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Chapter 2

The main applications of ultrasound are identification of a palpable breast lump and clarification of a confusing mammographic finding. In the past, a common reason that sonographic applications were limited was that the ultrasound examiner could not cross correlate the physical examination or mammographic findings with the sonographic information. This inability to cross correlate the ultrasound examination with the physical examination or mammographic asymmetry is frustrating and leads to long, sonographic examinations. In order to develop the ability to cross correlate sonography with mammography, one should have optimal sonographic equipment and technique, be able to palpate breast masses, be familiar with normal mammographic and sonographic breast anatomy, recognize mammographic and sonographic signs of malignancy, and apply anatomic knowledge to sonographic scanning.

Ultrasound Equipment and Technique

Equipment

In the past, breast ultrasound has required the least sophisticated equipment because there were few sonographic breast applications and these applications required only simple equipment. However, if one wishes not only to have a high rate of localizing solid masses as well as an optimal image to characterize the mass, then one needs a sophisticated machine. In this book, when I refer to high frequency, I am generally referring to imaging with frequencies equal or greater than 10 MHz. To have maximal flexibility, one should have a machine that has linear transducers with frequencies ranging from 7 to 15 MHz.

High frequency is important as many breast structures are small. An important aspect of the technical advancement of mammography is the improvement of spatial resolution. Because of high mammographic resolution, mammographers are identifying smaller and subtler abnormalities. To be an effective adjunctive test, high sonographic spatial resolution is needed to clarify these subtle findings. Because normal breast structures such as ducts and terminal duct lobular units are small, high spatial resolution allows the ultrasound examiner to quickly recognize normal breast architecture and identify small malignant masses in the ductal system.

Besides being able to identify smaller malignancies, high spatial resolution improves the sonographic image so one can better characterize masses. This improved image is similar to the visual effect experienced by a nearsighted person who starts wearing glasses. The image is sharper, and subtle or smaller details are clearer (Fig. 2–1; also see Section 4 Case 57). For breast malignancies, the most important information produced by high-frequency ultrasound is the improved ability to see the margin of the mass and identify secondary signs of malignancy such as spiculation or architectural distortion. Occasionally, one can trace the path of the malignancy through the ductal system and identify the extent of the disease better than mammography (see Section 10, Cases 200 and 201).

Imaging Techniques

Besides the availability of high-frequency transducers, sophisticated ultrasound machines have more technical factors that can be manipulated to improve imaging quality. For breast ultrasound, an important factor in image quality is being able to obtain excellent contrast resolution. The reason contrast resolution is important is that one must be able to distinguish a variety of masses from the background parenchyma. When the breast is fatty, focal masses such as complex cysts, lymph nodes, fibroadenomas, and cancers may be difficult to identify. When the breast is dense, fat necrosis and surgical or radial scars may be hard to locate. Many factors can improve contrast resolution. High spatial resolution produced by high-frequency imaging improves contrast resolution because the assignment of gray shades is more precise. Reducing the dynamic range may improve contrast resolution as this method exaggerates differences between the gray shades of structures. A variety of proprietary postprocessing programs improve contrast resolution by enhancement of specified gray shades on a point-by-point basis. One type of proprietary postprocessing program improves contrast resolution by enhancement of specified gray shades on a region-by-region basis. One should consult the manufacturer of one's equipment to learn which imaging techniques are available (Fig. 2–2; also see Section 3 Case 18).

Figure 2–1. (A). Right MLO mammogram. (B). Right CC mammogram. (A,B). In the upper outer right breast there is a lobulated density (circled). (C). Right radial breast sonogram: A 5 MHz transducer does not clearly demonstrate the lobulated mass (arrows). The inadequate size and contrast resolution results in poor definition of the mass. (D). Right radial breast sonogram: An 8 MHz transducer improves the definition of the mass. This result allows an observer to confidently localize this mass. This mass is a fibroadenoma.

