AJR 2003; 181:1295-1299
© American Roentgen Ray Society
Accuracy of a Collagen-Plug Biopsy Site Marking Device Deployed After Stereotactic Core Needle Breast Biopsy
Eric L. Rosen1,
Jay A. Baker and
Mary Scott Soo
1 All authors: Department of Radiology, Breast Imaging Division, Duke University
Medical Center, Box 3808, Durham, NC 27710.
Received January 29, 2003;
accepted after revision May 1, 2003.
Address correspondence to E. L. Rosen.
Abstract
OBJECTIVE. The goal of this study was to compare the accuracy of
clip placement of a collagen-plug biopsy marking device with that of the more
conventional, previously evaluated metallic tissue-marking clips.
SUBJECTS AND METHODS. The placement accuracy of 31 collagen-plug
marking devices was compared with the placement accuracy of 43 metallic marker
clips deployed at biopsies performed between August 1, 2002, and November 20,
2002. The precision of marker placement was assessed by determining the
position of the clip relative to the targeted mammographic lesion. Statistical
analysis comparing the distance from the clip to the targeted lesion was
performed.
RESULTS. Using a two-group Wilcoxon's rank sum test, we found the
clip-to-target distances for the collagen-plug central titanium marker were
significantly different from the clip-to-target distances of the conventional
metallic marker clips (p = 0.04). There were significantly fewer
cases in which the clip-to-target distance was 1 cm or greater on at least one
mammographic projection with the collagen-plug marker (5/31) than with the
conventional metallic marker clip (19/43) (chi-square test, p =
0.02).
CONCLUSION. The collagen-plug marking device is an effective
alternative to existing marker clips, and use of this device may result in
fewer cases in which the marker clip is substantially displaced (
1 cm)
away from the actual biopsy site.
Introduction
Metallic marker clips are frequently deployed after a stereotactic biopsy.
They are intended to mark the biopsy site when the biopsy target is not
visible after biopsy in case future localization is necessary. Prior reports
have shown that these clips tend to be displaced away from the biopsy site in
the z-axis when compression is released and mammograms after the
procedure are obtained. This phenomenon, called the "accordion
effect," is of concern because the amount of displacement can be several
centimeters away from the actual biopsy site and may hamper future
localization if further surgery is needed. The accordion effect has been
hypothesized to occur when the marker clip is deployed next to but not within
the biopsy cavity. This distance, although small when the patient's breast is
compressed, may become substantial when compression is released.
Recently, a new type of marker clip became clinically available. The
MammoMark (Artemis Medical, Hayward, CA) biopsy site identifier consists of a
titanium clip that is embedded centrally in a collagen plug (Fig.
1A,
1B,
1C). Instead of attaching to
the cavity wall, this clip was designed to be deployed directly into the
biopsy cavity. Once the clip is deployed, the collagen plug expands to fill
the biopsy cavity. Several possible advantages are associated with this type
of clip. First, deployment directly into the biopsy cavity may eliminate the
accordion effect phenomenon because the clip rests within the cavity and
should therefore correspond to the biopsy site when compression is released,
regardless of the imaging obliquity. Second, the collagen plug is
sonographically visible, so future localization can be performed with
sonography rather than mammography. Third, collagen has a hemostatic effect
and may result in decreased bleeding and hematoma formation.
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Fig. 1A. —MammoMark (Artemis Medical, Hayward, CA) biopsy site
identifier. Close-up photograph shows introducer of biopsy site marking device
contains collagen plug, which is introduced through biopsy probe and deployed
by depressing plunger.
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The goal of this study was to compare the accuracy of clip placement for
the MammoMark clip with that for the more conventional metallic marker clip
commonly deployed after stereotactic core needle breast biopsy.
Subjects and Methods
Between August 1, 2002, and November 20, 2002 (3 months 3 weeks), 105
consecutive patients were referred to our institution for stereotactic
vacuum-assisted breast biopsies of 114 mammographically suspicious lesions.
All biopsies were performed using a dedicated prone biopsy unit with digital
imaging (StereoGuide DSM, LoRad, Danbury, CT) and a vacuum-assisted biopsy
system with an 11-gauge biopsy probe (Mammotome, Ethicon Endo-Surgery,
Cincinnati, OH). A minimum of six specimens was obtained for each lesion. The
decision to obtain additional specimens was based on the size of the lesion,
results of specimen radiographs in cases of microcalcifications, and
evaluation of stereotactic images. After the biopsy, digital imaging of the
biopsy site was performed while the breast remained immobilized in compression
on the procedure table. These images were optimized to determine whether the
mammographic lesion had been excised. If the biopsied lesion was no longer
visible on the postprocedure images, a marker clip was placed at the
discretion of the radiologist performing the procedure.
