AJR 2000; 174:745-752
© American Roentgen Ray Society
Efficacy of Step-Oblique Mammography for Confirmation and Localization of Densities Seen on Only One Standard Mammographic View
Kathryn L. Pearson1,
Edward A. Sickles,
Steven D. Frankel and
Jessica W. T. Leung
1
All authors: Department of Radiology, University of California at San
Francisco, Box 1667, San Francisco, CA 94143.
Received May 24, 1999;
accepted after revision August 24, 1999.
Presented at the annual meeting of the American Roentgen Ray Society, New
Orleans, May 1999.
Address correspondence to E. A. Sickles, 2330 Post St., Ste. 180, San
Francisco, CA 94115.
Abstract
OBJECTIVE. Step-oblique mammography is a technique used to determine
with confidence whether a mammographic finding visible on multiple images on
only one projection (but not elucidated using standard additional mammographic
projections such as the roll view) represents a summation artifact or a true
mass, and to precisely localize the true mass for further evaluation (if
applicable). This paper describes the step-oblique technique and evaluates its
efficacy.
MATERIALS AND METHODS. Between January 1, 1993 and December 31,
1998, 69 consecutive women underwent step-oblique mammography for the
evaluation of densities seen on multiple images in only one standard
projection. Additional images were obtained at 15° stepped increments in
obliquity. If a one-projection-only finding was not seen on step-oblique
images, the density was judged to represent a summation artifact, completing
the examination. If a density was visualized and could be triangulated
concordantly on step-oblique images ranging from the craniocaudal to the
90° lateral projection, then it was judged to represent a real lesion.
Such a lesion was further characterized (mass, neodensity, architectural
distortion, focal asymmetric density) and was localized precisely in three
dimensions, permitting imaging-guided tissue diagnosis, if appropriate. For
all study patients, we also recorded BI-RADS (American College of Radiology
Breast Imaging and Data Reporting System) assessment categories; pathology
results for biopsied lesions; and mammographic follow-up, clinical follow-up,
and linkage to regional tumor registry for nonbiopsied lesions for which at
least 2 years had elapsed since step-oblique mammography.
RESULTS. Step-oblique mammography differentiated 50 real lesions
from 19 summation artifacts. All 50 real lesions, although initially visible
on only one standard projection, were successfully localized in three
dimensions. Subsequent management resulted in the prompt detection and
diagnosis of seven breast cancers and 21 benign lesions. None of the remaining
findings managed by follow-up rather than biopsy have subsequently been found
to be malignant.
CONCLUSION. Step-oblique mammography is an effective means of
evaluating the mammographic finding visible on multiple images on only one
standard projection.
Introduction
In the mammographic evaluation of a noncalcified density seen on only one
standard projection, a single additional image usually provides sufficient
information to differentiate a superimposition of normal structures (a
summation artifact) from a true mass obscured by surrounding dense
fibroglandular tissue
[1,2,3,4,5,6,7,8,9,10,11].
This additional image may involve spot compression, magnification, 5°
angled oblique projection, roll-view positioning, or a combination of these
maneuvers. The finding that is no longer visible on the additional image is
judged to represent a summation artifact. For the finding that does remain
visible, one more image is then obtained, often in a 90° lateral
projection, to confirm the presence of a true mass and to more precisely
localize it for further evaluation (i.e., sonography or imaging-guided tissue
diagnosis).
Occasionally, a noncalcified density is encountered that remains visible on
similar mammographic projections but is not readily visible on a 90°
lateral view. Although most of these findings are true masses obscured by
adjacent isodense fibroglandular tissue on 90° lateral projection, some
are unusual cases of summation artifacts seen on two or more images because
these images were inadvertently produced using essentially identical
projections. It may be tempting to use sonography to further evaluate such
cases; however, this approach is unwise because sonography is effective as a
problem-solving tool primarily when the three-dimensional location of the
targeted lesion is known, and also because failure to visualize a lesion at
sonography does not rule out the presence of a true mass. Similarly, it is
unwise to attempt stereotactically guided percutaneous biopsy of a
mammographic finding until the possibility of a summation artifact has been
excluded.
