• Synonym: proliferative bronchiolitis obliterans
  
• Patchy peripheral consolidation, slight preference for lower lung zones
  
• Other patterns: lobular sized nodules, solitary mass, diffuse interstitial thickening
  
• Causes: idiopathic, infection, drugs, transplants, toxic fume inhalation
• Cough, SOB, low grade fever
  
• Restrictive pulmonary function tests
  
• Steroid responsive

Chest radiograph

• Patchy, bilateral variable sized areas of consolidation
  
• Unilateral 5%
  
• Favors the lower lung zones
  
• Normal heart size, no adenopathy
  
• Lung volumes preserved
  
• Less common: solitary mass (usually upper lung zone)
  
• Less common: diffuse reticular interstital thickening
  
• May wax and wane (also termed migration)

CT/HRCT

• Peripheral opacities range from ground glass density to consolidation
  
• Consolidation often triangular in shape
  
• Consolidation may extend along bronchi (peribronchovascular pattern)
  
• Mild mediastinal adenopathy common (not seen chest radiographs)
  
• Lobular sized nodules with well defined margins in random distribution
  
• Diffuse reticular interstitial thickening primarily basilar, less common
  
• Solitary mass may have air bronchograms or cavitate, usually upper lobe location
  
• Occasional small effusion

• Chronic eosinophilic pneumonia
• Usual interstital pneumonia (UIP)
  
• Lymphoma
  
• Bronchioloalveolar cell carcinoma (BAC)
  
• Sarcoid
  
• Lung cancer (solitary mass)
  
• Mycobacterial infection
  
• Lipoid pneumonia
  
• Differentiation
• Eosinophilic pneumonia usually upper lung zone, eosinophilia absent in BOOP
  
• UIP- honeycombing and decreased lung volumes absent in BOOP
  
• Solitary form usually resected on premise that it is lung cancer
  
• Lymphoma and BAC not peripherally predominant, BAC usually ground glass density
  
• Lipoid pneumonia may have fat density in areas of consolidated lung at CT

• Buds of loosely organized granulation tissue extends through pores of Kohn to next alveolus (“butterfly” pattern)
  
• Granulation tissue extends into airway lumen (Bronchiolitis component)
  
• Mononuclear cell interstitial infiltration
  
• Lung architecture preserved (no fibrosis)
  

  Causes

  • Idiopathic
    
  • Infection (mycoplasma, viruses, atypical bacteria)
    
  • Drugs (amiodarone, bleomycin, sulfasalazine)
    
  • Connective tissue disease (rheumatoid arthritis, Sjögrens)
    
  • Transplant (lung, bone marrow)
    
  • Toxic fume inhalation (silo fillers disease)
    
  • Radiation therapy
    
  • Aspiration
    
  • Wegener’s

• Adults, no gender preference
  
• Cough
  
• SOB
  
• Low grade fever
  
• PFT’s usually restrictive, maybe mixed restrictive and obstructive

  Treatment

  • Steroids, less dramatic response then eosinophilic pneumonia
    
  • Resolves over period of weeks
    
  • May relapse on discontinuation of steroids

Davison AG, Heard BE, McAllister WA, et al. Cryptogenic organizing pneumonitis Q J Med 52:382-394, 1983
Lee KS, Kullnig P, Hartman TE, et al. Cryptogenic organizing pneumonia: CT findings in 43 patients AJR 162:543-546, 1994
Cordier JF. Organising pneumonia Thorax 55:318-328, 2000