Finding Early Invasive Breast Cancers

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REVIEWS AND COMMENTARY
Finding Early Invasive Breast
Cancers: A Practical Approach1
䡲 REVIEW FOR RESIDENTS
Jennifer A. Harvey, MD
Brandi T. Nicholson, MD
Michael A. Cohen, MD
Detection of early invasive breast cancer is important, as
patient survival is high when the cancer is 2 cm or smaller.
Invasive breast cancers typically manifest mammographically as focal asymmetries or masses. Strategies for detecting focal asymmetries and masses on screening mammograms include side-by-side comparison, looking for parenchymal contour deformity, close inspection of the retromammary
fat, identifying the presence of associated findings, and
comparison with prior mammograms. Focal asymmetries
are often normal but are concerning when there is distortion of the normal breast architecture. Masses and focal
asymmetries are best evaluated in the diagnostic setting by
using spot compression and true lateral views and, frequently, ultrasonography. Management of a lesion depends on the worst imaging feature. Indications for an
assessment of probably benign findings are very specific
but are often misapplied. This review for residents provides a practical approach to the detection and management of breast masses and focal asymmetries.
娀 RSNA, 2008
1
From the Department of Radiology, University of Virginia
Health Sciences Center, PO Box 800170, Charlottesville,
VA 22908. Received February 21, 2006; revision requested April 24; revision received January 5, 2007; accepted February 9; final version accepted July 24; final
review by J.A.H. February 27, 2008. Address correspondence to J.A.H. (e-mail: [email protected]).
姝 RSNA, 2008
Radiology: Volume 248: Number 1—July 2008
61
REVIEW FOR RESIDENTS: Finding Early Invasive Breast Cancers
I
nvasive breast cancer typically manifests as a mass at mammography.
Before developing into a mass, a cancer may manifest as a focal asymmetry.
Early detection of these masses and
asymmetries that represent invasive
carcinoma is important in reducing
breast cancer mortality. Women with
invasive cancers of 1 cm or smaller have
a 95% chance of survival at 10 years,
while those with invasive cancers 1–2
cm and 2–5 cm in size have, respectively, 85% and 60% survival at 10
years (1). For large invasive cancers,
survival is dependent on tumor grade
(1). However, survival is high for women
with small invasive cancers, whether
the cancer is low or high grade (2).
Thus, detection of small invasive cancers substantially affects breast cancer
mortality.
The Breast Imaging Reporting and
Data System (BI-RADS) (3) defines a
mass as “a space occupying lesion seen
in two different projections.” The BIRADS lexicon states that a focal asymmetry “is visible as a confined asymmetry with a similar shape on two views,
but completely lacking borders and the
conspicuity of a true mass” (3). A poten-
Essentials
䡲 Look for asymmetry, contour deformity, lesions in the retromammary fat, and associated findings
to identify early breast cancer.
Use studies 2 or more years old
for comparison when available,
but beware of stability. Suspicious
morphology outweighs stability.
䡲 Perform diagnostic evaluation
when a concerning mass or focal
asymmetry is identified at screening mammography and include a
true lateral view, spot compression views in both craniocaudal
and mediolateral oblique projections, and, often, a US study.
䡲 Management depends on the
worst imaging feature. The assessment of “probably benign” has
very specific indications and is
frequently misapplied. Biopsy
should be considered when suspicious features are present.
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tial mass is termed a focal asymmetry if
it does not meet the three-dimensional
criteria of a mass. Thus, if a lesion has
definable borders but is only visualized
in one projection, it is considered a focal
asymmetry.
The detection of breast masses and
focal asymmetries on screening mammograms is largely a challenge of perception. Once a lesion is detected, management is relatively straightforward.
This is in contrast to breast calcifications, where perception of the finding is
not as difficult, but disposition is more
challenging. Diagnostic evaluation of breast
masses and focal asymmetries includes
additional mammographic views and often breast ultrasonography (US).
This Review for Residents is intended
to provide a practical approach to the detection and management of breast masses
and focal asymmetries. We will describe
an approach to screening mammography
with the goal of improving identification
of breast masses and focal asymmetries,
develop strategies for evaluating breast
masses and focal asymmetries in the diagnostic setting, and describe proper
application of the BI-RADS assessment
and recommendation categories. The
techniques and findings that we describe pertain primarily to invasive ductal carcinoma, which is the most common type of breast cancer. We have
previously reviewed the findings of unusual breast cancers, which may provide clues to a diagnosis other than invasive ductal carcinoma (4).