This article introduces the technique of step-oblique mammography as a
means of determining with confidence whether the unusual occurrence of a
mammographic finding visible on multiple images on only one projection
represents a summation artifact or a true mass and of precisely localizing the
mass for further evaluation, if a mass is found.
Materials and Methods
Step-oblique mammography involves obtaining additional images at stepped
increments in obliquity, usually 15° increments, beginning from the view
in which the density is seen and proceeding toward the view in which the
density is not seen. At the start of a workup, these images are taken at the
degrees of obliquity between those of the two standard views already obtained.
For example, if a noncalcified density is visible on multiple 60°
mediolateral oblique views but not on a craniocaudal or 90° lateral view,
additional step-oblique images are obtained as mediolateral oblique views at
45°, 30°, and 15° of obliquity. Similarly, if a noncalcified
density is visible on multiple craniocaudal views but not on a 45°
mediolateral oblique view or a 90° lateral view, then step-oblique images
are taken as 15° and 30° mediolateral oblique views.
If the mammographic finding is not seen on the step-oblique views, it
represents a summation artifact and no further evaluation is needed. If the
finding remains visible but changes substantially in size, shape, and opacity
on the step-oblique views, then it usually represents a focal deposit of
benign fibroglandular tissue. This is judged to be a normal variant, also
requiring no further evaluation, unless it was not present on previous
mammograns (in which case it is described as a developing density or
neodensity) or unless it is associated with architectural distortion (in which
case it might represent invasive carcinoma, especially lobular).
If a noncalcified density displays similar size, shape, and opacity on one
standard mammographic projection and on all the step-oblique views, then it
should be judged to represent a mass, which (as for the developing density and
density associated with architectural distortion) requires additional imaging
evaluation. The next step is to determine by triangulation the precise
three-dimensional location of the finding in the breast. Once localized and
adequately visualized in two planes, the finding may then be assessed as
suspicious for malignancy, probably benign, or having benign
characteristics.
Several accurate methods of triangulation have been described in lectures,
textbooks, and journal articles
[2,
6,
8,9,10,11,12,13,14].
One of these methods is particularly well suited for use with step-oblique
images. If standard craniocaudal, step-oblique, and standard mediolateral
oblique mammograms are mounted on a viewbox side by side, in sequence of
either increasing or decreasing angle of obliquity and according to the
specifications illustrated in Figure
1, then a reasonably straight line will join a mass as it is seen
on all images. It is important that the films are mounted with the nipple at
the same level on all images, so that a straight horizontal line joins the
nipple as seen on these views. At one extreme in the stepwise progression of
images from the cramiocaudal to the standard mediolateral oblique view, the
lesion will not be visible. However, one can trace an imaginary line through
the lesion as seen on all views in which it is indeed visible, and extend the
line to determine the expected location of the lesion on the other view.
Depending on the specific circumstances of the case, the radiologist will then
choose either to obtain all the remaining even-steeper-angled step-oblique
images up to and including a 75° mediolateral oblique mammogram, or to
extend the imaginary line through all these not-yet-obtained mediolateral
oblique views, so that the expected location of the lesion is then estimated
at 90° lateral projection (Fig.
2A,2B,2C,2D,2E,2F,2G,2H,2I).
The procedure is completed by obtaining a 90° lateral view using spot
compression magnification technique (or spot compression alone), at the
expected site of the lesion as determined by triangulation and extrapolation,
to confirm the three-dimensional location of the lesion. Figure
3A,3B,3C,3D,3E,3F,3G
illustrates a typical clinical application of step-oblique mammography, in
this case as further workup of a mammographic finding visible on two different
images in craniocaudal projection but not visible initially on either a
standard mediolateral oblique or a 90° lateral view.
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Fig. 1. —Drawing shows how to mount step-oblique mammograms on viewbox and
perform triangulation. Progressive step-oblique images from 90°
mediolateral (ML) projection to 0° craniocaudal (CC) projection, performed
in 15° mediolateral oblique (MLO) increments, are mounted on viewbox with
projection markers at top. Nipples point in same direction and are aligned
horizontally. Note that straight line can connect lesion on all sequential
step-oblique images, which permits triangulation as follows. Using subset of
full complement of step-oblique images (i.e., lesion not yet identified on
either 90° or 0° projection, or both), draw imaginary line through
lesion on available images and extend line to left, right, or both to indicate
expected location of lesion on orthogonal projections. In this case, lesion is
in upper inner left breast.
