AJR 2000; 174:753-756
© American Roentgen Ray Society
Mammographic Abnormalities Caused by Percutaneous Stereotactic Biopsy of Histologically Benign Lesions Evident on Follow-Up Mammograms
Robert L. Lamm1 and
Roger J. Jackman
1
Both authors: Department of Radiology, Palo Alto Medical Clinic, 795 El Camino
Real, Palo Alto, CA 94301
Received October 19, 1998;
accepted after revision August 9, 1999.
Supported in part by an educational grant from Biopsys Medical, Inc., to
the Palo Alto Medical Foundation.
R. J. Jackman was formerly a shareholder in and a clinical consultant to
Biopsys Medical, Inc.
Address correspondence to R. L. Lamm.
Abstract
OBJECTIVE. The purpose of our study was to evaluate how often a
mammographic abnormality thought to be produced by the biopsy procedure was
evident on the initial follow-up mammogram after percutaneous biopsy of
impalpable histologically benign lesions. We compared three stereotactic
percutaneous biopsy methods.
CONCLUSION. A mammographic density seen well only in the projection
parallel to the biopsy needle tract was evident in 2% (5/226) of the lesions
for which 11-gauge directional vacuum-assisted biopsy was used, 0% (0/96) of
the lesions for which 14-gauge directional vacuum-assisted biopsy was used,
and 0% (0/422) of the lesions for which 14-gauge automated large-core biopsy
was used. No mammographic abnormalities assessed as BI-RADS categories 3, 4,
or 5 (according to the American College of Radiology's Breast Imaging
Reporting and Data System) and thought to be produced by the biopsy procedure
were evident after any of the biopsy methods.
Introduction
Percutaneous stereotactic breast biopsy is rapidly gaining acceptance as
the procedure of choice in obtaining a histopathologic diagnosis for
impalpable mammographic lesions requiring biopsy. Methodologic options include
14-gauge automated large-core biopsy and directional vacuum-assisted biopsy
(Mammotome; Biopsys Medical [Ethicon Endo-Surgery], Cincinnati, OH) with 14-
and 11-gauge probes. In prior studies, investigators have found no suspicious
changes or distortion thought to be caused by the biopsy procedure on the
first mammogram after biopsy of histologically benign lesions with either of
the 14-gauge devices
[1,2,3]
or the 11-gauge probe [3].
We describe a postbiopsy mammographic density seen well only in the
mammographic projection parallel to the biopsy needle tract on the initial
mammogram obtained 6-8 months after stereotactic biopsy of histologically
benign lesions. The density was evident only after 11-gauge directional
vacuum-assisted biopsies. We suggest the density is caused by minor postbiopsy
scar tissue that is most prominent when viewed along the z-axis of
the biopsy probe.
Materials and Methods
From July 1991 through December 1997 we performed 1367 percutaneous
stereotactic breast biopsies on impalpable mammographically detected lesions
using a prone table (Mammotest; Fischer Imaging, Denver, CO). Percutaneous
histologic results were benign in 824 lesions. Twenty-nine of these lesions
were biopsied a second time (27 surgical biopsies and two percutaneous
biopsies) before mammographic follow-up and were excluded from the study. Of
the remaining 795 lesions, mammographic follow-up was performed in 744
lesions, which constitute our study group. Of these 744 lesions, 422 were
biopsied from July 1991 to mid-April 1995 using 14-gauge automated large-core
technique; 96 from mid-March 1995 to mid-June 1996 using 14-gauge directional
vacuum-assisted technique; and 226 from mid-May 1996 through December 1997
using 11-gauge directional vacuum-assisted technique. The mean number of
specimens for each technique was nine, 18, and 18, respectively. During the
1-month overlaps between biopsy techniques, the availability of the newer
biopsy probe determined which technique was used. Mammographic follow-up of
the histologically benign lesions was advised to occur at 6 or 12 months after
biopsy and was actually performed at 1-53 months (median, 7 months). Of these
744 follow-up mammograms, 22 were performed 1-4 months after biopsy, 700 were
performed 5-18 months after biopsy, and 22 were performed 19-53 months after
biopsy.
A retrospective review of the first postbiopsy mammograms for these 744
lesions with benign histology was performed to assess the presence or absence
of postbiopsy mammographic changes. All first postbiopsy mammograms consisted
of craniocaudal and mediolateral oblique views with additional views obtained
only if requested by the radiologist initially interpreting the follow-up
examination.
Results
In none of the cases did the first follow-up mammogram after benign
percutaneous breast biopsy reveal a postbiopsy abnormality assessed as
category 3, 4, or 5 (in the American College of Radiology's Breast Imaging
Reporting and Data System [BI-RADS])
[4] thought to be caused by the
biopsy procedure. In 2% (5/226) of the lesions biopsied with 11-gauge
directional vacuum-assisted technique, the first follow-up mammogram revealed
a density (BI-RADS category 2) with similar features in each case. None of
these densities was evident on follow-up mammograms after 14-gauge automated
large-core biopsy or 14-gauge directional vacuum-assisted biopsy.
