Comments

Note that the pulmonary vessels are the only structures seen within the air-filled lung. They branch, taper, and are barely visible as they reach the pleura. Bronchi are barely visible beyond the inner half of the lung.

Comments

This is like looking at the anatomy through a frosted shower door or glass. The lung is an intermediate shade of gray but the pulmonary vessels are visible within the grey areas. The diminished aeration may be due to (1) decreased air in the alveoli caused by partial alveoli filling, (2) decreased air in the alveoli caused by thickened interstitium encroaching on the alveoli, or (3) decreased air in the alveoli due to hypoventilation and atelectasis.

Causes

• 
  

  atelectasis

  
  
• 
  

  aspiration pneumonitis

  
  
• 
  

  infection, such as pneumocystis

  
  
• 
  

  edema, acute respiratory distress syndrome (ARDS)

  
  
• 
  

  pulmonary hemorrhage

  
  
• 
  

  idiopathic (e.g., desquamative interstitial pneumonitis, chronic organizing pneumonia)

Comments

Acute or chronic thickening of the interlobular septa or the bronchovascular bundles cause linear or lacelike thickening. This may be smooth or irregular.

Causes

• 
  

  edema (Kerley lines)

  
  
• 
  

  lymphangitic tumor

  
  
• 
  

  sarcoidosis

  
  
• 
  

  Langerhans histiocytosis (eosinophilic granuloma)

  
  
• 
  

  fibrosis (any cause)

Comments

Tiny, sharp, discreet nodules (<3 mm) are seen throughout the lung. They are generally the size of birdseed (millet seeds). It is often difficult to detect the individual nodules on chest x-ray but not on computed tomography (CT).

Causes

• 
  

  miliary disease, hematogenous spread of granulomas infection (tuberculosis or fungal).

  
  
• 
  

  metastatic cancer

  
  
• 
  

  silicosis

  
  
• 
  

  sarcoidosis