Viral Pneumonia

Jud W. Gurney, MD, FACR

Key Facts

Terminology

Pulmonary infection with viral pathogen typically affects respiratory epithelium from trachea to terminal bronchioles
Pneumonic (alveolar involvement) less common but often severe and rapidly progressive

Imaging Findings

Centrilobular nodules 4-10 mm in diameter and ground-glass opacities in peribronchial distribution
Course
- Insidious: Tracheobronchitis, typically slow development over 7-14 days
- Fulminant: Pulmonic pattern, typically rapid progression disease from noncardiogenic edema or hemorrhage
- Late: Bronchiolitis obliterans due to damage of small airways
Bacterial superinfection, consider if sudden worsening, development of cavitation, or enlarging pleural effusion

Top Differential Diagnoses

Pathology

Portal of entry
- Inhalation droplets or contact with contaminated surfaces (droplets may remain viable for 24-48 hours)

Axial NECT shows centrilobular nodules

with indistinct ground-glass edges. Note the faint tree-in-bud opacities in the left upper lobe

Axial NECT shows centrilobular nodules

admixed with ground-glass opacities

in this patient with community-acquired pneumonia from viral pneumonia.

TERMINOLOGY

Abbreviations and Synonyms

Cytomegalovirus (CMV), severe acute respiratory syndrome (SARS), Epstein-Barr virus (EBV)

Definitions

Pulmonary infection with viral pathogen, typically affects respiratory epithelium from trachea to terminal bronchioles
- Pneumonic (alveolar involvement) less common but often severe and rapidly progressive

IMAGING FINDINGS

General Features

Best diagnostic clue: Centrilobular nodules and ground-glass opacities in peribronchial distribution
Patient position/location: Peribronchial centrilobular nodules
Size: Centrilobular nodules 4-10 mm in diameter
Morphology: Centrilobular nodules in patchy distribution most helpful finding to distinguish infectious vs. noninfectious disease

CT Findings

Variable and nonspecific appearance
Bronchiolitis (small airways involvement)
- Centrilobular nodules
  - 4-10 mm in diameter, may be miliary
  - Patchy peribronchial distribution
  - Ill-defined edges, may have ground-glass halos
  - Usually associated with background of ground-glass opacities
  - Pathologic correlate: Viral involvement of terminal airways
- Mosaic attenuation (correlate of hyperinflation)
- Tree-in-bud opacities less common than in bacterial pneumonia
Tracheobronchitis (larger airways involvement)
- Bronchial wall thickening
- Segmental consolidation
Pneumonic (lung involvement)
- Consolidation and ground-glass opacities
  - Pathologic correlate: Noncardiogenic pulmonary edema or diffuse hemorrhage
- Distribution: Focal or diffuse
- Thickened interlobular septa
Course
- Insidious: Slow development over 7-14 days
  - Primary pattern: Centrilobular nodules
- Fulminant: Rapid progressive disease
  - Primary pattern: Diffuse ground-glass opacities and consolidation
- Late: Bronchiolitis obliterans
  - Pathologic correlate: Healed response to damage of small airways
  - Uncommon, lung usually returns to normal

Radiographic Findings

Imaging Recommendations

Best imaging tool
- Chest radiography: Usually sufficient for documenting pattern and extent of disease and monitoring therapy
- CT: More sensitive; important in immunocompromised patients to document disease and begin early treatment

DIFFERENTIAL DIAGNOSIS

Hypersensitivity Pneumonitis