Chapter 4 Mammographic and Ultrasound Analysis of Breast Masses
Mammographic Technique and Analysis
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.
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).
Box 4-1
American College of Radiology BI-RADS® Associated Findings
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.
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.
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.
Box 4-3
Ultrasound Features of Solid Breast Masses
From Stavros AT, Thickman D, Rapp CL, et al: Solid breast nodules: use of sonography to distinguish between benign and malignant lesions, Radiology 196:123–134, 1995.
Correlating Palpable and Nonpalpable Masses on Mammography and Ultrasound
Box 4-5
American College of Radiology BI-RADS® Mass Reporting
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.
Masses with Spiculated Borders and Sclerosing Features (Box 4-6)
Cancer
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).
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.
Radial Scar
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.