Pathology.—The term acute interstitial pneumonia is reserved for diffuse alveolar damage of unknown cause. The acute phase is characterized by edema and hyaline membrane formation. The later phase is characterized by airspace and/or interstitial organization (5). The histologic pattern is indistinguishable from that of acute respiratory distress syndrome.
Radiographs and CT scans.—In the acute phase, patchy bilateral ground-glass opacities are seen (6), often with some sparing of individual lobules, producing a geographic appearance; dense opacification is seen in the dependent lung (Fig 1). In the organizing phase, architectural distortion, traction bronchiectasis, cysts, and reticular opacities are seen (7). [Fleischner Society]