Besides adjusting image contrast, one should be aware of software methods to optimize resolution. These methods include increasing the line density of the image, increasing the persistence, and adjusting the focal zones. The main disadvantage of these methods is a slower frame rate. If one is merely characterizing a lesion, a slower frame rate may not be a problem. However, the slower frame rate may be disconcerting with real-time imaging of interventional procedures.

Color or power Doppler is a useful method to quickly assess vascularity. Breast vascularity is low, so one should be aware of methods to optimize the color or power Doppler. Generally, this means that one is using a color or power Doppler frequency slightly lower than the gray scale frequency and the focal zone adjusted at the correct depth. The filter and scale should be low. The Doppler gain is optimized by initially increasing the gain until the entire screen is filled with color and then by slowly reducing the gain until the color appears only within pulsating vascular structures. If no color is detected using these methods, then the sample volume size should be increased. Increasing the sample volume size reduces color resolution. The color may “bleed” and be demonstrated outside of the vessel walls. Color or power Doppler is useful to delineate vessels or highly vascular structures such as arteriovenous malformations. This Doppler technique is also useful to clarify whether a hypoechoic or anechoic mass is cystic or solid (Fig. 2–3; also see Section 3 Case 32).

Figure 2–2. (A). Left MLO mammogram. (B). Left CC mammogram. (C). Left MLO spot magnification mammogram. (A–C). In the left upper outer quadrant, there is a small irregular mass (circle). (D). Left antiradial (8 MHz) breast sonogram: Sonographic examination of the mammographic mass with a low-contrast technique poorly demonstrates the mass (arrows). The hypoechogenicity of the mass blends into the surrounding fat. (E). Left antiradial (8 MHz) breast sonogram: Sonographic examination of the same location as Figure 2–2D with high-contrast technique greatly improves the conspicuity of the mass. This mass is a mucinous carcinoma.

Figure 2–3. (A). Right MLO mammogram. (B). Right CC mammogram. (A,B). The patient and the breast surgeon have identified some small palpable lumps at the 9:00 position of the right breast. The lumps are arranged in a linear pattern. The left breast has similar lumps that are less conspicuous. Bilateral mammograms are normal. (C). Right radial breast sonogram: Gray scale sonographic examination of the palpable lumps shows normal tissue. (D). Right radial breast sonogram: Color Doppler examination of the palpable lumps demonstrates that the lumps are due to the lateral blood vessels of the breast. Each lump corresponds to the superficial curve of the blood vessel (arrows) (see Color Plate 2–3D).

Dynamic clips are useful to document vascularity and to demonstrate the spatial relationship of multiple lesions. Dynamic clips are the ideal method to show color flow in pseudoaneurysms or intravenous contrast enhancement of solid masses. Until high-resolution three-dimensional (3-D) imaging is universally available, dynamic clips are an excellent way to demonstrate the relationship of multiple cysts to a solid mass or to show debris or calcifications moving within a complex cyst.

Wide field of view compound imaging is sometimes useful to document larger masses or the relationship of multiple masses in the same plane. The wider field of view provides observers with more landmarks so cross correlation with mammography and magnetic resonance imaging (MRI) may be easier.

Newer sonographic techniques that may have more applications in the future include 3D imaging and harmonic imaging. Like compound imaging, 3-D imaging may produce a wide field of view that would be similar to a mammogram or magnetic resonance image. In the future, 3-D imaging may also allow surgeons and patients to better appreciate the location and size of sonographic findings and facilitate surgical planning.

Harmonic imaging may improve image resolution and increase both gray scale and color Doppler sensitivity for intravenous sonographic contrast agents. These contrast agents may improve both vascular and gray scale characterization of masses.

