Bronchopneumonia

Chronic bronchopneumonia (Image sourced from Bristol Biomed Image Archive with permission)

• Originates and extends from terminal bronchioles
• Acute inflammatory exudate initially fills alveolar spaces radiating from the bronchioles causing areas of solidification of lung tissue termed consolidation
• In bronchopneumonia this consolidation is oriented around terminal bronchioles
• Most commonly occurs in cranioventral lung lobes and correlates with aerogenous portal of entry and gravitation of infectious droplets
• Most common form of pneumonia seen in domestic animals and the most common causes are bacterial and mycoplasma infections or aspiration
• Gross pathology:
  • Affected parts are firmer (consolidated) than surrounding non-affected tissue
  • Colour varies from red to pink to grey depending upon the stage of infection
  • Extent of the lesion varies with the aetiological agent and the lobulation/septation of the species
• Micro pathology:
  • Early cases centred upon the bronchiolar alveolar junction with exudation, which extends into neighbouring alveoli
  • Exudate contains many neutrophils, macrophages and oedema
  • Alveolar capillaries are hyperaemic
  • Some haemorrhages in severe cases - later stages contain more cells than fluid
• Spread of the inflammation within the lung is usually by extension from lobule to lobule along the airways, or by necrosis of alveoli and septa in the case of toxin-producing bacteria
• Sequel to bronchopneumonia:
  • Mild catarrhal inflammation resolves in 7 days and the lung is back to normal within 3 weeks
  • More severe inflammation becomes chronic with fibrosis or bronchiectasis
  • Abscess formation with pyogenic bacteria
  • Pleuritis in severe fibrinous pneumonia with adhesions
  • Death in fulminating cases due to hypoxaemia and toxaemia

• Suppurative bronchopneumonia
  • Purulent or mucopurulent exudate in airways
  • Generally confined to individual nodules, more obvious in species with prominent lobulation
  • Sometimes referred to as lobular pneumonia
  • Lung colour changes from red to grey to white with time
  • Good exapmle are enzootic pneumonias of cattle, sheep and pigs
• Fibrinous pneumonia
  • Predominantly fibrous exudate
  • Exudate moves through pulmonary tissue to involve whole lung lobe
  • Sometimes referred to as lobar pneumonia (below)
  • Generally more severe than suppurative pneumonias
  • Externally - severe congestion and haemorrhage, intense red colour with fibrinous plaques
  • May develop into sequestra of necrotic tissue encapsulated by connective tissue
  • Microscopically - massive exudation of plasma proteins into bronchioles and alveoli
  • Rarely resolves completely, leaves scars - pulmonary fibrosis and pleural adhesions