Figure 1.

Representative pathological findings of pulmonary cysts from patients with Birt–Hogg–Dubé syndrome (BHDS). A, A cyst in the subpleural area has, macroscopically, a very thin, translucent wall with an intracystic septum indicated by a white arrow (scale bar: 5 mm). B, The cyst shown in A was located in the area adjacent to an interlobular septum including pulmonary veins, and has a very thin intracystic septum (indicated by the black arrow) (Elastica–Masson trichrome stain). C, Vessels in the interlobular septa frequently protrude into the cyst. Note that the connective tissue surrounding one of the of the vessels is decreased (indicated by a small black arrow) (Elastica–Masson trichrome stain). D, Two subpleural cysts abut on an interlobular septum (small arrowheads), and the opposite side of each cyst wall is composed of thin pleural wall (CL indicates a centrilobular area). E, An intrapulmonary cyst abuts on an interlobular septum (large arrowheads), and the other side of the cyst wall is composed of thin alveolar wall (CL indicates a centrilobular area.). F, Approximately half of all cysts that we examined in this study were composed of normal alveolar walls with neither cell proliferation nor inflammatory cell infiltrates (* indicates intracystic area). However, some cysts from BHDS have inflammation, and representative photomicrographs of subpleural cysts are presented in G and H. In G, the basal side of a subpleural cyst abuts on an interlobular septum without inflammation, whereas its pleural side shows thickened visceral pleura with fibroblast proliferation. In H, the very thin wall of a subpleural cyst shows but lymphocyte infiltration but no fibrous thickening.