Membranous Fibrosis of the Lung
Membranous fibrosis of the lung depicts a morphological feature of the fibrous tissue which covers alveolar duct walls. Membranous sheets of fibrous tissue usually bridge and obstruct the mouths of alveoli, and attach only at the tips of the septa; i.e., the alveolar duct walls, and often provoke a collapse of alveolar spaces. There seem to be two types of membranous fibrosis. The first type is, in fact, a fibrous replacement of pre-existing hyaline membrane, while the second is a de novo formation of membranous fibrous tissue which has little or no preceding hyaline membrane. We consider that both of these changes result from damage to the alveolar duct walls and may constitute forms of the fibrosing alveolar ductitis syndrome. Recognition of this type of fibrosis gives us a better understanding of the morphogenesis of so-called diffuse alveolar damage.