Advances in Concept and Imaging of Interstitial Lung Disease

Although idiopathic pulmonary fibrosis (IPF) is a type of idiopathic interstitial pneumonia (IIP), it is different from other IIPs. IPF also differs from interstitial lung disease (ILD) with known causes, including connective tissue disease, exposure, cysts and/or airspace filling disease, and sarcoidosis. More than 90% of IPFs demonstrate progressive disease. Non-IPF ILD has been classified as progressive pulmonary fibrosis on the basis of disease behavior (progressive disease that gets worse over time) as opposed to classification based on cause and/or morphologic characteristics. Progressive fibrosis predictors in ILD include demographic characteristics, underlying connective tissue disease, more extensive disease at CT, honeycombing and usual interstitial pneumonia (UIP) pattern at CT, and greater impairment of lung function. Hypersensitivity pneumonitis (HP), a type of ILD, is separated into fibrotic and nonfibrotic types. Extensive peribronchiolar metaplasia supports the diagnosis of fibrotic HP over UIP, as does predominantly peribronchiolar disease with relative subpleural sparing at CT. Interstitial lung abnormality (ILA) is incidentally identified at CT; thus, ILA is under radiologist purview. Subpleural fibrotic ILA is a prognostic imaging biomarker, predictive of worse prognosis. Photon-counting CT can provide high spatial resolutions of up to 125 μm (in-plane) and 200 μm (through-plane) for improved evaluation of abnormalities.