• What is it:
  • A ground-glass nodule (GGN) in the lung is a focal, hazy opacity visible on CT imaging.
  • ≤3 cm in diameter
  • It is characterized by increased attenuation without obscuring underlying bronchial structures or pulmonary vessels, distinguishing it from consolidations.
• Etymology:
  • The term “ground-glass” originates from the hazy appearance resembling frosted or ground glass.
  • “Nodule” refers to its discrete, focal nature.
• AKA:
  • Subsolid nodule (if partially solid components are present).
• How does it appear on each relevant imaging modality:
  • Chest CT (preferred):
    • Parts:
      • Pure GGN: Uniform hazy opacity.
      • Part-solid GGN: A ground-glass opacity with a denser, solid component.
    • Size: Defined as ≤3 cm in diameter; larger lesions are considered masses.
    • Shape: Typically round or oval, with smooth or irregular margins.
    • Position: Can occur in any lung lobe; often peripheral.
    • Character:
      • Non-calcified opacity.
      • Persistent GGNs (seen on follow-up imaging) raise concern for malignancy, especially adenocarcinoma spectrum lesions.
  • Chest X-ray:
    • Usually not visible or poorly defined due to low contrast resolution for subtle attenuation differences.
  • PET-CT:
    • Often shows low or absent FDG uptake, as
      • GGNs generally
        • even if malignant.
        • have
          • low metabolic activity, and are
          • paucicellular
• Differential diagnosis:
  • Inflammatory/Infectious:
    • Fungal infections (e.g., pneumocystis pneumonia).
    • Organizing pneumonia.
    • Viral pneumonitis.
    • Hypersensitivity pneumonitis (focal form).
  • Neoplastic:
    • Adenocarcinoma spectrum
      • adenocarcinoma with lepidic growth
      • atypical adenomatous hyperplasia [AAH],
      • adenocarcinoma in situ [AIS],
      • minimally invasive adenocarcinoma [MIA]).
    • Metastatic lesions (rare).
  • Idiopathic:
• Recommendations:
  • Further evaluation:
    • Follow-up with low-dose chest CT (per Fleischner Society Guidelines):
      • For GGNs ≤5 mm: Routine follow-up not typically required.
      • For GGNs >5 mm: Surveillance CT at 3-6 months and subsequent periodic imaging.
    • Biopsy or surgical resection
      • if the nodule increases in size,
      • develops a solid component,
  • Clinical correlation:
    • Evaluate for systemic symptoms such as fever, weight loss, or hemoptysis.
    • Assess for risk factors like smoking or prior malignancy.
• Key considerations and pearls:
  • Persistent GGNs >10 mm or those developing a solid component have a higher likelihood of malignancy.
  • Pure GGNs are less likely to be malignant than part-solid nodules but may represent early adenocarcinomas.
  • Regular follow-up with low-dose CT is essential for tracking changes in size, density, or morphology.
  • PET-CT has
    • limited sensitivity for GGNs due to their
    • low metabolic activity
    • but if they are
      • increasing in size or
      • develop solid components
    • can be extremely helpful.

Sarcoidosis

 

• Links and References

  • TCV
    • Map of Nodules