In 93 of the 114 stereotactic vacuum-assisted biopsies, a tissue marker was
deployed at the conclusion of the biopsy to radiographically mark the location
of the biopsy. Of these 93 cases, 31 cases of collagenplug clip and 43 cases
of metallic clip deployment were available for review. During the study
period, the MammoMark clips were not always readily available; no selection
criteria were used to determine which type of clip was deployed. If a
collagen-plug marker clip was available, it was used. This collection of 74
cases constitutes our study population.
In all cases, the collagen-plug marker clip was positioned at the biopsy
site using the technique described in the instruction manual. The introducer
was advanced through the vacuum-assisted device probe until the black ring on
the introducer reached the edge of the collection chamber closest to the
breast. A mark on the introducer was then aligned with the thumb wheel of the
vacuum-assisted device probe, and the plunger was then pushed to deploy the
collagen plug. After clip placement, digital images were obtained to confirm
clip deployment by documenting the presence of the titanium clip. In addition,
final mammographic images were obtained in at least two projections
(craniocaudal and mediolateral oblique) to verify placement and the accuracy
of placement. If a prebiopsy mediolateral view was available, a corresponding
postbiopsy mediolateral projection was also obtained in addition to the
standard projections. If a discrepancy between the clip and the biopsy target
was present, it was typically recorded at the time of the biopsy in the
procedure report.
The mammograms obtained before and after biopsy from the 74 cases of
stereotactic breast biopsy with marker clip deployment were retrospectively
reviewed. Images obtained immediately after the biopsy were examined to
determine if the targeted lesion had been completely removed during needle
biopsy, if it was obscured by hematoma, or if it remained visible. The
precision of marker placement was assessed by determining the position of the
metallic marker clip relative to the targeted mammographic lesion. The
clip-to-target distance (defined as the distance from the center of the target
to the metallic marker clip) was measured in craniocaudal and mediolateral
oblique projections by two radiologists. Measurements were made by first
aligning the prebiopsy craniocaudal and mediolateral oblique images with the
corresponding postbiopsy images using parenchyma and soft-tissue landmarks
(e.g., the nipple and the pectoralis muscle). If the mammographic lesion was
identified on the postbiopsy images, a line was drawn from the center of the
targeted lesion to the clip and the distance was recorded. If the postbiopsy
images showed that the lesion was completely excised but the biopsy cavity
could be identified, the line was then drawn between the center of the biopsy
cavity and the titanium clip. Statistical analysis comparing the distance from
the clip to the targeted lesion was performed using a Student's t
test and the chi-square test.
Results
For the 31 cases in which the collagenplug device was deployed, the average
titanium clip-to-target distance was 5.1 mm based on measurements obtained
from two mammographic projections. The titanium clip was located 10 mm or more
from the target on at least one projection in five (16%) of 31 cases. Of the
five cases in which the titanium clip was more than 1 cm away from the
targeted lesion, the actual distances measured were 10, 18, 21, 29, and 47 mm.
There were no cases in which the titanium clip was 10 mm or more from the
target on both mammographic projections
(Table 1).
For the 43 cases in which a conventional metallic marker clip was deployed,
the average clip-to-target distance was 7.3 mm. The clip was located 1 cm or
more from the target in 19 (44%) of 43 cases. In three cases, the clip was
more than 1 cm from the target on both mammographic projections.
Analysis of the data with a two-group Wilcoxon's rank sum test, revealed a
statistically significant (p = 0.04) difference between the
clip-to-target measurements obtained for the collagen-plug and those obtained
for the conventional marking devices. Using a chi-square test, we found
significantly fewer cases in which the clip-to-target distance was 1 cm or
greater on at least one mammographic projection with the collagen-plug marker
clip (5/31) than with the conventional metallic marker clip (19/43)
(p = 0.02).
Discussion
Biopsy marker clips are deployed when the original biopsy target has been
removed or becomes obscured during the core biopsy procedure. These clips are
intended to provide a mammographically visible target that can be localized if
surgical excision is required. Deployment of these clips has become
commonplace during stereotactic biopsies, but to be effective, these marking
devices must be readily visible and remain in close proximity to the original
biopsy site in case further surgery or imaging evaluation is required.
The MicroMark clip (Ethicon, Cincinnati, OH) was the first marker clip
designed specifically for use during breast biopsy and is deployed through the
biopsy probe while vacuum pressure is applied so that the clip attaches to the
side wall of the biopsy cavity. Although this clip generally performs well,
there are a substantial number of cases in which the clip is located more than
1 cm away from the actual biopsy site on postprocedure mammograms
[1]
(Fig. 2). Typically this
displacement occurs in the z-axis and has been termed the
"accordion effect"
[1–5].
