Traditionally, the role of ultrasound in the assessment of breast masses has been to differentiate solid from cystic masses and to guide interventional procedures. However, this role is expanding to include its use as a valuable adjunct to mammography, and ultrasound has improved accuracy of the diagnosis of breast cancer. This article details sonographic features that can help to differentiate benign from malignant masses.
is a Clinical Assistant Professor of Radiology, Thomas Jefferson
University Hospital, Breast Imaging Center, Philadelphia,
Ultrasound plays a vital role in the assessment of breast
masses. Its primary use has been for the differentiation of solid
from cystic masses and as guidance for interventional procedures.
However, in recent years, ultrasound as an adjunct to mammography
has improved accuracy in the diagnosis of breast cancer.
Certain ultrasound features can help differentiate benign from
In solid masses, evaluation of the shape, margins and
width-to-anteroposterior (AP) ratio can be useful in avoiding
unnecessary excisional biopsy.
Assessment of the walls of cystic lesions, as well as the presence
of septations and intracystic masses, is important in determining
whether a biopsy is warranted.
In the evaluation of asymmetric densities seen at mammography, the
presence of an ultrasound abnormality can raise the index of
suspicion for malignancy.
As it has become more widely utilized, studies have shown that the
most beneficial role of ultrasound may lie in the evaluation of a
mammographic mass that is partially obscured or in dense breast
tissue where mammography is unable to fully characterize or detect
Evaluation of breast masses
Sickles described the systematic approach for evaluation of a
mammographically detected mass.
Size, location, density, shape, clarity of margins, and interval
change from prior studies are factors to be evaluated when
analyzing mammographic masses.
A method for the analysis of sonographic masses was described by
Rahbar et al.
The authors reported that sonographic features that most reliably
indicate if a mass is benign are a round or oval shape,
circumscribed margins, and a width-to-AP dimension ratio >1.4.
Masses with an irregular shape, microlobulations, spiculations, and
a width-to-AP dimension ratio ≤1.4 are more likely to be malignant.
It can be concluded from these studies that the evaluation of
the shape and margins are the most important factors in the
mammographic and sonographic assessment of masses (Figures 1 and
Improvement in diagnostic accuracy with
Ultrasound utilized as an adjunct to mammography increases
Zonderland et al
performed a 2-year prospective study in which 4811 mammograms were
evaluated and classified into one of the following 5
Benign with no abnormalities seen.
A lesion or cluster of microcalcifications with a high probability
of being benign.
Equivocal with a lesion or microcalcifications that are
indeterminate, requiring histopathologic examination.
Probably malignant with a lesion or microcalcifications that arouse
suspicion of malignancy.
Malignant when a highly suspicious lesion was present in
combination with associated features of malignancy.
Ultrasound was then performed on possible cysts, palpable
abnormalities, and mammographically detected lesions. Of the 4811
mammograms evaluated, 1103 were followed by ultrasound. The
ultrasounds were then categorized as follows:
A simple cyst was considered benign.
A cystic lesion with debris-like contents was considered probably
benign. A solid lesion with smooth or lobulated margins
that was sharply defined, with homogeneous hypoechoic contents
and a horizontal orientation was assumed to be a fibroadenoma and
classified as probably benign.
A complex cyst with internal echoes and septa was classified as
equivocal. Solid, hypoechoic lesions with irregular margins and an
indeterminate or horizontal orientation but without a definite
probability of being malignant or benign were considered equivocal.
A thickened wall and the presence of an intracystic mass were
classified as probably malignant. Hypoechoic lesions with irregular
and poorly defined margins with shadowing and vertical orientation
were placed in this category.
Lesions with infiltration into the surrounding fatty tissue or
other associated features of malignancy.
Definitive diagnoses were then obtained for all 4811 cases after
a mean follow-up of 30 months. The results showed that mammography
identified 282 of 338 breast cancers. An additional 25 cancers were
diagnosed with ultrasound. Ultrasound, therefore, increased the
sensitivity by 7.4%.
