What is BI-RADS?
BI-RADS (Breast Imaging-Reporting and Data System) is a standardized classification system developed by the American College of Radiology that categorizes breast imaging findings from 0 to 6 based on their likelihood of malignancy, with each category directly linked to specific management recommendations. 1, 2
Core Purpose and Function
BI-RADS serves three essential functions in breast imaging:
- Standardizes terminology used to describe abnormalities on mammograms, ultrasound, and MRI, ensuring consistent communication between radiologists and clinicians 2, 3
- Provides assessment categories that are predictive of malignancy probability, eliminating ambiguous reporting that previously left clinicians uncertain about management 4
- Creates a framework for data collection, quality control auditing, and research across institutions 3, 5
The Seven Assessment Categories
Category 0: Incomplete Assessment
- Additional imaging evaluation is required, typically used in screening situations when more views or ultrasound are needed for complete assessment 1
- Requires comparison with prior films and/or diagnostic mammogram with or without ultrasound 6
Category 1: Negative
- No abnormalities found; breasts are symmetric with no masses, architectural distortion, or suspicious calcifications 1
- Resume routine annual screening 1
Category 2: Benign Findings
- Negative mammogram with definitively benign findings such as calcifying fibroadenomas, oil cysts, lipomas, or vascular calcifications 1
- Resume routine annual screening 1
Category 3: Probably Benign
- Less than 2% likelihood of malignancy, requiring short-interval follow-up rather than biopsy 1
- Specific follow-up protocol: diagnostic mammograms at 6 months, then every 6-12 months for 1-2 years 6, 1
- At first 6-month follow-up, perform unilateral mammogram of the affected breast; at 12 months, bilateral mammograms for women ≥40 years 6
- If stable or resolved, resume routine screening; if changes occur, proceed to biopsy 1
Category 4: Suspicious Abnormality
- Findings warrant tissue biopsy, with malignancy risk greater than Category 3 but less than Category 5 1
- Tissue diagnosis required using core needle biopsy (preferred method) or needle localization excisional biopsy 1
Category 5: Highly Suggestive of Malignancy
- ≥95% probability of cancer, requiring immediate tissue biopsy without delay 7, 1
- Typical features include spiculated masses and malignant-appearing pleomorphic calcifications 7
- Core needle biopsy is the standard approach before definitive management 7
- Critical pitfall: Even if biopsy shows benign results, surgical excision is still recommended due to high suspicion features on imaging 7
Category 6: Known Biopsy-Proven Malignancy
- Used for lesions confirmed malignant through biopsy but before definitive treatment 1
- Management according to breast cancer treatment guidelines 1
Clinical Application Principles
The overall BI-RADS assessment is based on the most worrisome finding when multiple abnormalities are identified 1. When both mammography and ultrasound are performed, the categories represent cumulative findings of both modalities 1.
Key Management Algorithms by Category:
- Categories 0: Complete diagnostic workup first 6
- Categories 1-2: Annual screening 1
- Category 3: Structured short-interval follow-up protocol 6, 1
- Categories 4-5: Tissue biopsy required 7, 1
- Category 6: Cancer treatment protocols 1
Critical Pitfalls to Avoid
- Never delay biopsy for additional imaging or clinical correlation when Category 4 or 5 is assigned 7
- Do not assign Category 5 unless positive predictive value is truly ≥95% 7
- Pathology-imaging concordance is essential: when pathology and imaging are discordant, repeat imaging and/or additional tissue sampling is required 1
- Do not accept benign biopsy results at face value for Category 5 lesions without surgical excision 7
Current Limitations
Despite widespread adoption, substantial interobserver variability exists in BI-RADS application 2. The 5th edition has ambiguous diagnostic criteria for MRI assessment Categories 3 and 4 compared to mammography or ultrasound 5. Some areas still lack fully standardized terminologies 5.