classifying-imaging-findings

name	classifying-imaging-findings
language	en
description	Applies standardized classification systems (BI-RADS, LI-RADS, TI-RADS, Lung-RADS, PI-RADS) to imaging findings. Use when categorizing imaging findings, applying RADS classifications, or determining follow-up recommendations.
tags	["radiology"]
metadata	{"author":"casemark","practice_areas":["Radiology","Diagnostic Imaging"],"document_types":["Report"],"skill_modes":["Analysis"]}

Classifying Imaging Findings

Applies standardized classification systems (BI-RADS, LI-RADS, TI-RADS, Lung-RADS, PI-RADS) to imaging findings.

Why This Skill Exists

Radiology classification systems translate complex imaging findings into standardized categories with defined management pathways. These systems — BI-RADS (breast), LI-RADS (liver), TI-RADS (thyroid), Lung-RADS (lung cancer screening), PI-RADS (prostate), and others — are mandated by the ACR for their respective organ systems and represent decades of evidence-based development. Incorrect classification directly impacts patient management: an under-classified breast lesion may delay cancer diagnosis; an over-classified thyroid nodule may lead to unnecessary biopsy. Medicare and many commercial payers require appropriate RADS classification for reimbursement. The Joint Commission and ACR accreditation programs audit classification accuracy as a quality metric.

Each classification system uses specific imaging features scored against defined criteria to produce a category that maps to a management recommendation. Radiologists must understand the precise criteria, applicable modality, and patient-population requirements for each system. This skill consolidates the major RADS systems into a single reference with their scoring rubrics, management algorithms, and common pitfalls.

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Checkpoint A: Pre-Draft Intake (Mandatory)

1. Which classification system is required? (Default: Determine from organ system and modality)
2. What imaging modality was used? (Default: Identify — CT, MRI, US, mammography, PET/CT)
3. Is the patient in a screening or diagnostic population? (Default: Diagnostic)
4. What is the patient's relevant risk history? (Default: Average risk — update with actual history)
5. Are prior studies available for comparison? (Default: No priors)
6. Is the patient in the appropriate population for this classification system? (Default: Verify eligibility)

Documents to Request

• Current imaging study with all sequences/phases
• Prior imaging in the same modality for comparison
• Relevant clinical history (cancer history, risk factors, cirrhosis status, PSA levels)
• Prior biopsy results if applicable
• Requisition with clinical indication

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Step 1: Select the Appropriate Classification System

Organ System	Classification	Applicable Modality	Population Requirement
Breast	BI-RADS (5th ed.)	Mammography, US, MRI	All breast imaging
Liver	LI-RADS v2018	CT, MRI (with extracellular or hepatobiliary contrast)	At-risk for HCC (cirrhosis, chronic HBV, prior HCC)
Thyroid	ACR TI-RADS 2017	Ultrasound	All thyroid nodules on US
Lung	Lung-RADS v1.1	Low-dose CT	LDCT lung cancer screening only
Prostate	PI-RADS v2.1	Multiparametric MRI (T2W, DWI, DCE)	Pre-biopsy or active surveillance
Ovary	O-RADS	Ultrasound, MRI	Adnexal masses
Kidney	Bosniak v2019	CT, MRI	Renal cystic masses
Adrenal	ACR Incidental Findings	CT, MRI	Incidentally discovered adrenal nodules
Coronary	CAD-RADS 2.0	Coronary CTA	Suspected coronary artery disease

Critical rule: Never apply a classification system outside its intended population (e.g., LI-RADS only applies to patients at risk for HCC, not all liver lesions).

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Step 2: Apply the Classification Criteria

BI-RADS (Breast Imaging)

Category	Assessment	Management	Cancer Likelihood
0	Incomplete	Additional imaging needed	N/A
1	Negative	Routine screening	0%
2	Benign	Routine screening	0%
3	Probably benign	Short-interval follow-up (6 months)	≤2%
4a	Low suspicion	Biopsy recommended	2–10%
4b	Moderate suspicion	Biopsy recommended	10–50%
4c	High suspicion	Biopsy recommended	50–95%
5	Highly suggestive of malignancy	Biopsy required	≥95%
6	Known malignancy	Surgical management	100%

LI-RADS (Liver — HCC Risk Population Only)

Category	Criteria	Management
LR-1	Definitely benign	Return to surveillance
LR-2	Probably benign	Return to surveillance
LR-3	Intermediate probability	Repeat diagnostic imaging in 3–6 months
LR-4	Probably HCC	Multidisciplinary discussion; may biopsy
LR-5	Definitely HCC	Treat as HCC without biopsy
LR-M	Probably or definitely malignant, not HCC-specific	Biopsy to determine histology
LR-TIV	Tumor in vein	Treat as HCC with vascular invasion

LI-RADS major features: arterial-phase hyperenhancement (APHE), nonperipheral "washout," enhancing "capsule," size, threshold growth (≥50% increase in ≤6 months).