A closer look at the 25 additional cancers diagnosed with
ultrasound reveals that for 12 patients, the lesion was not
recognized on the mammograms and even following retrospective
review, 8 of the cancers remained occult. The other 13 cases had
been characterized as probably benign on mammography but were
reclassified and biopsied following ultrasound.
A review of the 13 cases that had been characterized as probably
benign on mammography and then reclassified as suspicious on
ultrasound reveals the need for ultrasound evaluation of masses
seen at mammography. Two of the 13 cases were masses with
well-defined margins on mammography. The level of suspicion was low
and they were placed in the probably benign category. Subsequent
ultrasound also found well-defined margins, but the presence of
"debris-like contents" in the masses raised the level of suspicion,
and biopsy yielded the diagnosis of intracystic papillary
carcinomas. In the other 11 cases, the mammogram indicated a
circumscribed lesion, a subtle architectural distortion, or an
asymmetric density classified as probably benign. Follow-up
ultrasound revealed characteristics raising the suspicion of
These results show that ultrasound, when utilized as an adjunct
to mammography, improves breast cancer detection with increased
accuracy and characterization of lesions. In particular, it appears
to be useful in the evaluation of asymmetric dense tissue seen at
Cystic lesions of the breast
Berg et al
identified 150 cystic lesions from a database of 2072 image-guided
procedures. Lesions were placed into 7 categories: simple cyst;
complicated cyst; cyst with thin septations; clustered microcysts;
mass with thick wall and/or thick septations, intracystic mass,
mixed cystic and solid; and solid mass with eccentric cystic
No malignancies were found in the first 4 categories. Among
these studies, 23 masses had thick, indistinct walls or thick
septations and 7 of these were malignant. A total of 18 intracystic
or mixed cystic and solid lesions were biopsied, and 4 proved to be
malignant. Solid masses (n = 38) with eccentric foci were sampled,
yielding 7 malignancies.
The authors concluded that cystic lesions with thick indistinct
walls and/or thick septations, intracystic masses, and
predominantly solid masses with eccentric cystic foci should be
biopsied. Of the 79 complex masses in one of these 3 categories, 18
Focal asymmetric densities and ultrasound
Ultrasound plays a fundamental role in the workup of asymmetric
breast tissue, densities seen in one projection, architectural
distortion, and focal asymmetric densities. Samardar et al
discussed the usefulness of ultrasound when a mammogram detects a
focal asymmetric density. Breast Imaging Reporting and Data System
(BIRADS) categorizes 4 types of asymmetric breast findings:
Asymmetric breast tissue; densities seen in one projection;
architectural distortion; and focal asymmetric densities.
Additional mammographic imaging is the first means of evaluating
asymmetric breast findings. Follow-up ultrasound evaluation should
then be performed to search for a solid mass or focal shadowing
that would raise suspicion for malignancy and warrant biopsy.
Alternatively, ultrasound may find a cyst that would yield a benign
diagnosis and warrant only routine follow-up.
Mammographic features of fat necrosis have been documented. They
include radiographically lucent oil or lipid cysts, circumscribed
water density masses, areas of increased density, pleomorphic
clustered microcalcification, and suspicious spiculated masses.
Soo et al
described ultrasound findings associated with fat necrosis. The
features varied, ranging from anechoic masses with posterior
enhancement to solid masses. The authors placed their findings into
6 groups: Solid; complex with mural nodule; complex with echogenic
band; anechoic with posterior acoustic enhancement; anechoic with
acoustic shadowing; and no discrete mass.
