What do the different Breast Imaging-Reporting and Data System (BI-RADS) categories for a mammogram mean?

BI-RADS Categories for Mammogram Interpretation

The Breast Imaging-Reporting and Data System (BI-RADS) categorizes mammogram findings into 6 assessment categories that standardize reporting and guide clinical management based on the likelihood of malignancy.

BI-RADS Assessment Categories

• Category 0: Incomplete Assessment

  • Requires additional imaging evaluation and/or prior mammograms for comparison
  • Almost always used in screening situations
  • May recommend spot compression, magnification, special views, or ultrasound 1

• Category 1: Negative

  • Negative mammogram with no abnormalities
  • Breasts are symmetric with no masses, architectural distortion, or suspicious calcifications
  • Management: Resume routine screening 1

• Category 2: Benign Findings

  • Negative mammogram but with benign findings present
  • Examples: benign calcifications, calcifying fibroadenoma, oil cyst, lipoma, intramammary lymph nodes
  • Management: Resume routine screening 1

• Category 3: Probably Benign

  • Findings have <2% risk of malignancy
  • Management: Short-interval follow-up with diagnostic mammograms at 6 months, then every 6-12 months for 1-2 years
  • If stable or resolving, return to routine screening
  • If increasing in size or changing characteristics, proceed to biopsy
  • Exception: May proceed directly to biopsy if patient has strong family history, desires biopsy, or follow-up uncertain 1, 2

• Category 4: Suspicious Abnormality

  • Wide range of malignancy probability (higher than category 3, lower than category 5)
  • Management: Tissue diagnosis using core needle biopsy (preferred) or needle localization excisional biopsy 1
  • Subcategories often used:
    • 4A: Low suspicion
    • 4B: Moderate suspicion
    • 4C: High suspicion 3

• Category 5: Highly Suggestive of Malignancy

  • High probability (≥95%) of being cancer
  • Examples: spiculated mass or malignant-appearing pleomorphic calcifications
  • Management: Tissue diagnosis required 1, 4

• Category 6: Known Biopsy-Proven Malignancy

  • For lesions confirmed malignant by biopsy but before definitive therapy
  • Management: Treat according to NCCN Guidelines for Breast Cancer 1

Important Clinical Considerations

1. Overall Assessment Category: When multiple imaging methods are used (mammography and ultrasound), the BI-RADS category represents the cumulative findings of both 1

2. Multiple Abnormalities: If multiple abnormalities are identified, the overall BI-RADS assessment is based on the most worrisome finding 1

3. Pathology-Imaging Concordance: When biopsy is performed, concordance between pathology and imaging findings must be verified. Discordant results require repeat imaging, additional tissue sampling, or surgical excision 1

4. Category 3 Considerations:

   • Should not be used in screening without comprehensive diagnostic evaluation
   • In mammography, validated for grouped round calcifications, oval circumscribed masses, and nonpalpable asymmetries
   • In ultrasound, appropriate for oval circumscribed parallel solid masses and complicated cysts 2

5. Category 5 Reliability: Studies show that properly applied category 5 assessments achieve the intended ≥95% positive predictive value for malignancy 4

Pitfalls to Avoid

• Using Category 3 without proper diagnostic evaluation
• Failing to follow up on discordant findings between clinical, radiological, and pathological assessments 5
• Not performing bilateral mammography in symptomatic patients 5
• Inconsistent application of recommendations for Category 3 findings (most variable category in terms of management) 6

By understanding and properly applying the BI-RADS categories, clinicians can standardize communication about mammographic findings and ensure appropriate management based on the likelihood of malignancy.