breast density
Meaning of breast density: A description of what a mammogram shows rather than of how a breast feels, and it cannot be judged by touch.
Definition of breast density
Breast density describes how much of a breast is made up of glandular and fibrous tissue rather than fat, as seen on a mammogram. Fat lets the x-ray beam through and appears dark, while glandular and fibrous tissue block it and appear white. A breast with a large white share is called dense. Each mammogram is sorted into one of four density categories.
Why does it make a mammogram harder to read?
Everything dense shows up white on a mammogram, and a tumor is dense. Against a background of fat, which appears almost black, a small white mass is obvious. Against a background of white glandular tissue, the same mass can vanish, in the way a snowflake disappears in a snowstorm. This masking is why the test finds a smaller share of cancers in dense breasts. It works in the other direction too, since normal overlapping tissue can imitate a mass and prompt a recall that turns out to be nothing.
Is dense tissue itself a risk?
Yes, and separately from the masking problem. More glandular tissue means more of the cells from which breast cancer arises, and those in the highest density category carry a higher risk than those whose breasts are mostly fat. Density falls with age, after menopause and after childbearing, and rises with hormone therapy. It has nothing to do with breast size, firmness or lumpiness and produces no sensation, so it cannot be judged by a person or by an examining hand, and it is not a disease.
What are the four categories?
| Category | What the film shows |
|---|---|
| Almost entirely fatty | Little dense tissue, so a mass stands out clearly |
| Scattered fibroglandular | Dense patches among mostly fat |
| Heterogeneously dense | Enough dense tissue to hide a small mass |
| Extremely dense | Detection falls furthest here |
The grading is a visual judgment, so two radiologists reading the same film may not pick the same category, and software that measures the proportion directly is used in some centers to make the call reproducible. A breast reported as fatty replaced sits at the opposite end of the same scale. Scanning with ultrasound or magnetic resonance imaging on top of the mammogram finds additional cancers in dense breasts, and also raises the number of false alarms, which is why practice around it varies.
Also known as
Used in a sentence
The report described heterogeneously dense breast tissue, which may lower the sensitivity of mammography.
Good to know
Density is a property of the mammographic image, not of how a breast looks or feels, and it is unrelated to breast size or firmness, so neither self-examination nor clinical examination can assess it.