What is the recommended follow-up approach for incidental lung nodules (ILNs)?

Management of Incidental Lung Nodules

Follow incidental lung nodules based on size, attenuation (solid vs. subsolid), patient risk factors, and nodule multiplicity using the Fleischner Society 2017 guidelines, which provide specific CT surveillance intervals tailored to these characteristics. 1

Technical Requirements for Optimal Nodule Assessment

Before implementing any follow-up strategy, ensure proper imaging technique:

• Obtain thin-section CT (≤1.5 mm, typically 1.0 mm) with multiplanar reconstructions for all nodule evaluations to enable accurate characterization and measurement 1, 2
• Use low-dose CT technique (approximately 2 mSv) for all follow-up examinations to minimize radiation exposure 2
• IV contrast is NOT required for identifying, characterizing, or determining stability of pulmonary nodules 1, 2
• Thick sections preclude accurate nodule characterization and should be avoided 1

Solid Nodules: Size and Risk-Based Algorithm

Single Solid Nodules

For nodules <6 mm:

• Low-risk patients: No routine follow-up required 1
• High-risk patients (suspicious morphology, upper lobe location, smoking history): Optional CT at 12 months 1
• The minimum threshold for follow-up is based on cancer risk ≥1% 1

For nodules 6-8 mm:

• Low-risk: CT at 6-12 months, then consider CT at 18-24 months 1
• High-risk: CT at 6-12 months, then CT at 18-24 months 1

For nodules >8 mm:

• Consider CT at 3 months, PET/CT, or tissue sampling regardless of risk status 1
• For high pretest probability (>65%): proceed directly to biopsy or surgical resection without PET 3
• For moderate probability (5-65%): FDG-PET/CT followed by biopsy if PET-positive 3

Multiple Solid Nodules

Use the most suspicious nodule to guide management:

• Low-risk patients with nodules <6 mm: No routine follow-up 1
• Low-risk patients with nodules 6-8 mm: CT at 3-6 months, then consider CT at 18-24 months 1
• High-risk patients with nodules <6 mm: Optional CT at 12 months 1
• High-risk patients with nodules 6-8 mm or larger: CT at 3-6 months, then at 18-24 months 1

Subsolid Nodules: Extended Surveillance Required

Subsolid nodules require longer follow-up periods (up to 5 years) due to their indolent nature 1

Single Ground-Glass Nodules

• <6 mm: No routine follow-up 1
• ≥6 mm: CT at 6-12 months to confirm persistence, then CT every 2 years until 5 years 1
• In certain suspicious nodules <6 mm, consider follow-up at 2 and 4 years 1

Single Part-Solid Nodules

• <6 mm: No routine follow-up 1
• ≥6 mm: CT at 3-6 months to confirm persistence 1
• If unchanged and solid component remains <6 mm, perform annual CT for 5 years 1
• Persistent part-solid nodules with solid components ≥6 mm should be considered highly suspicious and warrant consideration for resection 1

Multiple Subsolid Nodules

• CT at 3-6 months regardless of size 1
• If stable, consider CT at 2 and 4 years 1
• Subsequent management based on the most suspicious nodule(s) 1
• Multiple <6 mm pure ground-glass nodules are usually benign, but consider follow-up in high-risk patients at 2 and 4 years 1

Critical Risk Factors to Consider

High-risk features that may warrant more aggressive surveillance include: 1

• Smoking history
• Age >35 years
• Upper lobe location
• Spiculated margins
• Family history of lung cancer
• Emphysema or pulmonary fibrosis

Important Exclusions and Special Populations

These guidelines do NOT apply to: 1

• Lung cancer screening programs (which have separate protocols)
• Patients with known primary cancers at risk for metastases
• Immunocompromised patients at risk for infection
• Children and adults <35 years (infectious causes more likely; minimize serial CT use) 1

Common Pitfalls to Avoid

• Do not perform routine follow-up on nodules with benign calcification patterns (diffuse, central, laminated, or popcorn calcifications) or macroscopic fat (hamartomas) 1
• Perifissural nodules (likely intrapulmonary lymph nodes) typically do not require follow-up even if >6 mm 2
• Do not use chest radiography for follow-up of nodules <1 cm, as most are not visible 1, 3
• Avoid partial thoracic scans—always image the entire chest to avoid missing important findings 2, 4
• Do not use FDG-PET/CT for nodules <8 mm due to limited spatial resolution 2, 3

Stability Assessment

If a solid nodule has been stable for ≥2 years on prior imaging, no additional diagnostic evaluation is needed 4