Ferruginous bodies

Ferruginous bodies are a histopathologic finding in patients with fibrotic lung diseases. They appear as small brown nodules in the septum of the alveolus. Ferruginous bodies are typically indicative of asbestos inhalation (when the presence of asbestos is verified they are called "asbestos bodies"). In this case they are fibers of asbestos coated with an iron-rich material derived from proteins such as ferritin and hemosiderin. Ferruginous bodies are believed to be formed by macrophages that have phagocytized and attempted to digest the fibers.