is the Section Head, Ultrasound, Virginia Mason Medical Center,
Breast imagers commonly encounter focal asymmetric densities as
well as densities that are seen on only one mammographic view.
Traditionally, these lesions have been worked up with additional
mammographic views. However, in some cases, mammographic evaluation
does not resolve the diagnostic question completely. In these
situations, high-resolution sonography has the potential to
facilitate the diagnosis.
Definition of Focal Asymmetric Densities
Mammographic focal asymmetric densities and densities visible on
one view are closely related findings in that both do not meet the
criteria for a mammographic mass, a real mass exhibiting a
consistent structural identity on two orthogonal mammographic
views. Some focal asymmetric densities may be visible on two views,
but they do not appear to have the same appearance on both views.
With spot compression classically, a focal asymmetric density that
is not a mass will disappear or blend into the surrounding
Mammographic Evaluation of Focal Asymmetric
The evaluation of focal asymmetric densities should start with
additional mammographic views. The goals of this assessment should
be to: 1) determine the location of the density, and 2) determine
if the density is a true mass. When the density is only visible on
one view, exaggerated, rolled, or oblique views are useful to
locate it if it is outside of the field-of-view (FOV) of standard
screening mammographic views. If the lesion is expected to be
within the FOV but is not visible because it is obscured by the
surrounding fibroglandular tissues, spot compression views are also
useful to identify it.
If a density disappears on focal spot compression views, then it
is usually benign breast tissue. However, breast imagers have
realized that focal asymmetric densities that disappear with spot
compression may on occasion represent neoplasms that are either
extremely pliable or very small. In order to avoid the pitfall of
missing a pliable neoplasm, breast imagers have advocated doing
large FOV mammograms performed at different angles (eg, rolled
views, 90° mediolateral views, oblique views). These large FOV
mammograms not only demonstrate the three-dimensional
characteristics of the density, but also provide information about
the location of the density.
Even after carefully evaluating these densities with additional
mammographic views, it may not always be possible to determine
whether or not a focal asymmetric density represents a real mass.
Furthermore, since these densities are subtle in other views, it
may not be possible to identify the exact location of the density.
If the mammographic assessment of a focal asymmetric density or of
a density visible only on one view is not adequate, then
high-resolution sonography should be considered.
Sonographic Evaluation of Focal Asymmetric
Sonographic evaluation of focal asymmetric densities is one of
the most challenging situations in breast sonography. The
sonographic examination of a focal asymmetric density consists of
two steps. The first step is a survey of the general area in which
the density may be located. Usually, it is only necessary to
examine a quadrant of the breast, but sometimes, half of the breast
must be examined. During this stage, it is generally best to use a
lower frequency to cover the entire thickness of the breast from
the skin to the chest wall. In order to quickly cover a large area,
a high frame rate and a larger transducer are useful. Finally, for
this survey stage, it is advantageous to use an imaging program
that provides a high sensitivity for identifying focal breast
masses. In our institution, we use the Advanced Imaging Package
available on the Sequoia 15L8W ultrasound system (Acuson, Mountain
View, CA) for these examinations.
Several features of this system are well adapted to breast
imaging. The transducer's width is ideal for surveying large areas
of the breast. The 14 MHz center frequency has sufficient depth
penetration. When used with the Tissue Equalization Control (TEQ)
button, the 14 MHz can usually penetrate approximately 4 to 5 cm,
so most breasts may be surveyed at this frequency. The imaging
package also makes it possible to use multiple transmit zones with
the 14-MHz transducer without significant reduction in frame rate.
Since it is possible to create custom programs within the Sequoia,
a low dynamic range program is routinely used for the survey mode.
This program produces superior tissue contrast, and allows the
sonographer to spot focal lesions within the breast quickly.
Once a focal abnormality is identified, the second step of the
breast sonographic examination is the diagnostic evaluation. High
resolution is important to evaluate margin irregularities.
Gray-scale contrast manipulation is useful to characterize lesions.
We have found that the Sequoia Advanced Imaging Package technology
is also useful for the diagnostic assessment of lesions. The TEQ
allows the sonographer to optimize the appearance of the lesion
rapidly. For cysts or fibroadenomas, some sonographers may prefer
to use a compound frequency, which increases the conspicuity of
focal masses and produces sharp margins. Compound frequency imaging
is the result of sending multiple frequencies simultaneously and
combining the image information from all of these frequencies. For
lesions with irregular margins the highest center frequency
technique is preferred to the use of compound frequencies. For
calcifications, a high delta setting strongly highlights small
hyperechoic foci. Delta is a type of postprocessing technique that
preferentially enhances or supresses signals on a region-by-region
basis rather than the traditional point-by-point method. Elevated
delta settings appear superior to high-contrast postprocessing or
low-dynamic range programs in accentuating subtle margin
irregularities and microcalcifications.
Using the above techniques, the diagnosis of a mammographic
focal asymmetric density can generally be made. If a hypoechoic,
irregular, or heterogeneous mass is identified, then an ACR
Category 4 (suspicious--biopsy recommended) is given. If benign
hyperechoic tissue is demonstrated, then an ACR Category 3 finding
is given (probably benign--recommend 6-month follow-up). If the
density is a benign lesion, such as a cyst or lymph node, then a
Category 2 is reported (benign) (Figure 1). If short-term follow-up
is needed, a recommendation is made for a mammographic follow-up.
Rarely, the mammographic density cannot be explained
sonographically. In these cases, the mammographic findings are used
to plan the next course of action.
There are several advantages to utilizing high-resolution
sonography to characterize focal asymmetric densities.
High-resolution sonography is useful to localize lesions that
cannot be identified on two mammographic views. Furthermore,
high-resolution sonography increases diagnostic confidence by
characterizing these lesions and may prevent a highly compressible
neoplasm, such as lobular carcinoma, from being missed. Finally, if
a focal asymmetric density is a sonographic mass, sonography can be
used to biopsy the mass. *