On completion of this chapter, you should be able to:
Describe breast anatomy and sonographic layers
Discuss breast physiology
Explain the difference between breast screening and breast imaging
Summarize the indications for the use of ultrasound in breast imaging
Describe the correct sonographic technique for imaging the breast
Know how to use methods of identifying and labeling breast anatomy and masses
Identify the sonographic characteristics associated with benign and malignant breast masses
Identify the mammographic characteristics associated with malignant breast masses
Discuss ultrasound-guided interventional procedures
One out of eight American women will develop breast cancer. It is the most common type of cancer among women in the United States and is the second leading cause of cancer death among women between the ages of 40 and 59. It is estimated that the lifetime risk of breast cancer development is approximately 12%. Early detection of breast cancer is vital, because cancer can be difficult to eradicate once it has spread. Ultrasound evaluation of the breast plays a significant role in the early detection and characterization of breast masses and provides real-time guidance during interventional breast procedures. This chapter presents an overview of breast anatomy, physiology, sonographic evaluation techniques, and breast pathology with emphasis on breast cancer diagnosis and staging.
John Wild published the first paper on breast ultrasound in 1951. This early paper described the A-mode technique of ultrasound imaging. Advancements in ultrasound equipment design allowed increased tissue characterization, and by 1970, gray-scale ultrasound technique had significantly improved diagnostic accuracy. Dedicated whole-breast ultrasound units were tested as a potential screening method for the detection of breast cancer. This effort, unfortunately, failed. Whole-breast ultrasound imaging units gave way to smaller units with handheld transducers for breast evaluation. Although ultrasound was not an effective primary tool in breast cancer screening, its usefulness as an adjunctive tool to mammography for breast lesion characterization has become increasingly evident. Screening mammograms have long been considered the gold standard for breast cancer screening, although accumulating evidence suggests that ultrasound screening in conjunction with mammography may be beneficial in patients with very dense tissue, complicated mammograms, or very high risk factors for breast cancer.
Most clinical laboratories today use high-resolution, real-time sonography as an adjunct to mammographic screening. Although screening the entire breast with ultrasound is not routinely done, most ultrasound laboratories currently perform the breast examination within a localized area to characterize palpable lesions or suspicious areas seen on a mammogram. High-frequency 10- to 15-MHz transducers have the optimum resolution and the short-to-medium focus necessary for obtaining high-quality images of the breast parenchyma. The high frame rates available with real-time ultrasound systems in use today facilitate ultrasound guidance during interventional procedures of the breast, including cyst aspirations, core biopsies, preoperative localization techniques, and vacuum-assisted biopsies for small lesion diagnosis and removal.
Emerging sonographic technologies
Technical improvements over the past 30 years have led to advances in breast imaging. Aside from advances in gray-scale imaging, there have been significant software and hardware developments that have enhanced breast imaging. These new technologies not only provide additional information about the breast, but have the potential to change the way breast sonograms are performed.
Introduced in 1991, elastography, also known as elasticity imaging, has recently shown its usefulness in improving the diagnosis of diseases in many parts of the body. This technology produces images based on the relative stiffness of tissues and maps their elastic properties. By applying compression to the breast, elastography is able to produce images, which show the differences in firmness in breast tissue. Breast cancers, generally firmer than benign lesions, appear darker when compared with surrounding tissue or as red in commonly seen green/red color scale. Although elastography appears as a promising adjunct to gray-scale imaging, it is still being studied for its value in improving diagnostic performance. With researchers actively redesigning elastography hardware and software, elastography may soon show its benefits in diagnostic sonographic breast imaging.
Automated whole-breast sonography
When used on a localized area of the breast, sonography is an important tool in a patient’s diagnosis. As previously mentioned, whole-breast sonography is not routinely done for screening purposes due to it being completely operator dependent. It is difficult to have exact documentation of the entire breast with a handheld device projecting a small field of view. In response to this issue, there has been commercial interest in developing an automated ultrasound system for the breast.