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Fig. 2A Step-oblique mammography obtained for poorly defined noncalcified density
(arrows) in inner left breast not clearly seen at first on
mediolateral oblique (MLO) projection. Progressive 15° incremental
step-oblique images show density represents true mass, localized to lower
inner left breast. Imaging-guided tissue diagnosis (not shown) revealed
infiltrating ductal carcinoma. ML = mediolateral, CC = craniocaudal
projection. Screening mammograms at 60° MLO projection (A)
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Fig. 2B Step-oblique mammography obtained for poorly defined noncalcified density
(arrows) in inner left breast not clearly seen at first on
mediolateral oblique (MLO) projection. Progressive 15° incremental
step-oblique images show density represents true mass, localized to lower
inner left breast. Imaging-guided tissue diagnosis (not shown) revealed
infiltrating ductal carcinoma. ML = mediolateral, CC = craniocaudal
projection. 0° CC projection (B).
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Fig. 2C Step-oblique mammography obtained for poorly defined noncalcified density
(arrows) in inner left breast not clearly seen at first on
mediolateral oblique (MLO) projection. Progressive 15° incremental
step-oblique images show density represents true mass, localized to lower
inner left breast. Note nipple (white dots). Imaging-guided tissue
diagnosis (not shown) revealed infiltrating ductal carcinoma. ML =
mediolateral, CC = craniocaudal projection. Step-oblique mammograms at 0°
CC projection (C)
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Fig. 2D Step-oblique mammography obtained for poorly defined noncalcified density
(arrows) in inner left breast not clearly seen at first on
mediolateral oblique (MLO) projection. Progressive 15° incremental
step-oblique images show density represents true mass, localized to lower
inner left breast. Note nipple (white dots). Imaging-guided tissue
diagnosis (not shown) revealed infiltrating ductal carcinoma. ML =
mediolateral, CC = craniocaudal projection. 15° MLO projection
(D)
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Fig. 2E Step-oblique mammography obtained for poorly defined noncalcified density
(arrows) in inner left breast not clearly seen at first on
mediolateral oblique (MLO) projection. Progressive 15° incremental
step-oblique images show density represents true mass, localized to lower
inner left breast. Note nipple (white dots). Imaging-guided tissue
diagnosis (not shown) revealed infiltrating ductal carcinoma. ML =
mediolateral, CC = craniocaudal projection. 30° MLO projection
(E)
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Fig. 2F Step-oblique mammography obtained for poorly defined noncalcified density
(arrows) in inner left breast not clearly seen at first on
mediolateral oblique (MLO) projection. Progressive 15° incremental
step-oblique images show density represents true mass, localized to lower
inner left breast. Note nipple (white dots). Imaging-guided tissue
diagnosis (not shown) revealed infiltrating ductal carcinoma. ML =
mediolateral, CC = craniocaudal projection. 45° MLO projection
(F)
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Fig. 2G Step-oblique mammography obtained for poorly defined noncalcified density
(arrows) in inner left breast not clearly seen at first on
mediolateral oblique (MLO) projection. Progressive 15° incremental
step-oblique images show density represents true mass, localized to lower
inner left breast. Note nipple (white dots). Imaging-guided tissue
diagnosis (not shown) revealed infiltrating ductal carcinoma. ML =
mediolateral, CC = craniocaudal projection. 60° MLO projection
(G)
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Fig. 2H Step-oblique mammography obtained for poorly defined noncalcified density
(arrows) in inner left breast not clearly seen at first on
mediolateral oblique (MLO) projection. Progressive 15° incremental
step-oblique images show density represents true mass, localized to lower
inner left breast. Note nipple (white dots). Imaging-guided tissue
diagnosis (not shown) revealed infiltrating ductal carcinoma. ML =
mediolateral, CC = craniocaudal projection. Step-oblique mammograms at 75°
MLO projection (H)
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Fig. 2I Step-oblique mammography obtained for poorly defined noncalcified density
(arrows) in inner left breast not clearly seen at first on
mediolateral oblique (MLO) projection. Progressive 15° incremental
step-oblique images show density represents true mass, localized to lower
inner left breast. Note nipple (white dots). Imaging-guided tissue
diagnosis (not shown) revealed infiltrating ductal carcinoma. ML =
mediolateral, CC = craniocaudal projection. 90° ML projection
(I).
