Table 1

Summary of some histopathological changes in ARDS

	Exudative phase	Proliferative phase	Fibrotic phase
Macroscopic	• Heavy, rigid, dark	• Heavy, grey	• Cobblestoned

Microscopic	• Hyaline membranes	• Barrier disruption	• Fibrosis
	• Oedema	• Oedema	• Macrophages
	• Neutrophils	• Alveolar type II cell proliferation	• Lymphocytes
	• Epithelial>endothelial damage	• Myofibroblast infiltration	• Matrix organisation
		• Neutrophils	• Deranged acinar architecture
		• Alveolar collapse	• Patchy emphysematous change
		• Alveoli filled with cells and organising matrix
		• Epithelial apoptosis
		• Fibroproliferation

Vasculature	• Local thrombus	• Loss of capillaries	• Myointimal thickening
		• Pulmonary hypertension	• Tortuous vessels