The cardinal features of UIP on CT include subpleural reticular opacities (intralobular and interlobular septal lines) and honeycombing, increasing from the apex to the base. Ground-glass opacities are inconspicuous or absent in UIP, but focal areas of GGO may be present [16] . On histology, the hallmark is a geographically and temporally heterogeneous parenchymal fibrosis against a background of continuing mild inflammation (Fig. 4c) [17] .