Indications
Breast ultrasound is a diagnostic rather than a screening procedure; it
is targeted to a specific clinical or focal mammographic finding in the
vast majority of patients. Breast ultrasound should be performed on
palpable lumps when the mammogram in the area of the lump is negative or
nonspecific. Although, there are now a few studies on whole breast
screening ultrasound.
Equipment
Breast ultrasound must have excellent spatial and contrast resolution.
Both the axial and lateral components of spatial resolution must be
good. Broadband, high frequency linear electronically focused probes
currently offer the best combination of spatial and contrast resolution
for breast ultrasound.
Axial
Resolution
Excellent axial resolution is important in identifying normal structures
which course parallel to the skin (such as mammary ducts and the fascial
planes surrounding the mammary zone) and in identifying the
characteristics of the capsules around cysts and solid nodules.
Lateral Resolution
Lateral resolution at all depths within the breast is important in order
to minimize volume averaging of surrounding normal breast tissues with
pathological lesions. Such volume averaging may cause
mischaracterization of small cystic lesions as solid and may even cause
small solid lesions to be indistinguishable from surrounding tissues.
Lateral spatial resolution is also a complex subject. For linear probes
there are two planes which determine lateral resolution; the long axis
and short axis (elevation plane focus).
The
long axis of the linear probe can be electronically focused. Continuous
electronic focusing may be done on receive or transmit phases. The
degree of electronic focusing upon receive depends upon many factors,
including:
-
number of channels
-
aperture size
-
number of elements
-
number of scan lines
-
apodization
In
general lateral resolution improves with increasing; the number of
channels, aperture size, number of elements in the transducer and scan
lines. Electronic focusing on transmit depends on many of the same
factors as receive focusing, but is more limited. It depends upon the
number of transmit zones. In general, the more transmit zones, the
better the lateral resolution. However, increasing the number of
transmit zones, decreases the frame rate. In general, multiple transmit
focal zones in the first 2cm are very beneficial in breast sonography.
Elevation Plane
The
elevation plane (short axis) of the probe cannot currently be
electronically focused. The elevation plane is focused at a fixed depth
by an acoustic lens. The manufacturer decides how deeply to focus this
plane before the probe is built. Elevation plane, focal lengths are
usually decided by the application for which the probe will primarily be
used. Dedicated small parts or near field probes should be focused at
about 1.5cm or even more superficially.
5MHz
linear array probes were designed with peripheral vascular applications
in mind and are focused in the elevation plane of about 3 to 4cm. This
is too deep for most breast imaging, the elevation plane would be
focused in the pectoralis muscle in most patients. In general a 7.5 to
13MHz transducer, with an elevation plane of about 1.5cm, is the best
breast ultrasound transducer currently available.
Above figure: If a 5MHz transducer is used and the lesion of interest is
small and superficial, volume averaging of adjacent normal tissues will
be a problem. Cysts may fill-in and be misclassified as solid. Small
solid lesions may be completely missed.
If
a palpable nodule is pea or bee-bee sized, then it is very small and
near the skin. In such cases, even optimally focused transducers may
have difficulty resolving and characterizing the lesion. In such
circumstances, the sonographer should use a 1cm standoff pad or a large
"glop" of gel in order to move the elevation plane focus closer to the
skin. Remember if too thick of a standoff pad (3cm pad) is used, then
the elevation plane will be centered in the pad and not in breast
tissue.
Annotation
Labeling your films can be very time consuming. Most ultrasound
departments utilize the clock method. In our lab we also use the ABC and
123 to label the exact location of a lesion. This is particularly
helpful if you need to follow-up a lesion of is the patient is sent to
another facility for a biopsy.
First
a clock position is stated. Secondly, the location of the lesion is
noted. There are five possible choices for the 123, location. 1 through
3 is divided into 3 concentric rings. If a lesion is near the nipple,
this location is 1, mid way out in the breast is 2 and in the periphery
is 3. If a lesion is under the nipple we label this area SA for
subareolar and lesions in the axilla are labeled AX.