Approach to a Palpable Mass

In many breast centers, palpable masses are the most common reason for a breast sonogram. Therefore, it is important that sonographic breast imagers learn how to palpate breasts. Usually, the patient will be able to identify the palpable lump. When the patient locates the lump, the breast imager should confirm the presence of the lump by palpating the area identified by the patient. Even if the lump is obvious, the imager should scan the lump and reconfirm the location of the lump by moving a finger into the scan plane. If the imager cannot detect the lump or if the patient is not sure of the exact location of the lump, then palpation of the entire quadrant is useful. By palpating a larger area, one is able to detect asymmetries within the region. Finally, if palpating the quadrant isn't helpful, then one may palpate the comparable area in the opposite breast. Commonly, the parenchymal pattern of patients is symmetric, so the physical exam is also symmetric. By palpating the corresponding contralateral quadrant, one may detect abnormal asymmetries. This technique is particularly useful with malignancies that are commonly difficult to feel such as lobular carcinoma.

Cross Correlation of Sonographic and Mammographic Image

To accurately, efficiently, and confidently sonographically identify a mammographic abnormality, the personnel who perform the breast sonographic examination should be familiar with mammographic imaging. Furthermore, the ultrasound examiner should be able to review the mammogram and identify internal landmarks that can be cross correlated with the ultrasound. Finally, by confirming the mammographic landmarks sonographically, the examiner should be able to pinpoint the location of the mammographic abnormality in the breast with ultrasound and consequently be able to explain the etiology of the puzzling mammographic finding.

Unfortunately, sometimes the ultrasound examiner does not attempt to closely cross correlate anatomically the ultrasound examination with the mammogram. In some cases, the examiner does not attempt to correlate the exams because he or she does not routinely interpret mammograms and is uncomfortable reviewing mammograms. However, more common reasons for lack of close cross correlation include the following: (1) The sonographic image has a small field of view compared with the mammographic global field of view. (2) The patient position for an ultrasound examination is completely different than the position for the mammographic examination. Therefore, the position of a breast mass for these exams appears extremely different. (3) Even if one places the patient in the same position, the difference in technology between ultrasound and mammography creates different orientations of tissue visualization. (4) Unlike other organs, the breast does not have a uniform or constant normal anatomy. The breasts of different individuals have different breast architecture. Furthermore, some individuals have a right breast that exhibits a pattern different from the left breast. Finally, the breasts of many individuals change with age.

As a result of the reasons stated above, ultrasound examiners commonly ignore internal breast anatomic landmarks and estimate the location of the mammographic abnormality using external landmarks. The most commonly used systems are the “O'clock” method and the quadrant method. The O'clock method views the breast as a circular clock with the nipple in the center of the circle: 12:00 is directly above the nipple; 3:00 is to the left of the nipple; 6:00 is below the nipple; 9:00 is to the right of the nipple. The quadrant method divides the breast into four parts or quadrants. These quadrants are defined by drawing a horizontal and a vertical line through the nipple. The quadrants label four regions of the breast: upper outer quadrant, upper inner quadrant, lower outer quadrant, and lower inner quadrant.

There are several problems with using external anatomic landmarks for locating mammographic abnormalities: (1) Mammographic estimation of location is not accurate and may be difficult to determine if the abnormality is only on one view; (2) The change in patient position between the mammogram and the ultrasound commonly results in changes in the relative position of internal breast structures compared to external landmarks; (3) The external breast position of a handheld transducer does not correlate to a specific internal imaging position.

Estimating location on a mammogram is commonly inaccurate as the standard mammographic views are the craniocaudal (horizontal) and mediolateral oblique views. The greatest source of error is related to the mediolateral oblique view because this view is not oriented 90 degrees to the craniocaudal view. Furthermore, this views long axis angle varies with the anatomy of the patient. For example, a mass that is deep to the nipple on the craniocaudal view and directly above the nipple in the mediolateral oblique view may be identified as being located at 12:00 but may actually be located between 11:30 and 9:30.