Lesion, biopsy, and follow-up variables of the five lesions with postbiopsy
densities are shown in Table 1.
These five biopsied lesions consisted of two masses and three clusters of
microcalcifications; all were assessed as BI-RADS category 4 (suspicious)
lesions. No complications were present during or immediately after the biopsy
in any of the five cases. The five biopsied lesions had removal of 12-26
specimens (mean, 19 specimens) as compared with removal of 4-70 specimens
(mean, 18 specimens) for the entire cohort of 11-gauge directional
vacuum-assisted biopsied lesions in the study group.
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TABLE 1 Lesion Type on II-Gauge Directional Vacuum-Assisted Biopsy and Variables
on Follow-Up Mammography for Five Lesions
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Histopathologic study revealed nonspecific benign findings in all five
lesions. Nonproliferative fibrocystic changes were found in both masses and
one of the microcalcification lesions. The other two microcalcification
lesions revealed fat necrosis, inflammation, and fibrosis and proliferative
and fibroadenomatous changes, respectively. Specimen radiographs revealed
calcium in all three microcalcification lesions.
Immediate postbiopsy stereotactic digital images were obtained in four of
these five patients and showed that the lesion in question was gone; no
postbiopsy hematomas were evident. In these same four patients, a
stainless-steel clip (Micromark; Biopsys Medical) was deployed to mark the
biopsy site. Each clip was less than 10 mm from the biopsy cavity margin. At
the time of the first follow-up mammogram, obtained 6-8 months after biopsy,
the biopsied lesion was gone and a new mammographic density was present in all
five patients. The densities were small (maximum diameter, 5-10 mm; mean
diameter, 8 mm), dense, and round or oval with irregular or spiculated margins
in the craniocaudal projection only. In all five patients, a craniocaudal
needle biopsy approach was used (i.e., the density was well seen only along
the z-axis of the biopsy probe). In the mediolateral oblique
projection, the densities were imperceptible in two patients (Fig.
1A,1B,1C,1D)
and were extremely faint in three patients with a maximum diameter of 23-30 mm
(mean, 27 mm).
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Fig. 1A. —73-year-old woman with history of benign percutaneous right breast
biopsy using 11-gauge directional vacuum-assisted technique. Craniocaudal
(A) and mediolateral oblique (B) prebiopsy right mammograms show
8-mm cluster of pleomorphic microcalcifications in upper outer quadrant.
Calcification anterior to clustered biopsied calcifications on B is
located 8 cm medially.
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Fig. 1B. —73-year-old woman with history of benign percutaneous right breast
biopsy using 11-gauge directional vacuum-assisted technique. Craniocaudal
(A) and mediolateral oblique (B) prebiopsy right mammograms show
8-mm cluster of pleomorphic microcalcifications in upper outer quadrant.
Calcification anterior to clustered biopsied calcifications on B is
located 8 cm medially.
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Fig. 1C. —73-year-old woman with history of benign percutaneous right breast
biopsy using 11-gauge directional vacuum-assisted technique. Craniocaudal
(C) and mediolateral oblique (D) right mammograms obtained 6
months after percutaneous biopsy show 7-mm spiculated density on C and
no perceptible density on D. Metallic clip marks biopsy site. Slight
increase in density of background scattered fibroglandular tissue is presumed
related to hormone replacement therapy that was started 6 months before these
mammograms were obtained. Calcification inferior to metallic clip on D
is situated 8 cm medial to biopsied calcifications. Punctate opacity anterior
to metallic clip on D represents artifact.
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Fig. 1D. —73-year-old woman with history of benign percutaneous right breast
biopsy using 11-gauge directional vacuum-assisted technique. Craniocaudal
(C) and mediolateral oblique (D) right mammograms obtained 6
months after percutaneous biopsy show 7-mm spiculated density on C and
no perceptible density on D. Metallic clip marks biopsy site. Slight
increase in density of background scattered fibroglandular tissue is presumed
related to hormone replacement therapy that was started 6 months before these
mammograms were obtained. Calcification inferior to metallic clip on D
is situated 8 cm medial to biopsied calcifications. Punctate opacity anterior
to metallic clip on D represents artifact.
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Discussion
The mammographic changes after surgical excisional breast biopsy for both
benign and malignant lesions have been well described and include skin
thickening and distortion, architectural distortion, parenchymal scar (poorly
defined mass, often with spiculated margins, detected on right-angle
projections), calcifications, opaque foreign body, fat necrosis, and
asymmetric glandular tissue defect
[5,6,7,8,9,10].