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Fig. 3A. —Step-oblique mammography requiring additional spot compression
magnification (SCM) mammography for lesion seen well only with fine-detal
technique. Poorly defined density (arrow, B), seen at first in
inner right breast only on screening craniocaudal (CC) view, persists on
craniocaudal spot compression magnification (CC SCM) image, in which margins
appear spiculated. Density not seen on screening 60° mediolateral oblique
(MLO) view. Step-oblique images obtained in 15° increments using SCM (over
expected region of density) show spiculated density much more readily than on
whole-breast step-oblique images (not shown), validating presence of mass and
permitting precise localization. Imaging-guided tissue diagnosis (also not
shown) revealed infiltrating ductal carcinoma. Screening mammograms at 60°
MLO projection (A) and 0° CC projection (B).
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Fig. 3B. —Step-oblique mammography requiring additional spot compression
magnification (SCM) mammography for lesion seen well only with fine-detail
technique. Poorly defined density (arrow, B), seen at first in
inner right breast only on screening craniocaudal (CC) view, persists on
craniocaudal spot compression magnification (CC SCM) image, in which margins
appear spiculated. Density not seen on screening 60° mediolateral oblique
(MLO) view. Step-oblique images obtained in 15° increments using SCM (over
expected region of density) show spiculated density much more readily than on
whole-breast step-oblique images (not shown), validating presence of mass and
permitting precise localization. Imaging-guided tissue diagnosis (also not
shown) revealed infiltrating ductal carcinoma. 0° CC projection
(B).
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Fig. 3C. —Step-oblique mammography requiring additional spot compression
magnification (SCM) mammography for lesion seen well only with fine-detail
technique. Poorly defined density (arrow, B), seen at first in
inner right breast only on screening craniocaudal (CC) view, persists on
craniocaudal spot compression magnification (CC SCM) image, in which margins
appear spiculated. Density not seen on screening 60° mediolateral oblique
(MLO) view. Step-oblique images obtained in 15° increments using SCM (over
expected region of density) show spiculated density much more readily than on
whole-breast step-oblique images (not shown), validating presence of mass and
permitting precise localization. Imaging-guided tissue diagnosis (also not
shown) revealed infiltrating ductal carcinoma. Screening mammogram at 0°
CC projection with area of interest photographically enlarged.
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Fig. 3D. —Step-oblique mammography requiring additional spot compression
magnification (SCM) mammography for lesion seen well only with fine-detail
technique. Poorly defined density (arrow, B), seen at first in
inner right breast only on screening craniocaudal (CC) view, persists on
craniocaudal spot compression magnification (CC SCM) image, in which margins
appear spiculated. Density not seen on screening 60° mediolateral oblique
(MLO) view. Step-oblique images obtained in 15° increments using SCM (over
expected region of density) show spiculated density much more readily than on
whole-breast step-oblique images (not shown), validating presence of mass and
permitting precise localization. Imaging-guided tissue diagnosis (also not
shown) revealed infiltrating ductal carcinoma. SCM mammogram at 0° CC
projection with area of interest photographically enlarged.
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Fig. 3E. —Step-oblique mammography requiring additional spot compression
magnification (SCM) mammography for lesion seen well only with fine-detail
technique. Poorly defined density (arrow, B), seen at first in
inner right breast only on screening craniocaudal (CC) view, persists on
craniocaudal spot compression magnification (CC SCM) image, in which margins
appear spiculated. Density not seen on screening 60° mediolateral oblique
(MLO) view. Step-oblique images obtained in 15° increments using SCM (over
expected region of density) show spiculated density much more readily than on
whole-breast step-oblique images (not shown), validating presence of mass and
permitting precise localization. Imaging-guided tissue diagnosis (also not
shown) revealed infiltrating ductal carcinoma. Step-oblique SCM mammograms
with area of interest photographically enlarged at 15° MLO projection
(E).
