Radiologic Diagnosis of Interstitial Lung Diseases

Diffuse interstitial lung diseases (DILD) are a group of chronic disorders showing varying degrees of active inflammation and established fibrosis mainly involving the interstitium of the lungs. DILD can be classified into two groups in an etiologic aspect; idiopathic and DILD with known-cause, such as connective tissue diseases associated with DILD. Although there had been complexity and variability in the classification of idiopathic interstitial pneumonia (IIP), an international standard was established for the classification of IIPs including seven clinical-radiologic-pathologic entities; idiopathic pulmonary fibrosis (IPF), nonspecific interstitial pneumonia (NSIP), cryptogenic organizing pneumonia (COP), acute interstitial pneumonia (AIP), respiratory bronchiolitis-associated interstitial lung disease (RB-ILD), desquamative interstitial pneumonia (DIP), and lymphoid interstitial pneumonia (LIP). The prognosis of fibrotic NSIP and IPF is much poorer compared to those of other spectrum of IIPs, such as COP, RB-ILD, DIP, and LIP. Therefore, fibrotic NSIP and IPF can be considered separately as a group of fibrotic IIPs. Trying to predict the prognosis of IIPs, there has been an effort to differentiate inflammation-predominant lesions from fibrosis-predominant lesions in patients with fibrotic IIPs. Radiologic features of low fibrotic scores at high-resolution CT and early enhancement patterns at dynamic enhancement of MRI can be useful prognostic determinants for the prediction of disease improvement in patients with fibrotic IIPs.