Intraluminal Polypoid Fibrosis of the Lung
The present communication describes the morphology and pathogenesis of intraluminal (or intra-alveolar) polypoid fibrosis of the lungs, which is a condition characterized histologically by the presence of polypoid fibrous tissue masses protruding into and filling lumens of the airways or airspaces. Intraluminal polypoid fibrosis is further subclassified into three types. The first type probably represents a primary injury of respiratory bronchioles and alveolar duct walls which directly leads to polypoid fibrous tissue formation. This fibrous tissue is generally uniform in appearance and lacks a fibrinous component. The second type results from fibrous replacement of preceding fibrinous inflammation in the airspaces, such as lobular (broncho-) and lobar pneumonia. It is histo logically characterized by an admixture of fibrin and fibrous components. The third type superimposes on hyaline membrane formation. The spaces surrounded by the hyaline membrane along the alveolar duct walls are filled with loose fibrous tissue. In all three types, the process of organi zation originates in the alveolar duct walls, especially at the edge of alveolar mouths. Therefore, we propose the term of "fibrosing alveolar ductitis syndrome" for such disease entities as BOOP, BIP, and organized DAD. in which damage of the alveolar duct wall results in fibrosis.