Imaging tests for dense breasts: mammogram or ultrasound?

Thanks to Mrs Victoria Hipperson, Consultant Radiographer, breast imaging, from Whipps Cross hospital in London who wanted to help raise awareness of the challenges that exist in imaging dense breasts.

Imaging tests to assess breast problems

Women are often familiar with routine mammograms for screening those without any symptoms. These start from around the age of 50 years under the NHS Breast Screening Programme (NHS, 2018). However women and men who have a breast problem often require breast imaging tests outside of this service. These patients typically visit their GP (General Practitioner) who refer them for a ‘One Stop’ breast clinic appointment.

A One Stop breast clinic appointment is the first line of tests and examinations carried out in a hospital following referral from the GP. These tests includes clinical breast examination from a specialist breast doctor/surgeon, imaging tests of the breast – mammograms and or ultrasound scan and sometimes biopsies. This is also known as triple assessment.

In the United Kingdom, national guidelines (Willett et al, 2010) recommend that women over 40 years of age are offered mammography as first line imaging for breast complaints. A similar system operates in the USA (United States of America) (Brem et al, 2015).

However, those women under 40 years are referred for breast ultrasound. This is due to breast density. This will be explained further below. Most NHS Trusts provide male patients with breast complaints, the same service.

While having their mammograms, many patients ask why they are having a mammogram can they just not have an ultrasound, and similarly those who are having an ultrasound as a first line examination ask if they should have a mammogram. Well, here’s the answer…

Mammograms

A mammogram is an x-ray of the breast tissue using low dose x-rays. It allows a specialist to check both breasts in their entirety. The reason for performing mammography in patients 40 years and older is based upon breast anatomy and the sensitivity of mammography in women who are younger.

Breasts are made up of:

  • breast tissue (the milk producing tissue)
  • fatty tissue (fat).

    Breast anatomy showing fat and breast tissue (lobules, ducts and nodes)

The younger a woman is the more breast tissue there is. In the clinical setting we refer to this as breast density – how dense is the breast? As a woman ages the amount of breast tissue she has decreases and by replaced as fat. In younger women, the breasts are often very dense  for example before 35 years there is lots of breast tissue; in older women, 60 years for example, the breasts are typically almost entirely fatty tissue.

Whilst these changes are usually the case sometimes younger women have fatty breasts earlier on and older women keep a lot of their breast tissue and remain dense into their 60’s (Brem et al, 2015). The younger the patient is the higher the breast density is likely to be and therefore the lower the sensitivity of the mammogram (RCR, 2013).

Where the breasts are made up mostly of fatty tissue it is much easier to see changes in the tissue.

Breast imaging test mammogram

Mammogram in fatty breast showing cancer (arrow)

Breast imaging test

Dense breasts in a young patient

However, in mammograms where there is a lot of breast tissue it can be difficult to confidently exclude any abnormality.  This is because in dense breasts abnormalities seem to be obscured by the breast tissue (Winkle et al, 2015).

Unfortunately, breast cancer does occur in young women with just over 40 women being diagnosed in the UK aged under 34 years between 2013-2015 (Cancer Research UK, 2018). An alternative imaging technique to mammography is therefore required for younger women. This is where ultrasound comes in.

Breast Ultrasound

Breast ultrasound uses a different type of technology to examine the breast tissue and is free from X-Rays. It uses sound waves in a similar way to sonar. It is normally used to focus on a particular region of the breast. It can be very effective particularly in women with dense breasts because it works in a different way to a mammogram (Rebolj et al, 2018).

Ultrasound is particularly good at showing the difference between a lump filled with water and another that is made of soft tissue. This is because sometimes on a mammogram we can say a lump is there but cannot describe it any further. As a result ultrasound is often used alongside a mammogram to help determine the nature of the problem.

However ultrasound is not effective as a screening tool like mammography when used alone (RCR, 2013).  This is because it is not as good when compared to a mammogram at identifying early stage breast cancer, particularly that seen as calcification  Calcification is seen as very small white flecks on the mammogram which indicate a cancer might be present.Mammograms are therefore beneficial at demonstrating breast disease that is only visible as calcification and allow the specialists to give a size to the abnormal region.

On occasions the breast ultrasound shows something worrying in a woman under 40 years of age. Therefore a mammogram is taken as an overview of both breasts and to see if any abnormalities can be seen. Quite often a breast cancer seen in a young woman using ultrasound isn’t seen on a mammogram, however it can still be useful to check both breasts and look for other abnormalities and can then be used as a baseline for ongoing mammograms.

Case Study

This lady was a 43 year old who had a lump in her left breast. On mammography both her breasts were dense. In the left breast there was a subtle area of distortion partially masked by the dense breast. It was not possible to calculate the size. On ultrasound this was clearly seen as a suspicious appearing lump. In the right breast several cysts were also seen. It was not possible to see these on the mammograms.

Summary: 6 important things to remember

  1. Patients will be offered mammograms or ultrasound based on age.
  2. Patients under 40 years will undergo ultrasound as a first line examination.
  3. Patients 40 and over will be offered mammography as a first line investigation.
  4. The rationale for this is based on the ability of mammograms to identify cancers in dense breasts. Women under 40 tend to have a greater breast density than women over 40.
  5. Male patients are offered the same imaging pathway as women.
  6. Mammograms can still be performed in patients under 40 years of age where there is concern of breast cancer. These are used as baseline images for ongoing review.

Tell us what you think

The Mayo Clinic has a useful page on dense breasts and explains a little more about other imaging tests such as MRI. The Mayo Clinic reflects practices in the USA. Do you think we do enough for women with dense breasts in the UK?

References

Willett, A.M., Michell, M.J. and Lee, M.J.R. (ed) (2010) Best practice diagnostic guidelines for patients presenting with breast symptoms. Association of Breast Surgery.

Brem, R.F., Lenihan, M.J., Lieberman, J. and Torrente, J. (2015) Screening breast ultrasound: Past, present and future. American Journal of Roentgenology. 204(2).

RCR (The Royal College of Radiologists). (2013). Guidance on screening and symptomatic breast imaging. Third Edition.

 

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