Breast imaging-reporting and data system (BI-RADS)

BI-RADS (Breast Imaging-Reporting and Data System) is a risk assessment and quality assurance tool developed by American College of Radiology that provides a widely accepted lexicon and reporting schema for imaging of the breast. It applies to mammography, ultrasound, and MRI. This article reflects the 5th edition, published in 2013 ¹.

Classification

Breast imaging studies are assigned one of six assessment categories:

• BI-RADS 0: incomplete
  • need additional imaging evaluation (additional mammographic views or ultrasound) and/or
  • for mammography, obtaining previous images not available at the time of reading
• BI-RADS 1: negative
  • symmetrical and no masses, architectural distortion, or suspicious calcifications
• BI-RADS 2: benign
  • 0% probability of malignancy
• BI-RADS 3: probably benign
  • <2% probability of malignancy
  • short interval follow-up suggested
• BI-RADS 4: suspicious for malignancy
  • 2-94% probability of malignancy
  • for mammography and ultrasound, these can be further divided:
    • BI-RADS 4A: low suspicion for malignancy (2-9%)
    • BI-RADS 4B: moderate suspicion for malignancy (10-49%)
    • BI-RADS 4C: high suspicion for malignancy (50-94%)
  • biopsy should be considered
• BI-RADS 5: highly suggestive of malignancy
  • >95% probability of malignancy
  • appropriate action should be taken
• BI-RADS 6: known biopsy-proven malignancy 

When there are multiple findings, the BI-RADS category for the exam is assigned the highest category in the following hierarchy, from lowest to highest: 1, 2, 3, 6, 0, 4, 5.

The vast majority of screening mammograms fall into BI-RADS 1 or 2 ⁴. Screening mammograms with suspicious findings should generally be assigned BI-RADS 0 to indicate a callback for diagnostic evaluation, meaning additional views to confirm and further evaluate the finding.

Radiographic appearance

BI-RADS provides standardized terminology to describe breast imaging findings.

Ultrasound

Tissue composition

These terms are only used in screening ultrasounds and not in the diagnostic setting.

• homogeneous background echotexture - fat
• homogeneous background echotexture - fibroglandular
• heterogeneous background echotexture

See main article on breast echotexture.

Masses

• shape
  • oval
  • round
  • irregular
• orientation
  • parallel
  • not parallel
• margin
  • circumscribed
  • angular
  • microlobulated
  • indistinct
  • spiculated
• echo pattern (in comparison to subcutaneous fat)
  • anechoic
  • hyperechoic
  • hypoechoic
  • isoechoic
  • heterogeneous
  • complex cystic and solid
• posterior features
  • no posterior features
  • enhancement
  • shadowing
  • combined pattern

See main article on breast masses.

Calcifications

• calcifications in a mass
• calcifications outside of a mass
• intraductal calcifications

Associated features

• architectural distortion
• duct changes
• skin changes
  • skin thickening
  • skin retractions
• edema
• vascularity
  • absent
  • internal vascularity
  • vessels in rim
• elasticity assessment
  • soft
  • intermediate
  • hard

Special cases

• simple cyst
• clustered microcysts
• complicated cyst
• mass in or on skin
• foreign body including implants
• intramammary lymph nodes
• axillary lymph nodes
• vascular abnormalities
  • arteriovenous malformations/pseudoaneurysms
  • Mondor disease
• postsurgical fluid collection
• fat necrosis

Mammography

Breast composition

• fatty: the breasts are almost entirely fatty
• scattered fibroglandular: there are scattered areas of fibroglandular density
• heterogeneously dense: the breasts are heterogeneously dense, which may obscure small masses
• extremely dense: the breasts are extremely dense, which lowers the sensitivity of mammography

See the main article on breast density.

Masses

• shape
  • round
  • oval
  • irregular
• margin
  • circumscribed
  • obscured
  • microlobulated
  • indistinct
  • spiculated
• density
  • high density
  • equal density
  • low density
  • fat-containing

See main article on breast masses.

