Mammogram – What does my breast density mean?

Every screening mammogram report should include an assessment for breast density. It may include a callback letter requesting you return for further evaluation.

Mammographically, the breasts are made of two types of tissue: fat and fibroglandular tissue (glands and ducts for milk production and the supporting structures and ligaments). By convention from old film screen developed in dark rooms, the fat looks blackish and the fibroglandular tissue looks whitish. Mammography is heavily regulated and the American College of Radiology designates four categories of breast density with an approximated distribution among the general population being:

  • Extremely Dense (10%)

Extremely Dense

  • Heterogeneously Dense (40%)

Heterogeneously dense

  • Scattered Areas of Fibroglandular Density (40%)

Scattered fibroglandular

  • Almost Entirely Fatty Tissue (10%)


The fat generally does nothing, but the fibroglandular tissue is where cancers form. Therefore, the more fibroglandular tissue the greater the chance of developing a cancer. Relative to the general population, there is an approximate 1.2X increased chance of developing breast cancer for women with heterogeneously dense breasts and 2X for women with extremely dense breasts. Of course, this is all massively oversimplified. The younger you are the denser your breasts will appear commensurate with peak child bearing years. Being overweight or underweight will influence the composition of your breasts. There are also genetics and family history to consider when determining a person’s individual risk for potentially developing a breast cancer.

Your breast density should be included in every mammogram report issued. Every report should also include a Breast Imaging – Reporting and Data System (BI-RADS) score. So stay tuned and I will break down the BI-RADS for you later this week.



A personal thought: Women are spectacularly amazing. I could not survive without my wife. I may be a respected physician at work, but at home she is the executive director. In fact, I work closely with our radiology practice, Washoe County Medical Society, and Nevada State Medical Association executive directors, all women, and all outstanding, professional, and well-respected among their peers. I have partnered with hard-working, driven, kind ladies on many group projects and counted myself very fortunate. I just returned from a week at Boy Scout camp with my two oldest boys where the three highest ranking staff members were all hired women. Women, and especially my wife, are very beautiful creatures. Yes, I love my wife more and more, most days…


Posted by

I am an American Board of Radiology certified Diagnostic Radiologist with a certificate of additional qualification in Neuroradiology. I absolutely love my job. I have learned a tremendous amount about the human body, including its’ expected complications given our extraordinary complexity, and get to use that knowledge to help people. I personally have experienced emotional devastation and loss, which has made me compassionate and empathetic. I really care about people, and I hope I can use this site to help you. I graduated medical school in 2004 from New York Medical College. My wife and I had our first son in NY where we bought our 900 sf two bedroom one bath starter home. I stayed at Westchester Medical Center for radiology residency, where we had our second son. I obtained a neuroradiology fellowship position at Yale New Haven Medical Center commuting about an hour and a half each way for a year while we had our third boy. Upon graduation I was fortunate to return to Westchester Medical Center to work in Neuroradiology, Body Imaging, and Women’s Imaging departments, a rarity in academic medicine. Almost a decade later and I am living in a larger home in Reno working in a private practice community based outpatient radiology group which contracts with a rural hospital in Elko, Nevada. My wife and I now have four boys and gave up on the girl. We also have a male Bernese mountain Dog named Helmut and female Newfoundland named Lucy. Despite all its hardships and tremendous struggles, I have an absolutely amazing life, which is a gift I cherish. It’s down to my philosophy. I am a firm believer in teamwork. So much comes down to communication. When healthcare providers talk to each other one-on-one, the patient care is always improved, every time! We might not find an answer to your problem, but our collective knowledge sure can help improve your chances. At Yale the best conference I ever regularly attended was a head and neck tumor board. The head and neck surgeon (otolaryngologist = ENT) presented the patient’s clinical history, the radiologist showed the images, the oncologist discussed the tumor and chemotherapy options, and the patient came to the conference and we all did a physical exam looking into their mouth to directly visualize a tumor. It was incredible! Patients came from far and wide to see this highly trained, world-renowned, humble, Japanese, gentleman surgeon. It was also an epiphany. I found that when I see the patient, talk to them, listen to their story, examine them and discuss the patient with my colleagues, the patient felt better and I had a lot of fun. It’s weird but reminds me of seeing a comedy where it is always funnier in a packed theater with everyone laughing. Knowledge and compassion are both infectious and contagious. My greatest days are helping patients deal with some of their most difficult days, and I am good at it.

4 thoughts on “Mammogram – What does my breast density mean?

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s