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Thursday 27 January 2005

Definition: Bronchiolitis obliterans-organizing pneumonia (BOOP) is a ubiquitous entity, known to occur either idiopathically or in association with various pulmonary disorders. See also "organizing pneumonia"

Clinical synopsis

- acute onset
- cough
- dyspnea
- fever
- malaise


- organizing pneumonia

  • fibroblastic plugs (Masson’s bodies) filling air spaces
  • myxomatous connective tissue plugs present in the lumen of bronchioles with extension into the alveoli
  • Masson bodies (serpiginous plugs of fibroblastic tissue filling the alveolar spaces)
  • plug of spindle mesenchymal cells obstructing terminal bronchioles
  • typically elongated to serpiginous shape
  • formed by spindle to stellate fibroblasts embedded in pale-staining matrix

- focal fibrosis of some alveolar septa
- reactive pneumocytic hyperplasia
- fibrin deposition and chronic inflammation in the surrounding parenchyma
- clusters of foamy macrophages
- few scattered neutrophils
- thickening of alveolar septa
- Characteristic patchy appearance on low-power examination (important in differential diagnosis with usual interstitial pneumonia - UIP)
- Rare unfavorable (steroid-unresponsive) cases: scarring and remodeling of lung parenchyma.


- organizing pulmonary infections

  • bacterial pulmonary infections
  • fungal pulmonary infections

- organ allograft

- organizing diffuse alveolar damage (scarring DAD)
- distal to bronchial obstruction
- aspiration penumonia
- drug reactions
- toxic reactions
- dysimmunity

  • connectivitis (collagen vascular diseases or systemic connective tissue diseases)

- extrinsic allergic alveolitis (hypersensitivity pneumonia)
- chronic eosinophilic pneumonia
- chronic bronchiolitis
- diffuse panbronchiolitis
- nonspecific reactions

  • chronic bronchitis
  • emphysema
  • bronchiectasis
  • cystic fibrosis
  • bronchial aspiration
  • peripheral reactions to
    • Wegener granulomatosis
    • pulmonary abcess
    • pulmonary necrosis

- unknown cause (idiopathic BOOP)

Differential diagnosis

- pulmonary organizing diseases
- constrictive bronchiolitis

Nota bene: Bronchiolitis obliterans unassociated with abnormalities in more distal air spaces is extremely rare and has been designated obliterative bronchiolitis.


- Generally excellent
- Rarely unfavorable (steroid-unresponsive)

See also

- bronchiolitis obliterans syndrome (BOS)
- chronic airway rejection
- obliterative bronchiolitis

- pulmonary lesions

  • bronchiolar lesions

- pulmonary lesional syndromes

  • bronchiolar lesional syndromes


- Proliferative activity in fibrosing lung diseases: a comparative study of Ki-67 immunoreactivity in diffuse alveolar damage, bronchiolitis obliterans-organizing pneumonia, and usual interstitial pneumonia. El-Zammar O, Rosenbaum P, Katzenstein AL. Hum Pathol. 2009 Apr 13. PMID: 19368952

- Intraluminal fibromyxoid lesions in bronchiolitis obliterans organizing pneumonia are highly capillarized. Lappi-Blanco E, Kaarteenaho-Wiik R, Soini Y, Risteli J, Pääkkö P. Hum Pathol. 1999 Oct;30(10):1192-6. PMID: 10534166

- Siddiqui MT, Garrity ER, Husain AN. Bronchiolitis obliterans organizing pneumonia-like reactions: a nonspecific response or an atypical form of rejection or infection in lung allograft recipients? Hum Pathol. 1996 Jul;27(7):714-9. PMID: 8698317

- Bronchiolitis obliterans-organizing pneumonia (BOOP)-like variant of Wegener’s granulomatosis. A clinicopathologic study of 16 cases. Uner AH, Rozum-Slota B, Katzenstein AL. Am J Surg Pathol. 1996 Jul;20(7):794-801. PMID: 8669527

- Cordier J-F, Loire R, Brune J. Idiopathic bronchiolitis obliterans organizing pneumonia. Definition of characteristic clinical profiles in a series of 16 patients. Chest. 1989;96:999–1004.

- Epler GR, Colby TV, McLoud TC, Carrington CB, Gaensler EA. Bronchiolitis obliterans organizing pneumonia. N Engl J Med. 1985;312:152–158.

- Katzenstein AL, Myers JL, Prophet WD, Corley LS, Shin MS. Bronchiolitis obliterans and usual interstitial pneumonia. A comparative clinicopathologic study. Am J Surg Pathol. 1986;10:373–381.

- Yousem SA, Lohr RH, Colby TV. Idiopathic bronchiolitis obliterans organizing pneumonia/cryptogenic organizing pneumonia with unfavourable outcome: pathologic predictors. Mod Pathol. 1997;10:864–871.

- Uner AH, Rozum-Slota B, Katzenstein AL. Bronchiolitis obliterans-organizing pneumonia (BOOP)-like variant of Wegener’s granulomatosis: a clinicopathologic study of 16 cases. Am J Surg Pathol. 1996;20:794–801.