cancers were identified in women undergoing MRI for the assessment of disease extent (multifocal cancer in the ipsilateral breast in two, multicentric cancer in the ipsilateral breast in one, and contralateral cancer in one), and four were detected in women who are at high-risk for breast cancer undergoing MRI for screening. The four screening-detected cancers were in two women: one woman with bilateral breast cancer and one woman with multifocal invasive breast cancer. The median histologic size of infiltrating carcinoma was 0.8 cm (range, 0.2–1.5 cm).
Correlating Vacuum-Assisted Biopsy and Surgical Histology
Vacuum-assisted biopsy and surgical histology are correlated in
Table 1. Among these 27
lesions, histology was benign at vacuum-assisted biopsy and at surgery in 19
lesions (70%) (Fig. 2A,
2B,
2C,
2D,
2E,
2F,
2G,
2H,
2I), including one lesion that
yielded benign findings at vacuum-assisted biopsy and a microscopic focus of
atypical ductal hyperplasia at surgery.
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Cancer was found at vacuum-assisted biopsy in six (22%) of 27 lesions. In five of these six cancers, surgical excision confirmed the diagnosis of cancer. The sixth cancer was a 0.7-cm mass in which the imaging target may have been excised at MRI-guided vacuum-assisted biopsy, and histologic analysis of vacuum-assisted biopsy specimens yielded infiltrating lobular carcinoma; the surgical specimen showed fibrosis and changes related to prior biopsy, with no residual carcinoma (Fig. 3A, 3B, 3C).
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In one (4%) of the 27 lesions, a 5.0-cm non–mass lesion sampled at vacuum-assisted biopsy, vacuum-assisted biopsy histology revealed markedly atypical ductal hyperplasia and lobular carcinoma in situ (LCIS); surgical excision showed markedly atypical ductal hyperplasia focally reaching the level of low-grade cribriform DCIS, arising in a background of florid mammary sclerosing adenosis and columnar cell changes, as well as extensive LCIS (Fig. 4A, 4B).
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In one (4%) of the 27 lesions, a 0.4-cm smooth mass in a woman with Paget's disease of the nipple, MRI-guided vacuum-assisted biopsy yielded fibroadenoma and stromal fibrosis; MRI after vacuum-assisted biopsy showed that the MRI target may have been excised. A second lesion became increasingly hyperintense on delayed images and underwent MRI-guided needle localization without biopsy during the same procedure, yielding another fibroadenoma and stromal fibrosis at surgery. The nipple, which enhanced at MRI, was excised without localization and yielded DCIS. Surgical excision of the site that had vacuum-assisted biopsy showed a few scattered foci of DCIS with high nuclear grade at the anterior margin of resection (Fig. 5A, 5B, 5C).
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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MRI-guided vacuum-assisted biopsy, pioneered by Sylvia Heywang-Kobrunner, has advantages compared with other biopsy methods for the diagnosis of MRI-detected lesions [25]. Vacuum-assisted biopsy is faster, less invasive, and less expensive than surgery, and it causes no deformity [32]. Compared with fine-needle aspiration biopsy, vacuum-assisted biopsy has a higher technical success rate and fewer inadequate specimens [11, 15, 19–21]. Compared with automated core biopsy, vacuum-assisted biopsy retrieves a large volume of tissue, which can help compensate for decreasing lesion conspicuity during MRI-guided biopsy, and provides better characterization of lesions containing atypical ductal hyperplasia and DCIS [32]. Vacuum-assisted biopsy also facilitates placement of a clip that can be used for subsequent needle localization [33]. MRI-guided vacuum-assisted breast biopsy, which has been successfully performed in more than 500 lesions in Europe [29], was recently approved for use in the United States.
In our initial experience with a new method, the technical success rate of MRI-guided vacuum-assisted biopsy was 95%. In more than two thirds of the lesions (70%), both vacuum-assisted biopsy and surgery yielded benign results. The high proportion of benign lesions encountered emphasizes the potential benefit of MRI-guided vacuum-assisted biopsy, which may spare most women with MRI-detected lesions the need for surgical excision. Imaging–histologic correlation, essential after breast biopsy using any guidance method [34], is particularly important after MRI-guided biopsy because of the limitations of other methods to confirm lesion retrieval. Further work characterizing MRI patterns of specific benign and malignant lesions is necessary.
In approximately one quarter of lesions (23%), cancer was found at MRI-guided vacuum-assisted biopsy. Cancers diagnosed included multicentric, multifocal, or contralateral disease in women with proven cancer and cancers found at MRI screening of women at high risk for breast cancer. We hypothesize that the diagnosis of cancer by MRI-guided vacuum-assisted biopsy, like diagnosis of cancer by stereotactic or sonographically guided biopsy, will expedite patient management. Previous studies have shown that the likelihood of undergoing a single therapeutic operation is significantly higher in women with cancers diagnosed by percutaneous biopsy rather than surgical biopsy [32].
Histologic underestimation was observed in one lesion. In that instance, sampling of a large lesion with MRI-guided biopsy yielded markedly atypical ductal hyperplasia and LCIS, whereas subsequent surgical excision revealed DCIS. Underestimates have been encountered with every existing percutaneous biopsy method. The frequency of cancer at surgery is 20–56% for lesions yielding atypical ductal hyperplasia at 14-gauge automated core biopsy and 10–27% for lesions yielding atypical ductal hyperplasia at 11-gauge vacuum-assisted biopsy [32]. The diagnosis of atypical ductal hyperplasia at percutaneous biopsy is an indication for surgical excision [32]. Although it remains controversial, excision may also be warranted for lesions yielding LCIS at percutaneous biopsy [35]. High risk lesions such as atypical ductal hyperplasia and LCIS will very likely be more prevalent at percutaneous biopsy in women having breast MRI because they are at high risk for breast cancer than in the general population [36].
