Stage
Stage
Histopathology

Exudative (1)

0-7days
  • Acute inflammatory reaction in the lung caused by insult to the epithelium
  • Alveoli fill with neutrophils, blood and a protein-rich pulmonary oedema (0.5)
  • Associated alveolar epithelial and capillary endothelial damage, with loss of alveolar cells and structural integrity (0.5)
  • Hyaline membranes form composed of cellular debris and plasma proteins (peak 4–5 days) (0.5)
  • Destruction of the pulmonary vascular bed
  • Dysregulation of coagulation and fibrinolysis leads to microthrombus formation
  • Capillary thrombosis occurs (0.5)

    (Max 1)

Proliferative (1)

7-14 days
  • Proliferation of type II pneumocytes and fibroblasts (0.5)
  • Fibrin deposition (0.5)

    (Max 1)

Fibrotic (1)

>14 days
  • Chronic inflammation and fibrosis (0.5)
  • Neovascularization (0.5)
  • Global damage to underlying lung tissue

    (Max 1)