Automated whole-breast sonography may be performed with the patient supine or upright, depending on the design of the equipment. This water path system allows the breast to be compressed, which provides excellent visualization of the mammary tissue. The automated transducer has the ability to obtain images over the entire breast. The machine then correlates the B-mode data and appropriately places the lesion oriented to the nipple and quadrant of the breast. Finally, the data are then put together in a series of sonographic gray-scale cine images, which form a whole-breast image.
Three-dimensional (3D) imaging has been successfully used in other areas of sonography such as obstetrics and gynecology. Currently its diagnostic capabilities are comparable to two-dimensional (2D) imaging producing sensitivities and specificities that are close statistically. Unlike 2D imaging, 3D offers images of the coronal plane. In this plane, masses can be described in two new sonographic patterns: compression and converging, also known as retraction. Clinical findings show that the compression patterned masses have an oval shape and are associated with benign lesions, whereas the converging pattern masses appear with spiculations and are associated with malignant tumors.
Anatomy of the breast
The breast is a modified sweat gland located in the superficial fascia of the anterior chest wall. The major portion of the breast tissue is situated between the second and third rib superiorly, the sixth and seventh costal cartilage inferiorly, the anterior axillary line laterally, and the sternal border medially. In many women, the breast extends deep toward the lateral upper margin of the chest and into the axilla. This extension is referred to as the axillary tail of the breast, or the tail of Spence ( Figure 21-1 ).
The surface of the breast is dominated by the nipple and the surrounding areola. A few women may have ectopic breast tissue or accessory (supernumerary) nipples. Ectopic breast tissue and accessory nipples are usually located along the mammary milk line, which extends superiorly from the axilla downward and medially in an oblique line to the symphysis pubis of the pelvis.
Sonographically, the breast is divided into three layers located between the skin and the pectoralis major muscle on the anterior of the chest wall. These layers are the subcutaneous layer, the mammary (glandular) layer, and the retromammary layer ( Figure 21-2 and Box 21-1 ). The subcutaneous and retromammary layers are usually quite thin and consist of fat surrounded by connective tissue septa. Although fat is often highly echogenic in other parts of the body, it is the least echogenic tissue within the breast. The fatty tissue appears hypoechoic, and the ducts, glands, and supporting ligaments appear echogenic ( Figure 21-3 ).
Subcutaneous layer: thin layer
Mammary layer: functional portion of the breast
15 to 20 lobes radiate from the nipple.
Lactiferous ducts carry milk from acini to the nipple.
Terminal ductal lobular unit is made up of acini and terminal ducts.
Fatty tissue is interspersed between lobes.
Cooper’s ligaments extend from the retromammary fascia to the skin and provide support.
Retromammary layer: thin layer
Pectoralis major muscle
Pectoralis minor muscle
The mammary/glandular layer includes the functional portion of the breast and the surrounding supportive (stromal) tissue. The functional portion of the breast is made up of 15 to 20 lobes, which contain the milk-producing glands, and the ductal system, which carries the milk to the nipple. The lobes emanate from the nipple in a pattern resembling the spokes of a wheel. The upper outer quadrant of the breast contains the highest concentration of lobes. This concentration of lobes in the upper outer quadrant of the breast is the reason why most tumors are found here, as most tumors originate from within the ducts. The lobes of the breast resemble a grapevine branch; the major duct branches into smaller branches called lobules. Each lobule contains acini (milk-producing glands; singular acinus ), which are clustered on the terminal ends of the ducts like grapes on a vine. Literally hundreds of acini are present within each breast ( Figures 21-4 and 21-5 ). The terminal ends of the duct and the acini form small lobular units referred to as terminal ductal lobular units (TDLUs), each of which is surrounded by both loose and dense connective tissue. The TDLUs are invested within the connective tissue skeleton of the breast (see Figures 21-2 , 21-4 , and 21-5 ). Normal TDLUs measure 1 to 2 mm and usually are not differentiated sonographically. The TDLU is significant in that nearly all pathologic processes that occur within the breast originate here. The space between the lobes is filled with connective and fatty tissue known as stroma. These stromal elements are located both between and within the lobes and consist of dense connective tissue, loose connective tissue, and fat. The connective tissue septa within the breasts form a fibrous “skeleton,” which is responsible for maintaining the shape and structure of the breast. These connective tissue septa are collectively termed Cooper’s ligaments; they connect to the fascia around the ducts and glands and extend out to the skin.
