The Pathologist's Approach to Acute Lung Injury

Context.—Acute lung injury and acute respiratory distress syndrome are significant causes of pulmonary morbidity and are frequently fatal. These 2 entities have precise definitions from a clinical standpoint. Histologically, cases from patients with clinical acute lung injury typically exhibit diffuse alveolar damage, but other histologic patterns may occasionally be encountered such as acute fibrinous and organizing pneumonia, acute eosinophilic pneumonia, and diffuse hemorrhage with capillaritis. Objective.—To review the diagnostic criteria for various histologic patterns associated with a clinical presentation of acute lung injury and to provide diagnostic aids and discuss the differential diagnosis. Data sources.—The review is drawn from pertinent peer-reviewed literature and the author's personal experience. Conclusions.—Acute lung injury remains a significant cause of morbidity and mortality. The pathologist should be aware of histologic patterns of lung disease other than diffuse alveolar damage, which are associated with a clinical presentation of acute lung injury. Identification of these alternative histologic findings, as well as identification of potential etiologic agents, especially infection, may impact patient treatment and disease outcome.