For
the ABC; A, is if a lesion is near the surface or close to the
transducer. B is mid way down (and represents the mammary zone) in the
breast and C is against the chest wall.
Diagram of a right breast lesion about 4 cm directly superior to the
nipple and 3 cm deep which was scanned in a radial plane would typically
be described as "Rt 12 2C RAD". The left breast lesion in the
upper outer quadrant about 6 cm from the nipple and near the chest wall
which was scanned in an anti-radial plane would be labeled "Lt 1:30
3C AR". This cryptic method of annotating ultrasound images is very
advantageous. It saves keystrokes and shortens the examination time.
Positioning
The patient is positioned in a supine position with the ipsilateral hand
raised above the head. The patient is rolled into a contra-lateral
posterior oblique
position to a degree, which minimizes breast thickness in the quadrant
being scanned. Lesions in the medial quadrants may be scanned in a
straight supine position. Lesions in the lateral quadrants require the
greatest degree of obliquity. Generally, greater degrees of obliquity
are required for larger breasts.
This
positioning accomplishes two things:
-
First, the breast is thinned to the greatest extent possible, so
that the high frequency, near-field probes used, has adequately
penetrate to the chest wall and the focusing characteristics of the
probe are optimized.
-
Secondly, the tissue planes of the breast, which are conical in the
upright and prone positions, are pulled into a plane, which is
parallel to the skin line. This minimizes critical angle shadowing
and improves penetration and prevents degradation of focusing
characteristics.
Scan
Plane – Radial and Anti-radial
All
solid lesions should be scanned in the plane of the ductal system
(radial and anti-radial) in order to demonstrate subtle projections that
course towards the nipple or branch outward in the breast.
If a
nodule is scanned only in the conventional method of longitudinal and
transverse, these subtle findings may be missed, and the lesion may
appear spheroid or ellipsoid, and be misclassified as probably benign.
System Optimization
Ensure that your system is optimized for breast imaging before starting
your scan. If the gain is not set correctly, solid lesions can look
cystic or a cyst look solid. Before starting to scan the area of
interest, find an area in the breast with fatty tissue. Most patients
have some fat, usually in the inner aspect of the breast. Set your gain
so the fat is medium gray.
Compare all lesions in the breast to fat. If the gain is set correctly
and fat is medium gray, glandular tissue and most benign lesions, such
as fibroadenomas, appear isoechoic to mildly hypoechoic compared to fat.
Malignant lesions can be mildly hypoechoic to markedly hypoechoic and
cysts are markedly hypoechoic to anechoic compared to fat. The
structures that are hyperechoic compared to fat are skin, fibrous tissue
and calcifications.
Mammographic vs. Sonographic Correlation
When
the main indication for breast ultrasound is a palpable lump, it is
imperative that the lump be palpated while scanning. A breast biopsy can
be avoided if it can be shown that the lump is due to a simple cyst or
normal fibroglandular tissue. Both can cause palpable lumps. Simple
cysts are so common in some age groups that they are virtually a variant
of normal. Fibroglandular tissue is present in at least some part of the
breast, in the majority of all women -- especially those who are within
the reproductive years and even in postmenopausal women who are
undergoing hormonal replacement therapy
When
the main indication for breast ultrasound is a mammographic nodule,
mass, or focal asymmetrical density, it is essential that size, shape,
location, and density of surrounding tissues are the same on mammograms
and ultrasound. As for the palpable lumps, merely showing a simple cyst
or focal collection of fibroglandular tissues does not prove that either
is the cause of the mammographic abnormality. Either could easily be an
incidental finding,
especially if the breasts are mammographically dense or if there are
multiple mammographic densities. Only if the size, shape, location, and
density of surrounding tissues are similar on mammography and sonography,
are we sure that a simple cyst or fibrous pseudo-tumor is the cause of
the mammographic density
When
correlating breast ultrasound with mammography, one should compare the
CC view of the mammogram with the transverse view on ultrasound. The
shape of a mammographic lesion will be easier to reproduce
sonographically if the scan plane is identical to the projection plane
of the mammogram. The MLO view of the mammogram may vary from 30o
to 60o. It is difficult to reproduce the exact degree of
obliquity on the ultrasound that was used on the MLO view of the
mammogram.
