Lung, Cryptogenic organizing pneumonia

Cryptogenic organizing pneumonia is a distinct clinical entity of unknown etiology with features of pneumonia. The characteristic histopathological lesions are excessive proliferation of granulation tissue within small airways and alveolar ducts associated with chronic inflammation in the surrounding alveoli. The histologic pattern is a common nonspecific reaction to wide variety of types of lung injury - collagen vascular disease, drug reaction, HIV infection, viral related, radiation, nonspecific reaction adjacent to other lesions and infections. With diffuse involvement of the lung, secondary causes are usually not found.