Novel patterns of interstitial lung disease

The 2002 ATS/ERS Idiopathic Interstitial Pneumonia Classification provided diagnostic criteria for seven well-known entities. Since then, new information has enriched our knowledge about these conditions and rare new entities have been proposed by different authors. Among these, pleuroparenchymal fibroelastosis has been recognized as a distinct clinicopathologic entity characterized by pleura and subpleural parenchymal fibrosis, predominantly composed of elastic fibres. Moreover, unusual histologic patterns, including acute fibrinous and organizing pneumonia and airway-centred interstitial fibrotic diseases, have also been described. The former is characterized by intra-alveolar fibrin deposition and associated organizing pneumonia in the absence classical hyaline membranes, while the latter includes a group of patterns remarkable for inflammation and fibrosis centred around the bronchioles. Whether these latter two patterns represent distinct entities or variants of existing idiopathic lung diseases requires further study. Since the practicing pathologists should to be aware these rare entities and patterns, this paper highlights the current knowledge about these conditions.