Viral Pneumonia



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



  • Hypersensitivity Pneumonitis


  • Bacterial Pneumonia


  • Mycobacterial Avium Complex


Pathology



  • Portal of entry



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







Axial NECT shows centrilobular nodules image with indistinct ground-glass edges. Note the faint tree-in-bud opacities in the left upper lobe image.






Axial NECT shows centrilobular nodules image admixed with ground-glass opacities image 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



  • Radiography



    • Variable and overlapping appearance


    • Tracheobronchitis



      • Often normal


      • Segmental opacities (from airway obstruction or pneumonia)


      • Atelectasis: Discoid to segmental atelectasis (from mucus plugs)


    • Bronchiolitis



      • Vague small nodular opacities, patchy distribution


      • Bronchial wall thickening


      • Hyperinflation (less common in adults than in children)


    • Pneumonia



      • Diffuse consolidation from noncardiac edema or hemorrhage, normal heart size


      • Pleural effusions, if present, small


    • Complications



      • Bacterial superinfection; consider if sudden worsening, development of cavitation, or enlarging pleural effusion


    • Uncommon findings



      • Hilar or mediastinal adenopathy: Measles (in children), EBV (infectious mononucleosis)


    • Splenomegaly



      • EBV (infectious mononucleosis)


    • Cardiac enlargement from pericardial effusion



      • Hantavirus


    • Pleural effusions



      • Rare except for adenovirus, measles, hantavirus, herpes simplex type 1


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



  • Farmer’s lung often mistaken for pneumonia: Tends to be recurrent with repeated exposure to offending antigen


  • May also be febrile


Bacterial Pneumonia



  • Patchy centrilobular nodules more common in viral or atypical pneumonias


  • Culture required for management

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Sep 20, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Viral Pneumonia

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