Brenda Spriggs, MD, MPH, MBA
Most women over the age of 40 receive regular mammograms to help monitor the health of their breasts. A mammogram serves as an important diagnostic tool that allows doctors to observe the internal structure of the breast, helping to identify regions of abnormal breast growth. Breast density on a mammogram appears as regions of lightness, while surrounding fatty tissue appears dark. The causes of breast density can range from healthy tissue to breast diseases.
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Healthy Glandular Tissue
One cause of breast density is healthy glandular breast tissue. The glands of the breast contain two structures: ducts and lobules. The breast ducts are long tubes of glandular tissue that carry milk to the nipple, where it can be expelled during lactation. The breast lobules contain the specialized cells that generate breast milk. Each bulb-shaped lobule contains epithelial cells that synthesize milk proteins and fats, then secrete those chemicals out into the center of the lobule, where they mix with fluid to form breast milk. Both the lobules and ducts appear as light, dense tissue on a mammogram. Though doctors may not see individual ducts and lobules with the naked eye, collections of these tissues appear as dots and lines on the mammogram. Close analysis of the structure of the lobules and ducts on a mammogram helps doctors to assess the health of the breast.
In some cases, breast density may result from benign growths within the breast, which may appear as lumps of dense tissue. According to Imaginis, some benign lumps contain densely packed breast cells, proliferating out of control to form benign tumors. Other lumps may contain dense fibrous tissue or calcifications due to benign diseases within the breast. Finally, some breast lumps may appear on a mammogram as a hollow lump, corresponding to a fluid-filled breast cysts. Following the detection of a benign breast lump on a mammogram, doctors typically perform a breast biopsy to confirm the condition causing the growth. Depending on the benign breast condition present, doctors may perform treatments such as cyst drainage or surgery to remove harmful breast growths.
Another potential cause of breast density is breast cancer, which can appear on a mammogram as dense breast growth affecting the ducts or lobules of the breast. Beast cancer most commonly occurs in the breast ducts, with invasive ductal cancer accounting for around 80 percent of breast cancers, according to BreastCancer.org. Breast cancer often appears as a dense region on a mammogram, since a tumor contains densely-packed proliferating cells. In advanced or large breast cancers, the center of the tumor may appear less dense, due to cellular death and necrosis at the center of the tumor. Upon detecting a region of abnormal breast growth, doctors will perform breast biopsies to diagnose breast cancer. Following diagnosis, breast cancer patients may receive a number of therapies, including breast surgery, drug treatments and radiation therapy.