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Fig. 3F. —Step-oblique mammography requiring additional spot compression
magnification (SCM) mammography for lesion seen well only with fine-detail
technique. Poorly defined density (arrow, B), seen at first in
inner right breast only on screening craniocaudal (CC) view, persists on
craniocaudal spot compression magnification (CC SCM) image, in which margins
appear spiculated. Density not seen on screening 60° mediolateral oblique
(MLO) view. Step-oblique images obtained in 15° increments using SCM (over
expected region of density) show spiculated density much more readily than on
whole-breast step-oblique images (not shown), validating presence of mass and
permitting precise localization. Imaging-guided tissue diagnosis (also not
shown) revealed infiltrating ductal carcinoma. 45° MLO projection
(F).
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Fig. 3G. —Step-oblique mammography requiring additional spot compression
magnification (SCM) mammography for lesion seen well only with fine-detail
technique. Poorly defined density (arrow, B), seen at first in
inner right breast only on screening craniocaudal (CC) view, persists on
craniocaudal spot compression magnification (CC SCM) image, in which margins
appear spiculated. Density not seen on screening 60° mediolateral oblique
(MLO) view. Step-oblique images obtained in 15° increments using SCM (over
expected region of density) show spiculated density much more readily than on
whole-breast step-oblique images (not shown), validating presence of mass and
permitting precise localization. Imaging-guided tissue diagnosis (also not
shown) revealed infiltrating ductal carcinoma. 90° mediolateral projection
(G).
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To show the efficacy of step-oblique mammography as a problem-solving tool,
we evaluated all cases involving the technique among the 27,633 consecutive
diagnostic mammography examinations performed in our institution during the
6-year period from January 1, 1993 through December 31, 1998. Cases were
identified by computerized search of all mammography interpretations for the
words "step oblique." We judge this to be an accurate if not
entirely comprehensive method of case identification because all radiologists
in our practice routinely used the term "step oblique" throughout
the study period to describe the mammographic approach discussed in this
article. Once identified, mammography interpretations were further
characterized according to imaging outcome. Efficacy was determined on the
basis of subsequent clinical course, ranging from routine mammography
screening for findings judged as representing summation artifacts to biopsy
for lesions assessed as suspicious for malignancy. We also linked our study
cases with data in our regional Surveillance, Epidemiology and End Results
(SEER) tumor registry to identify cancer not detected by mammography. Linkage
was performed a minimum of 2 years after mammography. This delay between
imaging and linkage allows for the routine 1-year interval that we recommend
between mammography examinations and for another year so that outcomes data
from newly diagnosed cancers can be entered in the database of the tumor
registry.
Results
We identified 69 cases involving step-oblique imaging for the evaluation of
densities seen on multiple images on only one standard projection.
Step-oblique mammography identified 19 summation artifacts, which were
assessed as normal findings (Fig.
4A,4B,4C,4D,4E).
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Fig. 4A —Step-oblique mammography used to identify summation artifacts. Oval
density (straight arrow, B-D) seen at first in inner right
breast on screening craniocaudal (CC) view but not on screening mediolateral
oblique (MLO) view. Note second poorly defined density (curved arrow,
B) in central right breast seen only on screening CC view, confidently
judged to represent summation artifact without need for further imaging
evaluation. Oval density (straight arrow, C), persistent on
0° craniocaudal spotcompression magnification (SCM) view but not seen on
90° lateral SCM view (not shown), was subsequently shown on step-oblique
images to represent summation artifact created by looping blood vessel
(straight arrow, D). Screening mammograms at 60° MLO
projection (A)
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Fig. 4B —Step-oblique mammography used to identify summation artifacts. Oval
density (straight arrow, B-D) seen at first in inner right
breast on screening craniocaudal (CC) view but not on screening mediolateral
oblique (MLO) view. Note second poorly defined density (curved arrow,
B) in central right breast seen only on screening CC view, confidently
judged to represent summation artifact without need for further imaging
evaluation. Oval density (straight arrow, C), persistent on
0° craniocaudal spotcompression magnification (SCM) view but not seen on
90° lateral SCM view (not shown), was subsequently shown on step-oblique
images to represent summation artifact created by looping blood vessel
(straight arrow, D). 0° CC projection (B)
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Fig. 4C —Step-oblique mammography used to identify summation artifacts. Oval
density (straight arrow, B-D) seen at first in inner right
breast on screening craniocaudal (CC) view but not on screening mediolateral
oblique (MLO) view. Note second poorly defined density (curved arrow,
B) in central right breast seen only on screening CC view, confidently
judged to represent summation artifact without need for further imaging
evaluation. Oval density (straight arrow, C), persistent on
0° craniocaudal spotcompression magnification (SCM) view but not seen on
90° lateral SCM view (not shown), was subsequently shown on step-oblique
images to represent summation artifact created by looping blood vessel
(straight arrow, D). SCM mammogram at 0° CC projection
with area of interest photographically enlarged.
