Mammographic and Ultrasound Analysis of Breast Masses

Chapter 4 Mammographic and Ultrasound Analysis of Breast Masses

The American College of Radiology (ACR) Breast Imaging Reporting and Data System (BI-RADS®) lexicon defines a breast mass as a three-dimensional space-occupying lesion seen on at least two mammographic projections. Benign masses do not invade surrounding tissue and will usually have pushing or round borders. Malignant masses extend through the basement membrane and invade the surrounding glandular tissue. Because of this, and with few exceptions, cancers produce an irregularly shaped mass with indistinct or spiculated margins. Thus, radiologists look carefully at the shape of a mass and at its margins to determine if it represents cancer.

Ultrasound goes hand in hand with mammography in evaluation of breast masses. Ultrasound shows whether the mass is a cyst or a solid mass, and defines the shape, border, and internal characteristics of solid masses to help determine if the mass is malignant or benign. This chapter reviews mammographic and ultrasound analysis of breast masses.

Mammographic Technique and Analysis

On mammograms, a true mass is a ball-shaped object. The mass should look about the same size, shape, and density in orthogonal mammogram projections because the hard mass is harder than the surrounding glandular tissue. Radiologists often struggle to determine if a focal asymmetry is a mass or if it represents overlapping normal breast tissue. Fine-detail views such as spot compression or spot compression magnification mammograms show the shape and margins of the mass in greater detail. Mass shapes and borders are easiest to assess when displayed against a fatty background; thus, spot magnification views are most optimal in a projection in which the mass overlies fat.

The ACR BI-RADS® lexicon (Table 4-1) defines mass shapes as round, oval, lobular, or irregular. As the mass shape becomes more irregular, the probability of cancer increases (Fig. 4-1A).

Table 4-1 American College of Radiology BI-RADS® Mass Descriptors

Shape Margin Density

BI-RADS®, Breast Imaging Reporting and Data System.

From American College of Radiology: ACR BI-RADS®—mammography, ed 4, In ACR Breast Imaging and Reporting and Data System, breast imaging atlas, Reston, VA, 2003, American College of Radiology.

The ACR BI-RADS® lexicon describes mass margins as circumscribed (well-defined or sharply defined), microlobulated, obscured by surrounding glandular tissue, indistinct, or spiculated (see Fig. 4-1B to E). As with mass shape, as the mass margin becomes more spiculated the probability of cancer increases. Masses with well-circumscribed borders are likely to be benign, and less than 10% of cancers are smooth. Microlobulated masses have small undulations, like petals on a flower, and are more worrisome for cancer than are smooth masses. An obscured mass has a border hidden by overlapping adjacent fibroglandular tissue; as a result, that border cannot be assessed. An indistinct mass is worrisome for carcinoma because it suggests that the surrounding glandular tissue is infiltrated by malignancy. Finally, spiculated masses are characterized by thin lines radiating from the central portion of the mass and are especially worrisome for cancer. When caused by cancer, spiculations are due to productive tumor fibrosis or growth of tumor into the surrounding glandular tissue.

Mass density is described by noting how white a mass looks compared to an equal volume of fibroglandular tissue. High-density masses are whiter than fibroglandular tissue, and low-density masses are blacker than fibroglandular tissue. High-density masses are especially worrisome for cancer, because they may contain cells with a higher atomic number than normal glandular tissue and fat. Low-density masses and masses with density equal to that of surrounding fibroglandular tissue are less worrisome for cancer. However, low-density cancers, such as mucinous cancers, do exist; these cancers are low-density because they contain mucin.

Fat-containing masses are almost always benign, except for the rare liposarcoma. Fat-containing masses include lymph nodes, oil cysts, hamartomas, and fat necrosis.

Masses can have associated findings that can indicate cancer (listed in Box 4-1). Associated findings worrisome for cancer include skin or nipple retraction, skin or trabecular thickening, axillary adenopathy, architectural distortion, and calcifications (see Fig. 4-1F to I).

Associated calcifications in or around a suspicious mass are important for two reasons. If the mass is cancer, calcifications around it may represent ductal carcinoma in situ (DCIS). Subsequent excisional biopsy must remove both the mass and all surrounding suspicious calcifications to excise the entire malignancy (Box 4-2). Knowing the extent of the suspicious calcifications helps the surgeon plan the excision (Fig. 4-2). Second, suspicious calcifications inside a mass may be the only clue that the mass is a cancer.

