Breasts are composed of fat, fibrous (connective/supportive) tissue, and glandular tissue (the stuff that makes milk and carries it to the nipple). On a mammogram, fat is gray, while fibrous and glandular tissue, also known as fibroglandular tissue, is white. Every mammogram shows some combination of white and gray, ranging from almost entirely fatty to almost no fat, also known as “extremely dense”.

When a radiologist is reading a mammogram, they must make a determination regarding how “dense” a woman’s breasts are. This is important because, on a mammogram, masses are white. If a woman’s breast looks mostly white on a mammogram because she has very little fat and lots of fibroglandular tissue, a mass will be harder to see. Here are examples of the four breast density categories:

A. Almost entirely fatty – about 10% of patients
B. Scattered areas of fibroglandular density – about 25% of patients
C. Heterogeneously dense, which may obscure small masses – about 25% of patients
D. Extremely dense, which lowers the sensitivity of mammography – about 10% of patients

We’ll let you know what your breast density is after your mammogram. If your breasts are dense, you may be eligible for additional screening services, such as ultrasound.

Visit Dense Breast Info for more information.