Radiologic Approach to the Idiopathic Interstitial Pneumonias

Oh, Yu Whan

Abstract

Idiopathic interstitial pneumonias (IIP), a heterogeneous group of diffuse parenchymal lung diseases, include seven clinicopathologic entities: idiopathic pulmonary fibrosis (IPF), nonspecific interstitial pneumonia (NSIP), cryptogenic organizing pneumonia (COP), acute interstitial pneumonia (AIP), respiratory bronchiolitis (RB)-associated interstitial lung disease (ILD), desquamative interstitial pneumonia (DIP), and lymphoid interstitial pneumonia (LIP). Each of these entities has a typical histologic pattern that correlates well with imaging features. Thus, imaging plays an essential role in classifying and differentiating this group of diseases. The characteristic HRCT findings of IPF are reticular opacity with honeycombing and traction bronchiectasis in a predominantly basal and peripheral distribution. NSIP manifests as basal ground-glass opacity and reticular opacity. Honeycombing is rare. COP is characterized by patchy peripheral or peribronchovascular consolidation. AIP appears as extensive, mixed ground-glass opacity and consolidation. RB-ILD and DIP are smoking-related diseases associated with CT features of poorly defined centrilobular nodules and ground-glass opacity. LIP is a rare disease characterized by ground-glass opacity sometimes associated with perivascular cysts. Although some of idiopathic interstitial pneumonias may show diagnostic CT features, the final diagnosis of IIPs is usually made by means of evaluation of all the combined clinical, radiologic, and pathologic findings.