Pathophysiology

1. dual circulation
   • usually from bronchial arteries and collaterals from axillary, intercostal, diaphragmatic and systemic arteries of thorax
   • 10% cases bleed from pulmonary arteries, capillaries or veins
2. vascular mechanisms
   • aneurysm formation
   • vasculitis
   • pulmonary embolism
   • inflammation
   • broncholithiasis
   • direct invasion central pulmonary artery trauma