An Approach to Detecting Masses and
Focal Asymmetries at Screening
Mammography
Screening mammograms may be interpreted “online” while the patient waits
for results or may be batch interpreted,
often on the next business day following
the examination. Online interpretation
of screening mammograms reduces patient stress for those women with abnormalities (5). Inefficiencies due to online interpretation of screening mammograms result in an increase in cost of
nearly $30 per study that most women
are not willing to pay (6). Batch interpretation is more efficient and results in
Harvey et al
improved specificity with equal cancer
detection rates (7,8). The percentage of
U.S. facilities using batch interpretation
increased from 20% in 1992 (9) to 93%
in 2002 (10).
A screening mammogram is two
views of each breast: the craniocaudal
(CC) view and the mediolateral oblique
(MLO) view. Our protocol is to review
the current CC views side-by-side (with
the chest wall of the left breast next to
that of the right breast) and the MLO
views (also side-by-side, as for the CC
views) on the lower panel of the rollerscope, with a comparison study obtained 2 or more years earlier hung in
an identical fashion on the panel above.
Your protocol may be different, but it
should be consistent. Consistency aids
in lesion detection as one becomes accustomed to reviewing studies with a
particular visual pattern.
A consistent approach to reading
will ensure that all aspects of the mammogram are reviewed. Ensure that you
are reading in an optimal environment
using high-luminance viewboxes (3500
nits) for screen-film mammography or
high-resolution monitors for digital
mammography, mask any extraneous
light around the images, and reduce
room light as much as possible. First,
confirm that the name and other patient
identifiers are correct (ie, you are reading the correct study) and that the images are of adequate quality. In mammography, the images must have good
contrast, compression, positioning, and
lack of blur or artifacts. In reviewing the
mammogram, an overview is helpful to
check for obvious abnormalities and
changes from the previous study. Next,
compare the MLO views side-to-side
and then the CC views (or vice versa) to
look for asymmetry in the breast paren-
Published online
10.1148/radiol.2481060339
Radiology 2008; 248:61–76
Abbreviations:
BI-RADS ⫽ Breast Imaging Reporting and Data System
CC ⫽ craniocaudal
MLO ⫽ mediolateral oblique
Authors stated no financial relationship to disclose.
chymal pattern, paying particular attention to the retromammary fatty regions.
Evaluate the contour of the breast parenchyma where it interfaces with fat.
Finally, with the magnifying glass,
closely examine the breast parenchyma
for architectural distortion and calcifications. If a finding is identified, compare with the prior mammograms to assess whether the finding is new, growing,
or stable by using studies more than 2
years older if need be.
Asymmetric Breast Tissue versus Focal
Asymmetry
Asymmetry in the breast may be global
or focal. Asymmetric breast tissue, or
global asymmetry, in which the parenchyma is overall greater in volume in
one breast compared with the other, is
common and usually normal. However,
global asymmetry is of concern when
there is associated architectural distortion, an apparent decrease in breast
size at mammography, skin thickening,
axillary adenopathy, or clinical findings.
Breast cancers manifesting as global
asymmetry are likely to be large.
Global asymmetry can be due to un-
derlying invasive lobular carcinoma,
particularly when associated with architectural distortion without a central
mass or an apparent decrease in breast
size (the “shrinking breast”) (11). Invasive lobular carcinoma accounts for
6%–9% of all breast cancers (12,13).
Most breast cancers enlarge en mass,
like a ball getting larger, whereas invasive lobular carcinoma spreads in single-layer sheets of tumor cells similar to
a spider web. The breast density may
increase and the breast tissue becomes
less compliant. This may result in architectural distortion, manifested as
straight lines, typically in a radial pattern in the breast. Use of the magnifying
glass helps to identify subtle architectural distortion.
Detecting Focal Asymmetries
Focal asymmetry is also frequently a benign finding in the breast, representing
summation of normal tissue. However,
early breast cancer may manifest as a
focal asymmetry on screening images. A
mass may become apparent on diagnostic images. The goal is to find breast
cancers at this early stage.
Harvey et al
Comparison.—If you wanted to
compare two different clothing items,
you would put them next to each other
to look at the differences. Look for early
cancers by comparing the breasts from
side to side in the manner mentioned
previously (Fig 1). This can be done as
the initial step in reading the mammogram after ensuring proper identification and quality.