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Fig. 4D —Step-oblique mammography used to identify summation artifacts. Oval
density (straight arrow, B-D) seen at first in inner right
breast on screening craniocaudal (CC) view but not on screening mediolateral
oblique (MLO) view. Note second poorly defined density (curved arrow,
B) in central right breast seen only on screening CC view, confidently
judged to represent summation artifact without need for further imaging
evaluation. Oval density (straight arrow, C), persistent on
0° craniocaudal spotcompression magnification (SCM) view but not seen on
90° lateral SCM view (not shown), was subsequently shown on step-oblique
images to represent summation artifact created by looping blood vessel
(straight arrow, D). Step-oblique mammograms at 15° MLO
projection (D)
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Fig. 4E —Step-oblique mammography used to identify summation artifacts. Oval
density (straight arrow, B-D) seen at first in inner right
breast on screening craniocaudal (CC) view but not on screening mediolateral
oblique (MLO) view. Note second poorly defined density (curved arrow,
B) in central right breast seen only on screening CC view, confidently
judged to represent summation artifact without need for further imaging
evaluation. Oval density (straight arrow, C), persistent on
0° craniocaudal spotcompression magnification (SCM) view but not seen on
90° lateral SCM view (not shown), was subsequently shown on step-oblique
images to represent summation artifact created by looping blood vessel
(straight arrow, D). 30° MLO projection (E).
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The remaining 50 lesions, although initially visible on only one standard
projection, were successfully localized in three dimensions using step-oblique
imaging, thus permitting further imaging evaluation with fine-detail
mammography, sonography, or both, which in all cases confirmed the presence of
real lesions. These lesions were subsequently assessed as benign (eight
cases), probably benign (12 cases), or suspicious for malignancy (30 cases)
(Table 1), on the basis of
their mammographic and sonographic features (if mammography and sonography
were performed). In making these assessments, determining the separate
contributions of step-oblique views, additional mammographic views, and
sonography was beyond the scope of this study.
Biopsy was performed for 28 of the 30 lesions in question, resulting in the
prompt diagnosis of seven breast cancers and 21 benign lesions. For the benign
lesions, the histologic findings were deemed concordant with imaging features
in all cases. One patient chose to have short-interval follow-up mammography
instead of biopsy, and the other patient has been lost to follow-up.
Lesions assessed as probably benign were monitored using surveillance
mammography, including step-oblique views if needed, initially for a year at
6-month intervals and then annually. Ten of the 20 benign lesions and probably
benign lesions have now been assessed at subsequent mammography for at least 2
years after step-oblique imaging, confirming benignity insofar as none of
these findings showed mammographic signs of progression. The remaining 10
lesions have not yet been monitored for a 2-year interval, although none show
mammographic (or clinical) signs of progression to date (follow-up interval:
range, 12-18 months; mean, 13.8 months).
The 19 findings shown at step-oblique imaging to represent superimposition
of normal fibroglandular tissue do not require further follow-up because, in
our experience, findings interpreted as summation artifacts after diagnostic
mammography have invariably proved to be benign
[10]. Indeed, these findings
were no longer visible at subsequent routine screening mammography in each of
the 15 patients in which subsequent mammography has been performed. Linkage of
these cases to our tumor registry has not identified missed cancers.
