Histopathology of pulmonary capillaritis

Lung histopathology from a patient with pulmonary capillaritis causing diffuse alveolar hemorrhage. Note the alveolar septal infiltration by neutrophils, which stream along the septal capillaries (arrow). Red cells admixed with neutrophils are seen leaking from the affected septa, resulting in marked accumulation within alveolar spaces (star). Nuclear fragmentation of neutrophils is present within the septa but not in alveolar space (Hematoxylin-eosin; magnification: x400).