Contour deformity: look for the
hook, slow down for the speed bump.—
Women with dense breast tissue typically have an outward convex margin to
their breast parenchyma. Cancers may
manifest with distortion to this outward
margin, similar to taking a crochet hook
and pulling in the tissue toward the cancer (Fig 2) (14). The subcutaneous fat is
drawn into this space, creating straight
lines (architectural distortion) with an
angular fat density invagination into
breast parenchyma. This may be the
only sign of a cancer hidden within
opaque breast tissue. When identified,
additional imaging including spot views
and US will usually unmask the hidden
lesion.
In contrast, women with scattered
Figure 1
Figure 1: Side-by-side comparison. Bilateral screening mammogram in a 69-year-old woman: CC (left) and MLO (right) views are hung side-by-side to evaluate for
asymmetry. When comparing side to side (rectangles), asymmetry is identified in the left breast at 9 o’clock position (arrows), with associated architectural distortion. At
subsequent diagnostic imaging, a suspicious mass was identified. Biopsy specimen showed invasive lobular carcinoma.
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Figure 2
Figure 2: Contour deformity. (a) The contour of
dense breast parenchyma is typically outwardly convex. Invasive breast cancer may cause contour distortion, with the parenchymal margin appearing to have
been pulled in as if with a crochet hook. (b) Left CC
view in a 28-year-old woman with a palpable abnormality demonstrates transition from outward convex
dense parenchyma (straight arrows) to a breast mass
causing distortion in the contour (curved arrow). Core
biopsy specimen showed invasive ductal carcinoma.
fibroglandular densities or heterogeneously dense breast tissue typically
have a scalloped or concave margin to
the breast parenchyma. A breast mass
may be detected by looking for an outward convex margin along the parenchymal margin (Fig 3). Think of this as a
speed bump when you are following the
edge of the parenchyma. Slow down
and take a closer look at the area.
Living in the wrong neighborhood
(triangle).—There are particular triangle-shaped zones of the breast that justify a higher level of suspicion when a
focal asymmetry is identified (Fig 4). On
the CC view, these zones are the retromammary fat between the breast tissue
and the chest wall and the medial or
inner triangle (Fig 4). On the MLO
view, these are the central space between the breast tissue and the chest
wall and the lower triangle (Fig 4).
These are all typically fatty areas, so the
presence of a focal asymmetry in these
areas should raise suspicion. The retromammary fat area on the MLO view is
often referred to as “the Milky Way,”
because we are searching for white
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Figure 3
Figure 3: Contour deformity. (a) The contour of the parenchymal margin in women with scattered fibroglandular densities or heterogeneously dense breast tissue is typically scalloped. (b) This is shown on the
lateral portion of a CC view, where the contour of the parenchyma is scalloped (line) except where a mass is
visualized with a convex margin (arrows). US demonstrated a simple cyst.
Figure 4
Figure 4: Living in the wrong neighborhood (triangle). Masses or focal asymmetries in the retromammary
fat should be viewed with suspicion. This includes triangles at the bottom of the images. (a, b) A 10-mm invasive ductal carcinoma (arrow) is present in the (a) medial triangle on the CC view and (b) inferior triangle on
the MLO view of the left breast in a 66-year-old woman. (c) A 12-mm invasive tubular carcinoma (arrow) in the
retromammary fat triangle on the CC view of the left breast in a 48-year-old woman. (d) An 8-mm invasive
ductal carcinoma (arrow) in the retromammary fat triangle on the right MLO view in a 46-year-old woman.
Harvey et al
stars on an otherwise featureless normal inky background (Fig 4).
The retroareolar area of the breast
is very difficult to evaluate because of
the complex anatomy of the region.
Mammography is less sensitive for
breast cancer detection in this area
(15). To improve detection of a subareolar cancer, having the nipple in profile on
one of the two screening views (CC or
MLO) may be helpful (Fig 5) (16). Once
well-positioned images have been obtained, assess the retroareolar regions
for asymmetry compared to the opposite side. Also be aware that not all
round masses and densities in the retroareolar area represent nipples out of
profile. True masses may look like nipples. Spot compression views of the
subareolar region with a radiopaque
marker on the nipple or with the nipple
in profile will typically resolve whether a
mass is present.
