Scattered fibroglandular densities is a breast tissue classification you’ll see on your mammogram report. It means your breasts contain mostly fatty tissue with some areas of denser glandular and connective tissue spread throughout. This is the second of four density categories used to describe breast composition, and it’s considered non-dense, which is the most reassuring end of the spectrum.
What the Four Density Categories Mean
Radiologists classify every mammogram into one of four categories based on how much dense tissue they see. These categories, labeled A through D, come from a standardized system used across the United States:
- Category A: Almost entirely fatty tissue
- Category B: Scattered areas of fibroglandular density (this is yours)
- Category C: Heterogeneously dense, meaning large portions of the breast are dense
- Category D: Extremely dense, with very little fatty tissue visible
Categories A and B are grouped together as “non-dense” or “low-density” breasts. Categories C and D are considered “dense.” That distinction matters because it affects both how well mammograms work and your overall breast cancer risk profile. If your report says scattered fibroglandular densities, you fall on the non-dense side of that line.
How It Looks on a Mammogram
Breast tissue is made up of two main types: fatty tissue and fibroglandular tissue. Fibroglandular tissue includes your milk glands, milk ducts, and the connective tissue that supports them. On a mammogram image, fatty tissue appears dark and transparent, making it easy to see through. Fibroglandular tissue shows up as solid white areas.
With scattered fibroglandular densities, most of your breast appears dark (fatty), but white patches of denser tissue are scattered throughout. This is important because tumors and calcifications also appear white on a mammogram. The more white tissue in the image, the harder it is to spot something abnormal hiding behind it. This is called the “masking effect.” With scattered densities, there’s enough fatty tissue that radiologists can still read the mammogram with good accuracy. The masking problem becomes much more significant in categories C and D, where mammography sensitivity can drop as low as 30 to 48%.
What This Means for Cancer Risk
Breast density and cancer risk are connected, but the relationship is strongest at the higher density categories. Women with extremely dense breasts (Category D) have a notably higher risk of developing breast cancer compared to women with mostly fatty breasts. Scattered fibroglandular densities sit closer to the low-risk end of this spectrum.
The risk with Category B is only slightly elevated compared to Category A, and many experts group both categories together when discussing screening recommendations. In practical terms, if your mammogram shows scattered fibroglandular densities, standard screening mammography is generally considered effective for you. Your radiologist can see through most of your breast tissue clearly, and any areas of concern are less likely to be hidden behind dense patches.
Why Your Report Mentions Density at All
As of September 2024, all mammography facilities in the United States are required by federal regulation to include breast density information in the results they send to patients. The FDA finalized this rule in March 2023 after years of state-level efforts pushing for greater transparency. Before this mandate, whether you learned about your breast density depended on which state you lived in.
The notification exists primarily to alert women with dense breasts (categories C and D) that mammograms may miss abnormalities in their tissue and that they might benefit from additional screening, such as breast ultrasound or MRI. If your report says scattered fibroglandular densities, the density notification is informational rather than a call to action. You’re receiving it because every patient now gets one, not because your density level raises specific concerns.
Factors That Affect Breast Density
Your breast density isn’t fixed for life. Several factors influence where you fall on the spectrum. Age is the biggest one: breasts tend to become less dense and more fatty after menopause. Hormone replacement therapy can increase density, as can lower body weight (since less body fat often means proportionally more fibroglandular tissue). Genetics also play a role, so density patterns can run in families.
Your density category can shift between mammograms. A woman classified as Category C in her 40s might move to Category B in her 50s or 60s as natural hormonal changes reduce glandular tissue. This is normal and doesn’t indicate that anything went wrong. If your category changes from one screening to the next, it simply reflects the gradual, expected evolution of your breast tissue over time.
Do You Need Extra Screening?
For women with scattered fibroglandular densities, routine mammography is typically sufficient. Supplemental screening tools like breast MRI or whole-breast ultrasound are generally recommended for women in the dense categories (C and D), where the masking effect makes mammograms less reliable. Research on masking risk consistently shows that women with heterogeneously or extremely dense breasts face the highest chance of a cancer being obscured on a standard mammogram.
That said, breast density is just one factor in your overall risk picture. If you have other risk factors, such as a strong family history of breast cancer, a known genetic mutation, or a history of chest radiation, your doctor may recommend additional imaging regardless of your density category. The density classification on your mammogram report is one piece of information, not the whole story.