Breast density is an important factor reported on a mammogram, describing the composition of breast tissue. “Scattered fibroglandular density” is a common technical classification. It means the breast is mostly composed of fatty tissue, with only small, non-uniform areas of denser tissue present. This classification is one of four standardized categories used by radiologists to communicate potential challenges for cancer detection during screening. Understanding this result involves knowing how different tissues appear on an X-ray.
Defining Fibroglandular Tissue and Density
The breast is composed of two primary tissue types that appear distinctly on a mammogram: fatty tissue and fibroglandular tissue. Fatty tissue appears dark or translucent on the X-ray image because it does not absorb many X-rays. This translucent appearance makes it easy for a radiologist to identify abnormalities, which appear as white spots.
Fibroglandular tissue is denser, consisting of fibrous connective tissue, milk ducts, and milk glands (lobules). This tissue absorbs more X-rays, causing it to appear white on the mammogram. Breast density is measured by comparing the ratio of this dense, white fibroglandular tissue to the darker, fatty tissue.
Density is purely an imaging concept, not a reflection of how the breast looks or feels physically. A physical examination cannot determine breast density; a mammogram is the only way to assess this characteristic. The measurement is a subjective but standardized assessment that helps determine how effectively a mammogram can identify cancer.
Understanding the Four Density Categories
Radiologists use a standardized system developed by the American College of Radiology (ACR) called the Breast Imaging-Reporting and Data System (BI-RADS) to classify density. This system defines four categories, labeled A through D, based on the amount of fibroglandular tissue relative to fat.
Category A, “Almost entirely fatty,” means the breasts contain very little dense tissue (about 10% of women). Category B, “Scattered Fibroglandular Density,” is the most common result, affecting approximately 40% of women. This category indicates the breast is mostly fatty tissue, with only scattered, small areas of dense tissue visible.
The remaining two categories are considered dense breast tissue. Category C, “Heterogeneously Dense,” means a large part of the breast is dense, which can obscure small masses. Category D, “Extremely Dense,” is the highest density classification, where nearly all of the tissue is dense (about 10% of women).
Implications for Cancer Detection
Breast density is clinically important for two reasons: its impact on mammography sensitivity and its correlation with cancer risk. The primary concern is the “masking effect.” This arises because both dense fibroglandular tissue and cancerous tumors appear white on a mammogram. The white dense tissue can hide a white tumor, making detection difficult.
Scattered Fibroglandular Density (Category B) presents a minimal masking challenge compared to categories C and D. Since the dense areas are small and scattered, the majority of the breast remains translucent, allowing for effective mammogram screening. However, even scattered areas of density may still occasionally obscure a tumor.
Density is also an independent factor linked to intrinsic breast cancer risk. Women with the highest density (Category D) have a higher risk of developing breast cancer compared to those with the lowest density (Category A or B). For patients with Scattered Fibroglandular Density, this intrinsic risk is considered lower than for those in the two higher density categories.
Standard Screening Recommendations
For patients whose mammogram results indicate Scattered Fibroglandular Density (Category B), the standard screening protocol is sufficient. This classification means annual screening mammography remains the most reliable and recommended examination for early cancer detection. The recommendation is to continue with routine annual mammograms, starting at an age determined by professional guidelines and personal risk factors.
The screening advice for Category B differs from recommendations for the higher density categories, C and D. For women with heterogeneously dense or extremely dense breasts, supplemental screening tests are frequently discussed with a healthcare provider. These additional tests might include a breast ultrasound or magnetic resonance imaging (MRI), which can improve cancer detection by providing a different view of the dense tissue.
Because Scattered Fibroglandular Density does not significantly impair mammogram effectiveness, supplemental screening is not typically warranted based on density alone. However, the most appropriate screening schedule is always personalized and should be determined in consultation with a healthcare provider, considering the density result along with other factors like family history and personal risk assessment.