Associated findings: looking for
more clues.—When a potential lesion is
identified, the level of suspicion is increased when associated findings are
also identified. Architectural distortion
that is present with a focal asymmetry is
suspicious (Fig 6). Calcifications associated with a focal asymmetry may represent ductal carcinoma in situ (calcifications) associated with invasive carcinoma (focal asymmetry) (Fig 7). The
presence of ipsilateral adenopathy likewise increases suspicion, as the focal
asymmetry may represent an invasive
cancer with metastasis to axillary lymph
nodes (Fig 8). Occasionally, axillary or
intramammary adenopathy may be mistaken for a primary breast carcinoma
(Fig 9).
Use of prior studies: beware of stability!—Breast cancers may grow
slowly. Therefore absence of substantial growth or change on a mammogram when compared to the previous
year’s mammogram may mislead one
to a false assumption that the lesion is
benign (Fig 10). Our standard practice
is to compare the current mammogram
to studies that are 2 or more years old.
If there is a finding for which change is
difficult to assess by using that previous
mammogram, older studies are reviewed. It is typical that comparison
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Figure 5
Figure 5: Subareolar region. Bilateral mammogram obtained in a 67-year-old woman with new right nipple retraction. Left: A small mass (arrow) with architectural
distortion is seen in the right subareolar region of the CC view. Right: The lesion is difficult to perceive on the MLO view because the nipple (arrow) is not in profile.
Figure 6
Figure 6: Architectural distortion. Left breast mammogram in a 68-year-old woman after remote right breast mastectomy with no current breast complaints. (a) Left
mammogram shows a focal asymmetry (arrows) in the central left breast. (b) Spot compression view in MLO projection shows numerous straight lines (arrows) associated with the focal asymmetry consistent with architectural distortion. The lesion was assigned BI-RADS category 5 (highly suggestive of malignancy). Core-needle biopsy specimen showed an invasive ductal carcinoma, which measured 7 mm at excision.
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Figure 7
Figure 8
Figure 7: Mass with calcifications. Close up of
a left CC view from a screening mammogram in a
53-year-old woman shows a 6-mm oval, spiculated, equal-density mass (straight arrows), with
associated amorphous microcalcifications
(curved arrow). Stereotactic-guided core-needle
biopsy specimen showed invasive ductal carcinoma with associated ductal carcinoma in situ.
Figure 8: Abnormal lymph node. (a) Right MLO view from a screening mammogram in a 67-year-old
woman shows a 20-mm round ill-defined mass (straight arrow). An abnormally dense axillary lymph node is
also noted (curved arrow). (b) US image of the right axilla confirms focal areas of thickening (outward contour)
of the lymph node cortex (arrows). Findings at US-guided core-needle biopsy of the right breast mass showed
invasive ductal carcinoma. Findings at US-guided core-needle biopsy with an 18-gauge Temno needle (Allegiance HealthCare, McGaw Park, Ill) showed metastatic adenocarcinoma.
Figure 9
Figure 9: Bilateral mammogram in a 29-year-old woman with palpable lump in the right breast at 10 o’clock position. The obvious axillary mass represents metastatic
adenopathy (straight arrows). Side-to-side comparison (rectangles) reveals focal asymmetry in the right upper outer quadrant (curved arrows), corresponding to the
palpable lump. Biopsy specimen of the focal asymmetry showed invasive ductal carcinoma, grade III.
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Harvey et al
Figure 10
Figure 10: Comparison mammograms. MLO views
of the left breast demonstrate a slow-growing mass
(arrows). The current mammogram (left) was not substantially different from that of the previous year (middle) but was considerably different from that of 3 years
earlier (right). Biopsy specimen showed invasive lobular carcinoma, grade I.
Figure 11
Figure 11: Normal focal asymmetry. (a) Bilateral digital mammogram obtained in a 42-year-old woman for baseline screening. A focal asymmetry is present in the left
breast at 12 o’clock position, posterior third (arrows). The asymmetry respects normal architecture of the breast, with no straight lines or outward convex margins. (b)
Looking at the black fat lobules (circles) rather than the white breast parenchyma can be helpful in assessing whether a focal asymmetry is respecting normal breast structures. This was assigned BI-RADS assessment category 2 (benign finding) and has remained stable for 2 years of follow-up.
with studies that are 4 or 5 years older
makes clear that a finding has been
present for some time and is unchanged, and thus likely benign, or that
the finding is indeed developing and recall is indicated. The exception is that
68
when a round or oval mass is identified
and a cyst is suspected, comparison
with studies from the previous year is
helpful if the mass was shown at US to
be a simple cyst at that time and has not
changed in size since then. Note, how-
ever, that a finding that looks suspicious
should not be discounted just because
someone worked it up last year and said
it was benign. In all cases, lesion morphology takes precedence over stability.
