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Chapter 1

General Overview

There are three critical factors that lead to identifying mammographic abnormalities: production of high-quality images, perception of a lesion, and characterization of the finding. A team of people is needed to produce high-quality mammograms. The radiologist and the technologist should constantly be evaluating images for film contrast, exposure parameters, patient position, and image processing. Furthermore, a radiation physicist should work with the technologists to monitor equipment performance.

Perception of mammographic abnormality is the first step in identifying a breast malignancy. Perception is aided by a systematic review of the mammographic examination. Consistent systematic review of the mammogram is critical in avoiding perceptual errors. Tabar and Dean's Teaching Atlas of Mammography has an excellent explanation of a horizontal and vertical masking technique that facilitates identification of abnormal mammographic asymmetries. Masking entails physically covering portions of the film so that only small corresponding regions of the two breasts are visible. In a busy practice, this technique may not be practical, but one can develop the ability to visually mask by focusing on a small area of the breast and comparing it to the equivalent area on the contralateral side. My personal method involves this latter technique. I visually horizontally mask all breast views and then perform a second focused review of the axilla and the subareolar regions (Fig. 1–1).

During the review of the mammographic examination, one may identify asymmetries or calcifications. One should classify the asymmetry as a density or architectural distortion. The densities should be further analyzed and subdivided into either masses or asymmetric densities. Using the following methods, the breast imager then analyzes the lesion and assigns an assessment category according to the American College of Radiology Breast Imaging Reporting and Data System (BI-RADS). These assessment categories are the following:

• Category 0—Need additional imaging evaluation. This evaluation may include additional mammographic views (e.g., spot compression) or other imaging modalities (e.g., ultrasound).

• Category 1—Negative. The breasts are normal.

• Category 2—Benign finding. The mammogram is normal, but there is a finding that the interpreter wishes to describe.

• Category 3—Probably benign finding. Short-interval follow-up suggested. The finding has a high probability of being benign and is not expected to change in appearance. In this book, I generally assume that the patient will be reimaged about 6 months after this assessment is made.

• Category 4—Suspicious abnormality. Biopsy should be considered. The radiologist has enough concern about the lesion that biopsy is being recommended.

• Category 5—Highly suggestive of malignancy. Appropriate action should be taken.

Patterns of Mammographic Abnormality

After finding an asymmetry, the breast imager should classify the finding into one of four patterns: mass, asymmetric density, calcifications, and architectural distortion.

Masses

If a density is identified, then the radiologist should first clarify if the density is a mass or a focal asymmetric density. A mass is a density that has a consistent shape when imaged at different angles and with different patient positions. If one concludes that the lesion is a mass, then one should determine whether the shape of the mass is circumscribed or irregular. Circumscribed masses are round, oval, or lobulated (see Section 3). Circumscribed masses are commonly benign. Only 1.4% of well-defined circumscribed masses are malignant. As there are many benign lesions in this category, diagnostic evaluation should be directed to excluding many of these benign lesions from being biopsied. The first step is to analyze the density of the mass. If the mass contains fat, then the abnormality is benign (Category 2) and does not require biopsy. If the mass has a density equal or greater than parenchyma, then further examination is necessary. The next step is to examine the margins of the mass. If the margins are sharp or obscured by the surrounding parenchyma, then the mass should be examined sonographically. If the mass clearly has ill-defined or spiculated borders, then biopsy is indicated (Category 4 or Category 5). This biopsy may be performed sonographically as almost all of these lesions are sonographically visible, particularly if they are larger than 4 to 5 mm.

Figure 1–1. (A–C). Systematic method to review mammograms. Horizontal examination: Initially, one should focus on a small region in the superior section of the right film and then compare it to the comparable left side. One should then proceed inferiorly in the mammogram and continue this process. In this case, there is trabecular thickening and architectural distortion at the 12:00 position of the left breast (arrows). This lesion is an infiltrating ductal carcinoma. (D). Systematic method to review mammograms (axillary and subareolar examination). After the horizontal examination, one should study the axillary and subareolar regions of each breast and compare each area to the contralateral side. The axillary region is important because the upper outer quadrant contains the highest percentage of breast cancers. Extra attention to the subareolar region is worthwhile as this area exhibits a complex architecture consisting of numerous ductal lines. Subareolar architectural distortion is commonly difficult to identify.

