Organizing pneumonia

Organizing pneumonia, abbreviated OP, is a histologic pattern in lung pathology. It fits into the larger category of diffuse lung diseases.

General

• Multiple causes, e.g. transplant rejection, infection.

Clinical diagnoses:

• Transplant rejection.
• Cryptogenic organizing pneumonia (COP), AKA (idiopathic) bronchiolitis obliterans organizing pneumonia (BOOP).
  • Should not be confused with constrictive bronchiolitis (AKA bronchiolitis obliterans).
• Collagen vascular disease.
• Toxic injury.
• Infection.
• Peri-tumor - in proximity to a space-occupying lesion (abscess, neoplasm).

Note:

• BOOP is used as a synonym for organizing pneumonia which has the long differential diagnosis above.
  • Confusingly, it may be used to refer to the idiopathic form of organizing pneumonia, now generally known as cryptogenic organizing pneumonia (COP).
    • In other words, strictly speaking, BOOP is not the same as COP; idiopathic BOOP is COP.

Microscopic

Features:

• Distal airway disease -- airways plugged with organizing exudate ("Masson bodies").
  • "Organized exudate" = fluffy light-staining paucicellular regions with stellate cells (fibroblasts & immature connective tissue).
• No hobnailing of pneumocytes.
  • Type 2 pneumocytes hyperplasia is absent.

DDx:

• Diffuse alveolar damage, proliferative phase - has type 2 pneumoncyte hyperplasia.
• Bronchiolitis obliterans.

Images

• 

  Masson body - intermed. mag. (WC/Nephron)

• 

  Masson body - very high mag. (WC/Nephron)

www:

• Masson body (150.59.224.157).
• BOOP (bmj.com).
• Masson body (flickr.com).

See also

• Diffuse lung disease.
• Pneumonia.