If the morphology is suspicious, work up
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Figure 12
Figure 12: Abnormal focal asymmetry. (a) Bilateral screening mammogram in a 62-year-old woman. A focal asymmetry (arrows) is present
in the left breast at 3 o’clock position, middle third. (b) At close evaluation,
the focal asymmetry demonstrates lack of respect of normal breast architecture, with outward convex margins (straight arrows) and straightening
of Cooper ligament lines (curved arrows). At subsequent diagnostic
imaging, lesion appeared masslike on spot compression views, and a
corresponding hypoechoic solid mass was seen at US (not shown). Coreneedle biopsy specimen showed invasive ductal carcinoma.
the lesion regardless of apparent stability.
When to ignore a focal asymmetry: respect for normal breast architecture.—When a focal asymmetry
represents summation of normal tissue, there will be no distortion of Cooper ligaments or the regular, symmetric, undulating interface between glandular tissue and subcutaneous fat (Fig
11). In other words, normal tissue will
respect normal boundaries. One approach is to look at the black on the
image instead of the white. You should
see oval fat lobules, with soft curved
Cooper ligaments separated by
strands of white breast tissue. Invasive
breast cancer grows through normal
structures and may result in abnormal
outward convex margins and straightening of Cooper ligaments. A focal
asymmetry should be recalled for evaluation, even if it appears to be respecting normal breast structures, if it
is new in comparison to prior mammograms, since early breast cancers may
cause little distortion. Spot compression views will help define if a focal
asymmetry is behaving respectfully.
A focal asymmetry that has outward
convex margins or is associated with
straight lines is not respecting the normal architecture of the breast and
should increase suspicion (Fig 12).
Breast cancer does not respect normal
breast structures but grows through
them instead creating abnormal lines.
These straight lines represent early
spiculation around a mass or focal
asymmetry (Fig 12).
Leave-alone masses.—Fat-containing masses in the breast are benign with
rare exception if circumscribed and
round or oval in shape (17,18). These
masses include: lymph node, lipoma, oil
cyst, hamartoma, and galactocoele. If a
mass identified at screening clearly represents one of these five, no additional
work-up is needed. However, fat-containing masses are not necessarily benign if the margins are irregular or spiculated, since cancers can engulf fat as
they grow.
Volume counts.—As with any task,
practice increases skill. Read as many
mammograms as possible during your
residency. At our institution, residents
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spend their first month of breast imaging seeing diagnostic imaging patients
so they will see many breast cancers.
The second month focuses on screening
mammography and breast procedures.
The third month focuses on managing
difficult diagnostic cases, as well as further experience in screening and procedures. We expect our residents to read
at least 500 screening mammograms
during each of their second and third
months. Even those who are planning to
perform a fellowship in another area of
radiology are likely to read mammograms if they are in private practice.
You will be much more confident if you
have first read at least 1000 mammograms with a mentor.
Double reading and computer-aided
detection.—Both double reading of mammograms and computer-aided detection,
or CAD, improve sensitivity (19,20). A
CAD system places marks on potentially
suspicious calcifications and possible
masses. Freer and Ulissey (20) found a
19.5% increase in cancer detection with
the use of CAD in a community breast
center, with an increase in screening
recall rate from 6.5% to 7.7%. However, the benefit can differ (21). If you
are a resident at an institution that uses
CAD, gain experience using the tool so
that you will be accustomed to its potential benefits and pitfalls before entering
practice.
Evaluating a Mass or Focal Asymmetry
Identified at Screening
The next step after identifying a mass or
focal asymmetry is diagnostic evaluation. Biopsy should not be recommended based on the findings of screening mammography. Additional imaging
in the diagnostic setting allows characterization of the mass or focal asymmetry to evaluate if the finding is real and
to permit the imager to develop a level
of suspicion. If a lesion is highly suspicious for breast cancer on the screening
images, recall for diagnostic evaluation
is still useful to evaluate for the extent of
disease, multifocality, and staging of the
axilla with US. In addition, diagnostic
evaluation allows the radiologist to discuss the findings with the patient, an70
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Figure 13
Figure 13: Spot compression in two views. (a) Left
breast mammogram in a 63-year-old woman with no
breast complaints. A focal asymmetry (solid circle) is
seen superiorly on the MLO view, posterior third. No
obvious corresponding lesion is seen in the CC projection. However, the most likely location can be localized by closely evaluating the region equal in distance
from the nipple as the finding in the MLO view (arrows). The most likely location is in the lateral breast
(dotted circle). (b) Spot compression view in CC projection shows corresponding 8-mm oval equal-density mass (arrow) with ill-defined margins at 2 o’clock
position in left breast. A corresponding oval hypoechoic solid mass with ill-defined margins was identified at US (not shown). Core-needle biopsy specimen
showed invasive ductal carcinoma.
