Pulmonary Emphysema

Interstitial emphysema (Image sourced from Bristol Biomed Image Archive with permission)

Histology of interstitial emphysema (Image sourced from Bristol Biomed Image Archive with permission)

Alveolar emphysema(Image sourced from Bristol Biomed Image Archive with permission)

Destructive emphysema - horse(Image sourced from Bristol Biomed Image Archive with permission)

• Excessive amount of air within the lungs
• In animals it is always secondary to other lesions
• In severe cases, the lungs fail to deflate upon opening the thoracic cavity, there are imprints of the ribs on the pleural surface of the lung

• Interstitial emphysema
  • The presence of air within the connective tissues and lymphatics of the lung
  • Mainly interlobular septae - also subpleural and around vessels/ airways
  • It implies that there is forced respiration
  • Mainly significant in the cow which by the nature of its well developed interlobular septae is susceptible to the lesion
  • It is not an uncommon agonal (to a minor degree as a reaction to slaughter in normal animals) event in the cow
  • More significantly, it is a prominent feature of acute interstitial pneumonia, chronic pneumonia, RSV infection, Acute Bovine pulmonary Edema and Emphysema in cattle

• Alveolar emphysema
  • The term ‘emphysema’ strictly speaking refers to alveolar emphysema and is classified by human pathologists as : "A condition of the lung characterised by abnormal, permanent enlargement of the air spaces …. Accompanied by destruction of their walls and without obvious fibrosis"
  • Permanent abnormal enlargement of airspaces distal to the terminal bronchioles with evidence of destruction of the alveolar walls, usually proteolytic digestion of elastin by macrophages
  • Forms air bubbles in pulmonary parenchyma
  • The mechanism is poorly understood but involves excessive macrophage activity in the alveoli due to chronic bronchiolitis, partial obstruction of the bronchioles; and the force of inspiration being greater than that of expiration
  • Naturally occurring emphysema is, however of little clinical significance in domestic animals with the following exceptions :
    • Congenital lobar emphysema in dogs - occurs secondary to aplasia or hypoplasia of bronchial cartilage.
    • Chronic obstructive pulmonary disease in the horse (COPD) Note, however, that emphysema is an inconsistent feature of the pathology in this disease.
    • In older animals, there may be a degree of alveolar emphysema along the ventral borders of lung lobes, however, it is of little clinical significance

• Compensatory
  • Adjacent to an area of consolidation (inflammation)
  • Consolidation tends to reduce the lung volume, the thoracic cavity remains the same volume and some lobules undergo a slight degree of emphysema
  • Gross pathology:
    • Alveolar - affected part enlarged and paler than normal
    • Interstitial - prominent gas-filled interlobular septa
  • Micro pathology:
    • Alveolar - enlarged airspaces with destruction of intervening capillary walls, the free ends of the broken walls may thickened due to retraction
    • Interstitial - septal lymphatics dilated with air; in unresolved chronic pneumonias in cattle, this emphysema may spread to the local lymphatics and even to the subcutaneous tissue along the back of the animal