Centrilobular fibrosis: a novel histological pattern of idiopathic interstitial pneumonia

The classification of idiopathic interstitial pneumonias (IIP) is still under debate. In this context, we observed in some of our patients with a clinical and radiological diagnosis of IIP a different histological picture with an aggressive centrilobular scarring centered in the bronchiolar epithelia, but involving the surrounding parenchyma, which underwent extensive remodeling. We hypothesized that this pattern is a form of IIP that could be separated out histologically from the previously described patterns, in particular from usual interstitial pneumonia (UIP) and non-specific interstitial pneumonia (NSIP). Forty-nine patients with clinical and radiological diagnosis of IIP and open-lung biopsies were retrospectively selected from 1982 to 1998. The biopsies were reviewed according to the following criteria: derangement of lobular architecture, temporal homogeneity and subpleural or bronchocentric distribution of the lesions, fibroblast foci, bronchial epithelium necrosis and regeneration, exposure of the basal membrane, squamous metaplasia, basophilic intraluminal contents, and foreign bodies within the remodeling airspaces. Three groups were found: UIP (24 patients), NSIP (13), and a third that we named centrilobular fibrosis (CLF) (12). All histological parameters were significantly different among the three groups (p < 0.001). CLF is a specific, homogeneous, and recognizable histological pattern of IIP, and can be isolated from UIP and NSIP.