Mammography: Masses

by Zaid Haddadin,MD, and Jane Dascalos, MD

According to the ACR BI-RADS (Breast Imaging-Reporting and Data System) atlas a breast mass is three-dimensional and occupies space. It is seen in two different mammographic projections. It has completely or partially convex (having an outline or surface curved like the exterior of a circle or sphere) outward borders and (when radiodense) appears denser in the center than at the periphery. If a potential mass is seen only on a single projection, it is called an asymmetry until its 3-dimensionality is confirmed. A breast mass is characterized using BI-RADS lexicon in the following three categories: 1) Shape 2) Margins 3) Density

Shape

1. Oval: an oval mass is elliptical or egg-shaped (may include two or three undulations).
2. Round: a round mass is spherical, ball-shaped, circular, or globular in shape.
3. Irregular: the shape of the mass is neither round nor oval.
   • For mammography, use of this descriptor usually implies a suspicious finding.

Margin

The margin is the edge or border of the lesion and is an important predictor of whether a mass is benign or malignant

1. Circumscribed: the margin is sharply demarcated with an abrupt transition between the lesion and the surrounding tissue. At least 75% of the margin must be well defined for a mass to qualify as circumscribed.
2. Obscured: An obscured margin is one that is hidden by superimposed or adjacent fibroglandular tissue. This is primarily when some of the margin of the mass is circumscribed, but the rest (>25%) is hidden.
3. Microlobulated: The margin is characterized by short cycle undulations.
   • For mammography, use of this descriptor usually implies a suspicious finding.
4. Indistinct: There is no clear demarcation of the entire margin, or of any portion of the margin, from the surrounding tissue.
   • For mammography, use of this descriptor usually implies a suspicious finding.
5. Spiculated: the margin is characterized by lines radiating from the mass. Use of this descriptor usually implies a suspicious finding.

Density

Density is used to define the x-ray attenuation of the mass relative to the expected attenuation of an equal volume of normal fibroglandular breast tissue.

1. High density: x-ray attenuation (reduction of the force or effect of something) of the mass is greater than the expected attenuation of an equal volume of fibroglandular breast tissue.
2. Equal Density: x-ray attenuation of the mass is the same as the expected attenuation of an equal volume of fibroglandular breast tissue.
3. Low Density: x-ray attenuation of the mass is less than the expected attenuation of an equal volume of fibroglandular breast tissue.
4. Fat Containing: This includes all masses containing fat, such as oil cyst, lipoma, or galactocele (a retention cyst containing milk or a milky substance), as well as mixed density masses such as hamartoma.
   • A fat-containing mass will almost always represent a benign mass.

References:

1. Sickles, EA, D’Orsi CJ, Bassett LW, et al. “ACR BI-RADS® Mammography.” In: ACR BI-RADS® Atlas, Breast Imaging Reporting and Data System. Reston, VA, American College of Radiology; 2013.
2. Radiologyassistant.nl. 2021. The Radiology Assistant : Bi-RADS for Mammography and Ultrasound 2013. https://radiologyassistant.nl/breast/bi-rads/bi-rads-for-mammography-and-ultrasound-2013.