Lung-RADS v1.1 (LDCT Screening Only)

Category	Finding	Management
1	Negative: no nodules, or definite benign (calcified)	Annual LDCT
2	Benign appearance: solid <6 mm, part-solid <6 mm total	Annual LDCT
3	Probably benign: solid 6–8 mm, part-solid ≥6 mm with solid <6 mm	6-month LDCT
4A	Suspicious: solid 8–15 mm, growing <8 mm	3-month LDCT or PET/CT
4B	Very suspicious: solid ≥15 mm, new/growing ≥8 mm	Tissue sampling or PET/CT + short-interval CT
4X	Additional suspicious features	As for 4A/4B with consideration of additional workup

PI-RADS v2.1 (Prostate MRI)

Category	Assessment	Likelihood of Significant Cancer
1	Very low	Clinically significant cancer highly unlikely
2	Low	Clinically significant cancer unlikely
3	Intermediate/equivocal	Equivocal
4	High	Clinically significant cancer likely
5	Very high	Clinically significant cancer highly likely

Zone-specific dominant sequence: T2W for transition zone; DWI/ADC for peripheral zone.

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Step 3: Document the Classification

For every classified finding, the report must include:

1. Finding description — size, location, morphologic features
2. Scoring features — itemize each criterion used (e.g., TI-RADS points per category)
3. Assigned category — explicit category with system version (e.g., "BI-RADS 4B per 5th edition")
4. Management recommendation — per the classification algorithm
5. Comparison — change from prior classification if available
6. Caveats — any features that could upgrade/downgrade the category

Documentation Template

[Organ] [Location]: [Size] [descriptor]
- Features: [list scored features]
- Classification: [System] [Category] ([version])
- Recommendation: [Management per algorithm]
- Prior: [Change from prior or "no prior comparison"]

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Step 4: Handle Edge Cases and Discordance

Scenario	Action
Features span two categories	Assign the higher category and document rationale
Technical limitation prevents scoring a feature	Note limitation; consider recommending repeat study
Prior biopsy yielded benign but imaging is suspicious	Recommend re-biopsy or short-interval follow-up with clear documentation
Patient outside target population (e.g., LI-RADS for non-cirrhotic)	Do NOT apply the system; describe findings descriptively
Multiple classification systems could apply	Apply the most specific system; note others considered
Subcentimeter lesion below size threshold	Document as "too small to characterize" with follow-up recommendation

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Checkpoint B: Post-Draft Alignment (Mandatory)

1. Is the correct classification system applied for the organ, modality, and population?
2. Are all individual scoring features documented?
3. Does the assigned category match the scoring criteria exactly?
4. Is the management recommendation consistent with the assigned category?
5. Are edge cases and limitations explicitly documented?

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Quality Audit

• Classification system version is stated (e.g., LI-RADS v2018, BI-RADS 5th ed.)
• Patient eligibility for the classification system is confirmed
• Each scored feature is individually documented
• Total score/category is stated explicitly
• Management recommendation matches the assigned category
• Finding is measured in the correct axis per system requirements
• Comparison with prior classification is included when available
• Multiple lesions are each individually classified
• Lesions below size thresholds are handled per system-specific rules
• Caveats and technical limitations are noted
• Report avoids applying classification systems outside their intended population
• Category assignment is not modified based on clinical suspicion (classifications are imaging-based)
• The specific management pathway is spelled out (not just the category number)

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Guidelines

1. Always state the classification system version — criteria change between editions and versioning prevents ambiguity.
2. Never apply LI-RADS to patients without established HCC risk factors (cirrhosis, chronic HBV, prior HCC).
3. Lung-RADS applies exclusively to low-dose CT lung cancer screening; do not use it for diagnostic CTs or incidental nodules.
4. For BI-RADS, always document density category (A through D) separately from the assessment category.
5. PI-RADS scoring uses a zone-specific dominant sequence — misapplying T2W as the dominant sequence in the peripheral zone is a common error.
6. When a lesion's features straddle two categories, assign the higher category and document the reasoning.
7. TI-RADS requires itemized point scores for all five feature categories — do not skip features or assign a level without documentation.
8. If a classification system does not apply, describe findings using standardized descriptors without forcing a RADS category.