Acute lung injury

Acute lung injury pattern is a term originally coined by Katzenstein1 to encompass the entities of diffuse alveolar damage (DAD) and bronchiolitis obliterans-organizing pneumonia (BOOP). The term was meant to emphasize the relatively acute clinical onset of both entities, as well as the histologic temporal uniformity resultant from a single pulmonary insult occurring at a single moment in time. Both entities tend to show active fibroblastic proliferation rather than the dense collagen seen in more chronic processes. The term is also useful in the setting of small biopsies when precise classification may not be possible due to sampling issues. The term acute lung injury pattern as Katzenstein defined it refers to the pathologic findings, and should not be confused with the clinical definition of acute lung injury discussed below, although most patients with DAD fulfill the clinical definition as well.2