Even if the location of a lesion is accurately identified by the mammogram, the relative position of this lesion may change when the patient changes position for the ultrasound. Usually, the mammogram is performed in the upright position and the ultrasound in the supine position. Because the breast is a flexible structure, the breast changes its shape from one position to the other. In the upright position the position of the breast drops due to gravity. Whereas in the supine position, the breast flattens against the chest wall. Compared with other external landmarks, the nipple may be lower in the upright position compared with the supine position. Therefore, a lesion above the nipple in the upright position may shift to the same level as the nipple in the supine position. For example a 10:00 lesion in the upright position may become a 9:00 lesion in the supine position. The larger the breast, the greater the movement of the breast.

Finally, the external position of the handheld transducer does not necessarily correlate with the internal position of the lesion. Even if a linear transducer is used, the examiner commonly uses a variety of angles and hand pressures to optimally visualize the abnormality. Even slight angulation will produce a discrepancy between the position of the sonographic transducer and the actual position of the lesion. Furthermore, transducer pressure may cause the lesion to shift position relative to the nipple. Both of these factors may produce a discrepancy between the mammographic position and the sonographic position.

Because external landmarks are not reliable in cross correlating mammographic/sonographic abnormalities, one should use internal landmarks. However, one must use a technique that addresses the problems listed earlier: (1) limited sonographic field of view compared with mammography, (2) differences between mammographic and sonographic patient position and technical orientation, and (3) nonuniformity of breast anatomy both between individuals and within the same individual.

By using internal breast anatomic landmarks, one immediately addresses the first two problems. If one identifies location by the internal anatomy of an organ, then relating the position of a focal abnormality from the limited sonographic field of view to a wide field of view modality is not a problem. Furthermore, unlike external landmarks, internal landmarks do not shift with body position. For example, in the abdomen, one is commonly challenged with the problem of sonographically deciding whether a small liver lesion previously identified on a computed tomography (CT) scan is cystic or solid. Even though the CT scan is a wide field of view modality, experienced examiners easily sonographically localize the position of the CT lesion. These examiners are able to confidently localize the lesion because they relate the lesion to the internal anatomy of the liver as displayed on CT and then sonographically find the same hepatic location using the same internal hepatic landmarks. Furthermore, this process of anatomic cross correlation would not be different even if the patient were lying prone because unlike external landmarks, internal anatomic landmarks do not change relative to each other.

Even though internal landmarks solve the problems of limited sonographic field of view and positional changes, many examiners are inhibited from using internal breast landmarks as there is great anatomic variation between different breasts. However, whenever one performs a breast sonogram to identify a mammographic abnormality, one should always have the corresponding mammogram. The mammogram provides an anatomic map to the patient's breast. If one is able to cross correlate mammographic structures with sonographic structures, then one may use the mammogram as a sonographic guide to locating the lesion. Therefore, ideally the sonographic examiner should be able to sonographically interpret the mammographic image.

To systematically cross correlate sonography with mammography, one should be familiar with normal breast anatomy. There are seven main sonographically different structures in the breast and chest wall of the average normal 45-year-old woman. These structures from superficial to deep are the following (Fig. 2–4):

1. Skin: The skin is a hyperechoic 3 mm layer on the surface of the breast.

2. Subcutaneous fatty layer: This structure lies under the skin and appears as an anterior hypoechoic layer of tissue, which tends to thicken at the periphery of the breast and is more prominent in the medial portion of the breast.

3. Superficial fascia: The superficial and deep layers of the fascia envelop the breast. The superficial layer is an undulating hyperechoic line within the subcutaneous fat that parallels the skin. The deep layer is an hyperechoic line within the retromammary fat that parallels the anterior chest wall muscles.

4. Cooper's ligaments: The ligaments are curved hyperechoic lines within the subcutaneous fat, which extend from the superficial fascia to the deeper adjacent tissue.

5. Glandular tissue: Normal glandular tissue consists of hyperechoic glandular lobes that are in a radial arrangement around the nipple. Each lobe is in the shape of a prolate ellipse and is surrounded anteriorly by the subcutaneous fat and posteriorly by the retromammary fat. Within the lobes, main ducts originate from the nipple and end in a series of terminal duct lobular units.