The pectoralis major muscle lies posterior to the retromammary layer. It originates at the anterior surface of the medial half of the clavicle and anterolateral surface of the sternum and inserts into the intertubercular groove on the anteromedial surface of the humerus ( Figure 21-6 ). The lower border of the pectoralis major muscle forms the anterior margin of the axilla. The pectoralis minor muscle lies superolateral and posterior to the pectoralis major. The pectoralis minor courses from its origin near the costal cartilages of the third, fourth, and fifth ribs to where it inserts into the medial and superior surface of the coracoid process of the scapula. These muscles sonographically appear as a hypoechoic interface between the retromammary layer of the breast and the ribs (see Figure 21-6 ). Although most lesions are found within the glandular tissue of the breast, it is important to evaluate tissue all the way to the chest wall.
The boundaries of the breast are the skin line, nipple, and retromammary layer. These generally give strong, bright echo reflections. The areolar area may be recognized by its slightly lower echo reflection compared with the nipple and the skin. The internal nipple may show low to bright reflections with posterior shadowing, and it has a variable appearance ( Figure 21-7 ).
Subcutaneous fat generally appears hypoechoic, whereas Cooper’s ligaments and other connective tissue appear echogenic and are dispersed in a linear pattern ( Figure 21-8 ). Cooper’s ligaments are best identified when the beam strikes them at a perpendicular angle; compression of the breast often enhances the ability to visualize them.
The mammary/glandular layer lies between the subcutaneous fatty layer anteriorly and the retromammary layer posteriorly ( Figure 21-9 ). The fatty tissue interspersed throughout the mammary/glandular layer dictates the amount of intensity reflected from the breast parenchyma. If little fat is present, a uniform architecture with a strong echogenic pattern (because of collagen and fibrotic tissue) is seen throughout the mammary/glandular layer. When fatty tissue is present, areas of low-level echoes become intertwined with areas of strong echoes from the active breast tissue. Analysis of this pattern becomes critical to the final diagnosis, and one must be able to separate lobules of fat from a marginated lesion.
The retromammary layer is similar in echogenicity and echotexture to the subcutaneous layer, although the boundary echoes resemble skin reflections ( Figure 21-10 ). The pectoral muscles appear as low-level echo areas posterior to the retromammary layer. The ribs appear sonographically as hyperechoic rounded structures with dense posterior shadowing. They are easily identified by their occurrence at regular intervals along the chest wall.
Several normal structures within the breast can appear abnormal, unless care is taken to prevent this during the sonographic examination. The ducts immediately behind the nipple frequently cause acoustic shadowing and can be mistaken for a suspicious breast mass. Angling of the transducer in the retroareolar tissue will usually improve visualization and eliminate doubt. The distinction of a subtle isoechoic or hypoechoic sonographic mass from normal fibroglandular tissue in the breast can sometimes be troublesome. The adipose or fatty tissue can situate itself in and among the areas of glandular tissue and, in some scanning planes, can mimic isoechoic or hypoechoic masses. It is helpful to turn on the structures to see if they are consistent or lengthen out within the scanning plane. To see whether a structure will lengthen out geometrically, one should rotate the transducer 90 degrees during real-time. In the case of a true sonographic mass, the mass will maintain its shape in both dimensions, confirming its 3D character, whereas glandular tissue elements will elongate and appear less like a mass.
The size and shape of the breasts vary remarkably from woman to woman. Some women have more glandular tissue, some have less. Some have more fatty tissue than others, and some have more connective tissue, thus resulting in firmer breasts. Some women have very little breast tissue. The size and shape of the breasts also vary over time because of changes that occur during the menstrual cycle, with pregnancy and breast-feeding, and during menopause. Most differences in breast size between women are due to the amount of fatty tissue within the breasts.
The involutional changes that occur in the breast throughout life affect the appearance and pattern of the breast parenchyma. Involution is hallmarked in breast imaging by the remodeling process that causes glandular tissue to be slowly replaced by fatty tissue. This accounts for differences in the size, shape, and architecture of breast tissue.
