Acute pulmonary hemorrhage is frequently seen in biopsies as a procedural artifact of the biopsy of this highly vascular organ. Lung trauma secondary to motor vehicle accidents, diving accidents, drowning or near drowning, for example, can also produce similar histologic changes. Localized pulmonary hemorrhage may be seen adjacent to, as well as involving, neoplasms, thromboemboli, pneumonia, and airway ulceration. Coagulopathy-associated pulmonary hemorrhage can appear identical to procedure-induced hemorrhage, and in these cases, clinical history, laboratory findings, and the presence of hemosiderin-laden macrophages, provide a clue to the underlying cause of hemorrhage. Idiopathic pulmonary hemosiderosis is a rare cause of hemorrhage without other histologic abnormalities. Changes of acute lung injury, erythrophagocytosis, or hemosiderin-laden macrophages strongly suggest hemorrhage attributable to an underlying process or disease.

Bacterial infections, including mycobacterial infections, with or without associated lung abscess, bronchiectasis, or bronchitis, may cause pulmonary hemorrhage, with potential bacterial etiologies including Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Viral infections, including cytomegalovirus and herpesvirus, may also cause pulmonary hemorrhage. In endemic areas, paragonimiasis is a parasitic cause of pulmonary hemorrhage. Fungal infections, with or without fungal invasion or mycetoma, may be a cause of pulmonary hemorrhage. Candida and Aspergillus organisms are two potential etiologies, among other fungal organisms.