Idiopathic interstitial pneumonias: Clinical findings, pathogenesis, pathology and radiologic findings

Idiopathic interstitial pneumonias are currently classified into four categ ories: usual interstitial pneumonia, nonspecific interstitial pneumonia wit h fibrosis, acute interstitial pneumonia and desquamative interstitial pneu monia. The fibrotic process in interstitial pneumonias appears to result fr om a complex interaction between fibroblasts, other lung parenchymal cells and macrophages. The complex relationship between the local release of grow th-promoting cytokines by alveolar macrophages and resident fibroblasts rep resents a necessary step for fibrosis or remodeling after lung injury. Inju ry to the epithelium and basement membranes is likely necessary for the fib rotic process to occur. Usual interstitial pneumonia, most frequent among i nterstitial pneumonias and has a poor prognosis, appears on high-resolution CT as patchy subpleural areas of ground-glass attenuation, irregular linea r opacity, and honeycombing. Nonspecific interstitial pneumonia with fibros is, the second most frequent and has a better prognosis than usual intersti tial pnemonia, appears as subpleural patchy areas of ground-glass attenuati on with associated areas of irregular linear opacity on CT. Acute interstit ial pneumonia with high mortality rate presents as extensive bilateral airs pace consolidation and patchy or diffuse bilateral areas of ground-glass at tenuation. Desquamative interstitial pneumonia with good prognosis presents as patchy subpleural areas of ground-glass attenuation in middle and lower lung zones.