[Imaging of fibrosing interstitial pneumonias]

The term fibrosing interstitial pneumonia covers several distinct entities, including usual interstitial pneumonia, non specific interstitial pneumonia acute interstitial pneumonia, desquamative interstitial pneumonia, and lymphoid interstitial pneumonia. Because of its very poor prognosis and different management, usual interstitial pneumonia, and particularly idiopathic forms (idiopathic pulmonary fibrosis), must be distinguished from other forms of interstitial pneumonia. The diagnosis of idiopathic pulmonary fibrosis is based on the CT or pathologic criteria of usual interstitial pneumonia, in the absence of asbestosis, chronic hypersensitive pneumonitis, and collagen vascular disease. In more than 50% of cases, idiopathic pulmonary fibrosis may be confidently diagnosed on the basis of CT findings, showing reticular opacities and honeycombing with a predominantly basal and subpleural distribution, without nodules, extensive consolidation or ground-glass opacities. Surgical biopsy may be necessary when these features are absent, given the overlap of CT findings between the different forms of interstitial pneumonia. In such cases, specific diagnosis of interstitial lung disease is based on a combination of clinical, radiological and histopathological findings.