Discussion
Step-oblique mammography is an accurate technique for determining whether a
mammographic finding visible on multiple images on only one projection (but
not elucidated using standard additional mammographic projections) represents
a summation artifact or a true mass and for precisely localizing the true mass
for further evaluation. The specific application of this technique in
problem-solving was effective in all of our cases, confirming either a
summation artifact or a real lesion. Seven of the real lesions were promptly
diagnosed as cancerous. Step-oblique images not only provided the means for
localizing all these lesions so that imaging-guided biopsy could be performed,
but also displayed the same (and sometimes additional) mammographic features
suspicious for malignancy that previously were visible on only one projection,
thereby reinforcing our assessment to recommend biopsy. Many of the other real
lesions were subsequently assessed as benign or probably benign, the
step-oblique images also displaying the same (and sometimes additional)
mammographic features that previously were visible on only one projection,
thereby reinforcing our assessment not to recommend biopsy. Thereafter, these
lesions were monitored appropriately, often using the step-oblique images on
which the lesion was best visualized. Although some of our cases interpreted
as negative (summation artifacts), benign, and probably benign have not yet
been followed up for 2 years (which establishes benignity), existing follow-up
has not suggested malignancy in any case, nor has linkage with our regional
tumor registry identified any missed cancers.
The diagnostic accuracy of step-oblique mammography will be maximized by
carefully observing technical requirements. All step-oblique images should be
taken with the breast in the same orientation (i.e., all mediolateral oblique
or all lateromedial oblique). The nipple should be in profile on all
step-oblique exposures and there should be no rolling of the breast
[14]. Also, the patient should
stand up straight during all step-oblique exposures (no leaning sideways as in
a Cleopatra view), because the angle of X-ray beam obliquity indicated on the
mammography unit will be misleading if the patient leans into the obliquity.
Finally, all step-oblique exposures should be taken by the same technologist
to reduce variability in breast positioning and in measuring X-ray beam
obliquity [15].
Step-oblique images can be obtained initially not just using projections
between those of the two standard views, but also in both directions starting
from the projection in which a one-view-only finding is visible. However, we
prefer the first approach because it is sufficient for differentiating between
summation artifacts and real lesions, and because it is more useful in
permitting precise three-dimensional localization of real lesions
(Fig. 1).
As with all diagnostic imaging workups, it is necessary to tailor the
step-oblique evaluation to the specific circumstances of each patient. For
example, step-oblique mammography may require spot compression or spot
compression magnification imaging for lesions seen well only with one of these
fine-detail techniques. The addition of spot compression (with or without
magnification) to a step-oblique projection exposure may indeed permit
visualization of a true lesion that otherwise might be obscured by adjacent
dense fibroglandular tissue. Estimating the location of the lesion from
initial whole-breast images will determine appropriate placement of the spot
compression paddle.
Common triangulation methods (using the mediolateral oblique view and
either a craniocaudal or 90° lateral view) are usually accurate in
indicating the quadrant location of a mammographic lesion, although perhaps
not for some lesions located in the superior, slightly lateral breast or in
the inferior, slightly medial breast
[16]. However, no method of
triangulation is sufficiently accurate to provide the degree of precision in
three-dimensional localization that is obtained by orthogonal projection
mammography (using craniocaudal and 90° lateral views). Step-oblique
mammography overcomes the limitations of triangulation by indicating true
lesions on orthogonal projections, thereby permitting planning of the optimal
approach for imaging-guided biopsy of those lesions that are suspicious for
malignancy.
Sonography is not an acceptable substitute for step-oblique mammography in
the further evaluation of an impalpable noncalcified density that is visible
only on very similar mammographic projections. Sonography should not be used
to exclude the presence of a true mass because some such mammographically
detected lesions, including some cancerous tumors, are not sonographically
visible. Furthermore, the usefulness of sonography is greatly enhanced when
the precise three-dimensional location of a targeted lesion is known.
Although step-oblique mammography is more frequently used to assess the
noncalcified density identified on only one standard mammographic projection,
it also can be helpful in evaluating grouped microcalcifications seen on only
one standard view. In a limited number of cases, we have observed that
step-oblique mammography established the presence of truly clustered calcific
particles and also permitted accurate three-dimensional localization of the
lesion. Occasionally, step-oblique mammography also is useful in indicating
the three-dimensional locations of more than one lesion in the same breast,
especially if two or more lesions display similar mammographic features and
are similar in distance from the nipple. This usually occurs when two or three
clusters of amorphous microcalcifications are present in one breast.