As noted earlier, circumscribed mammographic masses that have well-defined or obscured margins should be examined sonographically. Of these masses, sonographically identified cysts are obviously benign (Category 2). If the mass is well-defined and uniformly hyperechoic to fat, it is probably benign (Category 3). The mass is also probably benign (Category 3) if it has all of the following characteristics: (1) shape: round, oval, or one or two large lobulations; (2) margin: well defined with hyperechoic thin capsule; (3) echogenicity: uniformly hypoechoic; (4) size: 1 cm or smaller.

If the margin is extremely well defined but does not have a hyperechoic capsule, I also assess it as probably benign (Category 3). To characterize whether a margin is well defined one must have high-quality, high-resolution, and high-frequency (≥10 MHz) equipment. Furthermore, the entire margin must be well defined and clearly visible (Fig. 1–2). Finally, there should not be any other associated abnormality such as sonographic architectural distortion. In this situation, I am also assuming that I have seen the patient only once and there is no evidence of growth. If the lesion has been identified on earlier imaging exams and has grown in size or if it is larger than 1 cm, then I will recommend biopsy (Category 4).

The reason for biopsing large or growing well-defined lesions is that some of the masses in this category will be malignant. As long as a malignancy is small, it has a good prognosis since the probability of metastasis is low. However, to have a good prognosis, it is best for the patient to be Stage 1 (primary tumor smaller than 2 cm) at the time of diagnosis. Shortinterval follow-up of a small (< 1 cm) well-circumscribed mass that has a low probability of malignancy is a reasonable method to avoid unnecessary biopsies.

If the mass has any other sonographic characteristics, then it is Category 4 or Category 5. Examples of these lesions include: (1) solid masses within cysts, (2) masses that have any other shape or that are microlobulated, (3) lesions that exhibit heterogeneous echogenicity or that present as a focal area of intense shadowing, (4) tumors with either completely or partially ill-defined margins, (5) masses associated with other sonographic abnormalities such as architectural distortion.

Masses with microlobulations or other shapes that cannot be classified as circumscribed should be considered irregular in shape (see Section 4). Although benign etiologies may produce an irregular mammographic mass, all mammographically irregular masses should be pathologically examined unless the lesion is a benign scar. Scars resulting from previous surgery may appear similar to malignancies. A careful patient history with a map of the scar is necessary to correlate the mammographic abnormality with the clinical information. If this information is insufficient, previous films commonly document either stability or reduction of the lesion density and size. Occasionally, sonography may be necessary to differentiate scar from malignancy. In these cases, sonography may confidently exclude malignancy if only hyperechoic architectural distortion is present without mass. Furthermore, sonographically scars change in appearance with different transducer positions. Even if there is a wide area of severe shadowing in one view, the orthogonal view will demonstrate only a thin line of architectural distortion characteristic of scar. Because scar attenuates high-frequency more than low-frequency ultrasound, commonly low-frequency sonography is more effective in characterizing scar (see Case 178, Section 9).

Besides scar, other benign entities produce irregular masses. These lesions include fat necrosis, sclerosing adenosis, focal fibrosis, hematoma, abscess, and benign neoplasms such as fibroadenomas or papillary lesions. However, unless the patient has a clinical history or symptoms suggesting recent trauma, surgery, or infection, these lesions cannot be differentiated from malignancy and should be biopsied. When clinical information suggests that a hematoma or abscess may be responsible for the mammographic abnormality, then sonography is useful to identify these processes.

