A mammogram is a low-dose X-ray of the breast, serving as the primary tool for breast cancer screening and early detection, aiming to find changes before physical symptoms develop. A screening mammogram is a routine check for people without symptoms, usually involving two standard images of each breast. If an abnormality is found or if an individual has symptoms, a diagnostic mammogram is performed. This involves a more focused series of images, sometimes with magnification, to investigate the specific area of concern.
Interpreting Breast Tissue Density
A radiologist begins reading a mammogram by assessing the overall composition of the breast tissue, which is reported as breast density. Image contrast relies on the different X-ray absorption rates of fat and fibroglandular tissue. Fatty tissue appears dark or translucent, while fibrous and glandular tissues absorb more X-rays and appear white or opaque.
The radiologist uses a standardized scale to categorize the breast into one of four density types. Category A indicates the breast is almost entirely fatty, while Categories C (heterogeneously dense) and D (extremely dense) represent dense tissue. Dense tissue appears white, which can obscure potential masses, as masses also appear white on a mammogram, creating a “masking effect.” This density assessment is a factor the radiologist considers, but it is not a finding of disease.
Identifying Common Visual Markers
The radiologist searches the images for specific visual markers that may indicate a disease process. The most frequently encountered abnormality is a mass, a space-occupying lesion seen in two different mammographic views. The shape of a mass offers clues to its nature; a smooth, round, or oval mass is more likely to be benign, such as a cyst or fibroadenoma. Conversely, an irregular shape with spiculated (spiky) or ill-defined borders is considered more suspicious for malignancy.
Another common marker is the presence of calcifications, which are tiny calcium deposits within the breast tissue. Macrocalcifications are larger, coarser deposits that are almost always benign and often related to aging or past injury. Microcalcifications are much smaller and, if they appear tightly clustered or in a fine, linear pattern, may suggest early-stage cancer, specifically ductal carcinoma in situ. The pattern, rather than the mere presence, determines the level of concern for calcifications.
A third visual abnormality is architectural distortion, defined as a noticeable area where the normal pattern of breast tissue is pulled or retracted without a definite mass being visible. This distortion can be a subtle sign of an underlying process, sometimes representing scar tissue but also potentially indicating a malignant tumor.
Understanding the Standardized Reporting Score
To ensure consistent reporting, radiologists use the Breast Imaging-Reporting and Data System (BI-RADS). This standardized scoring system assigns a number (0 to 6) to summarize findings and recommend follow-up action.
- BI-RADS 0: The reading is incomplete, and additional imaging, such as a diagnostic mammogram or ultrasound, is required before a final category can be assigned.
- BI-RADS 1: The result is negative, indicating no significant abnormality was found. The patient should continue with routine annual screening.
- BI-RADS 2: Considered negative for cancer, but describes a clearly benign finding (e.g., benign calcifications or a simple cyst) documented for future comparison.
- BI-RADS 3: Signifies a probably benign finding, meaning the likelihood of cancer is very low, typically less than two percent. A short-interval follow-up mammogram, usually in six months, is recommended to confirm stability.
- BI-RADS 4: Indicates a suspicious abnormality requiring a biopsy to obtain a tissue diagnosis. The chance of malignancy ranges from two percent up to 95 percent, often sub-categorized into 4A, 4B, and 4C based on suspicion level.
- BI-RADS 5: Assigned to findings that are highly suggestive of malignancy, with a greater than 95 percent probability of cancer based on the imaging features. Biopsy is necessary.
What Happens After the Reading
The process following the radiologist’s reading depends entirely on the assigned BI-RADS score. If the score is 0, the patient will be called back for additional imaging, such as a diagnostic mammogram or an ultrasound. About 10 percent of women are called back after a screening mammogram, and most follow-up tests ultimately show no cancer.
If the finding requires monitoring (BI-RADS 3), a six-month follow-up imaging appointment is scheduled to monitor for any changes in the lesion’s size or appearance. For highly suspicious findings (BI-RADS 4 and 5), the next step is a biopsy. This procedure is the only definitive way to determine if the cells are cancerous, and the results guide any necessary treatment planning.