This displacement likely occurs when the clip is attached to tissue near but
not at the biopsy site while the breast is compressed. When compression is
released, the actual location of the clip is revealed and frequently is shown
to be displaced away from the biopsy cavity. The occurrence of this phenomenon
is unpredictable. The farther a clip is placed away from the biopsy site, the
less useful it is in localizing the actual biopsy site and serving as a target
for future localization.
Recently, a new type of biopsy marker clip, consisting of a collagen plug
with a centrally embedded titanium clip (MammoMark), became available for
commercial use. These clips are intended to improve the accuracy of biopsy
site identification by marking the central portion of the biopsy cavity both
in and out of breast compression. This new device consists of a self-expanding
collagen plug that contains a mammographically visible centrally embedded
titanium clip. Instead of attaching to the wall of the biopsy cavity, the clip
is intended to be placed within the biopsy cavity. After deployment of the
marking device, the collagen expands as it absorbs fluid and eventually fills
the biopsy cavity (Fig. 1A,
1B,
1C). Theoretically, the
accordion effect should not occur when these clips are deployed because the
marker is located within, not attached to the wall of, the biopsy cavity;
therefore, the marker should stay at the biopsy site on each mammographic view
when compression is released (Figs.
3A,
3B and
4A,
4B,
4C,
4D).
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Fig. 3B. —Displacement of marker as result of "accordion
effect" in woman with small irregular mass. Mammogram obtained after
biopsy shows air and hematoma (arrows) at biopsy site with metallic
marker clip displaced away from biopsy site.
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Fig. 4A. —54-year-old woman with new solid mass in inferior right
breast. Stereotactic biopsy was performed from inferior approach. Close-up of
craniocaudal (A) and mediolateral (B) mammograms before biopsy
shows solid mass (arrow) in inferior right breast.
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Fig. 4B. —54-year-old woman with new solid mass in inferior right
breast. Stereotactic biopsy was performed from inferior approach. Close-up of
craniocaudal (A) and mediolateral (B) mammograms before biopsy
shows solid mass (arrow) in inferior right breast.
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Fig. 4C. —54-year-old woman with new solid mass in inferior right
breast. Stereotactic biopsy was performed from inferior approach. Close-up of
craniocaudal mammogram after biopsy shows that mass was removed and that
positioning of marking device in x- and y-axes is
accurate.
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Fig. 4D. —54-year-old woman with new solid mass in inferior right
breast. Stereotactic biopsy was performed from inferior approach. Close-up of
mediolateral mammogram after biopsy shows accurate positioning of marking
device without measurable displacement in z-axis.
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In our study, we compared the frequency and degree of displacement of
collagen-plug marker clips with the more conventional metallic marker clips.
Our data suggest that the collagen-plug marker clip is significantly more
likely to be located within 1 cm of the actual biopsy site on postbiopsy
mammograms than a conventional metallic marker clip. The difference between
the clip-to-target distances of the two markers was statistically significant,
and these distances were consistently less with the collagen-plug device than
with the conventional marker clips.
In general, the collagen-plug marker clip is easy to use and deploys
reliably. However, if the introducer is not held firmly in place during
deployment, the introducer can back out of the probe, resulting in partial
deployment of the plug. If the probe is then withdrawn, the plug may become
dislodged and located superficially in the biopsy tract instead of in the
actual cavity. Similarly, if the collagen-plug marker clip introducer is
advanced too far, the plug may be deployed beyond the biopsy cavity. Either of
these scenarios may result in marker clip displacement away from the biopsy
site when compression is released, as occurred in five (16%) of 31 cases in
our study. In these five cases in which the clip did not perform as intended,
the clip-to-target distances were 1 cm or more on postbiopsy images. We
hypothesize that these instances occurred because of the errors in deploying
the marker, which we described earlier.
In conclusion, our study shows that the collagen-plug marking device is an
effective alternative to existing marker clips and may result in fewer cases
in which the marker clip is substantially displaced ( 1 cm) away from the
actual biopsy site. Further study is warranted to evaluate the hemostatic
effect, sonographic visualization, and long-term stability of this new biopsy
site marker because these were not evaluated as part of this study.
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PP. Clip placement after stereotactic vacuum-assisted breast biopsy.
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- Reynolds HE. Marker clip placement following directional,
vacuum-assisted breast biopsy. Am Surg1999; 65:59
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- Burbank F, Forcier N. Tissue marking clip for stereotactic breast
biopsy: initial placement accuracy, long-term stability and usefulness as a
guide for wire localization. Radiology1997; 205:407
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Abstract
Introduction