Figure 1–2. (A). Right MLO digital mammogram. (B). Left MLO digital mammogram. (C). Right CC digital mammogram. (D). Left CC digital mammogram. (E). Right MLO spot magnification mammogram. (F). Right CC spot magnification mammogram. (G). Right MLO spot magnification mammogram. (A–G). There is a palpable right breast mass that is labeled with a radiopaque dot at the 3:00 location near the nipple. The mass is not well delineated on either the screening or the spot magnification views (E,F). In the right upper outer quadrant in the middle third of the breast (square), there is an irregular mass that is confirmed on the spot magnification view (G). (H). Right antiradial breast sonogram: The palpable mass corresponds to a well-defined oval hypoechoic mass. On this view, the mass appears probably benign. (I). Right antiradial breast sonogram: This is the same mass as Figure 1–2H, but in a slightly different position. Subtle irregularity of the margin (arrow) is present. These features change the assessment so that the lesion is suspicious. This mass is infiltrating mucinous carcinoma. (J). Right antiradial breast sonogram: This hypoechoic irregular mass corresponds to the irregular mammographic mass (G). This mass is infiltrating ductal carcinoma.

Finally, radial scars also produce irregular masses. The mammographic characteristics of radial scars include: (1) change in appearance from one mammographic projection to another; (2) no dense central mass; (3) the radiating lines are long and thin; (4) the radiating structures are commonly dominated by radiolucent linear lines; (5) no skin thickening; (6) very little palpable abnormality. Although radial scars may be differentiated from malignancy, radial scars are commonly associated with malignant neoplasms and, therefore, should be excised.

Asymmetric Densities

Analysis of an asymmetric density should start with a close evaluation of the entire mammographic examination. It is important to initially define if the asymmetric density diffusely involves a large area of the breast or a small area (see Section 6). If the density is diffuse, then the skin should be carefully examined. If the density is only due to increased fibroglandular tissue, then a physiologic or pharmacologic etiology may be responsible. Heterogeneous or extremely dense parenchymal composition is more common in younger premeno-pausal women, but is also common in older women, especially those with fibrocystic changes. Medications such as estrogen replacement therapy sometimes increase the overall mammographic parenchymal density.

If skin thickening is present then the etiologies include axillary lymphatic obstruction, lymphatic spread of breast cancer, inflammation, and systemic fluid overload. Axillary lymphatic drainage may be blocked by ipsilateral breast cancer metastases or hematologic malignancies (e.g., lymphomas). Lymphatic spread of breast cancer to the contralateral breast will block lymphatic channels and produce lymphedema. Inflammation and abscess will thicken the skin and produce increased density, particularly around the areola. In this situation, the axillary portion of the breast is relatively spared. Finally, any condition that produces systemic fluid overload such as heart failure or renal failure will produce breast lymphedema.

If the asymmetric density involves a small area, then one should carefully examine the area to determine if the density represents a mass, normal asymmetric fibroglandular tissue, or overlap of normal parenchymal tissue. A focal asymmetric density is a density that cannot be reliably identified on more than one view. If the density is only visible on the craniocaudal (CC)view, a 90 degree mediolateral (ML) may demonstrate the mass better than the mediolateral oblique (MLO) view. Spot compression of a density may clarify the shape of the mass, but sometimes malignancies such as lobular carcinoma may compress and blend into the normal breast parenchymal background. For small or less-dense lesions, consider using rolled or oblique views to confirm the presence of the mass (Fig. 1–3). Normal fibroglandular tissue will blend into the adjacent tissue with oblique views. The tissue will have the same internal curvilinear pattern as the rest of the breast. Furthermore, the tissue will not exhibit any architectural distortion. If one cannot distinguish between a mass and normal fibroglandular tissue, then sonography may be useful. However, to adequately perform this differentiation, one must have high resolution and frequency, be familiar with the normal sonographic appearance of breast parenchyma, and be comfortable with cross correlating mammography with sonography (see Section 2). If the woman is high risk for malignancy and high-frequency sonography is negative or unavailable, then magnetic resonance is a reasonable method to clarify the etiology of a worrisome asymmetric density.

Calcifications

There are a wide variety of breast calcifications (see Section 5). Analysis of calcifications should start with excluding calcifications that are characteristic for benign lesions. If the calcification does not fit in these obviously benign categories, then the shape of the calcification should be analyzed and placed into patterns that can be related to American College of Radiology BI-RADS assessment categories.

