ABSTRACT
The pathological features of the lung in the acute respiratory distress syndrome (ARDS) have been collectively labeled diffuse alveolar damage (DAD) and represent a timedependent, stereotypic response to alveolar injury (1). DAD can be conveniently divided into three sequential and overlapping phases: the exudative phase of edema and hemorrhage, the proliferative phase of organization and repair, and the fibrotic phase of end-stage fibrosis (1-4) (Table 1). The latter two phases are frequently merged and designated as the fibroproliferative phase. For an individual patient, the histological features of DAD correlate more with the duration of injury than its initiating cause. Permeability pulmonary edema, an important consequence of acute alveolar injury, is prominent in the early stages and heralds the onset of rapidly progressive pulmonary fibrosis, which dominates the later course of the disease and is often a limiting factor for survival. In this chapter, each of the phases of DAD will be described separately and morphological features will be correlated with clinical events and proposed mechanisms of injury.