6. Anterior chest wall muscles: This layer is formed by the pectoralis minor and major muscles and appears as a hypoechoic solid layer posterior to the retromammary fat.

7. Chest wall: This structure consists of ribs connected by intercostal muscles and covered on the deep surface by pleura.

Figure 2–4. (A). A schematic diagram showing the normal structures of the breast: skin (1), subcutaneous fatty layer (2), superficial fascia (3), Cooper's ligaments (4), glandular tissue (5), anterior chest wall muscles (6), chest wall (7). (B). Radial breast sonogram (10:00 position): Sonographic image demonstrates the normal anatomic structures of the breast: skin (1), subcutaneous fatty layer (2), superficial fascia (3), Cooper's ligaments (4), glandular tissue (5), anterior chest wall muscles (6), chest wall (7). (C). Right MLO mammogram: This is the mammogram of the patient whose sonogram is seen in Figure 2–2B. In the upper outer quadrant, the sonographic image corresponds to the outer edge of the patient's fibroglandular density. Box denotes location of transducer.

Most of these anatomic structures are also generally identifiable mammographically

Rules of Cross Correlation

Once one is familiar with normal sonographic and mammographic breast anatomy, one will be able to anatomically cross correlate the two modalities. If one is not familiar with cross correlation of these modalities, one should not be intimidated by the task of cross correlating sonographic and mammographic structures. A simple way to start is to remember two basic imaging rules. The first rule is that the background breast tissue appearance is similar on the two modalities. This means that normal fibroglandular parenchyma is white (or dense) on mammography and white (or hyperechoic) on sonography. Furthermore, fat appears dark (or lucent) on mammography and dark (or hypoechoic) on sonography (Fig. 2–5). The main exception to this rule is the presence of dilated ducts that are sonographically dark (hypoechoic) and mammographically white (dense). When the breast tissue is filled with dilated ducts such as in ductal ectasias, the breast tissue appears white (dense) on mammography but has numerous linear dark structures (dilated ducts) on sonography.

When one is aware of the appearance of breast tissue with the two modalities, then when one reviews a mammogram one should be able to predict the sonographic appearance of the breast. For example, a mammographically fatty, lucent breast will be sonographically hypoechoic. Conversely, a mammographically dense breast usually sonographically exhibits diffusely hyperechoic fibroglandular parenchyma.

Generally, the breasts of most women are not completely dense or lucent. This system of pattern recognition is even more valuable in these breasts. When a breast has a mixture of tissues, these tissues form unique mammographic structural patterns that may be sonographically reproduced. For example, commonly the mammogram exhibits dense parenchymal tissue primarily in the upper outer quadrant. Sonographically, one can also outline this tissue by noticing the junction between the hyperechoic parenchyma and the adjacent hypoechoic fat. Furthermore, if the medial aspect of the mammogram is lucent, then the corresponding sonographic examination should display hypoechoic fat.

The second cross correlation imaging rule is that most focal breast masses have dissimilar appearances on the two modalities. For example, lymph nodes, cysts, and fibroadenomas appear white (dense) on mammography but dark (hypoechoic) on sonography. Neoplasms appear white (dense) on mammography but dark (hypoechoic or heterogeneous echogenicity) on sonography. The main common exceptions to this rule are benign scars, radial scars, and occasionally fat necrosis. These lesions are sonographically hyperechoic (white).

If one is familiar with mammographic and sonographic appearance of breast structures, then one will be able to sonographically localize a focal mammographic abnormality using internal anatomic landmarks. The steps that I use when faced with an anatomically difficult breast problem are the following:

1. Review the mammogram and identify the abnormality. Notice the parenchymal pattern between the nipple and the lesion. Also study the pattern of the breast tissue surrounding the abnormality. Estimate the general location of the abnormality (i.e., quadrant and finger breadths from nipple).

2. Place the transducer with one edge at the nipple and sonographically examine the breast in a radial orientation. Look for the same parenchymal patterns that one noticed on the mammogram. When one recognizes the parenchymal landmarks that surround the abnormality, sonographically focus the examination in this area.

