Histopathology of the idiopathic interstitial pneumonias (IIP): A review

The 2013 American Thoracic Society/European Respiratory Society consensus classification update of the idiopathic interstitial pneumonias (IIP) included several important modifications to the organization and spectrum of the diseases that were proposed in an earlier multidisciplinary consensus document in 2002. The histopathology of the now 'major' and 'rare' IIP is presented here with exposition of the newly included entity of a distinctive upper lobe fibrotic lung disease referred to as idiopathic pleuroparenchymal fibroelastosis. The 'rare histological patterns' of acute fibrinous and organizing pneumonia and bronchiolocentric patterns of interstitial pneumonia are illustrated and discussed.