• Etymology
  “Ground-glass” refers to the hazy, frosted-glass appearance seen on imaging, originating from glasswork terminology. A “nodule” is a small, rounded opacity in the lung.
• AKA and abbreviation
  Ground-glass nodule (GGN).
• What is it?
  A ground-glass nodule (GGN) is a specific subtype of ground-glass opacity (GGO), defined as a focal, hazy area of increased lung attenuation on CT imaging. GGNs are circumscribed, smaller than 3 cm, and do not obscure underlying bronchial or vascular structures. Unlike GGNs, GGOs are a broader category that includes diffuse, non-nodular hazy opacities.
• Characterized by
  • Hazy opacity on imaging, typically identified on high-resolution CT (HRCT).
  • Subdivided into:
    • Pure GGNs: No solid component.
    • Part-solid GGNs: A combination of ground-glass and solid components.
  • Size: Typically up to 3 cm in diameter; larger lesions may indicate malignancy.
• Caused by
  • Most Common Cause(s): Benign causes such as transient inflammation (e.g., atypical pneumonia, viral infections) are more frequent overall. Persistent GGNs are more commonly associated with atypical adenomatous hyperplasia (AAH) or early adenocarcinoma.
  • Other Causes Include:
    • Infection: Atypical pneumonia, fungal infections.
    • Inflammation/Immune: Organizing pneumonia, eosinophilic pneumonia.
    • Neoplasm: Invasive adenocarcinoma, metastatic disease.
    • Congenital: Rarely, congenital cystic adenomatoid malformation (CCAM).
• Resulting in:
  • Potential for malignant transformation if persistent or part-solid.
  • Misinterpretation if transient, leading to unnecessary interventions.
• Structural changes:
  • Alveolar or interstitial involvement without significant collapse or consolidation.
• Pathophysiology:
  GGNs arise due to partial filling of airspaces, interstitial thickening, or increased cellularity, which scatters x-rays and reduces air content. Persistent GGNs often represent early neoplastic processes, while transient GGNs are typically inflammatory or infectious.
• Pathology:
  • Pure GGNs: Often associated with atypical adenomatous hyperplasia (AAH) or early adenocarcinoma in situ (AIS).
  • Part-solid GGNs: More likely to indicate invasive adenocarcinoma.
  • Inflammatory GGNs: Alveolar exudates or interstitial infiltration.
• Diagnosis:
  • Clinical context: Symptoms (if any), patient history (e.g., smoking, exposure, immune status).
  • Imaging: HRCT for detection and characterization.
  • Follow-up: Serial imaging for persistent nodules.
  • Biopsy: Indicated for nodules with high suspicion of malignancy or growth over time.
• Clinical:
  Symptoms are usually absent but may include cough, hemoptysis, or constitutional symptoms if associated with malignancy or infection.
• Radiology Detail:
  • CXR
    • Findings: Rarely visible on CXR due to subtle density.
    • Associated Findings: Not specific unless part of a larger process (e.g., consolidation).
  • CT
    • Parts: Solitary or multiple.
    • Size: Usually <3 cm for nodules; larger lesions suggest higher suspicion.
    • Shape: Round or irregular.
    • Position: Can occur anywhere within the lung parenchyma.
    • Character: Pure ground-glass or part-solid.
    • Time: Stable, transient, or progressive (growth or increasing solid component).
    • Associated Findings: Pleural retraction, air bronchograms, satellite nodules.
  • Other relevant Imaging Modalities
    • PET-CT: Typically recommended for solid nodules ≥7 mm in size; GGNs may show lower metabolic activity due to paucicellularity. PET is more reliable for nodules with part-solid components or if the GGN exceeds 10 mm.
    • MRI: Rarely used but may provide soft-tissue contrast.
• Pulmonary function tests (PFTs):
  Usually normal unless associated with underlying lung disease.
• Recommendations
  • Fleischner Guidelines for GGNs:
    • Pure GGNs ≤6 mm: No routine follow-up is needed unless specific clinical risks are present.
    • Pure GGNs >6 mm: CT at 6-12 months, then every 2 years for up to 5 years if stable.
    • Part-solid GGNs >6 mm: CT at 3-6 months to confirm persistence; additional imaging based on growth or development of new solid components.
  • Follow-up should focus on growth and evolution, especially the development of solid components, which is concerning for adenocarcinoma with lepidic growth and may necessitate PET scanning or biopsy.
  • GGNs typically grow more slowly than solid nodules. While a solid nodule that remains stable for 2 years may not require further follow-up, GGNs often necessitate prolonged surveillance beyond 2 years to monitor for late malignant transformation.
  • Persistent GGNs, especially part-solid, warrant close monitoring to detect malignancy early.
• Key Points and Pearls
  • Persistent GGNs, especially those with part-solid components, require close follow-up due to higher malignancy risk.
  • Transient GGNs are often inflammatory or infectious and may resolve spontaneously.
  • GGNs are a subset of GGOs, which can include diffuse or patchy opacities. GGNs are circumscribed and focal.
  • A structured approach using Fleischner guidelines is essential for consistent management.
  • Evolution of solid components within GGNs is a critical marker for potential malignant transformation, highlighting the importance of serial imaging and timely intervention.
  • GGNs grow more slowly than solid nodules, necessitating a longer follow-up interval to detect changes indicative of malignancy.