One false-negative case occurred in a woman with Paget's disease. MRI-guided biopsy of a smooth mass yielded fibroadenoma and fibrosis; surgery revealed microscopic DCIS. MRI review suggests that the MRI target may have been excised and that the microscopic DCIS in the surgical specimen was occult at MRI (Fig. 5A, 5B, 5C): the reported sensitivity of MRI for DCIS has ranged from 40% to 100% [37]. This case, therefore, may reflect a false-negative on the part of the MRI study rather than the biopsy procedure. False-negative results are a potential problem during any biopsy: reported false-negative rates are 0–8% for stereotactic 14-gauge automated core biopsy, 3% for stereotactic 11-gauge vacuum-assisted biopsy, and 0–8% for needle localization and surgical biopsy [38, 39].
MRI-guided vacuum-assisted biopsy can be performed quickly. The average time to perform biopsy of a single lesion was 35 min in our study. This time is faster than prior reports of MRI-guided needle biopsy: in the largest series to date, average time to perform biopsy was 60 min for MRI-guided fine-needle aspiration [11], 60 min for MRI-guided automated core biopsy [23], and 70 min for MRI-guided vacuum-assisted biopsy [28]. The vacuum-assisted biopsy device used in our study allows rapid acquisition of multiple specimens, deferring specimen collection until after tissue acquisition is complete. The ability to perform biopsy quickly should improve accuracy. Because lesion conspicuity usually diminishes with time after contrast injection, sampling is dependent on identification of the lesion immediately after injection and immobilizing the lesion so that it remains in the same position. The faster the biopsy is accomplished, the less likely that the lesion will move. A faster biopsy also enables increased throughput in the magnet and is more comfortable for the patient.
The vacuum-assisted biopsy device is helpful for biopsy of posterior lesions. Some posterior lesions cannot be captured within the biopsy grid, a problem that can also be encountered when performing stereotactic biopsy with the patient in the prone position [40]. We found that if the lesion was close to but posterior to the grid, we could position the probe adjacent to the lesion and use the suction to acquire tissue in the posterior direction, enabling us to obtain diagnostic material. Automated core biopsy requires that the needle traverse a lesion in order to sample it. The ability to position the vacuum-assisted biopsy device adjacent to the lesion and still acquire tissue from the lesion is another advantage of vacuum-assisted biopsy over automated core biopsy [32].
Thin breasts pose challenges for MRI-guided vacuum-assisted biopsy, as for stereotactic biopsy [40]. We injected a generous wheal of anesthetic to increase breast thickness. Other maneuvers described for stereotactic biopsy that may be useful for MRI-guided biopsy of thin breasts include extrinsic circumferential pressure on the breast and use of a reverse-compression paddle; with the latter method, when the probe is placed deep into the breast, it displaces the skin and subcutaneous tissues into the aperture on the side opposite the skin entry site without piercing the skin [40]. Immobilizing the breast without excessive compression may be helpful during MRI-guided biopsy to maximize breast thickness, avoid interfering with lesion enhancement [28], and minimize the "accordion effect" described with clip placement [33].
Placement of a localizing clip, attempted in 26 lesions, was successful in 96% and was within 1.1 cm of the lesion site in 88%. A clip can enable subsequent localization under the guidance of mammography (or sonography, if it is sonographically evident). We found that the clip produced such little artifact on MRI that it was sometimes difficult to distinguish from low-signal foci of air introduced during the biopsy. Perhaps use of a clip with more artifact or using different pulse sequences would help to assess clip location on MRI. However, the clip can be readily identified on mammography. Obtaining a two-view mammogram after biopsy is essential to assess location of the clip with respect to the biopsy cavity.
We encountered some difficulties with clip deployment, with a second attempt necessary in almost one quarter of the cases. In these cases, the clip and collagen pledget fell back into the mouth of the biopsy device and did not deploy in the breast. Our anecdotal impression is that turning the biopsy device so that it faces downward (6-o'clock position) during clip deployment, removing the clip's introducer after clip deployment, and then removing and inspecting the biopsy handpiece to ensure that the clip deployed were helpful. Further work is needed to optimize clip conspicuity on MRI and methods of clip deployment.
One complication was encountered, a hematoma that resolved with compression. The 9-gauge biopsy device used in this study is larger than the 11-gauge systems most commonly used for stereotactic biopsy. The biopsy cavity may therefore be larger, and ensuring hemostasis is important. Compression with ice after biopsy followed by a pressure dressing may be helpful in this regard.
In conclusion, our initial experience suggests that MRI-guided vacuum-assisted biopsy is a fast, safe, and accurate procedure. This method provides an alternative to surgery and to existing MRI-guided needle biopsy methods in clinical use for histologic diagnosis of MRI-detected lesions. Further work with more women is necessary, including optimization of equipment and techniques for biopsy and clip placement, potential use of long-acting contrast agents, imaging–histologic correlation, and long-term follow-up, so that we can offer women the benefits of MRI in detecting breast cancer while minimizing surgeries for lesions that are benign.
Acknowledgments
We thank the 20 women who enrolled in the study for making this work
possible. We also thank Charles Nyman and David C. Perlman for invaluable
assistance.
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