Cryptogenic Organizing Pneumonia

Jud W. Gurney, MD, FACR

Key Facts

Terminology

Clinicopathological entity characterized by polypoid plugs of loose granulation tissue within air spaces

Imaging Findings

Multiple alveolar opacities (90%)
- Either subpleural or peribronchial, oval or trapezoid in shape
- May be migratory and wax and wane
- Air-bronchograms (often dilated) common
Perilobular pattern
- Consolidation outlines periphery of secondary pulmonary lobule
Reverse halo sign
- Central ground-glass opacity surrounded by denser crescentic (semicircular to circular) consolidation at least 2 mm in thickness
Solitary alveolar opacity (10%) mimics bronchogenic carcinoma

Top Differential Diagnoses

Chronic Eosinophilic Pneumonia
Bronchioloalveolar Cell Carcinoma
Sarcoidosis, Alveolar

Pathology

Polypoid granulations tissue in bronchiolar lumen (Masson bodies) and alveolar ducts associated with variable interstitial and airspace infiltration by mononuclear cells and foamy macrophages

Clinical Issues

Subacute symptoms over weeks
Treatment corticosteroids, relapses (despite treatment) in over 50%

Axial HRCT shows peribronchial consolidation, ground-glass opacities

, and irregular subpleural mass-like consolidation

Axial HRCT show a large area of consolidation

and smaller peribronchial consolidation

from cryptogenic organizing pneumonia.

TERMINOLOGY

Abbreviations and Synonyms

Cryptogenic organizing pneumonia (COP), secondary organizing pneumonia (SOP), proliferative bronchiolitis, idiopathic bronchiolitis obliterans organizing pneumonia (BOOP)

Definitions

Clinicopathological entity characterized by polypoid plugs of loose granulation tissue within air spaces

IMAGING FINDINGS

General Features

Best diagnostic clue: Bilateral, peripheral, basal, nodular consolidation
Patient position/location: Typically in mid and lower zones
Size: Tiny nodules to whole lobes

CT Findings

Multiple patterns
- Multiple alveolar opacities (90%)
  - Size of consolidation from few cm in size to whole lobe
  - Often admixed with ground-glass opacities
  - Air-bronchograms common, often dilated
  - Bilateral, lower zones
  - Lung volumes preserved
  - Axial plane: Subpleural or bronchovascular (75%)
  - May be migratory and wax and wane over weeks to months
  - More common in immunocompetent compared to immunocompromised patients
  - Presence of consolidation associated with greater likelihood of partial or complete response to treatment
- Multiple pulmonary nodules (10%)
  - < 5 mm diameter (40%), > 5 mm diameter (60%)
  - May have air-bronchograms
  - No zonal predominance
Solitary alveolar opacity (10%)
- Mimics bronchogenic carcinoma
- < 3 cm (60%) or > 3 cm diameter (40%)
  - Median diameter 1.9 cm
- More common upper lung zones (60%) vs. lower lung zones (40%)
- Subpleural (40%), peripheral bronchovascular (33%), or peripheral (30%)
- Round (30%); flat, oval, or trapezoidal (70%)
- Pleural tag (50%)
- Irregular margin (spiculated) (95%)
- Satellite nodules (55%)
- Vessels converge at edge of lesion (80%)
- May be cavitary
Reticular interstitial pattern (< 10%)
- Overlaps with idiopathic pulmonary fibrosis or nonspecific interstitial pneumonia
- Signifies fibrosis
Associated findings in patients with multiple alveolar opacities
- Band-like opacities, 2 patterns
  - Linear opacities paralleling bronchial course toward pleura
  - Subpleural lines, unrelated to bronchi
- Pleural effusions less common (10%), when present small
- Mediastinal adenopathy (20%)
Perilobular pattern
- Consolidation outlines periphery of secondary pulmonary lobule
- May form arcades and polygonal opacities that extend to pleural surface like fish scales or tiles on a roof (imbricate)
- Perilobular consolidation not as sharply defined as thickened interlobular septa in pulmonary edema
- More predominant in mid and lower lung zones
- Seen in 50% but not specific for COP
Reverse halo sign
- Central ground-glass opacity surrounded by denser crescentic (semicircular to circular) consolidation at least 2 mm in thickness
- Also known as atoll sign
- Seen in 20% but not specific for COP
  - Also described in lymphomatoid granulomatosis and paracoccidioidomycosis

Radiographic Findings

Radiography
- Findings less well identified compared to CT
- Focal or multifocal consolidation, remains chronic after course of antibiotic therapy; clue to conditions that give chronic consolidation pattern
  - Chronic consolidation arbitrarily defined as persistent more than 30 days
- Differential for chronic consolidation
  - Bronchioloalveolar cell carcinoma
  - Cryptogenic organizing pneumonia
  - Alveolar sarcoidosis
  - Alveolar proteinosis
  - Lymphoma or pseudolymphoma
  - Chronic eosinophilic pneumonia
  - Lipoid pneumonia
  - Chronic aspiration

DIFFERENTIAL DIAGNOSIS

Chronic Eosinophilic Pneumonia

Usually in upper lung zone (eosinophilia absent in COP)
Nodules, nonseptal linear pattern, reticulation and peri-bronchiolar distribution more common in COP
Septal lines more common in chronic eosinophilic pneumonia

Bronchioloalveolar Cell Carcinoma (BAC)

BAC not predominately subpleural
Foci usually predominantly ground-glass opacities

Sarcoidosis, Alveolar

Few large airspace masses with air-bronchograms
Preferentially involves upper lung zones
Usually associated with symmetric hilar and mediastinal adenopathy

Lung Cancer (Solitary Mass)

Organizing pneumonia more commonly has
- Broad contact with pleura or centered on bronchi
- Flat, oval, or trapezoidal shape
- Satellite lesions

Aspiration

Opacities not as chronic or peripheral as COP
Predominately in dependent lung segments
Typical predisposing conditions: Esophageal motility disorder, obtundation, alcoholism

Lipoid Pneumonia