3. Sonographically characterize the lesion (Fig. 2–6). Utilizing this method, one would first approach finding the mass in Figure 2–6 by noting the general mammographic location of the lesion near the left 9:00 position. The irregular mass is surrounded by fatty density but linked to the subareolar density by linear densities (Fig. 2–6A-C). One would initially place the transducer near the nipple and confirm the presence of dense (hyperechoic) subareolar tissue. In the inner breast one would extend the transducer away from the nipple following the strands of hyperechoic tissue that extend farthest away from the nipple. This “trail” of hyperechoic tissue will lead to the hypoechoic shadowing mass (Fig. 2–6D) that corresponds to the mammographic mass.

Figure 2–5. These schematic diagrams illustrate the anatomic cross correlation between mammography and sonography. In this patient, transducer A is positioned over the dense fibroglandular tissue in the upper outer quadrant. Sonographically, this tissue is hyperechoic (C). Transducer B demonstrates the fatty parenchyma in the inferior inner quadrant that is sonographically hypoechoic (D). (A). Schematic image of an MLO mammogram show two transducers, labeled A and B. (B). Schematic image of a CC mammogram showing position of transducers A and B. (C). Schematic image of breast sonogram that corresponds to tissue imaged by transducer A. (D). Schematic image of breast sonogram that corresponds to tissue imaged by transducer B.

This method is particularly useful when the mammographic abnormality is not easily visualized. Section 6 Case 120 demonstrates an asymmetric density that is only visible in one mammographic view. In this case, the abnormal density is at the distal border of the fibroglandular density. Therefore, to find this type of lesion, one should start near the nipple and confirm the presence of diffuse hyperechoic fibroglandular tissue. One should then move the transducer toward the outer breast until one visualizes fatty hypoechoic tissue. Then, one should only scan the border between the hyperechoic and hypoechoic tissue. One will then discover the hypoechoic malignant mass.

When evaluating the location of a lesion from the mammogram, internal parenchymal landmarks one should notice include: (1) location of the edge of the parenchyma—many lesions are at the border of the fibroglandular (white) tissue and the fat (dark); (2) configuration of fibroglandular tissue—lesion may be linked to the largest area of this tissue; (3) adjacent masses—mammogram may demonstrate another mass next to the questionable lesion. By cross correlating these mammographic landmarks on the breast sonogram, one will be more successful in identifying mammographic lesions (Fig. 2–7).

Figure 2–6. Figure 6A. (A). Left MLO mammogram. (B). Left CC mammogram. (C). Left LM spot compression mammogram. (A–C). At the 9:00 position of the left breast, there is an irregular mass (circle). This mass is primarily surrounded by fatty density but is linked with dense spiculations (arrows) to the main subareolar fibroglandular density. (D). Left radial breast sonogram: The mammographic irregular density corresponds to a heavily shadowing focal mass. These mammographic spiculations correspond to the hyperechoic curvilinear tissue (arrows). This mass is infiltrating ductal carcinoma.

Special Sonographic Problems

Shadowing

One difficulty in cross correlating mammography with sonography is sonographic shadowing. Shadowing is confusing. It is a nonspecific finding because it is associated with both benign and malignant entities. Shadowing is particularly a problem for those who use high-frequency equipment as all tissues more readily attenuate high frequencies and, therefore, shadowing is more frequent. To analyze shadowing, one should (1) be familiar with the etiologies of shadowing; (2) if the shadow hides the lesion, reduce or eliminate the shadow; (3) characterize the tissue that causes the shadow.