At histology DCIS constituting more than 25% of an invasive ductal cancer is said to be an extensive intraductal component (EIC); such a cancer is called EIC-positive (EIC+). Because EIC+ tumors have an increased risk of local recurrence, breast-conserving surgery is less successful. This is one of the reasons to always look for calcifications when a suspicious mass is present.

Other important associated mammographic findings include skin thickening, which may indicate breast edema or focal tumor invasion; skin retraction or nipple retraction as a result of focal tumor tethering; axillary lymph node metastases; and architectural distortion.

Ultrasound Technique and Analysis of Masses

The ACR BI-RADS® ultrasound lexicon describes terms and features of breast masses that are key for the diagnosis of cancer (Table 4-2). Stavros and colleagues established another set of terms that are often used in evaluating breast masses (Box 4-3). Illustrations of these features are shown in Chapter 5.

Evaluation of a breast mass on ultrasound starts with determining whether the mass is cystic or solid. Simple cysts are anechoic (all black inside), round or oval, circumscribed, have an abrupt interface with surrounding tissue, have a thin posterior wall, and are enhanced through sound transmission. Simple cysts can be dismissed. On the other hand, solid breast masses have internal echoes and could be either cancer or a benign mass. Radiologists look at masses to evaluate the mass boundary, internal echo pattern, and acoustic features; its effect on surrounding breast tissue; and the presence and location of calcifications to determine if a solid mass is cancer.

After scanning, the technologist takes representative pictures of the mass and labels the images to clarify the mass’s location in the breast. This makes the mass easier to find on repeat ultrasound examinations. Ultrasound labeling includes which breast was scanned (left or right), position of the mass in terms of breast clock face or quadrant, location in centimeters from the nipple, scan angle (radial or antiradial, transverse or longitudinal), and the technologist’s initials. The technologist captures the image without and with measuring calipers on the muscle (Box 4-4). It is also helpful to indicate whether the mass is palpable or nonpalpable.

Ultrasound findings suggestive of cancer include an irregular shape, noncircumscribed margins, a thick echogenic rim or halo, duct extension or other effect on surrounding breast tissue, microcalcifications, taller-than-wide configuration, and acoustic spiculation or acoustic shadowing. Benign ultrasound findings include no malignant features, a circumscribed border, intense homogeneous hyperechogenicity, fewer than four gentle lobulations, wider-than-tall configuration, and a thin echogenic capsule. Because benign and malignant features in solid masses overlap, common sense plays a major role in patient management for solid masses, especially if the mass looks benign but the clinical scenario is suspicious (new mass, strong family history).

Correlating Palpable and Nonpalpable Masses on Mammography and Ultrasound

A common problem is correlating palpable masses with ultrasound findings. To do this, the radiologist or technologist places an examining finger or a cotton-tipped swab directly on the palpable mass. The sonographer scans over the finger or cotton-tipped swab on the mass to generate a ring-down shadow. Subsequent removal of the finger or cotton-tipped swab from under the probe produces a scan of the palpable finding. Then the radiologist, technologist, and patient have no doubt that the palpable finding has been scanned because this technique ensures that the transducer is placed directly on the palpable finding.

Sometimes a palpable mass on the mammogram has to be correlated to the ultrasound and physical finding. Specifically, the radiologist has to show that the palpable mass, from the ultrasound and from the mammogram, are one and the same. To do this correlation, the radiologist or technologist finds the palpable mass, scans over it, and sees if an ultrasound mass is present. If a mass is present, the sonographer scans the mass and places a finger or cotton-tipped swab on the mass. The sonographer puts an indelible ink mark on the skin over the mass and places a skin marker over the palpable finding, then repeats the mammogram. If the marker is at or near the mammographic finding, the palpable, mammographic, and ultrasound findings all correlate with each other.

To correlate nonpalpable ultrasound findings with mammographic findings, the sonographer identifies the ultrasound finding and places a finger, cotton-tipped swab, or large unwound paper clip under the transducer so that a ring-down shadow is superimposed over the finding. The sonographer removes the transducer and marks this location on the skin with an indelible ink marker. A technologist places a metallic skin marker, such as a BB, on the ink spot and takes orthogonal mammographic views. The skin marker over the ultrasound finding should be in the same location as the mammographic finding on the films. It should be expected that even if the mammogram and ultrasound findings are the same, the mammographic finding might be 1 cm or more away from the skin marker on the films because the skin marker will be compressed away from the mass on the mammogram by the compression paddle.

