Panel A (original X 5), case 3, initial biopsy: this field shows variably fibrotic alveolar septae along with a small interstitial nonnecrotizing granuloma, a combination of findings typical of chronic hypersensitivity pneumonitis that has begun to fibrose. Panel B (original X 10), case 3, initial biopsy: this field shows peribronchiolar poorly formed nonnecrotizing granulomas and chronic inflammation.
Panel C (original X 2), case 1, biopsy at exacerbation: this low-power field shows an area of dense subpleural fibrosis (upper left), adjacent to a region of acute DAD characterized by thick eosinophilic fibrinous exudates (hyaline membranes) lining alveolar septae. Panel D (original X 10), case 1, biopsy at exacerbation: this high-power field shows dense eosinophilic hyaline membranes lining alveolar spaces. The septae contain highly reactive pneumocytes and show early fibroblastic expansion.
Panel E (original X 0.5), case 3, explanted lung: organizing acute lung injury is visible in the left side of this low-power field; there is the relatively diffuse septal expansion by fibroblastic tissue and airspace accumulation of fibrin and hemorrhage. In contrast, the right side of the field shows large cystically dilated spaces, or honeycombing, that indicates regions of preexisting advanced fibrosis. Panel F (original X 10), case 3, explanted lung: this high-power view shows the diffuse septal expansion by loose myxoid fibroblastic tissue admixed with chronic inflammatory cells.
In the organizing phase of DAD, most of the airspace fibrin and hemorrhage has been removed, and the airspace contains only scattered hemosiderinladen macrophages. There was no evidence of capillaritis, and immunohistochemical stain results were negative at autopsy. Concurrent DAH appears to be a rare histopathologic finding in AEs, as we are aware of only one case of AE-IPF presenting with both organizing DAD and DAH. The patient in this case report died within 3 days of hospitalization. Histopathology demonstrating lone idiopathic DAD, clinically termed acute interstitial pneumonia, or Hamman-Rich syndrome, is frequently associated with evidence of alveolar hemorrhage on BAL.