Figure 2–7. (A). Left MLO digital mammogram. (B). Left CC digital mammogram. (C). Left CC spot magnification mammogram. (A–C). A partially obscured oval density (arrow) is visible in the central area of the CC view. This density is not visible on the MLO view. In the CC view, the density is at the distal edge of the fihroglandular density. (D). Left radial breast sonogram: A hypoechoic mass is present at the 12:00 position of the breast. In this view, the parenchymal anatomy matches the mammographic anatomy of the CC view. On the side closest to the nipple, the tissue is white fihroglandular parenchyma. On the side away from the nipple, the tissue is hypoechoic fat. N, arrow points toward direction of nipple. (E). Left antiradial breast sonogram: The antiradial view demonstrates irregularity of the margins of the mass. This mass is a mixed infiltrating ductal and lobular carcinoma.

The etiologies of shadowing can be divided into two main categories: (1) reflection and (2) absorption. Reflection of sound is affected by two factors: (1) acoustic impedance and (2) angle of incidence. Acoustic impedance is a fundamental properly of matter and is related to the density of the material and the speed of sound in the material. A portion of a sound wave is reflected whenever the wave strikes an interface between two substances with different acoustic impedances. This principle is the basis for diagnostic sonography. The reflected sound is received by the ultrasound machine and transformed into visual information. The amount of reflection is dependent upon the difference in acoustic impedance between the substances. If the difference is great, then a large percentage of the sound wave is reflected. Acoustic impedance differences between most tissues within the breast such as fat and fibroglandular tissue are very small, so generally less than 1 % of the sound wave is reflected. However, air and bone have acoustic impedances that are very different from breast tissue. When the sound wave strikes a rib, about 90% of the sound is reflected and when the wave strikes the lung over 99% of the wave is reflected.

The second factor that affects the amount of reflected sound is the angle of incidence or the angle at which the sound strikes an object. The closer the sound beam is to a right angle (or perpendicular to the surface of the object), the less the reflection. The proportion of reflected sound increases with decreasing angles. When the sound beam strikes the object at an extremely acute angle (i.e., critical angle), all of the sound is reflected. This phenomenon is evident when sound hits the side of a curved mass such as a cyst. In this situation, the reflected sound produces thin shadows at the edges of the cyst.

Besides reflection, shadowing is caused by absorption. Absorption is the conversion of sound into heat. A shadow results if the material completely absorbs the sound beam. In the body, absorption is directly proportional to transducer frequency. Therefore, absorption is double for 14 MHz compared with 7 MHz. This increased absorption is the main reason that high frequency is associated with more shadowing than lower-frequency sonography.

Upon encountering a confusing shadow, a breast imager should initially judge whether the shadow is due to reflection or absorption. After making this decision, one should eliminate or reduce the shadow. If the shadow is due to reflection, then the shadow is either due to the acoustic impedance of the material or due to the angle of the sound beam. If the shadowing is due to acoustic impedance, the imager cannot eliminate the shadow, but the imager would have a short list of materials that would produce this shadowing (i.e., air, bone, metal). However, if the shadow is due to the angle of the sound beam, then changing the position of the transducer can eliminate the shadow. Many structures within the breast are curved and create this type of shadow. Pseudomasses may be created by several of these shadows that are close together. To distinguish a true mass from an artifactual one, an imager should routinely study the mass from multiple transducer angles (Figs. 2–8 and 2–9).

If the shadow results from absorption, then one should decrease the frequency of the transducer. This technique is useful to better characterize lesions associated with severe shadowing. Both benign and malignant masses appear as areas of focal shadowing. By lowering the transducer frequency, one may reduce or eliminate the shadowing and be able to visualize the lesion causing the shadow. This technique is useful to differentiate scars or highly absorbing fibroglandular tissue from masses. With lower frequency, no mass will be evident with scars or fibroglandular tissue. The main problem associated with this technique is that lower-frequency imaging still has the disadvantages of relatively poor resolution and contrast. One may miss masses because they may blend into the surrounding fibroglandular tissue. Margins and architectural distortion are poorly defined. To avoid missing masses, one should have a high degree of suspicion. One should closely examine the area for subtle inhomogeneity of architecture and echogenicity. (See Section 3 Cases 12 and 30 and Section 4 Case 47.)

