What every radiologist should know about idiopathic interstitial pneumonias.

The American Thoracic Society-European Respiratory Society classification of idiopathic interstitial pneumonias (IIPs), published in 2002, defines the morphologic patterns on which clinical-radiologic-pathologic diagnosis of IIPs is based. IIPs include seven entities: idiopathic pulmonary fibrosis, which is characterized by the morphologic pattern of usual interstitial pneumonia (UIP); nonspecific interstitial pneumonia (NSIP); cryptogenic organizing pneumonia (COP); respiratory bronchiolitis-associated interstitial lung disease (RB-ILD); desquamative interstitial pneumonia (DIP); lymphoid interstitial pneumonia (LIP); and acute interstitial pneumonia (AIP). The characteristic computed tomographic findings in UIP are predominantly basal and peripheral reticular opacities with honeycombing and traction bronchiectasis. In NSIP, basal ground-glass opacities tend to predominate over reticular opacities, with traction bronchiectasis only in advanced disease. COP is characterized by patchy peripheral or peribronchovascular consolidation. RB-ILD and DIP are smoking-related diseases characterized by centrilobular nodules and ground-glass opacities. LIP is characterized by ground-glass opacities, often in combination with cystic lesions. AIP manifests as diffuse lung consolidation with ground-glass opacities, which usually progress to fibrosis in patients who survive the acute phase of the disease. Correct diagnosis of IIPs can be achieved only by means of interdisciplinary consensus and stringent correlation of clinical, imaging, and pathologic findings. (c) RSNA, 2007.