What are ground glass nodules in the lungs?

Ground Glass Nodules in the Lungs: Definition and Clinical Significance

Ground glass nodules (GGNs) are focal, rounded opacities in the lungs that appear hazy on CT scans, often representing early-stage lung adenocarcinoma or its precursor lesions, requiring careful monitoring and management based on their size, appearance, and growth pattern. 1

Definition and Radiological Characteristics

• GGNs are focal opacities on CT imaging that appear as hazy increases in lung density without obscuring underlying bronchial and vascular structures 1
• They are categorized into two main types:
  • Pure ground-glass nodules (pGGNs): Entirely hazy appearance without solid components 1
  • Part-solid nodules (PSNs): Contain both ground-glass and solid components 1
• GGNs are best evaluated using lung window settings with an edge-enhancing (sharp) filter to accurately assess the presence and extent of solid components 1

Pathological Correlation

GGNs correlate with specific pathological entities based on their appearance:

• Pure ground-glass nodules (pGGNs):

  • Small pGGNs (<5 mm): Often represent atypical adenomatous hyperplasia (AAH), a premalignant lesion 1
  • Larger pGGNs (>5 mm up to 30 mm): Frequently adenocarcinoma in situ (AIS), a preinvasive lesion 1

• Part-solid nodules (PSNs):

  • PSNs with solid component <5 mm: Typically minimally invasive adenocarcinoma (MIA) 1
  • PSNs with larger solid components or solid nodules: Usually invasive adenocarcinoma 1

Clinical Significance and Malignancy Risk

• The presence of a solid component within a GGN is the strongest predictor of growth and malignancy 1, 2
• Approximately 20% of pure GGNs and 40% of part-solid GGNs will gradually grow or increase their solid components over time 3
• A solid component larger than 5 mm correlates with a substantial likelihood of local invasion 1
• Most persistent or growing GGNs represent lung adenocarcinomas or their preinvasive lesions 3

Management Approach

Management depends on nodule characteristics:

• For pure ground-glass nodules:

  • <6 mm: No routine follow-up needed in low-risk patients; optional CT at 2 and 4 years in high-risk patients 1
  • ≥6 mm: CT follow-up at 6-12 months to confirm persistence, then every 2 years for at least 5 years 1, 3

• For part-solid nodules:

  • <6 mm: No routine follow-up needed in low-risk patients; optional CT at 2 and 4 years in high-risk patients 1
  • ≥6 mm with solid component <6 mm: CT follow-up at 3-6 months to confirm persistence, then annual follow-up for 5 years 1
  • ≥6 mm with solid component ≥6 mm: Consider short-term CT follow-up, PET/CT, biopsy, or resection 1

Important Considerations and Pitfalls

• GGNs require longer follow-up periods (at least 5 years) compared to solid nodules due to their typically indolent growth 3
• Interobserver agreement on classifying nodules as solid, part-solid, or pure ground-glass is highly variable, with correct classification by all radiologists achieved in only 58% of cases 1
• Multiple GGNs may represent multifocal primary adenocarcinoma rather than metastatic disease 1
• While lobectomy remains the standard surgical procedure for lung cancer, limited surgery (wedge resection or segmentectomy) may be appropriate for small GGN-associated cancers with limited solid components 3, 4
• Smoking history and lesion size are important predictors of GGN growth, with EGFR mutations also potentially predicting growth 3