Figure 2–8. (A). Schematic of breast sonogram: When a transducer (T) is positioned over a curved object, the sound at the edges of the object is reflected so shadowing (S) is produced at the edges of the mass. (B). Schematic of breast sonogram: When the transducer (T1-T3) is repositioned around the curved object, shadowing is reduced.

Even after lowering the frequency, shadowing sometimes persists. In this situation, one should first attempt to discover whether the shadowing is caused by a mass or results from the patients dense fibroglandular tissue. To differentiate shadowing from these sources, one should compare the region of interest with normal fibroglandular tissue of the same breast or the opposite breast. Most women have symmetric fibroglandular tissue. Therefore, if the region of interest is in the right upper outer quadrant, then one should compare this area with the left upper outer quadrant. Or if the patients mammogram is completely white, then one may compare the region of interest with another area of the same breast. If the normal fibroglandular tissue does not shadow, then one should be suspicious that the shadowing represents an active process. If the patient's normal fibroglandular tissue shadows, then one should try to use a lower frequency in which the fibroglandular tissue appears hyperechoic. One may then use this new lower frequency to evaluate the region of interest.

Finally, if shadowing persists, one should evaluate the appearance of the shadow. Is it focal? Does it persist consistently in multiple angles? Masses that shadow have borders. Therefore, if the shadow has edges that define a focal area, then the shadowing should be considered suspicious for a mass.

Architectural Distortion and Focal Asymmetric Density

Mammographic architectural distortion and asymmetric density are difficult problems to sonographically correlate. When these findings are present without a mass, they are extremely subtle and commonly only visible in one mammographic view. Because obvious architectural distortion or asymmetry may generally be well characterized with mammography alone, sonography is most valuable when the mammographic findings are uncertain. Therefore, if one utilizes sonography for this purpose, one should only use high-resolution equipment and be experienced in cross correlating cases.

The principles for cross correlating architectural distortion and focal asymmetric density are the same as for a mass. One should match the internal sonographic landmarks to the mammogram. If the area of architectural distortion or focal asymmetry is dark sonographically, then one must suspect a mass (Fig. 2–10). Otherwise, the area will appear to be white fibroglandular tissue.

Generally, the sonographic findings are complementary to the mammographic information, so one is more confident about the final recommendation. However, occasionally, the sonographic and mammographic findings are discordant. In this case, if one of the modalities has information indicating malignancy, then one should recommend biopsy of the abnormality (American College of Radiology Breast Imaging Reporting and Data System Categories 4 and 5).

Figure 2–9. (A). This 35-year-old woman presents with a palpable lump. Sonographically, the lump has been found to be an ill-defined hypoechoic mass. The mass is considered suspicious and biopsy is recommended. The patient returns 2 days later for the biopsy. When the patient returns, the original hypoechoic area is identified (A), but by slightly changing the angle of the transducer, the hypoechoic area disappears (B). The hypoechoic “mass” represents unusual shadowing from a Cooper's ligament attachment. This attachment is also the etiology of the small superficial palpable lump. (A). Left radial breast sonogram of hypoechoic “mass.” (B). Left radial breast sonogram of same area as Figure 2–9A: Pressure on the transducer has slightly changed the incident sonographic angle. Cooper's ligament attachment (arrow).

Figure 2–10. (A). Right MLO mammogram. (B). Left MLO mammogram. (C). Right CC mammogram. (D). Left CC mammogram. (E). Left MLO spot compression mammogram. (F). Left CC spot compression mammogram. (A–F). Subtle architectural distortion (square) is present in the left upper outer quadrant. The architectural distortion blends into the normal central white fibroglandular density. (G). Left radial breast sonogram: Sonographic examination of the left upper outer quadrant demonstrates that the architectural distortion corresponds to an irregular hypoechoic mass with shadowing The mass is connected to hyperechoic tissue (arrows) that corresponds to the central mammographic fibroglandular density. The mass is a lobular carcinoma.