Sometimes it is still uncertain whether an ultrasound and mammographic finding are one and the same. If the patient agrees to a biopsy of the ultrasound finding, the radiologist places a metallic marker into the mass using an ultrasound-guided, percutaneously placed needle after the biopsy (Fig. 4-3). Repeat mammograms should show the marker in the mass if the two findings are the same. Alternatively, a retractable hookwire may be placed in the mass. A mammogram with the wire in place will show that the ultrasound finding and the mammographic finding represent the same mass. The radiologist can subsequently remove the retractable hookwire.

The mammography and ultrasound report for a breast mass should describe if the mass is palpable; the size, shape, margin, and density of the mass; its location and associated findings; and any change from previous examinations, if known. The report should also include ultrasound finding descriptors and whether it correlates with the mammographic finding. Finally, each report that includes a mammogram should be assigned an ACR BI-RADS® final assessment code indicating the level of suspicion for cancer and follow-up management recommendations (Box 4-5).

Masses with Spiculated Borders and Sclerosing Features (Box 4-6)


Invasive Ductal Cancer

Invasive ductal carcinoma is the most common breast cancer and accounts for approximately 90% of all cancers. Also known as invasive ductal carcinoma not otherwise specified (NOS), invasive ductal cancer usually grows as a hard irregular mass in the breast (Fig. 4-4). The classic appearance of invasive ductal cancer is a dense irregular or spiculated mass, occasionally containing pleomorphic calcifications or having adjacent pleomorphic calcifications representing DCIS. On the mammogram, the mass should be about the same size and density on two orthogonal mammographic views. Spot compression magnification views may show unsuspected calcifications in or around the mass or unsuspected irregular borders.

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Figure 4-4 A to D, Spiculated invasive ductal cancers. A, A screening craniocaudal (CC) mammogram with a scar marker and mole marker shows a possible spiculated mass in the outer breast at the edge of the film (arrow). A spiculated mass is seen in the axilla on B, the mediolateral oblique (MLO) view, and the patient is recalled for a spot view, a lateral view, exaggerated CC, and ultrasound. C, On the exaggerated outer right CC view the mass is seen to greater advantage. D, In another patient, a spiculated retroareolar invasive ductal cancer (arrow) has caused nipple retraction (double arrow). A radiopaque marker has been placed on the nipple. In another patient, two spiculated masses are seen on CC (E) and MLO (F) views. Ultrasound of the spiculated masses shows an irregular mass (G) and a round mass (H) without sonographic spiculation. I, Spiculated invasive ductal cancer on magnification view has two benign-appearing calcifications within it. Note that even though the calcifications look benign, the spiculated borders of the mass are so worrisome for cancer that the worst finding overrides the benign look of the calcifications. Biopsy showed invasive ductal cancer. One should judge a mass with calcifications based on the worst characteristics of either the mass or the calcifications. J to L, Typical invasive ductal cancer findings on magnetic resonance imaging (MRI). J, The MRI shows a large enhancing mass growing through the pectoralis muscle with associated skin thickening. K, The ROI over the enhancing portion of the cancer on MRI selects the area in which a kinetic curve will be drawn. L, The kinetic curve shows rapid initial enhancement with a late-phase washout. The kinetic curve showing a rapid initial uptake and washout of contrast is very typical of cancer.

On ultrasound, spiculated masses shown on mammograms may be round, irregular, or spiculated. Spiculated masses commonly produce acoustic shadowing as a result of either productive fibrosis or tumor extension. When present, acoustic spiculation looks like thin radiating lines extending from the tumor into surrounding breast structures. In a dense white breast, the ultrasound spicules are dark against the white glandular tissue. In a fatty breast, the spicules are white against the dark fatty background. On magnetic resonance imaging (MRI), the usual appearance of invasive ductal cancer is a brightly enhancing irregular mass with or without spiculation; enhancement is initially rapid, with a late-phase plateau or washout curve. Rim enhancement, central enhancement, or enhancing internal septations are other worrisome signs for invasive ductal cancer on MRI.

