Figure 5. Photomicrographs illustrating the most striking histological features of the usual interstitial pneumonia (Haematoxylin & Eosin stain, x 300): (a) Remodelled fibrotic cystic air spaces (arrowhead) are lined by bronchiolar epithelium containing mucinous debris and inflammatory cells (arrow). (b) A focus of organizing pneumonitis (asterisks) composed of spindled fibroblasts dispersed in pale oedematous-appearing stroma. (c) Area of diffuse alveolar damage with hyaline membranes (arrow) superimposed on a background of fibrotic lung parenchyma. (d) Prominent smooth muscle hyperplasia (arrowheads) in remodelled pulmonary septae.