Idiopathic pulmonary fibrosis

Pathologically, the large majority of patients with IPF show typical histological findings of usual interstitial pneumonia and/or desquamative interstitial pneumonia. The earliest histological abnormality in IPF is alveolitis with increased cellularity of the alveolar walls. This inflammatory process can lead to progressive fibrosis. Alveolar wall inflammation and intra-alveolar macrophages in IPF indicate disease activity and are potentially reversible. Fibrosis and honeycombing are irreversible.

The plain chest radiographic findings of IPF consist initially of ill-defined or ground glass opacity, presumably due to alveolitis. As fibrosis develops, a fine reticular pattern appears, which may be diffuse, but is often seen first and is more severe in the lower lung zones. As fibrosis progresses, the reticular pattern becomes coarser, and there is progressive loss of lung volume. In the end stage there is diffuse honeycombing (Fig.1 a).

On HRCT, IPF is characterized by the presence of reticular opacities, which correspond to areas of irregular fibrosis and reflect the typical pathologic features of usual interstitial pneumonia (UIP). Subpleural honeycombing, with a basal and posterior distribution usually predominates (Fig.1 b).

HRCT allows a distinction of active, potentially reversible alveolitis from irreversible fibrosis in the majority of patients with IPF, without the need for lung biopsy. In some patients with IPF, definite diagnoses of end-stage lung (honeycombing without ground-glass opacity) or active alveolitis (ground-glass opacity) can be made on the basis of HRCT findings.

RW