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Parenchymal patterns in breast imaging

Mammographic density is considered a risk factor for breast cancer, and it’s important in the way in which it affects mammographic screening sensitivity. Women with high-risk density patterns should be screened more frequently and / or with additional views per breast. Pioneers in classification of density was Leborgne in 1953 and Wolfe in 1967, which described an increased risk of breast cancer in radiographically dense breast, but the first qualitative classification of mammographic density patterns was described by Wolfe in 1976.

Wolfe Classification

Wolfe assign the mammograms to four parenchymal patterns (N1, P1, P2 and DY) according to the distribution of fat and the prominence of the ducts:

  • N1 : the breast consists mainly of fat (N=normal), corresponding to ACR 1 (lower risk for breast cancer)
  • P1 : this pattern includes fat as well as linear densities (enlarged ducts) occupying no more than 25% of the breast, corresponding to ACR 2 (low risk for breast cancer)
  • P2 : linear denisities (from enlarged ducts) occupying more than 25% of the breast. They are prominently in the upper outer quadrant but may be distributed throughout the breast (P=prominent ducts), corresponding to ACR3 (high risk for breast cancer)
  • Dy : dense, radiopaque breast (Dy=dysplasia) corresponding to ACR4 (highest risk for breast cancer) ; these patterns are again subdivided into low-risk (N1 and P1) and high-risk (P2 and DY) patterns. 

A fifth category has been later added by Wolfe to this four:

  • Qdy (quasi-dysplasia) : this group consists of young women whose dense breast have a somewhat spongy texture due to fatty infiltration
Boyd Classification  

An alternative, quantitative method  proposed by Boyd and collegues (1980)  was based on mammographic density percentage given by radiologists and divided into six categories of unequal intervals

  •  A :  0%
  •  B :  > 0 - 10%
  •  C :  > 10 - 25%
  •  D :  > 25 - 50%
  •  E :  > 50 - 75% 
  •  F :  > 75%

This method has been updated in 1995 with computer-assisted technique measuring. 

 BI-RADS Classification of density

The BI-RADS system too is a quantitative method  proposed by the American College of Radiology (2000) and  used in clinical radiology practice in the USA .BI-RADS classification is a modification of Wolfe’s classification, and is defined using percentages of density divided into quartiles:

  • type 1 : extremely fat
  • type 2 : minimal density
  • type 3 : heterogeneous density
  • type 4 : extremely dense
Tabar Classification 

Tabár (1997) classifies the mammograms in five patterns (I to V) based on an histologic-mammographic correlation with a three-dimensional, subgross (thick-slice) technique, and on the relative proportion of four “building blocks” (nodular denisties, linear densities, homogeneous fibrous tissue, radiolucent fat tissue): 

  • I : balanced proportion of all components of breast tissue with a slight predominance of fibrous tissue 
  • II : predominance of fat tissue (fat breast)
  • III : predominance of fat tissue with retroareolar residual fibrous tissue
  • IV : predominantly nodular densities
  • V : predominantly fibrous tissue (dense breast)

Patterns I, II and III are considered low-risk; patterns IV and V high-risk.

It is important to considere that some therapies may alter the pattern by increasing parenchymal density, as in hormone replacement therapy (HRT), or reducing it as in therapies with selective estrogen-receptor modulators (SERM).

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