<unk>  is a group of disorders involving pulmonary parenchyma. The exact pathogenesis of these disorders is not completely understood. There are multiple initiating factors that may lead to pulmonary injury. However, immunopathogenic responses of lung tissue are quite similar. The major histopathologic patterns in response to lung injury include inflammation, fibrosis and granulomatous response.<unk>  may be classified into several subtypes based on the lung response to tissue injury and the cause of injury. The underlying cause of<unk>  may include factors such as toxic environmental or occupational exposure, cigarette smoking, and radiation.<unk>  may also be idiopathic.
Interstitial lung disease
Alveolar lung disease
Pulmonary interstitial emphysema
Pulmonary alveolar proteinosis
Emphysema
Obstructive lung disease
Chemical pneumonitis
Cavitary pneumonia