A review is presented on the histological and radiological findings in idiopathic interstitial pneumonias, which are included among the diffuse parenchymal lung diseases. Although they may affect other compartments, the lung interstitium is the initial substrate of the parenchymal lesion due to different patterns of inflammation and fibrosis.

The current classification, proposed in 2002 as an international multidisciplinary consensus document promoted by the American Thoracic Society and the European Respiratory Society, includes 7 conditions. Based on histological criteria, each histological pattern is associated with an image pattern.

They are a group of conditions of unknown origin with common characteristics and differential features that enable them to be individualised as diseases with a different prognosis and treatment. They are rare as idiopathic forms, but share a morphological substrate with other more common diseases of unknown cause, which means they have to be excluded to reach a definitive diagnosis.

For this reason it is important that the radiologist is familiar with their characteristic imaging findings.