Radiologic imaging tests are not perfect, but they often help detect breast cancer at an earlier stage when it is easier to treat.Mammogram
Best known of these tests is the mammogram, an x-ray of the breast. A screening mammogram is done when a clinical breast exam is normal. It consists of two views of each breast: an up-and-down view (cranial-caudal, or CC) and a side-to-side view (medial-lateral-oblique, or MLO). A diagnostic mammogram is performed to evaluate an abnormality found during a breast exam (a lump, changes in the skin, or nipple discharge) or an irregularity on the screening mammogram. In addition to the standard CC and MLO views, the radiologist also may perform views at other angles, magnification, or compression views.
On a mammogram, interior breast structures appear in shades ranging from white to black. The white areas are mainly milk ducts. The hazy gray and black areas are fat tissue. Abnormalities appear as an opaque white haze called densities when they can be seen easily with the naked eye or calcifications when they are tiny and best viewed using a magnifying glass. A density with a starburst shape, dubbed spiculated, often indicates cancer. Noncancerous densities usually appear as a light spot with a smooth outline and no radiating arms.
Calcifications look like tiny, bright white dots the size of grains of sand. Benign calcifications are usually scattered randomly through both breasts, almost like a snowstorm. Sometimes, benign calcifications that are similar in size and possibly coarse looking are clustered in a small space. When calcifications appear as tiny dots of different sizes and shapes (pleomorphic) in a line (linearly arranged), they are likely to be inside a duct and generally indicate cancer. Keep in mind that suspicious calcifications will turn out to be benign 70 to 80 percent of the time.Figure: What the radiologist sees
The radiologist evaluating your mammogram may need to distinguish between a benign (noncancerous) mass and a suspicious mass. A benign mass (A) may appear as a low-density (translucent) area with clear borders. A suspicious mass (B) is more likely to be denser (more opaque) and to have irregular borders that radiate outward in a star-like pattern. The radiologist will also look for the small white dots known as calcifications. Tiny calcifications that appear in gravel-like clusters in one part of the breast (C) are considered suspicious while larger calcifications scattered individually throughout the breast are more likely to be benign.
This test is usually the next step when assessing a suspicious density found on a mammogram or when further evaluating a palpable breast mass. Ultrasound can visualize only small areas of the breast accurately, which is one reason why it is not used as a screening test. High-density sound waves create a picture called a sonogram that helps doctors evaluate whether a density is a fluid-filled cyst, a solid mass, or a variation of normal breast tissue. A cyst, which shows up on the sonogram as a black hole or spot because sound waves go through the fluid, is usually benign.
A solid mass appears as a white spot because sound waves echo off it. Generally, a benign mass is horizontally aligned with smooth borders, and one that is malignant is vertically oriented with irregular borders.Breast MRI
Breast MRI (magnetic resonance imaging) offers a high-resolution method to visualize the breast without radiation. Usually, MRI is used when a woman has a swollen underarm lymph node that is found to contain breast cancer cells, but the cancer cannot be located by physical exam or mammography. (This is called an occult breast cancer.)
Sometimes, doctors use MRI to examine the muscles of the chest wall for suspected cancer, because this area can be hard to reach with mammography. MRI has other uses as well. One is to determine the size and extent of a known tumor, particularly for invasive lobular breast cancers, which can be much larger than they appear during a physical exam or on a mammogram. MRI can also reveal whether anticancer drugs being administered to shrink a tumor before surgery (neoadjuvant chemotherapy) are working. In addition, breast MRI may be used to check for recurrences after lumpectomy and radiation treatment.
Breast MRI is an expensive and somewhat complex technology that requires special equipment and radiologists who are experienced in interpreting the images. It can produce a false positive result in which a benign abnormality might resemble cancer. Nevertheless, major medical centers are finding that breast MRI, when used with mammography and ultrasound, can be a powerful tool for certain women.
For information about breast cancer from the Faculty of Harvard Medical School, see Living Through Breast Cancer by Dr. Carolyn Kaelin. For monthly updates on what's new in Women's Health, subscribe to the Harvard Women's Health Watch.
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