Calcifications

• typically benign
  • skin
  • vascular
  • coarse or "popcorn-like"
  • large rod-like
  • round
  • rim
  • dystrophic
  • milk of calcium
  • suture
• suspicious morphology
  • amorphous
  • coarse heterogeneous
  • fine pleomorphic
  • fine linear or fine-linear branching
• distribution
  • diffuse
  • regional
  • grouped
  • linear
  • segmental

See main article on breast calcifications.

Other findings

• architectural distortion
• asymmetries
  • asymmetry
  • focal asymmetry
  • developing asymmetry
  • global asymmetry
• intramammary lymph node
• skin lesion
• solitary dilated duct

Associated features

• skin retraction
• nipple retraction
• skin thickening
• trabecular thickening
• axillary adenopathy
• architectural distortion
• calcifications

Location of lesion

• laterality
• quadrant and clock face
• depth
• distance from the nipple

MRI

Amount of fibroglandular tissue

• almost entirely fat
• scattered fibroglandular tissue
• heterogeneous fibroglandular tissue
• extreme fibroglandular tissue

See the main article on breast density.

Background parenchymal enhancement

• level
  • minimal
  • mild
  • moderate
  • marked
• symmetry
  • symmetric
  • asymmetric

See main article on background parenchymal enhancement.

Masses

• shape
  • round
  • oval
  • irregular
• margins
  • circumscribed
  • irregular
  • spiculated
• internal enhancement characteristics
  • homogeneous
  • heterogeneous
  • rim enhancement
  • dark internal septations

See main article on breast masses.

Non-mass enhancement

• distribution
  • focal
  • linear
  • segmental
  • regional
  • multiple regions
  • diffuse
• internal enhancement patterns
  • homogeneous
  • heterogeneous
  • clumped
  • clustered ring

See main article on nonmassnon-mass enhancement.

Other findings

• focus
• intramammary lymph node
• skin lesion
• ductal precontrast high signal on T1W
• cyst
• postoperative collections (hematoma/seroma)
• post-therapy skin thickening and trabecular thickening
• non-enhancing mass
• architectural distortion
• signal void from foreign bodies, clips, etc.

Associated features

• nipple retraction
• nipple invasion
• skin retraction
• skin thickening
• skin invasion
  • direct invasion
  • inflammatory cancer
• axillary adenopathy
• pectoralis muscle invasion
• chest wall invasion
• architectural distortion

Fat-containing lesions

• lymph nodes
  • normal
  • abnormal
• fat necrosis
• hamartoma
• postoperative seroma/hematoma with fat

Location of lesion

• location
• depth

Kinetic curve assessment / signal/signal intensity/time curve description

• initial phase
  • slow
  • medium
  • fast
• delayed phase
  • persistent
  • plateau
  • washout

See main article on breast MRI enhancement curves.

Implants

• implant material and lumen type
  • saline
  • silicone
    • intact
    • ruptured
  • other implant material
  • lumen type
    • single
    • double
    • other
• implant location
  • retroglandular
  • retropectoral
• abnormal implant contour
  • focal bulge
• intracapsular silicone findings
  • radial folds
  • subcapsular line
  • keyhole sign (teardrop, noose)
  • linguine sign
• extracapsular silicone
  • breast
  • lymph nodes
• water droplets
• peri-implant fluid

Radiology report

Findings should be identified in the radiology report if they are suspicious, new, enlarging, or more extensive than at prior exams. Findings should be accompanied by a description of their location and an assessment of suspicion for malignancy.

Treatment and prognosis

When used appropriately, the BI-RADS assessment categories accurately reflect their positive predictive value for cancer, which are on average as follows for mammographically identified lesions that underwent biopsy ³:

• BI-RADS 2: 0%
• BI-RADS 3: 2%
• BI-RADS 4: 30%
• BI-RADS 5: 97%

See also

There are other systems for classifying breast lesions:

• Nottingham classification
• Tabar 5-tier grading system
• ACR 5-tier grading system, a precursor to BI-RADS