Calcifications or densities simulating calcifications that may be excluded from further workup include technical artifacts, substances on the skin (e.g., lotions, deodorants), and calcifications that are pathognomonic for benign entities. Processor artifacts and dirty screens may produce tiny dots or irregularities that are confused for calcifications. These artifacts are generally whiter than calcifications and have unusual shapes. Constant evaluation of processing is critical to avoid these problems. Materials on the skin may also initially appear as calcifications. However, these densities are unusual in configuration and are commonly located in the axilla. Thorough cleansing of the skin prior to reevaluation generally removes these particles. Educating patients to avoid using these materials prior to mammography will also reduce encountering this problem. Certain calcifications are pathognomonic for benign entities. These include oil cyst, dermal, vascular, secretory, and milk of calcium calcifications (Figs. 1–3B,D,G). By reviewing these characteristic calcifications in texts or teaching files, one can confidently identify these benign calcifications.

Figure 1–3. (A). Right MLO digital mammogram. (B). Left MLO digital mammogram. (C). Right CC digital mammogram. (D). Left CC digital mammogram. (E). Right MLO spot compression mammogram (arrow points to mass). (F). Right CC spot compression mammogram. (G). Left LM digital mammogram (close-up). (A–G). The patient has had left lumpectomy and radiation therapy 7 years ago. The left breast demonstrates stable scarring and benign calcifications from fat necrosis (see 3B,D,G). In the right breast there is an asymmetric density (square) that is initially visible only on the CC view. However, spot compression views (E-F) demonstrate that it is an ill-defined mass (arrow). This mass is infiltrating ductal carcinoma.

If calcifications or densities are not included in the above categories, then further analysis is necessary. The first characteristic to examine is size. If the calcifications are large, then they are benign. Malignant calcifications are generally smaller than 0.5 mm. The smallest thickness or diameter of a benign calcification is more than 1 to 2 mm. These large calcifications may be confidently excluded from further evaluation.

If the calcification is small, then one should study the shape of the calcification. The shape of calcifications should be categorized into four patterns: (1) round or punctate, (2) amorphous or indistinct, (3) heterogeneous or pleomorphic, and (4) fine linear, branching, or casting calcifications. If the calcifications are round or punctate, then one should determine whether they are clustered or scattered. If they are scattered, then they are benign (Category 2). If they are clustered but have been stable for 3 years, then they are benign (Category 2). If they are new or on a baseline mammogram, then they are probably benign (Category 3) and should be followed by 6-month examinations for a total of 1 year and then yearly evaluations for a total of 3 years. If these calcifications change into a more suspicious shape or increase in number, then biopsy is warranted (Category 4). The reason that new clustered punctate calcifications should be followed is that occasionally, ductal carcinoma may present with punctate clustered calcifications. These calcifications may represent either a variant of the malignant amorphous pattern (see below) or cancerization of lobules (Section 5, Cases 83, 86).

If the calcifications are amorphous in shape, they should be biopsied (Category 4). Amorphous calcifications are commonly round, but they are hazy in appearance and do not have sharp, smooth edges. Malignant amorphous calcifications are generally clustered, but occasionally these calcifications may cover a larger area such as a segment or quadrant of the breast. Malignant amorphous calcifications are the result of superimposition of numerous tiny calcifications within the mucin secreted by cells of ductal carcinoma in situ. Sometimes, amorphous calcifications may overlap in appearance with the round, punctate pattern. Very early, tiny amorphous calcifications may appear punctate. If they are initially misidentified, this error would be discovered as long as the calcifications are closely followed.

Heterogeneous or pleomorphic calcifications are irregular in shape. Furthermore, they also vary in size and density (Fig. 1–4). These calcifications have also been described as resembling “crushed stones” or “granulated sugar.” The larger calcifications are commonly larger than amorphous calcifications, but they are still smaller than 0,5 mm in size. Malignant heterogeneous calcifications generally present in a cluster unless the patient presents with advanced disease. These calcifications are commonly the result of necrosis from intermediateor lower-grade ductal carcinoma in situ. Therefore, heterogeneous calcifications should be biopsied (Category 4).

Like heterogeneous calcifications, fine linear and branching calcifications are irregular calcifications that vary in size and density. However, unlike heterogeneous calcifications, these calcifications form thin, irregular lines that occasionally branch. These calcifications are generally clustered, but extensive disease will present with a segmental distribution. These calcifications should be biopsied (Category 4). High-grade ductal carcinoma in situ produces extensive calcified necrosis that fills the ducts. The configuration and alignment of these calcifications mirror the intraductal spread of malignancy. When a large number of these calcifications are present, they are extremely suspicious, and in those cases, assessment of these calcifications may be upgraded to Category 5.

