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• What is it:
  • A solitary pulmonary nodule (SPN) is a single, well-circumscribed lesion within the lung parenchyma, measuring ?3 cm in diameter, surrounded by normal lung tissue, and not associated with other abnormalities like atelectasis or lymphadenopathy.
  • SPNs are commonly detected incidentally on imaging.
• Etymology:
  • Derived from the Latin word solitarius, meaning “alone,” referring to the presence of a single lesion.
• AKA:
  • Coin lesion.
• Abbreviation:
  • SPN (Solitary Pulmonary Nodule).
• How does it appear on each relevant imaging modality:
  • Chest CT (preferred):
    • Parts: Typically a single, isolated lesion; may be solid, part-solid, or ground-glass (GGN).
    • Size: Defined as ?3 cm; larger lesions are classified as masses.
    • Shape: Round or oval with well-defined or irregular margins.
    • spiculated raises concern for malignancy but not pathognomonic
    • Position:
      • Can occur in any lung lobe;
      • sometimes bronchocentric
    • Character:
      • Calcifications: Benign patterns include central, laminated, or popcorn-like.
      • eccentric calcifications
        • raise the possibility of scar carcinoma.
      • Enhancement:
        • Malignant nodules show significant contrast enhancement (>15 HU).
  • Chest X-ray:
    • Appears as a
      • single,
      • round opacity,
      • well-defined or
      • slightly irregular, but smaller nodules may be missed.
  • PET-CT:
    • Increased SUV uptake (>2.5) is suspicious  malignancy.
    • SUV – 3-4 highly suspicious
    • False positives can occur with infections or inflammation.
• Differential diagnosis
  • Infection
    • Granulomas (e.g., tuberculosis, histoplasmosis, coccidioidomycosis).
    • septic emboli
    • pulmonary abscess (in early stages).
  • Inflammation:
    • Rheumatoid nodule.
    • Sarcoidosis.
  • Neoplasm:
    • Benign: Hamartoma.
    • Malignant: Primary lung cancer (e.g., adenocarcinoma, squamous cell carcinoma).
  • Circulatory: Pulmonary infarct (can mimic an SPN).
  • Idiopathic: Cryptogenic organizing pneumonia (COP).
  • Iatrogenic: Post-radiation fibrosis presenting as a nodule.
• Recommendations:
  • Further evaluation:
    • Low-dose chest CT for detailed characterization and follow-up.
    • PET-CT for SPNs ?8 mm to assess metabolic activity.
    • Biopsy (CT-guided or bronchoscopic) for indeterminate or suspicious nodules.
  • Surveillance:
    • Follow-up intervals based on size, density, and patient risk factors per Fleischner Society guidelines.
• Key considerations and pearls:
  • SPNs <6 mm in low-risk patients generally do not require routine follow-up.
  • Benign SPNs often show specific calcification patterns or fat content (e.g., hamartomas).
  • Malignant SPNs are more likely in older patients, smokers, or those with a history of cancer.
  • Upper lobe SPNs, spiculated margins, and rapid growth (doubling time <30-400 days) are concerning for malignancy.
  • Clinical history and risk assessment are crucial in guiding the workup of SPNs.