Figure 2.

Histopathological features of lungs affected by Birt–Hogg–Dubé syndrome (BHD): H&E staining of resected lungs from patients diagnosed with BHD by genetic testing. Cysts are indicated by stars. (A) A resected cyst from a 41-year-old woman. The cyst wall partially incorporates the pleura (arrowheads) and interlobular septum (arrows). (B) A double-spaced microscopic cyst from the same patient. The inner surface is lined by pneumocytes (inset) and is partially embedded in an interlobular septum (reproduced from Koga et al¹⁹ with permission of the publisher). (C) Innermost layer of a cyst: the lining cells show neither aberrant proliferation nor pleomorphic features. They are immunostained for proSP-C, suggesting pneumocytes. (D) A few alveoli abut on the innermost layer and are anastomosed to the cyst lining cells. (E) Finger-like protrusion of a vein into the cystic space. (F) Epithelial spores lining the inner layer of the cyst wall (left), which is highlighted by immunostaining for cytokeratin CAM5.2 (right).