Normal Sonographic Anatomy
The
skin is hyperechoic and approximately 2mm thick. The subcutaneous fat is
seen anterior to the pre-mammary fascia. Cooper’s ligaments may be seen
as hyperechoic bands coursing through the subcutaneous fat. The mammary
zone is where the majority of breast cancers, detectable by ultrasound,
are located. Posterior to the mammary zone is the retro-mammary fascia
and fat. And the most posterior structure is the pectoralis muscle and
then the lung.
Cysts
Breast cysts, like cysts elsewhere in the body, can be classified as
either simple or complex.
Simple Cysts
Strict criteria for a simple cyst include:
-
anechoic center
-
thin echogenic capsule
-
enhanced through transmission
-
thin edge shadows
Cysts
which strictly meet these criteria can be classified as simple and have
virtually no chance of containing malignancy. They do not need to be
aspirated (unless they are causing discomfort or are preventing adequate
mammographic compression and evaluation) and they do not need
short-interval follow-up. While malignancy inside a simple cyst is
virtually unknown, carcinoma can occur in the immediate vicinity of a
cyst, so it is necessary to survey the tissues surrounding the cyst as
well as the cyst itself.
Complex Cysts
All
cysts that do not meet strict criteria are, by default, classified as
complex cysts. However, the term complex breast cyst does not carry the
significance of a complex cyst of the kidney or liver. It is important
to understand that complex cystic breast malignancies are extremely
rare, and usually have other features, which are obviously malignant.
The vast majority of complex cysts fall within the broad spectrum of
fibrocystic change. For these reasons, the majority of complex breast
cysts are not worrisome, and do not need to be aspirated or biopsied.
With
the improved resolution of current high-end equipment, a large
percentage of breast cysts appear "complex". This is because there is
real "stuff" within most breast cysts, due to fibrocystic change. With
older equipment these internal cells and debris were not visible, and
the cysts appeared simple. Internal contents within breast cysts are
part of the spectrum of fibrocystic change and include:
-
protein globs
-
cellular debris
-
cholesterol crystals
-
foam cells
-
apocrine cells, floating and papillary
It is
necessary, therefore, to have a method of evaluating the relative risk
of an individual complex breast cyst for two complicating factors:
Categorizing complex cysts into categories can help assess their risk of
infection or neoplasm. Complex breast cyst categories include:
-
diffuse low level internal echoes
-
fluid-debris levels
-
septations
eccentric wall thickening
Thin - echogenic wall
/ Thick – isoechoic wall
Low
Level Internal Echoes & Wall Thickness
Complex cysts with low-level diffuse internal echoes should be evaluated
for wall thickness and particle mobility. Determine if the cyst has a
normal thin, echogenic wall or a uniformly thickened, isoechoic wall
which indicates inflammation. A cyst with a thickened wall should be
considered acutely inflamed, potentially infected, and should be
aspirated.
If
the cyst with low level internal echoes does not have a thickened wall,
then the size of the internal particulate matter should be evaluated.
Complex cysts with diffuse low-level internal echoes can contain either
light, subcellular particles or heavier cellular particles these
subcellular particles are merely part of the spectrum of fibrocystic
change, and are not worrisome.
