Diffuse alveolar damage.

Diffuse alveolar damage (DAD) is a characteristic histopathologic pattern that has time dependent findings: intraalveolar and interstitial oedema, and hyaline membranes in the acute phase, myofibroblastic accumulation in the alveolar spaces and type II alveolar cell proliferation in the proliferative phase and fibrosis in the more advanced phases. The diagnosis of DAD is sometimes feasible on small specimens obtained by transbronchial lung biopsy or on cytological slides. Surgical lung biopsy is rarely needed.