Radiology

Breast Asymmetry

by Bill Zhou, MD, and Anne Hoyt, MD

Asymmetry is a general term used to describe unilateral increased fibroglandular density without meeting criteria for mass, which is a three-dimensional space occupying finding usually with convex margins1. Asymmetries are common and see in 3% of mammograms2. They are nonspecific and can represent benign findings such as overlapping tissue or malignant etiologies such as invasive ductal carcinoma or invasive lobular carcinoma. In the absence of clear imaging stability, asymmetries seen on screening exams are usually recalled fora diagnosticwork up, including additional mammographic views and ultrasound if necessary.

There are four types of asymmetry according to the BI-RADS Atlas3.

Asymmetry:

An asymmetry is a finding onlyseen on one projection3. Asymmetries that have been evaluated without suspicious features but persist are likely benign and can be managed with 6-month short-term imaging follow up.

MLO views of the breast demonstrate an asymmetry in the left subareolar breast, middle depth. This finding is called an asymmetry if there is no corresponding finding on the CC view.

Focal Asymmetry:

A focal asymmetry is a finding seen on two projections3. Focal asymmetries that have been evaluated without suspicious features but persist are likely benign and can be managed with 6-month short-term imaging follow up.

CC views of the breast of the same patient as above demonstrate a correlate to the asymmetry seen on MLO view. This is now a focal asymmetry of the left breast at 3 o’clock.
CC views of the breast of the same patient as above demonstrate a correlate to the asymmetry seen on MLO view. This is now a focal asymmetry of the left breast at 3 o’clock.

Developing Asymmetry:

A developing asymmetry is an asymmetry that is larger or more conspicuous compared to prior exams3. Since breast tissue tends to become less dense with age, developing asymmetries are usually more concerning and may warrant additional workup such as biopsies.

Serial MLO view of the left breast (from oldest to newest) demonstrate increase density in the left superior breast consistent with a developing asymmetry. This particular case turned out to be biopsy-proven pseudoangiomatous stromal hyperplasia.

Global Asymmetry:

A global asymmetry is a finding seen on two projections of significantlyincreased breast tissue occupying greater than one quadrant. Global asymmetries that have been evaluated without suspicious features are most lynormal variantsand do not require additional follow up.

Implant displaced MLO and CC views of the breast demonstrate increased density through the left breast, consistent with a global asymmetry.

Common benign etiologies1:

  • Overlapping fibroglandular tissue
  • Anatomicvariant
  • Ectopic tissue
  • Post-surgical
  • Hematoma
  • Fat necrosis
  • Radial scar
  • Cysts
  • Sclerosing adenosis
  • Hormonal replacement
  • Oral contraceptives
  • Diabetic mastopathy

Common malignant etiologies1:

  • Invasive ductal carcinoma
  • Invasive lobular carcinoma
  • Lymphoma

References:

  1. Samardar P, De paredes ES, Grimes MM et-al. ”Focal asymmetric densities seen at mammography: US and pathologic correlation.” Radiographics 22(1):19-33. DOI: 10.1148/radiographics.22.1.g02ja2219
  2. Kopans DB, Swann CA, White G, et al. “Asymmetric breast tissue.” Radiology 1989; 171:639-64. DOI: 10.1148/radiology.171.3.2541463
  3. D’Orsi CJ, Sickles EA, Mendelson EB, Morris EA, et al. ACR BI-RADS® Atlas 5th Edition, Breast Imaging Reporting and Data System. Reston, VA, American College of Radiology; 2013. https://www.acr.org/Clinical-Resources/Reporting-and-Data-Systems/Bi-Rads