BI-RADS Categories Quick Reference
| Category | Assessment | Malignancy Probability | Management | Follow-Up |
|---|---|---|---|---|
| 0 | Incomplete | — | Additional imaging needed | Recall for workup |
| 1 | Negative | ~0% | Routine screening | Annual per guidelines |
| 2 | Benign | 0% | Routine screening | Annual per guidelines |
| 3 | Probably Benign | <2% | Short-interval follow-up | 6-month mammogram |
| 4A | Low Suspicion | 2–10% | Core needle biopsy | Per biopsy result |
| 4B | Moderate Suspicion | 10–50% | Core needle biopsy | Per biopsy result |
| 4C | High Suspicion | 50–95% | Core needle biopsy (urgent) | Per biopsy result |
| 5 | Highly Suspicious Malignancy | ≥95% | Biopsy + surgical consult | Staging workup |
| 6 | Known Biopsy-Proven Malignancy | 100% | Staging + treatment planning | Multidisciplinary team |
About BI-RADS 5th Edition
The Breast Imaging Reporting and Data System (BI-RADS), published by the American College of Radiology, provides a standardized lexicon and final assessment framework for breast imaging across mammography, ultrasound, and MRI. The current 5th Edition (2013) reduced variability in radiologist reporting and introduced more precise subcategories for BI-RADS 4 (4A, 4B, 4C) to better communicate biopsy urgency and malignancy probability to clinicians and patients.
Before BI-RADS standardization, breast imaging reports used inconsistent terminology that created communication barriers between radiologists and referring clinicians. Studies showed that BI-RADS adoption reduced inappropriate biopsy rates, improved biopsy concordance, and enabled population-level quality metrics for screening programs.
How to Use This Calculator
Select the imaging modality (mammography, ultrasound, or MRI). Then systematically enter the dominant imaging findings: mass characteristics (if a mass is present), calcification characteristics, architectural distortion, and asymmetry. The calculator assigns a BI-RADS category based on the most suspicious finding across all features entered. This mirrors the ACR 5th Edition approach where the final assessment is driven by the highest-suspicion element.
Key guidance for accurate use:
- Enter all findings present, not just the most suspicious one — the calculator will correctly assign the highest category.
- If a mass is present, entering shape and margin produces the most accurate result. Density alone without margin information defaults to BI-RADS 0 (incomplete).
- For calcifications, morphology is the primary driver. Distribution modifies the category. Benign morphology (skin, vascular, coarse, milk of calcium) will output BI-RADS 2 regardless of distribution.
- Developing asymmetry is automatically assigned BI-RADS 4B — it is the most suspicious asymmetry type and always warrants biopsy unless definitively attributed to a benign cause.
How Category Is Determined
BI-RADS category is driven by the most suspicious finding present. The dominant imaging features considered are:
- Mass features: Shape (irregular > round/oval), margin (spiculated > indistinct > microlobulated), and density (high-density solid mass > equal > fat-containing). A spiculated mass margin is the single most suspicious mammographic or ultrasound finding and is classified as BI-RADS 5 by itself.
- Calcification morphology: Fine pleomorphic or fine linear/branching calcifications are higher suspicion than amorphous; benign morphologies (vascular, skin, coarse, milk-of-calcium) do not elevate category. Amorphous calcifications represent BI-RADS 4A; fine pleomorphic and fine linear/branching represent BI-RADS 4B–4C depending on distribution.
- Calcification distribution: Segmental and linear distributions indicate ductal involvement and are higher suspicion than grouped or regional. Diffuse distribution, even with suspicious morphology, is typically BI-RADS 3 because it rarely represents malignancy.
- Architectural distortion: Distortion without a central mass on mammography or ultrasound is suspicious (BI-RADS 4B minimum) and warrants biopsy unless clearly at a prior biopsy site or surgical scar. Radial scar on tomosynthesis is a specific type of architectural distortion requiring pathologic correlation.
