BI-RADS Assessment Categories
The BI-RADS assessment system assigns a category (0–6) to each breast MRI examination, paired with a concordant management recommendation and an estimated likelihood of cancer.
Assessment Category Table
| Category | Name | Management | Cancer Likelihood |
|---|---|---|---|
| 0 | Incomplete | Additional imaging or prior comparison | N/A |
| 1 | Negative | Routine screening (including MRI per guidelines) | ~0% |
| 2 | Benign | Routine screening | ~0% |
| 3 | Probably Benign | 6-month follow-up or continued surveillance | >0% to ≤2% |
| 4 | Suspicious | Tissue diagnosis (biopsy) | >2% to <95% |
| 4A | Low suspicion | Tissue diagnosis | >2% to ≤10% |
| 4B | Moderate suspicion | Tissue diagnosis | >10% to ≤50% |
| 4C | High suspicion | Tissue diagnosis | >50% to <95% |
| 5 | Highly Suggestive of Malignancy | Tissue diagnosis | ≥95% |
| 6 | Known Biopsy-Proven Malignancy | Clinical follow-up; definitive local therapy | N/A |
Assessment Hierarchy
When multiple findings exist, use the highest-order actionable assessment:
5 > 4 > 0 > 6 > 3 > 2/1
Board Pearl
A category 4 finding supersedes a category 6 finding at the examination level. If a patient has biopsy-proven cancer (cat 6) in the right breast and a suspicious new finding (cat 4) in the left breast, the overall exam assessment is category 4 because it requires immediate action.
Category 0 — Incomplete
Use of Category 0 should be rare on MRI. Limited to three scenarios:
- Additional imaging needed for characterization (e.g., US to confirm likely lymph node)
- Prior imaging needed for comparison
- Technically inadequate exam (e.g., contrast not administered)
Category 0 should NOT be used when findings are sufficiently characterized by MRI and additional imaging is recommended for detection/guidance only.
Board Pearl
v2025 split Category 0 into two sub-types: “Need Additional Imaging Evaluation” and “Need Prior Imaging for Comparison” — matching the 2024 MQSA regulation update.
Category 3 — Probably Benign
Criteria
- Cancer likelihood: >0% to ≤2%
- Goal: decrease false-positive biopsy recommendations
- Desirable frequency: ≤5% of examinations
Imaging Features Supporting Category 3
Masses: Oval + circumscribed + homogeneous/dark septations + T2 hyperintense → cancer ≤2%
NME: Focal or regional distribution + homogeneous enhancement → frequently benign (but no single feature alone is sufficient)
No individual feature alone is sufficient for category 3 — combinations of features are required.
Follow-Up Timing
- 6 months → 12 months → 24 months
- Stable at 24 months → upgrade to Category 2
- Increase/progression → upgrade to Category 4 or 5
Category 3 in Current Breast Cancer
Avoid category 3 in the setting of current breast cancer. Findings that would otherwise be category 3 should be assigned category 4A to enable near-term tissue diagnosis for treatment planning.
Board Pearl
Caution with category 3 on non-baseline MRI: one study showed category 3 malignancy rate of 2% on baseline exams but 9% on non-baseline exams. New findings on follow-up MRI warrant more suspicion.
Category 4 — Suspicious
- Subdivisions (4A, 4B, 4C) are now optional for MRI (previously only for mammography/US)
- Management: tissue diagnosis
- Report should include method of recommended tissue diagnosis and contingencies
Category 5 — Highly Suggestive of Malignancy
- No individual feature alone confers ≥95% cancer likelihood
- Highest PPV features: spiculated margin, linear/segmental NME
- Combinations of suspicious features required
- Percutaneous tissue diagnosis remains standard of care (not excisional biopsy)
Category 6 — Known Biopsy-Proven Malignancy
When to Use
- Biopsy-proven malignancy before definitive local therapy
- Enhancing findings that are definitively the biopsy-proven cancer
- More extensive findings with high certainty of malignancy (same morphology, contiguous)
- No enhancement at known malignancy site (e.g., post-NAC complete MRI response)
Additional Close Findings (ACFs)
Category 6 may also include ACFs when ALL criteria met:
- Within 2 cm of biopsy-proven malignancy
- Do not increase total extent by >2 cm
- Would not change clinical management
Other separate suspicious findings → assign separate category 0, 4, or 5.
Board Pearl
The term “satellite” should NOT be used for additional findings near a known cancer — it is not sufficiently defined regarding proximity and suspicion level. Use “additional close finding (ACF)” instead.
Targeted Ultrasound for MRI Findings
- Use “targeted,” “MRI-targeted,” or “MRI-directed” — not “second-look” ultrasound
- Overall US detection of MRI findings: pooled rate 58%
- Masses: 66% US detection rate
- NME: only 29% US detection rate → lower threshold for MRI-guided biopsy