Breast composition is expressed as the proportion of fibroglandular parenchyma in relation to the fatty breast tissue. The BI-RADS lexicon describes breast tissue composition under the following four breast density categories:
- ACR category a: The breasts are almost entirely fatty.
- ACR category b: There are scattered areas of fibroglandular density.
- ACR category c: The breasts are heterogeneously dense, which may obscure small masses.
- ACR category d: The breasts are extremely dense, which lowers the sensitivity of mammography.
Normal mammogram, ACR category a (the breasts are almost entirely fatty)
Normal mammogram, ACR category b (there are scattered areas of fibroglandular density)
Normal mammogram, ACR category c (the breasts are heterogeneously dense, which may obscure small masses)
Normal mammogram, ACR category d (the breasts are extremely dense, which lowers the sensitivity of mammography)
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