Coding / Audit

Exam category

• Code each exam 0-4 based on the nodule with the highest degree of suspicion.
• Timing of follow-up is from the date of the exam being interpreted.
• Category 4A has a stepped pathway: if stable or decreased at 3-month follow-up, assign category 3 and continue with 6-month LDCT.

Audit definitions

• Negative screen: categories 1 and 2.
• Positive screen: categories 3 and 4.
• A negative screen does not mean the patient does not have lung cancer.

Measurement / Growth

Nodule measurement

• Measure long and short axis to one decimal point in mm; report mean diameter to one decimal point.
• Measurements may be made in any plane that best reflects true nodule size.
• If volume is used, report to the nearest whole number in mm³.

Thresholds and growth

• Size thresholds apply at first detection and when a nodule enlarges into a higher category.
• If a nodule crosses a new size threshold, reclassify by size even if it does not meet formal growth criteria.
• Growth: increase in mean diameter greater than 1.5 mm within a 12-month interval.

Special Patterns

Slow-growing nodules

• Slow-growing non-solid ground-glass nodules can remain category 2 until they meet another category criterion, such as developing a solid component.
• Slow-growing solid or part-solid nodules are suspicious and may be classified as category 4B even if they do not exceed the 12-month growth threshold.
• Slow-growing lesions may not be PET-avid; biopsy or surgical evaluation may be more appropriate when feasible.

Prior exams

• When prior CTs are pending, category 0 is temporary.
• Assign a new Lung-RADS category after comparison imaging becomes available.

Inflammation / Airway / Cysts

Infectious or inflammatory findings

• Category 0 with 1-3 month LDCT may be used for indeterminate infectious/inflammatory patterns.
• Examples include segmental or lobar consolidation, more than six new nodules, or a large new solid nodule appearing over a short interval.
• At follow-up, assign the new category based on the most suspicious nodule.
• Tree-in-bud nodules or new ground-glass nodules under 3 cm may often be categorized by existing size criteria instead of short-term follow-up.

Airway nodules

• Segmental or more proximal endotracheal/endobronchial abnormalities are category 4A.
• Subsegmental or multiple tubular endobronchial abnormalities often favor infection and may be category 0 or 2 if no obstructing nodule is present.
• Persistent segmental or proximal airway nodules at 3 months are upgraded to category 4B, typically prompting bronchoscopy or further clinical evaluation.

Atypical pulmonary cysts

• Thin-walled cysts with uniform wall thickness under 2 mm are benign and are not classified in Lung-RADS.
• Thick-walled or multilocular cysts are managed as atypical pulmonary cysts.
• Cavitary nodules are managed as solid nodules by total mean diameter.
• A cyst with an associated solid, part-solid, or ground-glass nodule is managed by the most concerning feature.

4B / 4X / Modifier S

Category 4B

• Management depends on clinical evaluation, comorbidities, patient preference, and malignancy probability.
• Risk tools such as the McWilliams/Brock model can help guide recommendations.

Category 4X

• 4X is a distinct category for category 3 or 4 nodules with additional imaging findings that increase suspicion.
• Examples include spiculation, lymphadenopathy, frank metastatic disease, or a ground-glass nodule that doubles in size in 1 year.
• X should not be used as a modifier.

S modifier

• Add S to categories 0-4 for clinically significant non-lung-cancer findings.
• Do not add S for findings already known and already being evaluated unless there is unexpected concerning change.
• Once lung cancer is diagnosed, additional imaging such as PET/CT is staging rather than screening.

Helpful Links

Risk and incidental findings

• McWilliams / Brock lung cancer risk calculators
• ACR Incidental Findings recommendations
• ACR LCS Incidental Findings Quick Reference Guide

Abbreviations

• LDCT = low-dose chest CT.
• GGN = ground-glass nodule.