Generally, in a young woman, fibrous tissue elements predominate, and the resulting appearance on mammography and ultrasound is a dense echogenic pattern of tissue ( Figure 21-11 ). In a pregnant or lactating woman, the glandular portions of the breast proliferate remarkably in both density and volume, creating interfaces that are less echogenic. As a woman ages, the glandular breast tissue undergoes cell death and is remodeled by the infiltration of fatty tissue. The tissue is progressively replaced by fat and, with the onset of menopause, the ducts atrophy, resulting in a mammographic and sonographic pattern with less fibrous tissue elements ( Figure 21-12 ). This fatty breast is most difficult to image by sonography, as all three layers of the breast appear hypoechoic, with less distinction between the layers. Sonographically, cancers can be difficult to differentiate in the fatty breast because most cancers appear hypoechoic and can be difficult to differentiate from normal breast tissue. Although sonography of the fatty breast is difficult, mammography images this type of breast very well.
The main arterial supply to the breast comes from the internal mammary and the lateral thoracic arteries. More than half of the breast—mainly the central and medial portions—is supplied by the anterior perforating branches of the internal mammary artery. The remaining portion—the upper outer quadrant—is supplied by the lateral thoracic artery; intercostals and subcapsular and thoracodorsal arteries contribute in lesser ways to the blood supply.
Venous anatomy largely parallels the arterial anatomy in the deep breast. However, venous drainage is mainly provided by unpaired superficial veins that can be seen sonographically just under the skin. These surface veins are often enlarged with superior vena cava syndrome or chronic venous thrombosis of the subclavian vein, as well as when arteriovenous shunts are placed in patients with chronic renal insufficiency. Figure 21-13 shows an example of a grossly dilated surface vein in the breast. When there is doubt concerning the vascular nature of a long, tubular, anechoic structure on breast ultrasound, such as the distinction between a dilated duct and a vessel, color flow vascular imaging or Doppler ultrasound techniques can easily resolve this situation.
Lymphatic drainage from all parts of the breast generally flows to the axillary lymph nodes. The flow of lymph is promoted by valveless lymphatic vessels that allow the fluid to mingle and proceed unidirectionally from superficial to deep nodes of the breast. The flow of lymph moves from the intramammary nodes and deep nodes centrifugally toward the axillary and internal lymph node chains. It has been estimated that only about 3% of lymph is eliminated by the internal chain, whereas 97% of lymph is removed by the axillary chain.
Part of the standard surgical therapy of invasive breast cancer involves axillary lymph node dissection. This is vital in the staging and management of breast cancer because nodal status affects the patient’s prognosis and is important in guiding adjunctive therapy. Although most tumors can infiltrate and spread via the axillary lymph nodes, they may begin their infiltration by using alternative lymph channels, such as the internal mammary chain within the chest, across the midline to the contralateral breast, deep into the interpectoral (Rotter’s) nodes, or into the supraclavicular nodes ( Figures 21-14 , 21-15 , and 21-16 ).
The male breast
In males, the nipple and the areola remain relatively small. The male breast normally retains some ductal elements beneath the nipple, but it does not develop the milk-producing lobular and acinar tissue. The ductal elements usually remain small but can hypertrophy during puberty and later in life under the influence of hormonal fluctuations, disease processes, or medications. This condition, in which the ductal elements hypertrophy, is called benign gynecomastia ( Figure 21-17 ). Imaging with mammography and ultrasound is often requested to exclude breast cancer as a cause.
Although breast cancer is uncommon in males, it does occur. Approximately 1300 new cases are diagnosed each year within the United Sates. The occurrence approximates 1% of the incidence in women. Box 21-2 lists male patients who have an increased risk for breast cancer.
History of prior chest wall irradiation (especially for Hodgkin’s lymphoma)
History of orchitis or testicular tumor
Genetic predisposition ( BRCA2 gene mutation, breast cancer in female relatives, p53 mutation)
Physiology of the breast
The primary function of the breast is fluid transport. The breast includes fat, ligaments, glandular tissue, and a ductal system that work together to provide fluid transport. The ductal system is critical in the transport of fluids within the breast. The ductal system is also where many pathologic conditions originate.