Supine Upright / Decubitus
Fluid
Debris Level
Cysts
with fluid-debris levels often also have a uniformly thickened wall
indicating acute inflammation and are often tender. The position of the
debris level within such complex cysts will shift with changes in
patient position in a manner similar to the movement of sludge within a
gallbladder. When a fluid debris level is suspected, the cyst should be
evaluated in left lateral decubitus or upright position, as well as in
the usual supine position. Complex cysts with fluid debris levels should
be aspirated.
Thin Septations Thick Septations
Septations
The
majority of thinly septated cysts can be more precisely defined as
clusters of simple cysts or as a large simple cyst with normal tissue
indenting it. These do not need to be aspirated or even followed. They
should be considered to be simple cysts.
Complex cysts with thick septations should undergo further diagnostic
evaluation. Aspiration alone is insufficient, the risk of false negative
cytology is too high. Additionally, should the cyst be aspirated and the
cytology later found to be atypical or malignant, it may be difficult to
find the lesion again for needle biopsy or needle localization unless
the fluid reaccumulates. If aspiration is performed, one should be ready
to follow aspiration immediately with large core needle biopsy.
Eccentric Wall Thickening
The
appearance of the cyst capsule immediately adjacent to the eccentric
wall thickening is very important. Complex cysts containing papillomas
or papillary carcinoma, more frequently have an irregular, angular outer
margin and lack the smooth thin echogenic capsule. For the purposes of
evaluating surface characteristics, the eccentric wall thickening is
assumed to be a solid nodule within a cyst. As in solid nodules, the
smooth, thin, echogenic capsule indicates a non-infiltrating, pushing
leading edge, more typical of benign lesions. The lack of a thin capsule
increases the likelihood of an infiltrating leading edge, a sign of
malignancy.
Implants
Complications of mammary implants can occur immediately after surgery
and be acute, or may occur months to years after surgery and cause
long-term problems.
Acute
complications include:
-
bleeding
-
infection
-
asymmetry
-
loss of nipple sensation
-
pain and tenderness
Long
term complications include:
-
capsular contracture
-
rupture
-
intracapsular
-
extracapsular
-
hematoma
-
herniation
-
migration
-
chronic infection
The
goals of imaging in patients with breast implants are two-fold:
evaluation of breast tissues and evaluation of implants for
complications.
Evaluation of implants may be the primary or secondary goal of
sonography. If the patient has a palpable lump or mammographic
abnormality for which sonography is indicated, the chief complaint
should be evaluated first. Only after the problem for which the sonogram
is indicated is solved, should evaluation for implant complications be
undertaken.
Normal Sonographic Implant Appearance
At
sonography a difference in the thickness and echogenicity of the
elastomer membrane of smooth and textured implants is apparent. Smooth
membranesappear thinner, more echogenic, and more sharply delineated
than do textured implants. The appearance of thin, smooth membranes will
vary, depending upon probe frequency. With 5 to 7.5 MHz transducer, the
shell will usually be seen as a single echogenic line. With the better
axial resolution of a 10-13 MHz, transducer, the inner and outer
surfaces of the shell may each create an echogenic line separated by a
lucency, which represents the thickness of the shell.
Implant Rupture
Intracapsular Rupture
Intracapsular implant ruptures occur when there is a breach in the
elastomer membrane around a single lumen silicone implant and silicone
escapes from the implant, but is still confined within the fibrous
capsule around the ruptured implant.
Folds of the collapsing elastomer membrane may be seen as a series of
thin, double echogenic lines which course parallel to the probe face.
This has been called the "stepladder sign" in sonographic literature
counterpart to the MRI finding called the "linguini sign".
Extracapsular Rupture
The
hallmark of extracapsular rupture is the presence of macroscopic amounts
of silicone outside the implant and also outside the fibrous capsule
surrounding the implant. The presence of extracapsular silicone implies
that there is also intracapsular rupture. Silicone within the soft
tissues of the breast is rapidly walled off by inflammatory response and
forms a silicone granuloma. The classical sonographic description of
silicone granuloma is that of the "snowstorm" appearance, which causes
"dirty" shadowing posteriorly and obscures the posterior border.
