Cryptogenic Organizing Pneumonia is characterized by polypoid plugs of loose organizing connective tissue called what?

• A. Granulation tissue
• B. Masson bodies
• C. Hyaline membranes
• D. Fibroblastic plugs

Answer: (B)

Masson bodies are polypoid plugs of loose organizing connective tissue within the lumens of small airways and alveolar spaces. These plugs are composed of granulation tissue with fibroblasts and capillaries and are the classic histologic hallmark of cryptogenic organizing pneumonia. This distinguishes COP from patterns like hyaline membranes seen in diffuse alveolar damage. While the tissue necrosis and granulation overlap describe granulation tissue, the specific named structure pathologists look for in COP is Masson bodies.