Of the 31 masses identified by ultrasound, 29 had corresponding
mammographic abnormalities. The remaining 2 masses were palpable
with no mammographic findings. The masses were placed in one of the
above-mentioned categories, and fat necrosis was diagnosed either
by histology or on the basis of initial or follow-up mammographic
Many of the sonographic features were nonspecific and could not
be distinguished from findings of a malignant lesion. These
included the masses placed in the category of a solid mass as well
as those in the complex mass with a mural nodule group. Fat
necrosis, which presents as an anechoic mass with acoustic
enhancement, is indistinguishable from a cyst. However, the study
did find that the indication of a complex mass with an echogenic
band in patients with a trauma history should strongly suggest the
diagnosis of fat necrosis. In these cases, aspiration or imaging
follow-up should be considered in lieu of biopsy. Similarly, an
anechoic mass with shadowing that corresponds to a mammographically
benign lesion, such as an oil cyst, should be followed.
Doppler evaluation of breast masses
Power Doppler ultrasound is useful in detection of the pattern
of distribution of blood vessels in breast masses. This is useful
in the prediction of malignancy and is one more factor to be
considered in the workup of breast lesions.
Raza and Baum
evaluated 86 solid breast masses that went on to biopsy. Grayscale
and power Doppler ultrasound were utilized, and patterns of
vascular distribution were assigned prior to biopsy. Vessels were
categorized as penetrating, peripheral, central, or absent.
Penetrating vessels were associated with malignancy. The results
revealed that, using penetrating vessels to indicate malignancy,
sensitivity for power Doppler ultrasound was 68%, specificity 95%,
positive predictive value (PPV) 85%, and negative predictive value
(NPV) 88% (Figure 3).
Dense breast tissue
Ultrasound is beneficial in dense breast tissue where the
mammogram is unable to fully delineate or detect a lesion.
Mammographic sensitivity for breast cancer declines with increasing
The American College of Radiology (ACR) defines 4 progressively
more dense patterns in the BIRADS: 1) almost entirely fat; 2)
scattered fibroglandular densities that could obscure a lesion; 3)
heterogeneously dense, which may lower the sensitivity of
mammography; and 4) extremely dense, which lowers the sensitivity
In patients with BIRADS category 3 or 4 density breast tissue,
bilateral whole-breast ultrasound is useful in detecting breast
cancer not discovered with mammography or clinical examination.
A similar benefit has not been proven in BIRADS categories 1 or 2,
in which mammography has a higher sensitivity. In short, the higher
the sensitivity of mammography, the smaller the benefit of
Ultrasound of microcalcifications
Moon et al
prospectively studied 100 mammographically detected
microcalcification clusters with ultrasound prior to biopsy. The
authors found that ultrasound depicted breast masses associated
with microcalcifications in approximately 45% of cases. Of these
masses, 23% were benign and 82% were malignant.
The percentage of detection of masses was much higher if only
clusters of malignant microcalcifications >10 mm were
considered. Ultrasound masses associated with this subgroup were
found in 100% of cases. Ultrasound can, therefore, be utilized in
the visualization of masses associated with clusters of
microcalcifications >10 mm that have a high suspicion of
malignancy. The potential benefit is that it provides an
alternative means of biopsy in patients who cannot undergo a
stereotactic biopsy and do not desire excisional biopsy.
A pilot study performed by Soo et al
performed ultrasound-guided biopsy with 100% success in 23 patients
with suspicious microcalcifications detected on mammography. The
authors commented on the need for further study to determine
whether sonographic targeting of microcalcifications might improve
the rate of underestimation of disease when compared with
Ultrasound plays an essential role in the evaluation of the
breast. It has progressed from its former limited role of
determining whether a mass is cystic or solid into a method to
assist in the differentiation of a benign from a malignant lesion.
It is particularly useful in dense breast tissue. The ability to
correlate a benign ultrasound mass with a mammographic mass
eliminates the need for further intervention. Alternatively, the
finding of a sonographically suspicious mass provides the necessary
information for determining the need for histologic diagnosis. An
added benefit is that the ultrasound-detected abnormality can be
biopsied with ultrasound-guided core biopsy, thereby eliminating
the need for excisional biopsy.