Lung-RADS does not apply to:
- Incidentally detected nodules on non-screening CT — use ACR Incidental Findings / Fleischner guidelines
- Nodules found after a lung cancer diagnosis — further imaging for staging is no longer considered screening
Nodule measurement: Measure in lung windows. Measure both long and short axis to one decimal point in mm; report mean nodule diameter to one decimal point. For round nodules, a single measurement suffices. Volumes, if obtained, are reported to the nearest whole number in mm³.
Exam coding: Each exam is assigned the Lung-RADS category of the most suspicious nodule.
Category Definitions and Management
Category 0 — Incomplete (est. prevalence ~1%)
Findings: Any of the following:
- Prior chest CT examination being located for comparison (see Note 9)
- Part or all of the lungs cannot be evaluated
- Findings suggestive of an inflammatory or infectious process (see Note 10)
Management: Comparison to prior chest CT; additional lung cancer screening CT imaging needed; 1–3 month LDCT.
Category 1 — Negative (est. prevalence ~39%; <1% malignancy)
Findings: No lung nodules OR nodule with benign features:
- Complete, central, popcorn, or concentric ring calcifications
- Fat-containing nodule
Management: 12-month screening LDCT.
Category 2 — Benign Appearance or Behavior (est. prevalence ~45%; <1% malignancy)
Findings (any of the following):
- Juxtapleural nodule: <10 mm (<524 mm³) mean diameter at baseline or new AND solid with smooth margins and oval, lentiform, or triangular shape
- Solid nodule: <6 mm (<113 mm³) at baseline OR new <4 mm (<34 mm³)
- Part-solid nodule: <6 mm (<113 mm³) total mean diameter at baseline
- Non-solid nodule (GGN): <30 mm (<14,137 mm³) at baseline, new, or growing OR ≥30 mm (≥14,137 mm³) stable or slowly growing (see Note 7)
- Airway nodule: subsegmental — at baseline, new, or stable (see Note 11)
- Category 3 lesion stable or decreased in size at 6-month follow-up CT
- Category 4B lesion proven benign following appropriate diagnostic workup
Management: 12-month screening LDCT.
Category 3 — Probably Benign (est. prevalence ~9%; 1–2% malignancy)
Findings (any of the following):
- Solid nodule: ≥6 to <8 mm (≥113 to <268 mm³) at baseline OR new 4 mm to <6 mm (34 to <113 mm³)
- Part-solid nodule: ≥6 mm (≥113 mm³) total mean diameter with solid component <6 mm (<113 mm³) at baseline OR new <6 mm (<113 mm³) total mean diameter
- Non-solid nodule (GGN): ≥30 mm (≥14,137 mm³) at baseline or new
- Atypical pulmonary cyst: growing cystic component (mean diameter) of a thick-walled cyst (see Note 12)
- Category 4A lesion stable or decreased in size at 3-month follow-up CT (excluding airway nodules)
Management: 6-month LDCT.
Category 4A — Suspicious (est. prevalence ~4%; 5–15% malignancy)
Findings (any of the following):
- Solid nodule: ≥8 to <15 mm (≥268 to <1,767 mm³) at baseline OR growing <8 mm (<268 mm³) OR new 6 to <8 mm (113 to <268 mm³)
- Part-solid nodule: ≥6 mm (≥113 mm³) total mean diameter with solid component ≥6 mm to <8 mm (≥113 to <268 mm³) at baseline OR new or growing <4 mm (<34 mm³) solid component
- Airway nodule: segmental or more proximal — at baseline (see Note 11)
- Atypical pulmonary cyst: thick-walled cyst OR multilocular cyst at baseline OR thin- or thick-walled cyst that becomes multilocular (see Note 12)
Management: 3-month LDCT. PET/CT may be considered if there is a ≥8 mm (≥268 mm³) solid nodule or solid component. Note: management of 4A lesions follows a stepped approach based upon follow-up stability or decrease in size.
Category 4B — Very Suspicious (est. prevalence ~2%; >15% malignancy)
Findings (any of the following):
- Airway nodule: segmental or more proximal — stable or growing (see Note 11) → Referral for further clinical evaluation (typically bronchoscopy)
- Solid nodule: ≥15 mm (≥1,767 mm³) at baseline OR new or growing ≥8 mm (≥268 mm³)
- Part-solid nodule: solid component ≥8 mm (≥268 mm³) at baseline OR new or growing ≥4 mm (≥34 mm³) solid component
- Atypical pulmonary cyst: thick-walled cyst with growing wall thickness/nodularity OR growing multilocular cyst (mean diameter) OR multilocular cyst with increased loculation or new/increased opacity (nodular, ground glass, or consolidation) (see Note 12)
- Slow-growing solid or part-solid nodule demonstrating growth over multiple screening exams (see Note 8)
Management: Diagnostic chest CT with or without contrast; PET/CT may be considered if there is a ≥8 mm (≥268 mm³) solid nodule or solid component; tissue sampling; and/or referral for further clinical evaluation. Management depends on clinical evaluation, patient preference, and probability of malignancy (see Note 13).
Category 4X — Very Suspicious + Additional Features (est. prevalence <1%; >15% malignancy)
Findings: Category 3 or 4 nodule with additional features or imaging findings that increase suspicion for lung cancer (see Note 14). Examples include spiculation, lymphadenopathy, frank metastatic disease, or a GGN that doubles in size in 1 year.
