A mammogram is a specialized X-ray imaging technique used to examine the internal structures of the breast. Its primary role is to screen for and detect breast changes, particularly early-stage cancers, often before they can be felt as a lump. By producing detailed images, this examination allows radiologists to identify subtle abnormalities. This discussion focuses on the specific visual features that may indicate the presence of a malignancy.
The Different Types of Mammograms
Mammograms are divided into two main categories based on the procedure’s goal. A screening mammogram serves as a routine preventive check for individuals who have no noticeable symptoms. This exam usually involves taking two standard views of each breast to detect early, non-palpable signs of disease. The images are reviewed by a radiologist after the patient has left the facility.
A diagnostic mammogram is a more focused examination performed when a patient has a specific symptom, such as a palpable lump, or when an abnormality is identified on a prior screening image. The radiologist is often present during this procedure to guide the technologist in taking extra images, including special views with spot compression or magnification. The goal is to obtain a clearer assessment of a localized area of concern.
Modern technology offers two formats: two-dimensional (2D) and three-dimensional (3D), also known as digital breast tomosynthesis (DBT). The 2D image is a single, flat projection of the breast tissue. In contrast, 3D mammography takes multiple thin X-ray slices as the machine moves in an arc. This slicing technique is beneficial for women with dense breast tissue, as it helps separate overlapping structures that might otherwise obscure a finding.
Visual Indicators of Malignancy on a Mammogram
Radiologists interpret mammogram images by looking for distinct patterns of tissue change, primarily focusing on masses, microcalcifications, and architectural distortion.
A mass appears as an area of abnormal density distinct from the surrounding tissue. Benign masses are typically round or oval with smooth, well-defined borders, often representing a fluid-filled cyst or a non-cancerous growth. In contrast, a mass suspicious for malignancy often presents with an irregular shape and indistinct or spiculated margins. Spiculated margins appear as sharp lines radiating outward from the mass, indicating potential invasion. Higher density relative to the surrounding breast tissue also increases concern.
Microcalcifications are tiny calcium deposits that show up as small white specks. While most calcifications are benign, the radiologist examines their size, shape, and distribution. Suspicious microcalcifications are typically very fine, irregular (pleomorphic), and appear tightly clustered or arranged in a linear branching pattern. This pattern can be a sign of ductal carcinoma in situ (DCIS), an early-stage cancer confined to the milk ducts.
Architectural distortion involves the normal structure of the breast tissue appearing pulled or distorted without a clearly visible mass. The tissue fibers seem to radiate toward a central point, disrupting the normal linear pattern of the breast’s elements. This finding, which can be subtle, warrants further evaluation as it may represent the earliest manifestation of breast cancer, such as invasive lobular carcinoma.
Understanding the BI-RADS Reporting System
To standardize the communication of mammogram findings, radiologists use the Breast Imaging Reporting and Data System (BI-RADS). This system assigns a category from 0 to 6 to every interpretation, translating visual findings into a risk assessment that guides patient care.
BI-RADS Categories
- BI-RADS 0: Incomplete assessment, requiring additional imaging evaluation.
- BI-RADS 1: Negative result; no abnormalities are reported, and the breast tissue appears normal.
- BI-RADS 2: Negative result with a definitively benign finding noted, such as a simple cyst or benign calcifications, requiring no follow-up.
- BI-RADS 3: Probably benign finding, suggesting a very low chance of malignancy (2% or less). A short-interval follow-up mammogram in six months is typically recommended.
- BI-RADS 4: Suspicious abnormality requiring further investigation, with the likelihood of cancer ranging from 2% to 95%. This category is subdivided into 4A (low suspicion), 4B (moderate suspicion), and 4C (high suspicion).
- BI-RADS 5: Highly suggestive of malignancy, with a probability of cancer being 95% or greater.
- BI-RADS 6: Known malignancy, meaning cancer has already been confirmed by a prior biopsy. This score is used to monitor the cancer’s response to treatment.
Next Steps After an Abnormal Finding
When a screening mammogram yields an abnormal finding, the first step is to conduct additional imaging for further characterization. This usually begins with a diagnostic mammogram using specialized techniques like spot compression. An ultrasound examination is also frequently performed, as it uses sound waves to determine if a mass is a simple, fluid-filled cyst or a solid lesion.
If the abnormality remains suspicious after these tests, the next procedure is a biopsy, which is the only definitive way to confirm or rule out cancer. A core needle biopsy is often preferred, where a hollow needle is guided by imaging to extract multiple tissue samples. These samples are then sent to a pathologist for microscopic analysis to determine the cellular composition of the finding.