BI-RADS: Breast Imaging Reporting and Data System
BI-RADS is a standardized classification system developed by the American College of Radiology (ACR) that categorizes breast imaging findings into seven assessment categories (0-6) based on malignancy risk, with each category linked to specific management recommendations. 1, 2
Purpose and Structure
BI-RADS was created to reduce variability between radiologists and establish uniform reporting standards for mammography, ultrasound, and MRI. 1, 3 The system includes three key components:
- Standardized lexicon with descriptive terms for breast abnormalities 4, 3
- Assessment categories that predict likelihood of malignancy 1, 2
- Management recommendations tied to each category 1, 2
The Seven Assessment Categories
Category 0: Incomplete Assessment
- Additional imaging or prior mammograms needed for comparison 2
- Typically used in screening situations requiring additional views or ultrasound 2
Category 1: Negative
- No abnormalities detected 1, 2
- Breasts are symmetric with no masses, architectural distortion, or suspicious calcifications 1, 2
- Management: Resume routine annual screening 2
Category 2: Benign Findings
- Negative mammogram with definitively benign findings 1, 2
- Examples include calcifying fibroadenomas, oil cysts, lipomas, intramammary lymph nodes, vascular calcifications, implants, or surgical changes 1, 2
- Management: Resume routine annual screening 2
Category 3: Probably Benign
- Malignancy risk less than 2% 1, 2, 5
- Requires short-interval follow-up to ensure stability 1, 2
- Management: Diagnostic mammograms at 6 months, then every 6-12 months for 1-2 years 2
- If stable or resolved, return to routine screening; if changes occur, proceed to biopsy 2
Category 4: Suspicious Abnormality
- Wide range of malignancy probability, but not definitively malignant 1
- Risk greater than Category 3 but less than Category 5 2
- Management: Tissue diagnosis required using core needle biopsy (preferred) or needle localization excisional biopsy with specimen radiograph 1, 2
Category 5: Highly Suggestive of Malignancy
- Malignancy probability ≥95% 2
- Examples include spiculated masses or malignant-appearing pleomorphic calcifications 2
- Management: Tissue diagnosis required using core needle biopsy (preferred) or needle localization excisional biopsy 1, 2
Category 6: Known Biopsy-Proven Malignancy
- Added in the fourth edition for lesions confirmed malignant by biopsy but before definitive treatment 1, 2
- Management: Follow breast cancer treatment guidelines 1, 2
Critical Clinical Principles
Assessment Based on Most Worrisome Finding
When multiple abnormalities are present, the overall BI-RADS category is determined by the most suspicious lesion. 1, 2
Cumulative Assessment with Multiple Modalities
When both mammography and ultrasound are performed, the BI-RADS category represents cumulative findings from both studies. 1, 2 The assessment can increase, decrease, or remain unchanged based on subsequent imaging. 1, 2
Pathology-Imaging Concordance is Mandatory
When biopsy is performed for Categories 4 or 5, concordance between pathology and imaging findings must be verified. 1, 2 For example, a negative fine needle aspiration with a spiculated Category 5 mass is discordant and unacceptable. 1 When discordance exists, repeat imaging and additional tissue sampling or surgical excision is required. 1, 2
Common Pitfalls to Avoid
Do not use Category 3 for classically benign findings - these should be Category 2. 5 Category 3 is reserved only when malignancy likelihood is truly less than 2%. 5
Do not skip biopsy for Categories 4 and 5 - tissue diagnosis is mandatory regardless of patient anxiety or preferences. 1
Do not ignore discordant pathology - when imaging suggests malignancy but biopsy shows benign findings, surgical excision is required if discordance persists. 1