Chapter 2 Mammogram Interpretation
Breast Cancer Risk Factors
Risk factors for breast cancer are important to consider when reading mammograms, because they indicate a pretest probability of breast cancer. Compiling risk information on the breast history sheet provides the interpreting radiologist quick and easy-to-use access to this information (Fig. 2-1). Breast cancer risk factors are listed in Box 2-1. The most important risk factors are older age and female gender; U.S. statistics indicate that breast cancer will develop in one in eight women, if the women have a 90-year life span. Men also develop breast cancer, but only 1% of all breast cancers occur in men.
Box 2-2 Family History Suggesting an Increased Risk of Breast Cancer
>2 relatives with breast or ovarian cancer
Breast cancer in relative age <50 years
Relatives with breast and ovarian cancer
Relatives with 2 independent breast cancers or breast plus ovarian cancer
Male relative with breast cancer
Family history of breast or ovarian cancer and Ashkenazi Jewish heritage
The Normal Mammogram
Box 2-4
ACR BI-RADS® Terms for Breast Density
The breast is almost entirely fat (<25% glandular).
There are scattered fibroglandular densities (approximately 25–50% glandular).
The breast tissue is heterogeneously dense, which could obscure detection of small masses (approximately 51–75% glandular).
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.
Mammographic Findings of Breast Cancer
Table 2-1 Reasons for Missed Cancers
Errors in technique | |
Errors in detection | |
Errors in interpretation | Radiologist sees and perceives finding, incorrectly interprets finding as nonactionable |
Tumor morphology | Tumor shape similar to background fibroglandular tissue displayed on the mammogram |
True negative study | Tumor cannot be seen even in retrospect |
The mammographic signs of breast cancer listed in Table 2-2 are discussed in further detail in Chapter 3 on breast calcifications, Chapter 4 on breast masses, and Chapter 10 on clinical problems. The trick is to see the cancer, perceive it and have it register in one’s mind, then interpret the findings correctly and act on the finding.
Table 2-2 Mammographic Findings of Breast Cancer
Finding | Differential Diagnosis |
---|---|
Pleomorphic calcifications | Cancer (most common), benign disease, fat necrosis |
Spiculated mass | Cancer, postsurgical scar, radial scar, fat necrosis |
Round mass | Cyst, fibroadenoma, cancer, papilloma, metastasis |
Architectural distortion | Postsurgical scarring, cancer |
Developing density | Cancer, hormone effect, focal fibrosis |
Asymmetry: focal or global | Normal asymmetric tissue (3%), cancer (suspicious: new, palpable, a mass containing suspicious calcifications or spiculation) |
Breast edema | |
Lymphadenopathy | |
Single dilated duct | Normal variant, papilloma, cancer |
Mass with calcifications | Cancer, fibroadenoma, papilloma; exclude calcifying oil cyst |
Nothing | 10% of all cancers are false-negative on mammography |
An Approach to the Mammogram
Many tools are available to help the radiologist correctly interpret mammograms (Table 2-3). The first is the breast history and physical findings. The breast history sheet alerts the radiologist to the patient’s risk factors for cancer and the patient’s pretest probability of cancer (see Fig. 2-1). The history sheet includes the patient’s clinical history of breast biopsies and a schematic diagram of their location so that old scars are not misinterpreted as cancer.
Table 2-3 Tools Used for Interpretation of Mammograms
Tool | Use |
---|---|
Breast history, risk factors | Evaluate patient’s complaint and risks |
Technologist’s marks | Show skin lesions, scars, problem areas |
Putting images back to back | |
Bright light (SFM) | View skin, dark parts of film |
Window/level (FFDM) | Contrast for masses, calcifications |
Magnifying lens or magnifier | Visualize mass borders, calcifications |
Old films | Compare for changes |
CAD (if available) | Look for CAD marks after initial interpretation |
CAD, computer-aided detection; FFDM, full-field digital mammogram; SFM, screen-film mammogram.