Lung-RADS Category 2 Nodule
A Lung-RADS Category 2 nodule is classified as benign, with less than 1% probability of malignancy, and requires no additional follow-up beyond routine annual screening. 1
Definition and Characteristics
Lung-RADS Category 2 encompasses several specific nodule types that are considered benign:
- Solid nodules less than 6 mm in diameter are automatically classified as Category 2, reflecting their extremely low malignancy risk 2
- Perifissural nodules (intrapulmonary lymph nodes) measuring 6 to <10 mm with triangular, polygonal, or ovoid shapes are classified as Category 2 3
- Pure ground-glass nodules ≤30 mm that remain unchanged are classified as Category 2 1
- Calcified nodules demonstrating benign patterns of calcification are Category 2 2
Clinical Significance
The malignancy probability for Category 2 nodules is established at less than 1%, though some data suggest the actual rate may be slightly higher at approximately 2.5% for certain subsolid nodules 4. This extremely low risk justifies the conservative management approach.
Management Recommendations
The American College of Radiology recommends return to annual screening (RTAS) for all Category 2 nodules, with no short-term follow-up imaging required. 2, 1
Key management points include:
- No additional CT scans are needed beyond the routine annual screening interval 1
- No biopsy or PET/CT is indicated for Category 2 findings 2
- Patients should be reassured that these findings are benign and do not require additional workup 1
Recent Updates to Classification
The 2022 Lung-RADS update expanded Category 2 criteria significantly:
- Pleural-attached nodules less than 10 mm with smooth margins and specific shapes (triangular, lentiform, oval, or semicircular) were downgraded from Category 3 or 4 to Category 2, eliminating unnecessary short-term follow-up 5
- This change recognizes that these morphologically benign-appearing pleural-attached nodules have high likelihood of benignity and do not warrant 3-6 month surveillance 5
Important Caveats
Transient nodules: Approximately one-third of benign nodules may be transient (resolve spontaneously), which supports the conservative approach to Category 2 management 4, 6
Size thresholds matter: The cutoff was increased from 4 mm (used in the original NLST trial) to 6 mm specifically to reduce false-positive results while maintaining sensitivity for clinically significant cancers 2
Subpleural location expansion: Evidence suggests that nodules with benign morphology (triangular, polygonal, or ovoid) in any subpleural location (not just perifissural) can be safely classified as Category 2, further reducing false-positives without compromising cancer detection 3
Common Pitfalls to Avoid
- Over-imaging benign findings: Resist the temptation to order short-term follow-up CT for Category 2 nodules, as this increases radiation exposure and healthcare costs without improving outcomes 1, 3
- Causing unnecessary patient anxiety: Use clear, reassuring language when communicating Category 2 findings, emphasizing their benign nature while still recommending continued annual screening 1
- Misclassifying nodules: Ensure accurate measurement technique using thin-slice CT (≤2.5 mm, preferably ≤1 mm) and appropriate window settings (lung windows for solid components) to avoid misclassification 2