Figure 14
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Figure 15
Figure 14: Shift in position for medial and
lateral lesion from MLO to mediolateral view. Medial lesions (star) will appear lower on the MLO
view (line) with relationship to the nipple (F) than
the true location. Lateral lesions (irregular mass
shape) will appear higher on the MLO view than
the true location. Lesions centrally located in the
breast will shift little in position between MLO and
mediolateral views, whereas far lateral or far medial lesions will shift considerably.
swer questions, and arrange for biopsy.
An important advantage to this approach is that scheduling of procedures
is very efficient, since biopsies will
rarely be cancelled if the lesion has been
characterized at imaging prior to the
procedure. If a lesion is highly suspicious on the screening mammogram,
recall of the patient should be prioritized, however, so that minimal delay
occurs between screening and diagnostic evaluation.
Diagnostic Evaluation of Masses and
Focal Asymmetries
Spot compression views.—All screening
recall examinations with a mass or focal
asymmetry should include spot compression views as well as a true lateral
view. Spot compression views should be
obtained in both CC and MLO projections without coning. Obtaining spot
compression views in both projections
is important because some cancers may
not appear masslike on a spot compression view in one projection but may appear spiculated in the other projection.
If a focal asymmetry is seen on only one
view, a “best guess” at location may be
approximated by using the distance of
the lesion from the nipple (Fig 13).
Many breast imagers prefer to obtain
Figure 15: Use of true lateral view to localize lesions. Left: Right MLO view in a 66-year-old woman with
history of prior benign breast biopsy findings (scar is marked by wire). A focal asymmetry with architectural
distortion is present superiorly (circle). Right: Mediolateral view shows that wire marking the scar moves
lower (solid arrow), indicating it is lateral in location, whereas the focal asymmetry rises, indicating it is in the
medial breast (dashed arrow). Spot compression views (not shown) of the focal asymmetry revealed a spiculated mass; subsequent core-needle biopsy specimen showed invasive ductal carcinoma.
spot compression views with magnification, although this is not routine at our
institution.
Go to the lateral view for more information.—The true lateral view may
be either a mediolateral or lateromedial
view. Our standard protocol is to obtain
a mediolateral view in all patients recalled for an abnormal screening examination. However, if the lesion is located
in the medial breast, then a lateromedial view may provide better visualization of the lesion, since it will be closer
to the film or digital receptor. Other
mammographic views such as rolled,
exaggerated CC lateral, and cleavage
views may also be useful in localizing a
lesion and to evaluate if a finding represents summation of normal tissue or a
suspicious lesion. US is frequently useful
for confirming that a focal asymmetry
represents normal tissue or characterizing a mass as benign or malignant.
Lesions seen on only one view.—If a
lesion is seen only on the CC view, it
may be obscured on the MLO view or
may be medial and superior, since this
is where the MLO view is most likely to
miss tissue. Obtaining a true lateral
view may reveal the finding. Rolled
views, in which the breast is rolled either medial or lateral in the CC projection, may be helpful in localizing the
lesion. The direction in which the lesion
moves on each rolled CC view provides
a clue to the true lesion location.
If a lesion is seen only on the MLO
view, it may be obscured on the CC
view or may be far lateral, since this
area may not be visualized on the CC
view. An exaggerated CC lateral view is
frequently helpful because most breast
cancers are located in the lateral breast.
A true lateral view (mediolateral or lateromedial) is very useful for localizing
the lesion if not seen on the CC or exag71
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Figure 16
Figure 16: Use of US with negative spot compression views. (a) Bilateral mammogram in a
48-year-old woman with no breast complaints
shows focal asymmetry in the left breast at 12
o’clock, posterior third (circles). (b) Spot compression views show no persistent abnormality.
