Fig. 4: Fibrotic hypersensitivity pneumonitis (HP).

A Same case as Fig. 3D. In this lobe is prominent peribronchiolar fibrosis with minimal subpleural fibrosis, a pattern that is against a diagnosis of usual interstitial pneumonia/idiopathic pulmonary fibrosis (UIP/IPF). A granuloma is shown in the inset. B Low power view of the biopsy shows minimal subpleural fibrosis with fine bridging fibrosis and peribronchiolar fibrosis. C Same case as Fig. 4B. High power view of another area showing prominent peribronchiolar metaplasia. Peribronchiolar metaplasia was present around more than 50% of bronchioles, a finding that supports a diagnosis of fibrotic HP. No source of exposure could be determined. D An example of fibrotic HP in which the underlying pattern of fibrosis is that of UIP, but there is peribronchiolar metaplasia around every airway in the field (arrows), a finding that favors fibrotic HP.