Of these findings, the skin changes and architectural distortion may mimic
indirect mammographic signs of malignancy, and the parenchymal scar and
calcifications may mimic direct mammographic signs of malignancy. When
detected in two projections, these postsurgical mammographic changes alone or
in combination produce a mammographic lesion suggestive of carcinoma (Fig.
2A,2B).
These lesions have been found to show regression or stability over time on
follow-up mammographic examinations
[6,7,8,9,10].
This allows the mammographer who is cognizant of the history and location of
prior surgical biopsy to follow such stable or regressing mammographic lesions
without further intervention.
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Fig. 2A. —75-year-old woman with history of needle-localized lumpectomy and
radiation therapy for right breast impalpable infiltrating ductal carcinoma.
Craniocaudal (A) and mediolateral oblique (B) right mammograms
show 12-mm spiculated mass in upper outer quadrant at lumpectomy site. Lesion
has been stable for 7 years after lumpectomy.
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Fig. 2B. —75-year-old woman with history of needle-localized lumpectomy and
radiation therapy for right breast impalpable infiltrating ductal carcinoma.
Craniocaudal (A) and mediolateral oblique (B) right mammograms
show 12-mm spiculated mass in upper outer quadrant at lumpectomy site. Lesion
has been stable for 7 years after lumpectomy.
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In patients who have undergone uncomplicated percutaneous stereotactic
automated large-core or directional vacuum-assisted biopsy for benign disease,
no mammographic lesions thought to be caused by the biopsy procedure have been
detected on follow-up mammograms
[1,2,3].
Our experience with the first follow-up mammograms for benign lesions biopsied
with the 14-gauge automated large-core technique and with the 14-gauge
directional vacuum-assisted technique has been similar to those of other
literature reports with no postbiopsy mammographic changes detected. In 2%
(5/226) of the benign lesions biopsied using the 11-gauge directional
vacuum-assisted technique, a postbiopsy mammographic density was observed.
Unlike the mammographic lesion after surgical excision, which is typically
well seen in two projections, the lesion after 11-gauge biopsy is only well
seen in one projection and is either faintly detectable or imperceptible in
the oblique or orthogonal projections. Because this lesion is seen as a
conspicuous finding in only one projection, it is best described as a density
in accordance with BI-RADS terminology
[4]. Knowing that the density
is at the site of a prior 11-gauge biopsy allows one to categorize it as a
BI-RADS category 2 (benign) lesion; proximity of a postbiopsy metal clip to
the density increases confidence in the benign categorization.
The mammographic features of this lesion are likely directly related to the
biopsy technique. Specifically, with the 11-gauge directional vacuum-assisted
biopsy, an approximately cylindric tissue sample, much longer than it is wide,
is removed. In every one of the lesions we observed, the density appeared
small and most dense in the projection parallel to the biopsy needle tract and
appeared vague or imperceptible in the oblique or orthogonal projection. In
other words, the lesion is thought to be a minor postbiopsy scar that appears
most conspicuous when viewed along the z-axis of the biopsy
probe.
Presumably a scar would be more apt to occur after biopsies in which more
tissue was removed. Although we obtained an average of 18 specimens per lesion
during directional vacuum-assisted biopsy with both 14-gauge probes and the
11-gauge probe, we did not find any lesions after 14-gauge biopsy. This
difference is likely explained by the greater average weight of an individual
specimen obtained with an 11-gauge probe (95 mg) than that obtained with a
14-gauge probe (37 mg)
[11,12,13].
We would expect an occasional lesion to occur after 14-gauge directional
vacuum-assisted biopsy, especially if a large number of specimens were
removed.
It is important that the mammographer interpreting follow-up mammograms
after biopsy of benign lesions with 11-gauge directional vacuum-assisted
technique is aware of the features of this lesion and its relation to the
biopsy procedure. We now specify the direction of the biopsy approach in our
dictated reports of all percutaneous breast biopsies to facilitate evaluation
of these lesions on follow-up mammograms. The recognition of this
characteristic finding should obviate further mammographic workup and should
prevent misinterpretation as a lesion requiring further intervention.
Additional studies are needed to evaluate the incidence of this finding in
larger series. In all five of our patients, a second follow-up mammogram was
obtained at 12-21 months (mean, 14 months), and in one patient, a third
follow-up mammogram was obtained at 25 months. In every patient, the
postbiopsy lesion was either unchanged or showed a definite decrease in
density. These results suggest that these postbiopsy lesions either remain
stable or regress with time in the same manner as the lesions seen after
surgical biopsy.
Acknowledgments
We thank Julie C. Clark for her diligence and perseverance in the
preparation of this manuscript.
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Abstract
Introduction
