Radiology

Mammography: Masses

by Zaid Haddadin, MD, Margit Szabari, MD, PhD 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 (Figure 1) is elliptical or egg-shaped (may include two or three undulations).
    Mammography: Masses Figure 1
    Figure 1: Targeted ultrasound examination of the right breast demonstrated an oval mass with circumscribed margins measuring 7 x 4 x 7 mm seen at 3 o'clock located 2 centimeters from the nipple. Oval mass is probably benign, sonographic follow-up in 6 months is recommended. BI-RADS Category 3: Probably Benign Finding.
  2. Round: a round mass (Figure 2) is spherical, ball-shaped, circular, or globular in shape.
    Mammography: Masses Figure 2
    Figure 2: A) On Mammogram rim-calcified round mass was noted in the right breast at 7 o'clock, lower outer quadrant located 1 centimeter from the nipple (white arrow). B) Ultrasound demonstrates a round mass with peripheral hyperechogenicity measuring 10 x 7 x 10 mm in the right breast at 7 o'clock located 1 centimeter from the nipple, favoring fat necrosis. BI-RADS Category: 2.
  3. Irregular: the shape of the mass is neither round nor oval (Figure 3).
    Mammography: Masses Figure 3
    Figure 3: A) Mammography of the left breast with MLO view demonstrates irregular, spiculated mass in the left breast at 12 o'clock (big white circle). Additional calcifications in the left breast at 8 o'clock at anterior depth located 2 centimeters from the nipple, three additional groups of calcifications in the central and lower inner left breast are also suspicious (small white circles). B) Ultrasound of the left breast represents an irregular, spiculated hypoechoic mass, BI-RADS Category: 4C suspicious finding. Ultrasound guided biopsy was recommended and confirmed invasive ductal carcinoma, grade 2.
    • 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 (Figure 1).
  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 (Figure 4).
    Mammography: Masses Figure 4
    Figure 4: Microlobulated right breast mass, containing calcifications, at 12:00 position 5 cm from nipple, BI-RADS CATEGORY 5 - SUSPICIOUS ABNORMALITY, ultrasound guided biopsy was recommended. Pathology confirmed invasive ductal carcinoma, Grade 3.
    • 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 (Figure 5, Figure 6).
    Mammography: Masses Figure 5
    Figure 5: Irregular hypoechoic mass with indistinct margin measuring 1.2 x 1.4 x 1.1 cm in the left breast at 1 o'clock, 3 cm from the nipple was visualized with ultrasound, biopsy was recommended. BI-RADS Category: 4C suspicious finding. Pathology confirmed invasive ductal carcinoma with focal lobular features, grade 2.
    • 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 (Figure 1A, Figure 6A).
    Mammography: Masses Figure 6
    Figure 6: A) Spiculated mass was visualized in the right breast with spot compression view on mammogram. B) Sonographic evaluation of the right breast was performed in the region of the mammographic finding. At the 8:00 position 9 cm from the nipple, there is an irregular hypoechoic solid mass with indistinct margins oriented antiparallel to the chest wall demonstrating posterior shadowing, BI-RADS Category: 4C suspicious finding. Pathology confirmed invasive ductal carcinoma, Grade 1.

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.