- Asymmetry: Developing asymmetry is the highest-risk asymmetry type (BI-RADS 4B). Focal asymmetry seen on two views is BI-RADS 4A. Global asymmetry is typically BI-RADS 3. One-view asymmetry requires additional imaging (BI-RADS 0) before a final category can be assigned.
Modality-Specific Notes
- Mammography: Primary modality for screening. Calcification characterization is most reliable on mammography (magnification views add detail). Architectural distortion and asymmetry are mammography-specific findings. Digital breast tomosynthesis (DBT, 3D mammography) has improved detection of architectural distortion and reduced recall rates compared to 2D mammography.
- Ultrasound: Adjunct to mammography; primary for evaluating palpable lumps in women under 30 and for characterizing masses seen on mammography. Best for cyst characterization — simple cysts are definitively benign (BI-RADS 2). Posterior acoustic features (shadowing = suspicious, enhancement = reassuring for cyst), orientation (parallel = less suspicious, non-parallel = more suspicious), and vascularity provide additional assessment criteria on ultrasound.
- MRI: Highest sensitivity (~95%) for invasive breast cancer. Used for high-risk screening (BRCA1/2 carriers, lifetime risk ≥20%), extent of disease before surgery, treatment response monitoring, and occult primary cancer evaluation. Background parenchymal enhancement (BPE) and internal enhancement kinetics (initial phase and delayed phase) are MRI-specific features. Kinetic curve type I (persistent) is most benign; type III (washout) is most suspicious. MRI has the highest false-positive rate and lowest specificity of the three modalities.
BI-RADS 3: Probably Benign — Follow-up Protocol
BI-RADS 3 is a provisional assessment requiring active surveillance. The standard follow-up schema:
- 6 months: Short-interval ipsilateral imaging (mammogram or ultrasound depending on finding type)
- 12 months: Bilateral mammogram (or bilateral ultrasound if US-detected finding)
- 24 months: Bilateral mammogram — if stable, downgrade to BI-RADS 2
If the finding enlarges or develops suspicious features at any follow-up, upgrade to BI-RADS 4 and recommend biopsy. Important caveats: BI-RADS 3 is not appropriate for symptomatic findings (palpable lump, bloody nipple discharge), new lesions in known cancer patients, or patients with BRCA mutations where even low-suspicion findings typically warrant biopsy.
Limitations and Considerations
This calculator uses ACR BI-RADS 5th Edition feature-based rules to suggest a category. Real-world category assignment has important nuances not fully captured:
- Prior imaging comparison is essential. A new finding is always more suspicious than a stable finding. Stability over 2+ years significantly downgrades a finding (BI-RADS 4A → BI-RADS 3 or 2). This calculator does not incorporate prior imaging data.
- Clinical history matters. Palpable lump, skin changes, bloody nipple discharge, or family history affect the pre-test probability and may warrant upgrading the category.
- High-risk patients. Patients with BRCA mutations, prior breast cancer, or lifetime risk ≥20% have elevated pre-test probability. A BI-RADS 3 finding in a BRCA1 carrier may clinically warrant biopsy despite the <2% rule-based probability.
- Multiple findings. When multiple findings are present, the most suspicious drives the final category. This calculator evaluates multiple features simultaneously and assigns the highest resulting category.
- Not a substitute for radiologist interpretation. This tool is for educational reference. Category assignment in clinical practice requires full imaging review, bilateral comparison, history integration, and radiologist judgment.
References
American College of Radiology. ACR BI-RADS Atlas: Breast Imaging Reporting and Data System. 5th ed. Reston, VA: ACR; 2013.
Sickles EA, D'Orsi CJ, Bassett LW, et al. ACR BI-RADS Atlas: mammography. In: ACR BI-RADS Atlas. 5th ed. Reston, VA: American College of Radiology; 2013.
Lehman CD, et al. MRI Evaluation of the Contralateral Breast in Women with Recently Diagnosed Breast Cancer. N Engl J Med. 2007;356(13):1295–1303.
Helvie MA. Digital Mammography Imaging: Breast Tomosynthesis and Advanced Applications. Radiol Clin North Am. 2010;48(5):917–929.