(c) US image shows 10-mm irregular solid mass
with posterior acoustic shadowing (arrow). Coreneedle biopsy specimen showed invasive ductal
carcinoma.
gerated CC lateral views (Fig 14). Lesions in the lateral breast project higher
on the MLO view than they are actually
located in the breast, because the MLO
view is obtained at an oblique angle.
Likewise, lesions in the medial breast
project lower on the MLO view than
they are actually located in the breast.
Thus, lesions that shift lower in position
on the mediolateral view are located in
the lateral breast while lesions that shift
higher in position on the mediolateral
view are located in the medial breast
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(Fig 15). This leads to the well-used adage, “Lead (lateral) sinks, muffins (medial) rise.” Note, however, that lesions
that are more central in the breast
(slightly lateral or slightly medial to the
nipple) will shift little or not at all between the MLO and mediolateral views.
The best approach is to think about the
geometry of the views rather than by
relying on a saying. Lesions seen in only
one projection can also be localized by
using step-oblique mammographic views,
where mammographic views are ob-
tained at 15° intervals between the true
lateral and CC views. Pearson et al (22)
successfully localized 50 of 50 true
masses in three dimensions by using
this technique.
Occasionally a lesion may be seen
well only in one projection, despite obtaining additional mammographic views. If
a lesion is suspicious at mammography,
biopsy can often still be performed in
most cases by using stereotactic guidance. If the lesion is too far posterior,
US or magnetic resonance (MR) imagRadiology: Volume 248: Number 1—July 2008
Figure 17
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MR imaging for problem solving.—
Current indications for breast MR imaging may include evaluation of extent
of a known breast cancer, detection of
an unknown primary breast carcinoma in patients manifesting malignant adenopathy with a normal mammogram, or screening in high-risk
women (24,25). Breast MR imaging is
not ordinarily indicated for routine
evaluation of masses or focal asymmetries on mammograms, and it should
never replace a thorough diagnostic
evaluation including additional mammographic views and US images. However,
breast MR imaging can be useful in
some circumstances, particularly when
a lesion is quite suspicious on one view
but cannot be localized despite appropriate and complete additional imaging
(Fig 18).
Management of Breast Masses and
Focal Asymmetries
The Worst Feature Wins
Lesions in the breast should be managed
based on their worst features. If the mammogram finding is suspicious but the US
examination is normal, or vice versa, biopsy should still be considered.
Figure 17: Use of US to confirm presence of normal tissue. (a) Left digital MLO view in a 42-year-old
woman referred for biopsy of a left 12-o’clock focal asymmetry (arrow) on baseline mammogram. (b) Focal
asymmetry appears to respect normal breast architecture on spot compression view, as it does not appear
masslike or have straight lines. (c) On US image, an island of normal hyperechoic breast tissue (arrows) is
identified that corresponds to the focal asymmetry in location. Biopsy was cancelled.
ing may be useful for localization. Placement of a marking clip at the time of
biopsy and a subsequent mammogram
documenting clip location can confirm
that the lesion identified at US or MR
imaging represented the mammographic finding.
Using US in the diagnostic setting.—
Early use of US in the diagnostic breast
evaluation setting was to differentiate
benign simple cysts from solid masses.
The work of Stavros et al (23) defined
benign and malignant characteristics of
breast masses, allowing more appropriate disposition of breast findings. At our
institution, we frequently use US as a
second check of a focal asymmetry identified at screening mammography when
the spot compression views do not show
an underlying mass, especially with
dense tissue (Fig 16). If a mass is not
identified at US, focal areas of shadowing or hypoechogenicity may be identified that would increase suspicion or,
alternatively, a corresponding island of
normal breast tissue may be identified
that may reduce the level of concern
(Fig 17). However, if a lesion is concerning at mammography, perhaps because it is new, a negative US finding
should not influence one to not recommend biopsy.
Malignant Features
Biopsy should be performed if malignant features are present at mammography or US. On mammograms, these
features include irregular shape, spiculated or irregular margins, or high
density. On US images these include
spiculation, angular margins, marked
hypoechogenicity, posterior acoustic shadowing, calcifications, duct extension,
branch pattern, or microlobulation
(23). For lesions with these characteristics, assessment of stability has no
role—for example, “stable” and “spiculated” do not belong in the same sentence in a report. Lesions should be
considered suspicious when the margins are ill defined or microlobulated
with any shape or density of lesion; biopsy should be considered.