An important function of the breast during the reproductive years is to make milk from nutrients and water taken from the bloodstream. Milk is produced within the acini and is carried to the nipple by the ducts. During lactation, the transport of milk depends on the action of the two epithelial cells that make up the ductal network: luminal cells, which secrete the milk components into the ductal lumen, and myoepithelial cells, which contract to aid in the ejection of milk.
The female breast is remarkably affected by changing hormonal levels during each menstrual cycle and is further affected by both pregnancy and lactation (breast-feeding). Breast development begins before menarche and continues until the female is approximately 16 years old. During this time, the ductal system proliferates under the influence of estrogen. During pregnancy, acinar development is accelerated to enable milk production by estrogen, progesterone, and prolactin. Prolactin is a hormone produced by the pituitary gland that stimulates the acini to produce and excrete milk. Prolactin levels usually rise during the latter part of pregnancy, but milk production is suppressed by high levels of progesterone. Expulsion of the placenta after the birth of a baby causes a drop in circulating progesterone, initiating milk production within the breasts. The physical stimulation of suckling by the baby initiates the release of oxytocin (produced by the hypothalamus and released by the pituitary gland), which further incites prolactin secretion, stimulating additional milk production. Full maturation of the acini occurs during lactation and is thought to be mildly protective against the development of breast cancer. At the end of lactation, the breast tissue parenchyma involutes. Breast evaluation by mammography can be difficult in a dense, lactating breast; therefore mammographic screening of the breast usually is not performed until at least 6 months after cessation of lactation.
Breast evaluation overview
The primary purpose of breast screening is the detection and diagnosis of breast cancer in its earliest and most curable stage. Accurate identification of benign breast lesions during cancer screening is also important for good care because it can save the patient from unnecessary surgical procedures and resultant tissue scarring.
Three general categories of diagnostic breast imaging are available, two of which involve breast ultrasound. These three categories include breast cancer screening (generally performed by physical breast evaluation with mammography), diagnostic interrogation (consultation, problem solving, workup), and interventional breast procedures (histologic diagnosis and/or localization).
Breast cancer screening is recommended in women without clinical signs of breast cancer ( Box 21-3 ). According to the American Cancer Society, breast cancer screening involves monthly breast self-examination (BSE), regular clinical breast examination (CBE) by a physician or other health care provider, and annual screening mammography. Monthly BSE is best performed at the end of menses and should begin at age 20. CBE should be performed once every 3 years from ages 20 to 39 and at least yearly from age 40 on. Screening mammography should be performed yearly starting at age 40. BSE and CBE are important steps in breast cancer screening because 70% of cancers are found as lumps felt during BSE and CBE. BSE and CBE may also identify other signs or symptoms of possible breast cancer that require further evaluation by diagnostic breast imaging ( Box 21-4 ).
Breast self-examination (BSE)
Monthly beginning at age 20
Clinical breast examination (CBE) by a health care provider
Ages 20 to 39: every 3 years
Ages 40 on: yearly
Yearly starting at age 40
Exceptions: Personal history of breast cancer, first-degree relative (mother or sister) with premenopausal breast cancer, atypical hyperplasia or lobular carcinoma in situ on prior breast biopsy, and known breast cancer gene mutation ( BRCA1 or BRCA2 )
New or growing dominant, discrete breast lump
Hard, gritty, or irregular surface
Usually (but not always) painless
Does not fluctuate with hormonal cycle
Different from “lumpy” breast texture
Unilateral single-duct nipple discharge
Spontaneous, persistent; serous or bloody
Surface nipple lesions
New nipple retraction
New focal skin dimpling or retraction
Unilateral new or growing axillary lump
Hot, red breast
Note: Although these clinical signs and symptoms may indicate the presence of breast cancer, it is important to understand that in most cases the cause is not cancer, but rather a benign condition.
