 Other histopathologic findings include fibrosis, bronchial artery neovascularization, venous remodeling, bronchiolitis, hemosiderin accumulation, increased tissue cellularity (i.e.hemosiderophages), multifocal areas of inflammation, and increased thickness of vascular and airway walls.EIPH occurs when blood enters the air passages of a horse's lung, due to fractured capillaries.