Important: 4X is a distinct Lung-RADS category, not a modifier. "X" should not be used as a modifier appended to another category (e.g., do not write "4A-X").
Management: More aggressive workup per multidisciplinary discussion. For new large nodules appearing on an annual repeat screening CT, a 1-month LDCT may be recommended first to exclude an infectious or inflammatory etiology before proceeding to invasive workup.
Modifier S — Significant or Potentially Significant (est. prevalence ~10%)
May be added to Lung-RADS categories 0–4 for clinically significant or potentially clinically significant findings unrelated to lung cancer (see Note 15). Examples:
- Significant coronary artery calcification
- Aortic aneurysm
- Unexpected mediastinal or hilar lymphadenopathy
- New or enlarging pleural effusion
Management of the S finding should adhere to available ACR Incidental Findings recommendations. Findings already known and under active evaluation do not require the S modifier.
Management: As appropriate to the specific finding. Example notation: 4A-S.
Solid Nodule Size Thresholds at a Glance
| Finding | Category | Management |
|---|---|---|
| <6 mm (<113 mm³) at baseline | 2 | 12-month LDCT |
| New <4 mm (<34 mm³) | 2 | 12-month LDCT |
| ≥6 to <8 mm (≥113 to <268 mm³) at baseline | 3 | 6-month LDCT |
| New 4 to <6 mm (34 to <113 mm³) | 3 | 6-month LDCT |
| ≥8 to <15 mm (≥268 to <1,767 mm³) at baseline | 4A | 3-month LDCT |
| Growing <8 mm (<268 mm³) | 4A | 3-month LDCT |
| New 6 to <8 mm (113 to <268 mm³) | 4A | 3-month LDCT |
| ≥15 mm (≥1,767 mm³) at baseline | 4B | Diagnostic CT ± PET/CT ± tissue |
| New or growing ≥8 mm (≥268 mm³) | 4B | Diagnostic CT ± PET/CT ± tissue |
Part-Solid Nodule Size Thresholds
| Finding | Category | Management |
|---|---|---|
| <6 mm (<113 mm³) total at baseline | 2 | 12-month LDCT |
| ≥6 mm total, solid component <6 mm (<113 mm³) at baseline | 3 | 6-month LDCT |
| New <6 mm (<113 mm³) total mean diameter | 3 | 6-month LDCT |
| ≥6 mm total, solid component ≥6 to <8 mm at baseline | 4A | 3-month LDCT |
| New or growing <4 mm (<34 mm³) solid component | 4A | 3-month LDCT |
| Solid component ≥8 mm (≥268 mm³) at baseline | 4B | Diagnostic CT ± PET/CT ± tissue |
| New or growing ≥4 mm (≥34 mm³) solid component | 4B | Diagnostic CT ± PET/CT ± tissue |
Non-Solid Nodule (Pure GGN) Thresholds
| Finding | Category | Management |
|---|---|---|
| <30 mm (<14,137 mm³) at baseline, new, or growing | 2 | 12-month LDCT |
| ≥30 mm (≥14,137 mm³) stable or slowly growing (see Note 7) | 2 | 12-month LDCT |
| ≥30 mm (≥14,137 mm³) at baseline or new | 3 | 6-month LDCT |
Key Notes from ACR Lung-RADS v2022
Note 4 — Nodule Measurement: Calculate nodule mean diameter by measuring both long and short axis to one decimal point in mm; report mean diameter to one decimal point. Volumes reported to nearest whole number in mm³.
Note 5 — Size Thresholds: Apply to nodules at first detection and those that enlarge into a higher size category. When a nodule crosses a new size threshold, reclassify and manage accordingly.
Note 6 — Growth: Defined as >1.5 mm (>2 mm³) increase in mean diameter within a 12-month interval.
Note 7 — Slow-Growing GGN: A GGN demonstrating growth over multiple exams but not meeting the >1.5 mm/12-month threshold may remain Lung-RADS 2. If the GGN develops a solid component, reclassify and manage per part-solid nodule criteria.
Note 8 — Slow-Growing Solid or Part-Solid: Growth demonstrated over multiple screening exams but <1.5 mm per 12-month interval → suspicious → classify as Lung-RADS 4B. These nodules may have low PET/CT metabolic activity; biopsy or surgical evaluation, if feasible, may be the most appropriate management.
Note 13 — Category 4B Management: Predicated on clinical evaluation (comorbidities), patient preference, and risk of malignancy. Radiologists are encouraged to use the McWilliams et al Assessment Tool when making recommendations.
Note 14 — Category 4X: Additional imaging findings that increase suspicion include spiculation, lymphadenopathy, frank metastatic disease, or a GGN that doubles in size in 1 year. 4X is a distinct Lung-RADS category; "X" should not be used as a modifier.
Note 15 — Modifier S: S modifier should not be applied to findings already known and under active clinical evaluation. Unexpected change in a known significant finding does warrant the S modifier.
Reference
American College of Radiology. ACR Lung CT Screening Reporting and Data System (Lung-RADS), Version 2022. Released November 2022. Available at: acr.org/Lung-RADS.