Recognizing the Findings in Breast Imaging

The most widely studied and utilized of all breast imaging studies is mammography. A mammogram is a type of low-dose x-ray imaging developed to evaluate clinical breast abnormalities and to screen patients for breast cancer ( Fig. 29.1 ).

• Mammograms are performed on specialized radiographic units that produce low-energy x-rays. Compression is applied to the breast and used to improve image quality by reducing the thickness that the tissue x-rays must penetrate, decreasing radiation scatter, reducing the required radiation dose , and preventing motion. Mammographic images today are almost exclusively captured digitally, rather than on film.

• Quality control is an important part of any mammography program. Radiologists are evaluated with regular audits to determine how well they are performing. These include evaluation of recall rate (number of mammograms read that require additional views and/or ultrasound) and positive predictive values (how many patients that undergo biopsy return positive, i.e., cancerous, results).

Digital breast tomosynthesis (DBT) (sometimes called 3D mammography ) is a type of mammography in which images are obtained at multiple different angles of the x-ray tube to create thin slices through the breast. It has been shown to reduce false-positive diagnoses while increasing invasive cancer detection ( Fig. 29.2 ).

Mammographic examinations are divided into screening mammography and diagnostic mammography. We discuss the differences between screening and diagnostic examinations later in this chapter.

Breast ultrasound is most commonly used in conjunction with diagnostic mammography, but may also be performed as an additional screening method.

Indications for US include:

• Problem-solving for asymptomatic patients recalled from a screening mammogram for additional breast imaging

• Evaluating symptomatic patients ( Fig. 29.4 )

  

• The initial study used in average-risk, symptomatic patients under 30 years of age

Studies have shown that screening high-risk patients and patients with dense breasts with ultrasound increases breast cancer detection over mammography alone.

Indications for MRI include:

• Screening certain high-risk patients ( Fig. 29.5 )

  

• Evaluating patients who have breast implants to determine the integrity of the implants

• Evaluating patients with positive lymph nodes and an unknown primary site

• Evaluating the response to neoadjuvant chemotherapy . Neoadjuvant chemotherapy refers to treatment that is given to reduce the size of a tumor in advance of more definitive therapy, such as surgery.

• In some cases, newly diagnosed breast cancer to look for extent of disease, contralateral disease, and multiple cancers

Breast MRI is the most sensitive of all breast imaging modalities, but also the most expensive. Some patients cannot tolerate an MRI because of feelings of claustrophobia from the scanner or because they have certain medical devices , such as pacemakers, or ferromagnetic foreign bodies, such as some surgical clips.

MRI is the gold standard for evaluating the structural integrity of silicone breast implants discussed later in this chapter.

Other modalities included under the umbrella of breast imaging include molecular breast imaging, positron emission tomography (PET), and even CT.

We will concentrate on the modalities of mammography , US, and MRI , the studies used most widely today.

The purpose of screening mammography is to try to detect breast cancer in asymptomatic patients.

The sensitivity of mammography in detecting a breast abnormality depends on breast density: as density increases (tissue becomes whiter) sensitivity decreases. As with all conventional radiography, fat appears gray on mammography, whereas the imaging signs of breast cancer are whiter. This is why the denser (“whiter”) a patient’s underlying breast tissue is, the more difficult it is to detect a cancer among normal tissue. Finding cancer in a dense breast has been likened to looking for a polar bear in a snowstorm.

Breast density is divided into four categories, ranging from almost entirely fatty to very dense (see Fig. 29.1 ).

Every screening mammogram consists of two views of each breast, the craniocaudal (CC) view and the mediolateral oblique (MLO) view ( Figs. 29.6 and 29.7 ).

Multiple randomized controlled trials (RCTs) have shown at least a 22% reduction in breast cancer mortality in women who undergo screening mammography versus those who do not. More current and larger-scale observational studies report a 38% mortality reduction from breast cancer among those screened.

The American College of Radiology (ACR) recommends annual mammographic screening beginning at age 40 for women at average risk and intermediate risk , such as women with a personal history of breast cancer ( Table 29.2 ). Other organizations also have guidelines.

Some organizations point to the risks or harms of mammography. These include mammograms that are interpreted as abnormal, but turn out to be normal, or biopsy recommendations that reveal benign disease (false-positive) as well as the issue of overdiagnosis, meaning detecting cancers that may not be lethal.

Although cancers may be low grade and grow slowly, they do not disappear without treatment. The ACR contends that overdiagnosis should not be a factor in deciding when to start screening or deciding the interval between examinations.

Screening recommendations from the ACR have level-one evidence to support clear guidelines: start yearly screening at age 40. Other organizations vary in their recommendations, which may make it difficult for patients to decide when and how frequently they should be screened.

At what age should screening mammograms stop? Randomized controlled trials proved the mortality reduction from screening stopped at age 74, but there have been numerous studies that show continued benefit for women over the age of 74. The ACR recommends that screening be stopped based on a woman’s health status and not on her age.

The indications for diagnostic mammography are listed in Box 29.2 .

A typical diagnostic imaging workup is shown in Fig. 29.8 for patients with breast symptoms.

Patients recalled because of prior screening mammography findings or undergoing a diagnostic mammogram may be evaluated using a variety of additional mammographic views. Some of these additional views are spot compression images, spot compression magnification views, true lateral or 90-degree lateral views, rolled views, exaggerated views, and cleavage views, as well as US.

Although the majority of symptomatic breast cancers will display an abnormality on mammography, US, or both, some cancers will have no imaging correlate to a clinically palpable finding or a reported symptom. For example, invasive lobular carcinomas are classically difficult to detect with imaging and can also be subtle clinically ( Table 29.3 ).

Therefore, anything that is clinically palpable , but has a negative imaging workup, should be evaluated clinically , often by a breast surgeon. The clinician can then decide whether to do follow-up studies or a biopsy.

Patients who undergo diagnostic mammography typically receive their results at the conclusion of the examination(s) so that they understand what to do next and have the opportunity to ask questions.