It is
also necessary to scan the tissue peripheral to the edge of the implant
as well as those anterior to the implant. In our experience, more
patients have silicone granulomas in the soft tissue peripheral to the
implant than in the breast tissue directly anterior to the implants. The
majority of extracapsular ruptures are seen in the upper outer
quadrants.
Counting the number of echogenic lines is most valuable in patients
where there is a question of intracapsular rupture with incomplete
collapse of the implant. Single lumen silicone gel implants should have
3 closely apposed echogenic lines at the anterior surface of the implant
– 1 representing the fibrous capsule, the 2nd representing the anterior
surface of the shell and the 3rd representing the posterior
surface of the shell. In cases of extracapsular rupture there will
either be only a single echogenic line representing the fibrous capsule
if collapse is complete or there will be an abnormal separation between
the echogenic line representing the fibrous capsule and the 2nd
echogenic line representing the anterior surface of the shell.
Solid Nodules
All
solid nodules should be considered worrisome and malignant findings
sought, and recorded as being present or absent. If a single malignant
feature is present, the nodule can not be classified as benign. If no
malignant features are found, specific benign features then need to be
sought. Only if benign findings are found, can the nodule then be
classified as benign. If specific benign features are not found, the
lesion should be classified, by default, as indeterminate.
Malignant Findings
Individual sonographic criteria are:
-
spiculation
-
taller-than-wide (larger AP than transverse dimensions)
-
angular margins
-
markedly hypoechoic (compared to fat)
-
shadowing
-
calcifications
-
duct extension
-
branch pattern
-
microlobulation
-
disruption of tissue planes
Benign Findings
Individual benign criteria (all are smooth and well-circumscribed)
-
absence of any malignant findings
-
markedly hyperechoic (compared to fat)
-
ellipsoid shape
-
3
or fewer gentle lobulations
-
thin, echogenic capsule
Ultrasound BIRADS Chart
(breast imaging reporting and data system)
Category |
risk of CA |
Description |
1 |
negative |
negative |
2 |
0% |
benign |
3 |
<
2% |
probably benign |
4a |
3 - 49% |
mildly suspicious |
4b |
50 – 89% |
moderately suspicious |
5 |
> 90% |
malignant |
Color
Doppler
Color
Doppler is often used in breast ultrasound to look for neovascularity.
We do not use color Doppler to tell benign from malignant nodules; we
use it more to help distinguish solid from cystic lesions. If there is a
question about a lesion being a complex cyst vs. a solid nodule, we will
look for the presence of flow. If there is no flow it does not mean that
the lesion is a cyst, but if there is flow then you know it is a solid
lesion. We have found that by applying slight pressure all flow in a
lesion can be temporarily ablated. If you are looking for the presence
of flow remember to scan with very light pressure. Some uses for color
Doppler include:
-
solid vs. cystic – fibrovascular stalk
-
inflamed vs. non-inflamed
-
inflamed vs. tumor
-
anatomic landmark – int mamm LN
-
IDP vs. inspissated secretions
-
normal from abnormal tissue – Fremitus
Fremitus
Fremitus is a thrill of the chest wall. Using Power Doppler and having
the patient hum, or say eee, the tissues around a lesion will vibrate
and create a power Doppler signal, the lesion will be void of the power
Doppler signal. Some have reported that this helps differentiate benign
from malignant lesions. We use it for telling;
-
fat from true solid nodule
-
artifactual shadowing vs. true
-
multifocal vs. unifocal disease
Conclusion
Breast Ultrasound is a valuable tool in the diagnosis of breast disease.
Most examinations are targeted at nonspecific, clinical or mammographic
abnormalities. Breast sonography is extremely operator dependent, it is
essential to use the appropriate equipment and be properly trained in
breast imaging to achieve a more specific diagnosis. |