Fibroglandular density

Fibroglandular density is a term most commonly used when referring to breast density.

Breast tissue is composed of milk glands, milk ducts and supportive tissue (dense breast tissue), and fatty tissue (non-dense breast tissue. The breast tissue is clearly visualised on a mammogram – which is an x-ray of the breast. The image is produced by a device that will compress and flatten the breast and surrounding tissue, providing a detailed x-ray photograph.

Fibroglandular density refers to the appearance of breast tissue on a mammogram. It is a normal and common finding, varying between individuals, however a higher finding of density makes breast cancer screening more difficult, which in turn increases the risk of breast cancer.

On a mammogram, fatty tissue will appear dark and transparent, as opposed to fibroglandular tissue, which will have the appearance of a solid white area on the image, which makes that part of the image more difficult to “see through” and therefore visualise.


The mammogram will be analysed and reported on by a radiologist, who will in turn determine the ratio of non-dense tissue to dense tissue and assign a level of overall breast density. Levels of density are described using a result reporting system called breast imaging reporting and data system (BI-RADS) The levels of density move from “A” – almost entirely fatty tissue to level “D” – extremely dense, indicating that nearly all of the breast tissue is fibroglandular (dense.

Some of the causes of fibroglandular density include a lower body mass index and hormone replacement therapy used to treat menopause. A higher level of fibroglandular density increases the risk that breast cancer may go undetected by a mammogram, merely because dense breast tissue can mask a tumor.


Mammography is an effective screening tool, and is recommended from the age of 40. Supplementary tests include breast tomosynthesis, MRI and ultrasound.


An annual mammogram will provide a clinical and diagnostic tool in the prevention and early detection of breast cancer.

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