Mammography, sonography, and magnetic resonance imaging (MRI) are the primary imaging tools used for diagnostic breast evaluation. Mammography provides a sensitive method of screening for breast cancer, whereas ultrasound and MRI are used to provide additional characterization and further interrogation of breast lesions that are not well visualized by mammography. The mammographic signs of breast cancer are listed in Box 21-5 . Because ultrasound examination is performed by scanning in cross-sectional planes, it is difficult to adequately screen the entire breast in most patients. Ultrasound may be used for screening purposes in young, dense breasts, which are difficult to penetrate by mammography; to evaluate palpable masses that are not visible on a mammogram; and to image the deep juxtathoracic tissue not normally visible by mammography. Ultrasound is also useful in differentiating structures within uniformly dense breast tissue in which mammography is limited (e.g., in differentiating solid, round masses from fluid-filled cysts and in visualizing tissue adjacent to implants or other structures that limit visualization by mammography). MRI is also a useful tool in breast imaging but is prohibitively expensive for screening purposes. Because a strong magnetic field is used to create images, not all patients are good candidates for MRI (e.g., patients with pacemakers or artificial joints). Patients who suffer from uncontrolled claustrophobia are also not good candidates for MRI.
|Common||Irregular (spiculated), high-density mass|
|Clustered pleomorphic microcalcifications|
|Focal distortion (with no history of prior biopsy, infection, or trauma)|
|Less common||Focal asymmetric density (with associated palpable lump or solid sonographic mass)|
|Common||Nipple or skin retraction|
The overall goal of breast evaluation is the proper classification of a breast lesion according to the level of suspicion for breast cancer. Thorough evaluation takes into account the results of both the breast imaging assessment and the clinical assessment. The appropriate next step in patient management is dictated by the level of suspicion for cancer in any breast lesion and takes into account the age and individual risk factors for each particular patient. Risk factors for breast cancer are listed in Box 21-6 .
Family history of breast cancer
Personal history of breast cancer
First-degree relative (mother, sister, daughter)
Premenopausal breast cancer
Multiple affected first- and second-degree relatives
Associated cancers (ovarian, colon, prostate)
Biopsy-proven atypical proliferative lesions
Lobular neoplasia (lobular carcinoma in situ)
Atypical epithelial hyperplasia
Prolonged estrogen effect
Late first pregnancy
It is important to recognize clinical signs or symptoms of possible breast cancer (see Box 21-4 ). Patients with clinical indications of breast cancer generally undergo diagnostic breast interrogation. Diagnostic imaging of the breast is tailored to the patient’s age and specific clinical problem. Clinical history and examination of the patient with a breast problem ( Box 21-7 ) help determine the next diagnostic step. In the patient with no signs or symptoms of possible breast cancer, screening mammography is typically the first diagnostic test performed.
Risk factors for breast cancer
Onset and duration of mass
Relation to menstrual cycle
Breast examination (for palpable mass)
Location of mass
Clock face or quadrant
Characteristics of mass:
Shape (round, oval, lobular, irregular)
Surface contour (smooth, irregular)
Consistency (soft, rubbery, firm, hard, gritty)
Mobility (movable, fixed)
In women age 40 and over who are asymptomatic (without clinical signs of possible breast cancer), annual screening by mammography is recommended. Usually less than 10% of these women will have abnormalities detected on the screening examination that require further workup. When a breast lesion is identified by mammography, it is normally described using guidelines contained within the Breast Imaging Reporting and Data System (BI-RADS). BI-RADS was developed by the American College of Radiology (ACR). A key component of this system is an overall outcome assessment category that indicates the suspicion of malignancy ( Table 21-1 ). Figures 21-18 , 21-19 , 21-20 , and 21-21 present mammographic and sonographic examples of various BI-RADS category masses.
|BI-RADS Category/Recommended Action||Description|
|Nothing to comment on. Breasts are symmetric; no masses, architectural distortion, or suspicious calcifications.|
|Involuting, calcified fibroadenomas, multiple secretory calcifications, fat-containing lesions.|
|Noncalcified circumscribed solid mass; focal asymmetry; cluster of round (punctate) calcifications. Less than 2% chance of malignancy.|
|Findings do not have classic appearance of malignancy but have wide range of probability of malignancy greater than those in Category 3.|
|Classic breast cancers with a 95% or greater likelihood for malignancy.|