The Idiopathic Interstitial Pneumonias: Histology and Imaging

Abstract

Introduction The idiopathic interstitial pneumonias (IIPs) are a subgroup of diffuse parenchymal lung diseases (DPLDs), the latter of which also includes DPLD of known causes, such as drugs, or association, such as collagen vascular disease; granulomatous DPLD, such as sarcoidosis; and other distinct forms of DPLD, such as lymphangioleiomyomatosis and pulmonary Langerhans cell histiocytosis. In the revised American Thoracic Society/European Respiratory Society Classification of the Idiopathic Interstitial Pneumonias, the IIPs are grouped as follows: (1) chronic fibrosing (idiopathic pulmonary fibrosis [IPF] and idiopathic nonspecific interstitial pneumonia [NSIP]); (2) smoking related (respiratory bronchiolitisinterstitial lung disease and desquamative interstitial pneumonia); and (3) acute or subacute (acute interstitial pneumonia [AIP] and cryptogenic organizing pneumonia [COP]). The idiopathic interstitial pneumonias are a heterogeneous group of nonneoplastic disorders of unknown etiology—“idiopathic,” characterized by variable inflammation and fibrosis of the lung parenchyma—“interstitial pneumonia.” There are commonalities in this seemingly disparate group. Firstly, patients present with dyspnea, decreasing lung volumes, and normal flow rates. Secondly, open lung biopsy demonstrates variable alveolar wall thickening and inflammation, which can be difficult for pathologists to classify because of the variability.