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• • What is it:
    A nodular pattern refers to the presence of discrete, rounded opacities (nodules) within the lungs visible on imaging. These nodules vary in size, distribution, and characteristics, providing crucial diagnostic information about the underlying pathology.
  • Etymology:
    The term “nodular” originates from the Latin word nodulus, meaning “small knot” or “lump,” reflecting the rounded appearance of these findings.
  • AKA:
    Pulmonary nodules.
  • How does it appear on each relevant imaging modality:
    • Chest X-ray:
      • Single or multiple round opacities with defined or ill-defined margins.
      • Nodules may vary in size and distribution across lung fields.
    • Chest CT:
      • Provides detailed assessment of nodules.
      • Parts: Solid, ground-glass, or mixed attenuation.
      • Size: Classified as
        • micronodules (<3 mm),
        • small nodules (3?10 mm), or
        • large nodules (>10 mm).
      • Shape: Typically round or oval, with smooth or irregular edges.
      • Position: Distribution may be
        • random,
        • centrilobular, or
        • perilymphatic.
      • Character:
        • solid
        • ground glass
        • calcified
        • cavitating
        • bronchocentric
        • fat containing
    • MRI:
      • Rarely used but can detect soft-tissue characteristics of nodules.
    • PET-CT:
      • Assesses metabolic activity in nodules, helping differentiate benign from malignant processes.
  • Differential diagnosis:
    • Infection:
      • Granulomatous diseases (e.g., tuberculosis, histoplasmosis).
      • Fungal infections (e.g., aspergillosis, cryptococcosis).
    • Neoplasm:
      • Primary lung cancer.
      • Metastatic disease.
    • Immune-related or inflammatory:
      • Sarcoidosis.
      • Rheumatoid nodules.
    • Infiltrative disorders:
      • Pulmonary amyloidosis (nodular form).
    • Congenital or inherited:
      • Hamartomas (benign lung nodules).
    • Circulatory:
      • Pulmonary talcosis with intravenous drug abuse should be considered in IV drug users presenting with nodular patterns, especially with a history of injecting adulterated substances.
      • Pulmonary arteriovenous malformations.
    • Iatrogenic:
      • Drug-related pulmonary nodules.
  • Recommendations:
    • Evaluate size, attenuation, and borders of nodules.
    • Assess distribution pattern (e.g., random, centrilobular, perilymphatic) to narrow down differential diagnoses.
    • Follow Fleischner Society guidelines for incidental pulmonary nodules.
    • Consider biopsy or advanced imaging (e.g., PET-CT) for nodules with concerning features (e.g., irregular borders, rapid growth, high FDG uptake).
  • Key points and pearls:
    • The distribution and characteristics of nodules provide critical clues to the etiology:
      • Random: Suggests hematogenous spread (e.g., miliary TB, metastases).
      • Centrilobular: Often related to small airway disease or inhalational exposures.
      • Perilymphatic: Associated with sarcoidosis or lymphangitic carcinomatosis.
      • Calcified nodules are often benign but should be further evaluated if atypical.