Confirmation of the precise three-dimensional location of each lesion by
step-oblique mammography permits planning of the optimal approach for
imaging-guided biopsy.
Step-oblique mammography is helpful primarily in solving the unusual
clinical problem posed by a mammographically detected lesion that is seen on
multiple images on only one projection. The frequency with which step-oblique
mammography might actually be used in a breast imaging practice can be
estimated on the basis of our reported experience. In a 6-year period during
which we performed 27,633 diagnostic mammography examinations, 87 (0.315%)
involved step-oblique imaging (for noncalcified densities or grouped
microcalcifications), of which 83% were generated from within our own
institution and 17% were performed to further evaluate unresolved cases
presenting for second-opinion review from outside facilities. Thus, a given
breast imaging practice might expect to perform one step-oblique mammography
evaluation for approximately every 300-325 diagnostic mammography
examinations. Expressed in other terms, a very busy practice that performs 30
diagnostic mammography examinations per day might use step-oblique imaging
once every 2 weeks, whereas a practice that performs eight diagnostic
examinations per day might use step-oblique imaging once every 2 months. No
matter how frequently one might expect to use step-oblique mammography, it is
important for the radiologist to learn the techniques involved and how to
interpret the resultant images. Step-oblique mammography is an accurate method
of determining whether a mammographic finding visible on multiple images on
only one projection represents a summation artifact or a true mass and of
precisely localizing the true mass for further evaluation (if applicable).
References
-
Logan WW, Janus J. Use of special mammographic views to maximize
radiographic information. Radiol Clin North Am
1987;25:953-959[Medline]
-
Sickles EA. Practical solutions to common mammographic problems:
tailoring the examination. AJR
1988;151:31-39[Free Full Text]
-
Feig SA. Importance of mammographic views to diagnostic accuracy.
AJR
1988;151:40-41[Free Full Text]
-
Berkowitz JE, Gatewood OMB, Gaylor BW. Equivocal mammographic
findings: evaluation with spot compression. Radiology
1989;171:369-371[Abstract/Free Full Text]
-
Sickles EA. Combining spot compression and other special views to
maximize mammographic information (letter). Radiology
1989;173:571
-
Eklund GW, Cardenosa G. The art of mammographic positioning.
Radiol Clin North Am
1992;30:21-53[Medline]
-
Sickles EA. Triangulating the location of a lesion by using the
oblique view. In: Sickles EA, Destouet JM, Eklund GW, Feig SA, Jackson VP,
eds. Breast disease (second series): test and syllabus. Reston,
VA: American College of Radiology,
1993:2-18
-
Eklund GW. Tailoring the mammographic examination. In: RSNA
categorical course in breast imaging. Oak Brook, IL: Radiological
Society of North America,
1995:117-120
-
Kopans DB. Breast imaging, 2nd ed. Philadelphia:
Lippincott-Raven, 1998:203-209,
721-739
-
Sickles EA. Findings at mammographic screening on only one standard
projection: outcomes analysis. Radiology
1998;208:471-475[Abstract/Free Full Text]
-
Brenner RJ. Asymmetries of the breast: extended use of the rolled
projection. Appl Radiol
1998;2:15-24
-
Swann CA, Kopans DB, McCarthy KA. Localization of occult breast
lesions: practical solutions to problems of triangulation.
Radiology
1987;163:577-579[Abstract/Free Full Text]
-
Kopans DB, Waitzkin ED, Linetsky L, et al. Localization of breast
lesions identified on only one mammographic view. AJR
1987;149:39-41[Abstract/Free Full Text]
-
Sickles EA. Determining lesion location using the oblique view. In:
Bassett LW, et al., eds. Breast disease (third series): test and
syllabus. Reston, VA: American College of Radiology, (in
press)
-
Sickles EA. Lesion seen on only one standard mammographic
projection. In: Sickles EA, Destouet JM, Eklund GW, Feig SA, Jackson VP, eds.
Breast disease (second series): test and syllabus. Reston, VA:
American College of Radiology,
1993:20-35
-
Rose GH. Medial or lateral mammographic lesions: down and out is
down and out...sometimes. Radiology
1998;209:276-278[Abstract/Free Full Text]
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Abstract
Introduction
