Chest ImagingViral pneumonia
lung infection, mainly due to the respiratory viruses. The influenza and parainfluenza groups are responsible for the majority of the epidemic viral pneumonias occurring in adults during late winter. Adenovirus and picornavirus cause nonepidemic respiratory infections. Respiratory syncytial virus is responsible for the majority of the epidemic lower respiratory tract infections in children. Other viruses, such as cytomegalovirus, herpes simplex, varicella-herpes zoster may cause pneumonia as part of the systemic infection.
The infection usually begins in the central airways. The chest radiograph is normal or shows bronchial wall thickening, reticular opacity and increased lung markings. When the small airways are involved, a bronchiolitis develops and airway obstruction may cause diffuse overinflation and air trapping in infants and young children. When the infection spreads to the alveoli, the disease remains limited to the parenchyma around the terminal bronchioles. As a result, the radiographic features consist of a reticulonodular pattern with focal and patchy areas of consolidation involving multiple lobes.
On CT scans, infectious bronchiolitis is seen as centrilobular nodules and tree in bud sign.
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