Pulmonary Emphysema
- 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