• Ground-glass nodules (GGNs) greater than 3 mm are considered SPNs if solitary and not associated with additional abnormalities.

• Discrete round or oval opacity surrounded by normal lung parenchyma.
• Lesion size between 3 mm and 30 mm; anything larger is categorized as a mass, while anything smaller is classified as a micronodule.
• Can be solid, partially solid (subsolid), or ground-glass in density.
• Sharp or poorly defined margins.

Characteristics:

• Smooth: Often benign (e.g., granuloma).
• Lobulated: Suggests malignancy due to differential growth rates.
• Spiculated: Highly suspicious for malignancy.
• Calcifications:
  • Central/popcorn: Suggest benignity (e.g., granuloma and less common hamartoma).
  • Eccentric/stippled: Suspicious for malignancy.
  • Lobular: May be associated with specific conditions such as amyloid deposits or Castleman’s disease.
• Cavitating: May indicate necrosis within a lesion; implications include possible malignancy, infections (e.g., tuberculosis), or vascular abnormalities.
• Fat-containing: Typically benign and associated with hamartomas; may also indicate lipomatous components or teratomas.

• Most Common Cause(s):
  • Granulomas (e.g., tuberculosis, histoplasmosis).
  • Malignancies (e.g., primary lung cancer or metastasis).
  • Benign neoplasms (e.g., hamartomas).
• Other Causes Include:
  • Inflammatory conditions:
    • Granuloma.
    • Lung abscess.
    • Rheumatoid nodule.
    • Pulmonary inflammatory pseudotumor: plasma cell granuloma.
    • Small focus of pneumonia: round pneumonia.
  • Infections: Fungal or bacterial infections.
  • Circulatory abnormalities:
    • Arteriovenous malformations.
    • Pulmonary artery aneurysm.
    • Pseudoaneurysm.
    • Pulmonary infarct.
    • Pulmonary hematoma.
  • Congenital lesions:
    • Arteriovenous malformation.
    • Lung cyst.
    • Bronchial atresia with mucoid impaction.
  • Infiltrative conditions:
    • Amyloid deposits.
    • Castleman’s disease.
  • Miscellaneous causes:
    • Intrapulmonary lymph node.
    • Mucoid impaction.
    • Normal confluence of pulmonary veins.

• Benign: Organized inflammation, fibrous tissue, or congenital defects.
• Malignant: Dysplastic cells with abnormal architecture, nuclear pleomorphism, and necrosis.

• Clinical history and risk factors (e.g., smoking, exposure to carcinogens).
• Imaging evaluation (e.g., size, shape, margins, and density on CT).
• Tissue sampling (e.g., biopsy or resection) if imaging is inconclusive.

• CXR:
  • Findings: Single, well-circumscribed round opacity.
  • Associated Findings: Absence of lymphadenopathy, pleural effusion, or atelectasis.
• CT:
  • Parts: Matrix and border.
  • Size: 3 mm to 30 mm.
  • Shape: Round, oval, irregular, spiculated, or lobulated.
  • Position: Variable, depending on underlying etiology.
  • Character:
    • Solid, ground-glass (GGN), or part-solid.
    • Calcifications:
      • Central, eccentric, irregular, psammomatous.
    • Fat.
    • Cavitation.
  • Time:
    • Stability over 2 years suggests benignity.
    • Malignant nodules typically double in size within 20-400 days.
      • For example:
        • A 3 mm malignant nodule may grow to approximately 4 mm to 5 mm within 60-90 days.
        • A 5 mm malignant nodule may grow to approximately 6-7 mm within 60-90 days.
        • A 7 mm malignant nodule may grow to approximately 9-10 mm within 60-90 days.
        • A 10 mm malignant nodule may grow to approximately 12-14 mm within 60-90 days.
    • GGNs grow more slowly than solid nodules, often necessitating prolonged follow-up to detect late malignant transformation.
  • Associated Findings: Calcification patterns, spiculation, or cavitation.
• Other relevant Imaging Modalities:
  • PET CT/NM/Useful for metabolic activity assessment (e.g., PET) or better tissue characterization (e.g., MRI).

• For solid nodules:
  • <6 mm: No routine follow-up required for low-risk individuals; optional follow-up for high-risk patients.
  • 6-8 mm: Follow-up CT at 6-12 months, then consider additional CT at 18-24 months if no growth.
  • >8 mm: Follow-up CT at 3 months, PET/CT, or tissue sampling based on patient risk factors and clinical context.
• For subsolid nodules (GGNs):
  • <6 mm: No routine follow-up required.
  • >6 mm: Initial follow-up CT at 6-12 months, then annual surveillance for 5 years.
  • Part-solid nodules >6 mm: Special attention is warranted to the solid component. Follow up with CT in 3-6 months; further management depends on stability or growth.

• Small, smooth, calcified nodules are likely benign.
• Nodules with spiculation or eccentric calcifications warrant further evaluation.
• Follow-up CT at appropriate intervals is crucial for risk stratification.
• Ground-glass nodules (GGNs) larger than 3 mm may represent SPNs and require long-term monitoring due to their potential for slow malignant transformation.  GGNs generally grow more slowly than solid nodules, necessitating prolonged observation.