Architectural Distortion

Generally, mammographers easily recognize asymmetric densities or calcifications unless these findings are small or partially obscured by normal fibroglandular tissue. However, perception of architectural distortion is more difficult since parenchymal patterns vary with different individuals. Perception and characterization of architectural distortion are aided by recognizing normal parenchymal anatomy. The breast parenchymal pattern consists of thin, curvilinear lines that are directed toward the nipple. This radiating pattern is only broken by blood vessels. Adjacent to the subcutaneous fat, the Cooper's ligaments form a scalloped parenchymal edge. The parenchymal edge generally thins out into the axilla and chest wall. These areas commonly form ill-defined curvilinear, feathery borders in patients with scattered or heterogeneously dense breasts. In patients with extremely dense breasts, these borders tend to be well defined. However, the contours are still curvilinear. With heterogeneously dense and extremely dense breasts, the superior corner of the MLO view and the medial and lateral corners of the CC view are also generally curvilinear or rounded.

Figure 1–4. (A). Right MLO digital mammogram. (B). Right CC digital mammogram. (C). Right MLO digital mammogram (close-up). (A–C). In the upper outer quadrant of the right breast, there is a palpable lump that is labeled with a radiopaque dot. Just distal to the dot are extensive heterogeneous calcifications. (D). Right antiradial breast sonogram: The palpable mass corresponds to a combination of a cyst and a spiculated hypoechoic mass with punctate calcifications. Mastectomy specimen shows that this sonographic mass and the mammographic calcifications are mixed infiltrating lobular and ductal carcinoma with an extensive intraductal component.

Architectural distortion may either be central or peripheral (see Section 7). Central distortion results when the ductal and trabecular lines deviate from the nipple. This distortion is commonly due to a spiculated lesion producing straight lines that point to the center of the abnormality. Commonly, these abnormal spiculations are thicker than normal trabecular lines (Fig. 1–5).

Abnormalities that affect the edge of the parenchyma cause peripheral architectural distortion. Lesions may cause retraction, flattening, straightening, or bulging of the parenchymal contours (Fig. 1–6). When the density in the superior parenchymal edge of the MLO view is affected, it may form a sharp triangular corner. Although some women normally have sharply angulated parenchymal corners, if there is asymmetry between the corners or if there has been a change in configuration, then one should search for a subtle spiculated lesion (Fig. 1–7). Retraction of the posterior edge of the parenchyma has been labeled the “tent sign” as the retraction produces a biconvex V-shaped border resembling the peak of a tent (Fig. 1–8).

When architectural distortion is present, the breast imager should perform additional mammographic views to identify a mass. Spot compression views may demonstrate a spiculated mass. Oblique views may clarify the location of architectural distortion that is initially visible only on one view. Magnification views may be useful to identify associated malignant calcifications.

Figure 1–5. (A). Right MLO mammogram. (B). Left MLO mammogram. (C). Right CC mammogram. (D). Left CC mammogram. (E). Left CC spot compression mammogram. (A–E). Central architectural distortion: In the lefi CC view (D) there is an area of focal architectural distortion (square). The lesion corresponds to the asymmetric density in the superior breast on the MLO view. This architectural distortion is due to a tumor consisting of lobular and infiltrating ductal carcinoma.

Figure 1–6. (A). Right MLO mammogram. (B). Left MLO mammogram. (C). Right CC mammogram. (D). Left CC mammogram. (A–D). Peripheral architectural distortion: A lobulated mass extends outside the posterior border of the fibroglandular border (square). This mass corresponds to an infiltrating ductal tumor.

Figure 1–7. (A). Right MLO mammogram. (B). Left MLO mammogram. (C). Right CC mammogram. (D). Left CC mammogram. (E). Right MLO spot magnification mammogram. (F). Right CC spot magnification mammogram. (A–F). Superior peripheral architectural distortion: An irregular mass (marked by a square) at 12:00 produces a sharp angulation of the superior parenchymal corner in the right MLO view (A). This mass represents tubular carcinoma.

