ACR BI-RADS Calculator

BI-RADS Categories Quick Reference

ACR BI-RADS 5th Edition assigns one of seven assessment categories — including three subcategories of category 4 — based on the most suspicious finding entered. The recommended management action and approximate malignancy probability follow:

Mass Lesions

A mass in BI-RADS is a space-occupying lesion seen in two projections. Three features determine the mass-level assessment:

• Shape — Oval (gentle lobulation, often benign) and round (sphere, less common in malignancy) are the most reassuring shapes; irregular shape is the most suspicious and drives higher BI-RADS subcategories.
• Margin — Circumscribed (well-defined) margins are most reassuring; spiculated (radiating fine lines) is the single most suspicious mammographic finding and is BI-RADS 5 by itself. Indistinct and microlobulated margins are intermediate.
• Density / Echogenicity — Fat-containing masses (lipoma, oil cyst, hamartoma) are always BI-RADS 2 (benign). Low-density/anechoic circumscribed masses suggest simple cysts (BI-RADS 2). High-density complex masses with internal heterogeneity raise suspicion.

A mass with only some features entered defaults to BI-RADS 0 (incomplete) until full characterization is available.

Calcifications

Calcifications are tiny calcium deposits seen on mammography. BI-RADS classification depends on morphology (what they look like) and distribution (where they appear):

• Typically benign morphology — skin, vascular, coarse, large rod-like, round, punctate, milk of calcium, suture — always BI-RADS 2, regardless of distribution.
• Suspicious morphology — amorphous, coarse heterogeneous, fine pleomorphic, fine linear/branching — drives the BI-RADS category based on distribution: segmental or linear → 4C; grouped → 4B; regional → 4A; diffuse with suspicious morphology → 3 (probably benign despite morphology).
• No morphology yet — BI-RADS 0 (additional imaging required).

Architectural Distortion

Architectural distortion is a mammographic finding where the normal breast parenchyma is distorted without a visible central mass — often with radiating lines or retraction. New architectural distortion is BI-RADS 4B minimum; biopsy is required unless the finding can be confidently attributed to a prior biopsy site or surgical scar (in which case it can be downgraded).

Asymmetry

Asymmetry refers to an area of fibroglandular tissue seen on one breast that lacks a corresponding matching area on the other. BI-RADS 5th Edition recognizes four asymmetry patterns:

• One-view asymmetry (seen on only one view) — BI-RADS 0: needs additional views before final assessment.
• Global asymmetry (large volume of tissue, seen on both views, no mass) — typically BI-RADS 2 or 3.
• Focal asymmetry (two-view, smaller) — BI-RADS 4A; biopsy often recommended.
• Developing asymmetry (new or growing) — BI-RADS 4B; always warrants biopsy as it carries the highest suspicion of asymmetric findings.

How to Use This Calculator

The BI-RADS calculator follows the ACR 5th Edition two-step approach. First, enter the imaging modality (mammography, ultrasound, or MRI — the calculator applies the same logic; terminology varies by modality). Second, enter each finding present: mass characteristics, calcification morphology and distribution, the presence of architectural distortion, and the asymmetry pattern. The calculator returns the BI-RADS category assigned by the most suspicious finding:

1. Modality — Mammography is the default; ultrasound and MRI use modified lexicons but the same category definitions.
2. Mass — Toggle Yes and select shape, margin, and density. Spiculated margin alone qualifies as BI-RADS 5.
3. Calcifications — Toggle Yes and select morphology (benign vs. suspicious) and distribution.
4. Architectural Distortion — Toggle Yes if present (BI-RADS 4B minimum).
5. Asymmetry — Pick one of the four asymmetry patterns or None.

The calculator takes the highest-suspicion finding across all entered items and maps it to a BI-RADS category. Multiple findings present simultaneously: only the most suspicious is reported.

Modality-Specific Notes

• Mammography: Primary screening modality. Calcification characterization is most reliable on mammography (magnification views add detail). Architectural distortion and asymmetry are mammography-specific findings.
• Ultrasound: Adjunct to mammography; primary for palpable lumps in women under 30 and for cyst characterization. Posterior acoustic features (shadowing = suspicious, enhancement = reassuring for cyst) and orientation (parallel = less suspicious, non-parallel = more suspicious) provide additional assessment.
• MRI: Highest sensitivity (~95%) for invasive breast cancer. Used for high-risk screening, extent-of-disease evaluation, treatment monitoring. Background parenchymal enhancement (BPE) and internal enhancement kinetics (initial and delayed phase) are MRI-specific. Kinetic curve type I (persistent) is most benign; type III (washout) is most suspicious.

BI-RADS 3 Follow-up Protocol

BI-RADS 3 (probably benign) has a defined short-interval follow-up schema before downgrade to BI-RADS 2:

• 6 months: Short-interval ipsilateral imaging (mammogram or ultrasound depending on finding type)
• 12 months: Bilateral mammogram (or bilateral ultrasound if US-detected finding)
• 24 months: Bilateral mammogram — if stable, downgrade to BI-RADS 2

If the finding enlarges or develops suspicious features at any follow-up, upgrade to BI-RADS 4 and recommend biopsy. BI-RADS 3 is not appropriate for symptomatic findings (palpable lump, bloody nipple discharge) or new lesions in known cancer patients; BRCA carriers often warrant biopsy even at BI-RADS 3.

Limitations

• Prior imaging comparison is essential. Stability over 2+ years significantly downgrades a finding; a new finding is more suspicious. This calculator does not incorporate prior imaging data.
• Clinical history matters. Palpable lump, skin changes, bloody nipple discharge, or family history affect pre-test probability and may warrant category upgrade.
• Multiple findings. The most suspicious drives the final category. The calculator evaluates multiple features simultaneously and assigns the highest resulting category.
• Not a substitute for radiologist interpretation. This tool is for educational reference. Real category assignment requires full imaging review, bilateral comparison, history integration, and radiologist judgment.