Purpura without vessel structural damage

Experiments on an animal model for vascular lesions, the chicken comb model, have demonstrated a bluish-grey discoloration phenomenon similar to that observed immediately after pulsed dye laser treatment of port wine stains. In the model, erythrocytes and cell nuclei are found in the extravascular matrix even where there is no sign of vessel wall rupture. It is believed that the vapour pressure of the boiling blood forces erythrocytes through passages in an elastically expanding vessel wall.