Invasive Lobular Carcinoma

Invasive lobular carcinoma (ILC) is most commonly seen as an equal- or high-density noncalcified mass, occasionally showing spiculations or ill-defined borders. ILC has a higher rate of bilaterality and multifocality than does invasive ductal cancer. ILC accounts for less than 10% of all invasive cancers, but historically is the most difficult breast cancer to see on mammograms (Box 4-7). ILC is the cancer that gives radiologists a bad name because it can be missed by mammography, at a rate reported by Brem and colleagues to be as high as 21%. This failure can be partly explained by the growth pattern of the carcinoma. Classically, ILC grows in single lines of tumor cells infiltrating the surrounding glandular tissue and may not produce a mass, making it difficult to see by mammography and difficult to feel by physical examination. ILC usually does not contain microcalcifications. It infiltrates the breast, is often seen on only one view, and may cause subtle distortion of the surrounding glandular tissue. When actually seen on the mammogram, ILC masses are often of equal or higher density than fibroglandular tissue and are seen because of the mass itself or its effect on surrounding tissue, such as architectural distortion and straightening of Cooper ligaments. As with any mass, distortion and tenting of glandular tissue caused by ILC are most easily seen in locations where Cooper ligaments extend out into surrounding fat, such as in the retroglandular fat or along the edge of the normal, scalloped fibroglandular tissue (Fig. 4-5).

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Figure 4-5 A to C, Invasive lobular cancer seen on only one view. Screening mediolateral oblique (MLO) (A) and craniocaudal (CC) (B) views; the suggestion of a spiculated mass behind the nipple is seen on the left CC view only. C, A spot compression CC view shows persistent spiculation and distortion caused by the invasive lobular carcinoma (ILC) behind the nipple on the left. The straight lines extending from the tumor into subcutaneous tissue are indicative of its presence. D, In another patient with ILC, a spiculated mass is seen at the edge of the film in the lower right breast on the right MLO view (arrow). The cancer looks very similar to the rest of the breast tissue and is seen only because of the spiculations extending into the fat and because it is a density where there is usually only fat. E, The MLO view in this patient shows a density behind the nipple, possibly a mass, but the nipple is not in profile. F, The right CC view with the nipple in profile now shows skin thickening and widespread architectural distortion throughout the entire breast tissue. G and H, On ultrasound, there is an extensive ILC with marked shadowing throughout the entire upper breast, with cancer in the entire breast on mastectomy. I and L, ILC presenting as a focal asymmetry. I, MLO paired mammograms show a focal asymmetry near the chest wall of the right breast. J, The CC mammogram shows a focal asymmetry in the medial right breast (arrow) roughly corresponding to the mass seen in the MLO view. K, Magnification cropped mammogram of the medial right CC study shows the mass that has caused the architectural distortion (arrow). L, Photographic magnification of the asymmetry shows not only a spiculated mass, but also tiny calcifications. This is invasive lobular cancer. Note that the mass is initially seen only because it is asymmetrically white on the initial mammograms.

On ultrasound, ILC is a hypoechoic, irregular, spiculated, or ill-defined mass that may or may not have acoustic shadowing. When ILC becomes very large, only the acoustic shadowing may be apparent; the mass itself can be difficult to see because of its large size. On MRI, invasive lobular cancer looks like a spiculated mass, with some limitations. Unfortunately, ILC has variable enhancing patterns; it can look like a mass, like a distortion of tissue, or like nodular regions connected by strands of tissue. Its enhancement kinetics can be similar to those of normal breast tissue and can thus be a cause of false-negative MRI examinations.

Postbiopsy Scar

On mammograms, an old postbiopsy scar looks like a spiculated mass that is impossible to distinguish from cancer. Postbiopsy scars show air and fluid at the biopsy site in the immediate postoperative period. Later, the air and fluid are absorbed and the surrounding glandular tissue is drawn to a central dense nidus of scar tissue. As a result, the mammogram shows a centrally dense spiculated mass (the scar) with straightening of the surrounding Cooper ligaments and indrawing of normal glandular tissue, simulating breast cancer. In some patients, no dense central nidus occurs, and the scar appears as a focal architectural distortion. On ultrasound, a postbiopsy scar is a hypoechoic mass with acoustic spiculation and shadowing, similar to cancer. There should be distortion of subcutaneous tissue extending from the scar on the patient’s skin down the plane of the incision to the spiculated postbiopsy scar.

