• Based on Size <3cms

  • Single or Multiple
  • Macronodules
  • Micronodules

• Based on Shape

  • Round
  • Stellate or Spiculated

• Based on Position

  • Centrilobular

  • 

• Based on Character

  1. Solid
  2. Subsolid
  3. Ground Glass 
  4. Calcified

Lung nodules, by definition are less than 3 centimeters in diameter and are quite common. Lung nodules can be categorized based on their appearance, size, and other characteristics. The most common types of lung nodules seen on CT scans include:

Solitary pulmonary nodule (SPN): This refers to a single lung nodule that appears as a well-defined round or oval lesion in the lung tissue.

Lung Nodule

• What is it:
  • A lung nodule is a small, round or oval lesion within the lung parenchyma.
  • It measures up to 3 cm in diameter; lesions larger than 3 cm are classified as masses.
• Etymology:
  • Derived from the Latin word nodulus, meaning “small knot,” emphasizing its discrete and localized nature.
• AKA:
  • Pulmonary nodule.
• Abbreviation:
  • LN (Lung Nodule).
• How does it appear on each relevant imaging modality:
  • Chest CT (preferred):
    • Parts: Can be solid, subsolid (part-solid), or ground-glass (GGN).
    • Size: Up to 3 cm in diameter; typically categorized into:
      • Small nodules (<8 mm).
      • Larger nodules (≥8 mm).
    • Shape: Typically round or oval with smooth or irregular margins.
    • concerning when it is spiculated
    • Position: Can occur in any lung lobe; may be single or multiple.
      • upper lung predominance
        • Common Causes:
          • Infection:
            • Tuberculosis (TB): Upper lobes are frequently affected due to higher oxygen tension, which supports the growth of Mycobacterium tuberculosis.
            • Fungal infections (e.g., histoplasmosis, aspergillosis).
          • Inflammation:
            • Sarcoidosis: Typically shows nodules in a perilymphatic distribution, often involving the upper lobes.
          • Neoplasm:
            • Primary lung cancers (e.g., adenocarcinoma, squamous cell carcinoma): More common in upper lobes, especially in smokers.
            • Pancoast tumors: Appear at the lung apex, a subset of upper lobe malignancies.

        Lower Lobe Nodules

        • Common Causes:
          • Infection:
            • Aspiration pneumonia: Often localized to the lower lobes due to gravity-dependent positioning.
            • Pulmonary abscess.
          • Inflammation:
            • Rheumatoid nodules and interstitial lung diseases (ILDs) such as nonspecific interstitial pneumonia (NSIP) commonly involve lower lobes.
          • Neoplasm:
            • Metastatic disease: Often found in the lower lobes due to the distribution of blood flow (hematogenous spread).

        Peripheral vs. Central Distribution

        • Peripheral nodules: Often associated with infections (e.g., fungal or septic emboli), metastatic disease, or inflammatory conditions like eosinophilic granuloma or organizing pneumonia.
        • Central nodules: More likely to be due to malignancy (e.g., squamous cell carcinoma), endobronchial infections, or lymph node enlargement.

        Diagnostic Implications of Position:

        1. Upper lobe nodules with a history of smoking or systemic symptoms are more concerning for malignancy or TB.
        2. Lower lobe nodules in patients with risk factors for aspiration or systemic infections (e.g., immunosuppression) are more likely infectious or inflammatory.
        3. Multiple nodules in specific regions (e.g., perilymphatic in sarcoidosis or random in metastasis) further refine the differential diagnosis.
    • Character:
      • Calcifications:
        • Central,
        • laminated,
        • popcorn-like (benign), or
        • eccentric (malignant).
      • Enhancement: Malignant nodules often show significant contrast uptake (>15 HU).
  • Chest X-ray:
    • Appears as a well-defined, round opacity; small nodules may not be detected.
  • PET-CT:
    • High SUV uptake (>2.5) suggests malignancy.
    • False positives can occur with infectious or inflammatory nodules.
• Differential diagnosis 
  • Infection:
    • Granulomas (e.g., tuberculosis, histoplasmosis, coccidioidomycosis).
    • Pulmonary abscess (in early stages).
  • Inflammation:
    • Rheumatoid nodule.
    • Sarcoidosis.
  • Neoplasm:
    • Benign: Hamartoma.
    • Malignant: Primary lung cancer (e.g., adenocarcinoma, squamous cell carcinoma), metastases.
  • Mechanical: Rounded atelectasis.
  • Circulatory: Pulmonary infarct (may mimic a nodule).
  • Idiopathic: Cryptogenic organizing pneumonia (COP).
  • Iatrogenic: Post-radiation fibrosis with nodule formation.
• Recommendations:
  • Further evaluation:
    • Low-dose chest CT for characterization and follow-up.
    • PET-CT for nodules ≥8 mm with suspicious features.
    • Biopsy (CT-guided or bronchoscopic) for indeterminate or enlarging nodules.
  • Surveillance:
    • Follow-up intervals based on nodule size and risk factors per guidelines (e.g., Fleischner Society).
• Key considerations and pearls:
  • Nodules <8 mm are often benign but require surveillance in high-risk individuals.
  • Calcifications and fat within a nodule strongly suggest benign etiology (e.g., hamartoma).
  • Spiculated margins, rapid growth, and high SUV uptake are concerning for malignancy.
  • Clinical history (e.g., smoking, prior malignancy, exposure to infectious agents) is essential for guiding the differential diagnosis.

 

Solid pulmonary nodule: These nodules appear as well-defined, dense lesions with a uniform density throughout. They can be benign or malignant.

Multiple pulmonary nodules: Sometimes, more than one nodule can be present in the lungs. These can be caused by various conditions such as metastases from cancer or infectious diseases.

Ground-glass opacity (GGO): GGO appears as hazy, increased lung density that does not obscure the underlying bronchial structures. It can be a sign of various conditions, including early-stage lung cancer or inflammation.

1. Ground Glass Opacity and Adenocarcinoma with Lepidic Growth

The Ground Glass Opacity (GGO) in this case  is  caused by partial filling of the alveolus with malignant cells                                                                                                                                                        Ground glass opacification may be caused by partial filling of the alveolus with cellular material resulting in  partial replacement of air with solid material.  The net density is gray rather than white in the situation where the  alveolus is fully replaced with cells or fluid. There is blending of the black of the subtending airways and  the white of the vessels  with the gray density of the cellular infiltrate and hence the normal vessels are not visualized in ground glass opacities.

Part-solid nodule: Part-solid nodules have both solid and ground-glass components. These can also be associated with lung cancer, particularly adenocarcinoma.

 

Calcified nodules:

Some lung nodules may contain calcium deposits, causing them to appear as dense spots on the CT scan. These are often benign and can result from previous infections or scarring.

 

Cavitating Nodule

Pseudocavitation