Organizing pneumonia

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

Organizing pneumonia
Diagnosis in short

Organizing pneumonia. H&E stain.

LM distal airway disease -- airways plugged with organizing exudate (fluffy light-staining paucicellular regions with stellate cells); no hobnailing of pneumocytes; type 2 pneumocytes hyperplasia is absent
LM DDx diffuse alveolar damage (proliferative phase), bronchiolitis obliterans.
Site lung - diffuse lung diseases

Prevalence uncommon
Prognosis dependent on underlying cause
Clin. DDx cryptogenic organizing pneumonia, transplant rejection, infection (pneumonia), collagen vascular disease, peri-tumour
Treatment dependent on underlying cause


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

Clinical diagnoses:[1]


  • BOOP is used as a synonym for organizing pneumonia which has the long differential diagnosis above.[1]
    • 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.



  • 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.



Masson body


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Lung, Right Lower Lobe, Open Lung Biopsy:
- Organizing pneumonia.
- Emphysematous changes.
- NEGATIVE for significant pulmonary fibrosis.
- NEGATIVE for malignancy. 

There is no evidence of granulomatous disease.


Organizing pneumonia with well-formed Masson bodies is seen subpleural and peribronchial. It is pathcy and mild. Significant fibrosis is absent. Eosinophils are not readily apparent.

See also


  1. 1.0 1.1 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 91. ISBN 978-0781765275.
  2. Klatt, Edward C. (2006). Robbins and Cotran Atlas of Pathology (1st ed.). Saunders. pp. 110. ISBN 978-1416002741.