The Breast Imaging Reporting and Data System (BI-RADS™) lexicon was developed by the American College of Radiology (ACR) in an effort to standardize terminology used in reporting mammograms.
The lexicon includes specific terminology for reporting breast composition, mammographic findings, such as masses and calcifications, and overall assessment of the likelihood of malignancy.
- almost entirely fat
- scattered fibroglandular densities
- heterogeneously dense
- extremely dense
The higher the breast density, the lower the sensitivity of mammography.
A mass is defined as a space-occupying lesion seen in two different projections. If a possible mass is seen on only one view, it is called a density until its three-dimensionality is confirmed. The lexicon includes specific terms to describe masses and calcifications. Possible mass shapes are round, oval, lobular or irregular. Architectural distortion is a special case of shape, in which there are radiating spicules with no central mass visible.
Mass margins can be circumscribed (well defined or sharply defined), microlobulated (undulant with short cycles), obscured (hidden by adjacent fibroglandular tissue), indistinct (ill defined) or spiculated (with lines radiating from the margins of the mass, which suggests a lesion that is invading surrounding tissue or inciting desmoplastic reaction). Special cases of masses include solitary dilated ducts (usually of minor significance), intramammary lymph nodes (of a reniform shape, with radiolucent notch due to fat in the hilum), asymmetric breast tissue (may be important when it corresponds to a palpable asymmetry), and focal asymmetric density (visible as asymmetry with similar shape on two views, but lacks the borders and conspicuity of a true mass).
Density of masses can be high, equal (isodense), low, or fat-containing/radiolucent (e.g., oil cyst, lipoma, galactocele or mixed lesions such as hamartoma).
The frequency of carcinoma as a function of mass shape and margins in a study by Liberman et al of lesions that had surgical biopsy is demonstrated in Table 6.1. The highest frequency of carcinoma was observed in masses that had irregular shape or spiculated borders.