For highly suspicious lesions (BIRADS category 5), US may be useful
for evaluating for additional masses
73
Harvey et al
Figure 18
Figure 18: Use of MR imaging to evaluate a “problem mammogram.” (a) Bilateral digital screening mammogram in 52-year-old woman shows small focal asymmetry
superior on right MLO view, posterior third (circle); lesion could not be identified on the CC view (left). The lesion shifted up on the mediolateral view (not shown), indicating the lesion was in the medial breast. Despite considerable effort by experienced breast imagers, the lesion could not be localized at US. Stereotactic biopsy was
thought difficult due to far posterior location. MR imaging was performed to aid in localizing the lesion. (b) T1-weighted gradient-echo sagittal MR image with fat suppression (repetition time msec/echo time msec, 15.0/4.5) obtained 2 minutes after intravenous administration of gadolinium-based contrast agent shows irregular lesion
(arrow) very high on the chest wall at 2 o’clock position in right breast. (c) Second-look US image shows a corresponding 5-mm hypoechoic solid mass (arrow). USguided core needle biopsy specimen showed invasive ductal carcinoma.
that may represent multifocal invasion
and for abnormal lymph nodes in the
axilla. Remember that lymph enters
the node on the capsule, not the hilum, so an abnormal outward contour
of the lymph node should be considered with suspicion (Fig 8). The most
predictive signs of axillary metastasis
in lymph nodes are maximum cortex
74
thickness greater than 2 mm and appearance of the cortex (26).
Benign Features
Masses have benign features if round,
oval, or lobular in shape with circumscribed margins. A focal asymmetry
has benign features when there are no outward convex margins or associated
straightening of Cooper ligaments.
Having prior mammograms for comparison is key in the disposition of lesions with benign features. Routine
follow-up can be performed if the lesion is stable for 2 or more years (BIRADS 2: benign finding). However,
when a lesion with benign features is
new, biopsy should be considered (BIRadiology: Volume 248: Number 1—July 2008
RADS 4: suspicious) unless shown to
be a simple cyst at US examination
(BI-RADS 2). If this was the patient’s
first mammogram (baseline) or it is
not possible to obtain earlier studies,
short-term follow-up imaging in 6
months (BI-RADS 3: probably benign)
is reasonable since the risk of malignancy is less than 2% (27).
Probably Benign
The BI-RADS 3 (probably benign) category is a frequently misapplied category (28). Probably benign does not
equate to “I am not sure what to do
with this lesion.” If you are not sure,
get more information by obtaining
more mammographic views or US images or get input from someone else.
The two primary indications for a
probably benign assessment are a
round or oval mass or grouped round
calcifications on a baseline mammogram. It is also okay to consider a
lesion probably benign if it is far posterior and that portion of the breast
was not visualized previously. A round
or oval mass that is new is not “probably benign” unless it represents a
specific benign diagnosis such as a
simple cyst or lymph node.
The key to successful application
of the BI-RADS 3 category is rigorous
evaluation of the lesion characteristics
and strict adherence to the criteria
differentiating benign from possibly
malignant. Many lesions that are assigned a BI-RADS 3 classification and
are ultimately determined to be malignant at follow-up examination were, in
retrospect, misclassified as BI-RADS 3
initially (29). Findings recalled from
screening for diagnostic evaluation
should be assigned a category of BIRADS 0 (needs additional evaluation),
not BI-RADS 3, even if the level of
suspicion is low that the finding represents a cancer.
Summary
Asymmetric breast tissue is usually normal but is worrisome when new or
when there are associated findings, including architectural distortion, a palpable lump, or thickening at clinical examRadiology: Volume 248: Number 1—July 2008
ination, or when the breast appears to
be smaller at mammography (“the shrinking breast”).
Look for asymmetry (side-by-side
comparison), contour deformities (look
for the hook, slow down for the speed
bump), lesions in the retromammary fat
(living in the wrong triangle), and associated findings to identify early breast
cancer.
Use studies that are 2 or more years
old for comparison when available, but
beware of stability. Suspicious morphology outweighs stability (“stable” and
“spiculated” do not belong in the same
sentence).
Diagnostic evaluation should be performed when a concerning mass or focal
asymmetry is identified at screening
mammography and should include a
true lateral view, spot compression
views in both CC and MLO projections,
and often US.
If in doubt about the finding after
obtaining additional mammographic views,
consider performing US. This will often
lower or raise the level of suspicion. If
still in doubt, biopsy can often be performed with stereotactic guidance, even
if the lesion is seen only on one view.
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Finding Early Invasive Breast Cancers

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