Figure 1–8. (A). Right MLO mammogram. (B). Left MLO mammogram. (C). Right CC mammogram. (D). Left CC mammogram. (E). Left MLO spot magnification mammogram. (F). Left CC spot magnification mammogram. (A–F). Posterior peripheral architectural distortion (tent sign): In the left CC view (D), the posterior parenchymal border exhibits retraction (marked with a V). Spot magnification view demonstrates that the architectural distortion is associated with amorphous calcifications (F). Although the abnormality is difficult to identify in the left MLO view (B), left spot magnification locates the lesion with microcalcifications in the superior breast (E). The mass is an infiltrating ductal carcinoma.

Causes of architectural distortion include focal fibrosis, sclerosing adenosis, fat necrosis, scar, radial scar, and malignancy. One identifies surgical scars and fat necrosis by correlating regions of previous surgery or trauma with the architectural distortion. Radial scars usually have thin spiculations and a radiolucent center. Neoplasms usually produce architectural distortion that is evident on two orthogonal views and is associated with a dense central mass. Occasionally, malignancies demonstrate very little central density. Therefore, if architectural distortion is not due to a surgical scar, then it should be biopsied (Category 4).

If the lesion is small or the breast composition is dense, the architectural distortion may only be visible on one view. In these cases, sonography may be useful to demonstrate a mass and localize biopsy. Sonographically, normal fibroglandular tissue and fibrosis will be uniformly hyperechoic. Fat necrosis may either be heterogeneous or hyperechoic echogenicity. Both surgical and radial scars strongly attenuate the sonographic beam so shadowing may be the predominant feature. If heavy shadowing is present, a lower-frequency examination may penetrate the scar and demonstrate no mass. However, in some cases, surgical scars cannot be differentiated from neoplasms and biopsy is necessary. If radial scar is suspected, then excision is necessary. Using high-frequency sonography, malignant masses are either hypoechoic or heterogeneous echogenicity. Sonographic architectural distortion is common. This distortion may appear as hyperechoic haze or spiculations radiating from the tumor. Cooper's ligaments and the anterior fascial line may be distorted.

Sonography may miss a malignant lesion for several reasons. The sonographic examination may miss small masses. However, usually if the neoplasm has created mammographic architectural distortion, there is enough desmoplasia or direct tumor extension for sonographic detection. Therefore, commonly the reasons for error are because the location of the neoplasm is missed or the examiner does not recognize the mass. Reasons for missing the location or not recognizing the mass include examiner inexperience and poor sonographic technique. Since the mammographic findings may be subtle, this sonographic application requires that the examiner be highly skilled in breast sonography. One should be able to cross correlate mammographic and sonographic landmarks to find the lesion.

Even if the examiner is experienced, poor technique or equipment may prevent the imager from identifying masses. Masses are difficult to identify with lower-frequency transducers (<10 MHz). Lower frequencies commonly penetrate masses better than higher frequencies so there is little shadowing and the masses appear hyperechoic. The hyperechoic tumors blend into the surrounding hyperechoic parenchyma. Furthermore, lower frequencies have poorer resolution so the indirect signs of malignancy such as spiculations or distortion of Cooper's ligaments are not visible. Although generally higher frequencies are better than lower frequencies, high-frequency examination also has pitfalls. If the frequency is too high, there may be excessive shadowing. A shadowing malignancy may be hidden by the shadows produced by surrounding fibroglandular tissue. One should use a frequency that allows one to visualize the chest wall. Normal fibroglandular parenchyma will be hyperechoic, but a malignancy will be shadowing, hypoechoic, or heterogeneous echogencity.

Even if one initially does not see a suspicious mass, one may use mammographic and sonographic landmarks (see Section 2) and identify the suspicious breast tissue. The imager may then increase the sonographic frequency and perform a targeted evaluation of the spot to find a subtle mass. If a mass is not discovered, then the sonographic examination should demonstrate the etiology of the mammographic architectural distortion. If the sonographic examination does not clarify the cause of architectural distortion, then the lesion should be classified as Category 4, suspicious, and should be biopsied.