Role of Diffusion Magnetic Resonance Imaging in Assessment of Mammographically Detected Asymmetric Densities

Although there is clearly a wide variation in breast size and parenchymal pattern, the breasts are generally symmetric structures with similar density and architecture. However, asymmetric breast tissue is encountered relatively frequently.

Asymmetric breast tissue is usually benign and secondary to variations in normal breast tissue, postoperative change from a previous biopsy, hormone replacement therapy , or merely poor positioning. However, an asymmetric area may indicate a developing mass or an underlying cancer.

The American College of Radiology (ACR), Breast Imaging Reporting and Data System (BI-RADS) defined four different types of asymmetric breast findings:

1. Asymmetric Breast tissue: refers to a greater volume or density of breast tissue in one breast than in the corresponding area in the contra lateral breast.
2. Densities seen in one projection: reflect a density seen in only one mammographic projection.
3. Architectural distortion: refers to a focal area of breast tissue that appears distorted with no definable central mass. Speculations radiate from a common point, and there is an area of focal retraction and tethering of normal parenchyma.
4. Focal asymmetric densities: refer to focal asymmetric densities that are seen on two mammographic views but cannot be accurately identified as a true mass.

These lesions are frequently encountered at screening and diagnostic mammography and are significant because they may indicate a neoplasm, especially if an associated palpable mass is present. Once these lesions are detected at standard mammography, supplementary breast imaging with additional mammographic views and ultrasonography (US) can be a key aspect of work-up.