This CT shows a ground glass nodule in the lung which is characterized by a small round hazy opacity that are usually less than 3cm in size (yellow arrows)Ashley Davidoff MD TheCommonVein.net29787L B.A

• Etymology
  “Ground-glass” refers to the hazy, frosted-glass appearance seen on imaging, originating from glasswork terminology. A “nodule” is a small, rounded opacity in the lung.
• AKA and abbreviation
  Ground-glass nodule (GGN).
• What is it?
  A ground-glass nodule (GGN) is a specific subtype of ground-glass opacity (GGO), which is defined as a focal, hazy area of increased lung attenuation on CT imaging. GGNs are circumscribed, smaller than 3 cm, and do not obscure underlying bronchial or vascular structures. Unlike GGNs, GGOs are a broader category that includes diffuse, non-nodular hazy opacities.
• Characterized by
  • Hazy opacity on imaging, typically identified on high-resolution CT (HRCT).
  • Subdivided into:
    • Pure GGNs: No solid component.
    • Part-solid GGNs: A combination of ground-glass and solid components.
  • Size: Typically up to 3 cm in diameter; larger lesions may indicate malignancy.
• Caused by
  • Most Common Cause(s): Benign causes such as transient inflammation (e.g., atypical pneumonia, viral infections) are more frequent overall. Persistent GGNs are more commonly associated with atypical adenomatous hyperplasia (AAH) or early adenocarcinoma.
  • Other Causes Include:
    • Infection: Atypical pneumonia, fungal infections.
    • Inflammation/Immune: Organizing pneumonia, eosinophilic pneumonia.
    • Neoplasm: Invasive adenocarcinoma, metastatic disease.
    • Congenital: Rarely, congenital cystic adenomatoid malformation (CCAM).
• Resulting in:
  • Potential for malignant transformation if persistent or part-solid.
  • Misinterpretation if transient, leading to unnecessary interventions.
• Structural changes:
  • Alveolar or interstitial involvement without significant collapse or consolidation.
• Pathophysiology:
  GGNs arise due to partial filling of airspaces, interstitial thickening, or increased cellularity, which scatters x-rays and reduces air content. Persistent GGNs often represent early neoplastic processes, while transient GGNs are typically inflammatory or infectious.
• Pathology:
  • Pure GGNs: Often associated with atypical adenomatous hyperplasia (AAH) or early adenocarcinoma in situ (AIS).
  • Part-solid GGNs: More likely to indicate invasive adenocarcinoma.
  • Inflammatory GGNs: Alveolar exudates or interstitial infiltration.
• Diagnosis:
  • Clinical context: Symptoms (if any), patient history (e.g., smoking, exposure, immune status).
  • Imaging: HRCT for detection and characterization.
  • Follow-up: Serial imaging for persistent nodules.
  • Biopsy: Indicated for nodules with high suspicion of malignancy or growth over time.
• Clinical:
  Symptoms are usually absent but may include cough, hemoptysis, or constitutional symptoms if associated with malignancy or infection.
• Radiology Detail:
  • CXR
    • Findings: Rarely visible on CXR due to subtle density.
    • Associated Findings: Not specific unless part of a larger process (e.g., consolidation).
  • CT
    • Parts: Solitary or multiple.
    • Size: Usually <3 cm for nodules; larger lesions suggest higher suspicion.
    • Shape: Round or irregular.
    • Position: Can occur anywhere within the lung parenchyma.
    • Character: Pure ground-glass or part-solid.
    • Time: Stable, transient, or progressive (growth or increasing solid component).
    • Associated Findings: Pleural retraction, air bronchograms, satellite nodules.
  • Other relevant Imaging Modalities
    • PET-CT: Typically recommended for solid nodules ≥7 mm in size; GGNs may show lower metabolic activity due to paucicellularity. PET is more reliable for nodules with part-solid components or if the GGN exceeds 10 mm.
    • MRI: Rarely used but may provide soft-tissue contrast.
• Pulmonary function tests (PFTs):
  Usually normal unless associated with underlying lung disease.
• Recommendations
  • Fleischner Guidelines for GGNs:
    • Pure GGNs ≤6 mm: No routine follow-up is needed unless specific clinical risks are present.
    • Pure GGNs >6 mm: CT at 6-12 months, then every 2 years for up to 5 years if stable.
    • Part-solid GGNs >6 mm: CT at 3-6 months to confirm persistence; additional imaging based on growth or development of new solid components.
  • Follow-up should focus on growth and evolution, especially the development of solid components, which is concerning for adenocarcinoma with lepidic growth and may necessitate PET scanning or biopsy.
  • GGNs typically grow more slowly than solid nodules, and follow-up intervals reflect this difference.
  • Persistent GGNs, especially part-solid, warrant close monitoring to detect malignancy early.
• Key Points and Pearls
  • Persistent GGNs, especially those with part-solid components, require close follow-up due to higher malignancy risk.
  • Transient GGNs are often inflammatory or infectious and may resolve spontaneously.
  • GGNs are a subset of GGOs, which can include diffuse or patchy opacities. GGNs are circumscribed and focal.
  • A structured approach using Fleischner guidelines is essential for consistent management.
  • Evolution of solid components within GGNs is a critical marker for potential malignant transformation, highlighting the importance of serial imaging and timely intervention.

Sarcoidosis

 

• Links and References

  • TCV
    • Map of Nodules