The scar is not of concern for cancer if it occupies a surgical site (Box 4-8). To distinguish postbiopsy scars from cancer, the radiologist looks at the previous biopsy locations on the breast history form and reviews older films to see if the “scar” is at the same location. Some facilities place a radiopaque linear metallic scar marker on the patient’s skin scar to show the location on the mammogram (Fig. 4-7A to D). The metallic linear scar marker should be on top of the “scar” (see Fig. 4-7E and F). If the “scar” does not correspond to a postbiopsy site, it is not a scar. Because spiculated masses may represent cancer, they should be considered suspicious and should undergo biopsy.

Fat Necrosis, Sclerosing Adenosis, and Other Benign Breast Disease

Fat necrosis is due to saponification of fat from previous trauma, usually from surgery or blunt trauma due to an injury, such as from a steering wheel or seat belt in an automobile accident. On mammography, fat necrosis typically contains a fatty lipid center and is round, but it occasionally has a spiculated appearance. Other appearances include asymmetric opacity, round opacity, and dystrophic or pleomorphic calcifications. The diagnosis may be established by eliciting a history of blunt trauma or previous surgery. On occasion, fat necrosis contains a dense or equal-density central nidus with radiating folds extending from its center, similar to cancer, prompting biopsy. On ultrasound fat necrosis can appear cystic with or without posterior acoustic enhancement or internal echoes in about 30%, showing increased echogenicity in 27% and solid in approximately 14%, as reported by Bilgen and colleagues. With true fat necrosis, follow-up should show a decrease in size of masses; the occasional increasing fat necrosis lesion should undergo biopsy, leading to the diagnosis.

Sclerosing adenosis is a proliferative benign lesion resulting from mammary lobular hyperplasia. It is characterized by the formation of fibrous tissue that distorts and envelops the glandular tissue. The resulting process produces sclerosis of the surrounding tissue. The small duct lumens can contain microcalcifications. This results in spiculations and calcifications that, in mammography, can be difficult to distinguish from invasive cancer, resulting in biopsy.

Both sclerosing adenosis and proliferative fibrocystic change may have a slightly spiculated appearance on mammography; they occasionally also contain calcifications and can simulate cancer. When spiculated and associated with calcifications, fat necrosis, sclerosing adenosis and proliferative fibrocystic disease undergo biopsy and are a cause of false-positive biopsies (Fig. 4-8).

Radial Scar

A radial scar is a benign proliferative breast lesion that has nothing to do with a postbiopsy scar but looks like a spiculated mass or postbiopsy scar. Both radial scars and their larger variants, called complex sclerosing lesions, may include adenosis and hyperplasia. In autopsy series, small radial scars are common but often may not be apparent on mammography. The central part of a radial scar undergoes atrophy, thereby resulting in a scarlike formation, with pulling in of the surrounding glandular tissue that produces a spiculated mass. On occasion, because of entrapment of breast ductules, the radial scar may be difficult for pathologists to distinguish from infiltrating ductal carcinoma. However, both epithelial and myoepithelial cells in benign radial scars distinguish them from breast cancer. Radial scars may contain or be associated with atypical ductal hyperplasia, atypical lobular hyperplasia, lobular carcinoma in situ, or cancer. This is one of the rationales for surgical excision. Some pathologists believe that a radial scar may be a precursor to tubular carcinoma and should be excised, although this position is controversial.

On mammography, a radial scar appears as a spiculated mass with either a dark or white central area that may or may not have associated microcalcifications (Fig. 4-9). It is a myth that radial scars have dark centers in the mass on mammography (Fig. 4-10) and can be distinguished from breast cancers, which have white-centered masses. Scientific studies have shown that radial scars and breast cancer can both have either white or dark centers on mammograms. This means that all spiculated masses not representing a postbiopsy scar should be sampled histologically (Box 4-9). On ultrasound, a radial scar is a hypoechoic mass, with or without acoustic shadowing.

Dec 24, 2015 | Posted by in BREAST IMAGING | Comments Off on Mammographic and Ultrasound Analysis of Breast Masses
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