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.
Applies standardized classification systems (BI-RADS, LI-RADS, TI-RADS, Lung-RADS, PI-RADS) to imaging findings.
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.
| 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).
| 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% |
| 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).
| 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 |
| 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.
For every classified finding, the report must include:
[Organ] [Location]: [Size] [descriptor]
- Features: [list scored features]
- Classification: [System] [Category] ([version])
- Recommendation: [Management per algorithm]
- Prior: [Change from prior or "no prior comparison"]
| 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 |