Pathogenesis of spontaneous pneumothorax. With special reference to the ultrastructure of emphysematous bullae.

We have performed 253 thoracotomies among a total of 334 cases of spontaneous pneumothorax during the past 17 years, subjecting 126 of these surgical cases to histologic examination by light microscope. Recently, we have classified 54 emphysematous bullae as Reid type 1 or 2 and have examined these, as well as giant bullae, by scanning electron microscope. This revealed exterior surface differences among the three types of cysts: type 1 exhibits a marked absence of mesothelial cells, whereas type 2 and giant bulla do not. At the bases of bullae, deteriorated pulmonary parenchyma, exposed to alveolar space, shows reticulated trabecula-like structures. Our study supports the possibility of air leaking through the wall of the bulla into the pleural cavity at a certain level of pressure, thus emphasizing the role of pleural mesothelial cells in the genesis of spontaneous pneumothorax.