Dense breast tissue makes mammograms harder to interpret

Women with dense tissue should look out for irregularities, may need additional imaging

Submitted by Parkview Health

Women who have a mammogram may receive a follow-up letter informing them about their breast density and the implications it can have for breast cancer screening.

That letter, which is required by state law, can be anxiety-inducing, especially for women who just had their first-ever mammogram, said Sarah Brady, breast surgery nurse practitioner with the Parkview Packnett Family Cancer Institute.

Still, it’s important for women to know what it is, what it means and what to look out for going forward, she said.

Dense breast tissue is common and, by itself, usually isn’t cause for concern. However, because dense tissue and tumors can both appear white on a mammogram, women with dense breasts are more likely to be called back for additional imaging to evaluate potential abnormalities.

“Everyone starts with that dense tissue,” Brady said. “In your 40s, most women are going to get that letter. If it’s your first mammogram and if we don’t have an earlier image for comparison, that may spark callbacks for extra looks. But if nothing was found on your mammogram, there really is no reason for alarm.”

What is dense tissue?

Breasts are made up of different types of tissues, and prior to menopause, everyone is going to have at least some dense tissue, Brady said.

There are three main categories of tissue in the breast: glandular tissue, made up of the milk-producing lobules and ducts to carry milk to the nipple; fibrous tissue that supports the shape of the breast and connects it to the chest; and fatty tissue that fills the spaces between.

When those first two types, also known as the fibroglandular stroma, are higher in concentration than the fat content, a breast is considered “dense.”

About 90 percent of all women have at least some dense tissue, with about 40 percent having heterogeneous tissue and about 10 percent having extremely dense breasts, according to the Centers for Disease Control and Prevention.

Fibroglandular tissue develops as a response to female hormones estrogen and progesterone. When women enter menopause and leave their child-bearing years, those hormone levels drop off. For most, the solid tissue is going to be replaced by fat, Brady said.

Women who are on hormone replacement regimens or who are taking hormonal birth control pills may maintain greater dense tissue even into menopause, she added.

How density affects screening

Although estrogen and progesterone can contribute to overall breast cancer risk, the biggest issue with dense tissue is that it’s difficult to see through, Brady said.

“Dense breast tissue is something that shows up cloudy, wispy or clumpy white on a mammogram,” Brady said. “If a mass were to show up white in a mammogram and the patient has dense breast tissue, it’s like trying to look for a snowball in a snowstorm.”

In other words, dense breast tissue can obscure a mass and make it difficult to determine whether it’s benign or the start of a cancerous growth.

However, catching cancer at its earliest development gives patients more options for treatment and better outcomes.

At Parkview, all mammography machines are equipped to capture and construct a three-dimensional image of the breast, Brady said. The scanning arms sweep over the breast, and after taking stationary pictures of the standard two views, the machine then knits those images together to create a 3D image.

3D imagery allows radiologists to look at the X-ray from different angles and that can sometimes help them better see through dense tissue. If they can’t get a clear view, patients may require additional imaging such as ultrasound and/or MRI to provide clarity on an abnormality, Brady said.

Each type of imaging has its strengths and weaknesses:

• Mammography, which uses X-rays, gives a good structural image but can’t see well through dense tissue.
• Ultrasound is good for determining the type (fluid vs. solid) and density of a mass but can’t show whether that mass is cancerous.
• MRI can provide the most detailed map of internal structures, but that super-high detail can draw undue attention and caution to structures that don’t need it. MRIs are also a pricier test and may not always be covered by insurance, Brady noted.

“All imaging modalities tell us something different,” Brady said. “An annual screening mammogram is really where women should start and then follow the radiologist recommendations.”

What to do

A woman with dense breast tissue should be aware of their body, but otherwise there’s no immediate action she needs to take.

“Don’t panic, understand that that is your normal anatomy; there’s nothing you could do or not do about it,” Brady said. “We’re all made up of lumpy, bumpy tissue. Just become familiar with your tissue.”

Brady said there’s no distinct difference in incidence among different types of women. Women who are overweight may have more fat in their breasts and thereby reduce the concentration of dense tissue, but the biggest determining factor is age, Brady said. Dense tissue is likely to remain until menopause when it’s replaced by more fatty tissue.

Outside of an annual mammogram, Brady recommends women simply be self-aware of their breasts. Harder, bumpier tissue is normal in the upper quadrants and around the nipple. Keep an eye out for visual abnormalities such as dimpling, puckering, or nipple deviation.

Natural breasts are not perfectly the same, but they should generally be “mirror images” of each other. If a person feels something in one spot on one breast, it should feel similar on the opposite side.

“If anything captures your attention as dominant or distinctly different on a sweep, then it may be time to reach out,” Brady said. “I recommend seeking evaluation with your primary care provider or gynecologist for a clinical breast exam first, and they may recommend and order diagnostic imaging if it is appropriate.”