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organizing pneumonia

Thursday 3 November 2005

organizing pneumonias, organizing pneumonia pattern

Digital case (Digital slides)

- HPC:397 : Organizing pneumonia


- Wikimedia: Organizing pneumonia

Definition: Organizing pneumonia is a non-specific pathological reaction pattern to a diverse variety of agents of injury.

The organizing pneumonia pattern may be seen in organizing diffuse alveolar damage, organizing infections, organization distal to airway obstruction, aspiration, drug reactions, fumes, and toxic exposures, collagen vascular disease, hypersensitivity pneumonitis, eosinophilic lung disease, inflammatory bowel disease, as a secondary reaction in chronic bronchiolitis, and as a reaction around other processes (abscess, neoplasm, and others).

In the absence of a known cause or association the diagnostic term cryptogenic organizing pneumonia (COP), is used.

Although COP is currently classified as one of the idiopathic interstitial pneumonias, it is primarily characterized by alveolar and terminal airways filling with fibroblasts and immature connective tissue combined with interstitial inflammation and expansion of alveolar walls producing nodular areas of lung consolidation often centered on bronchovascular bundles.

A previous term for this condition was "bronchiolitis obliterans organizing pneumonia" (BOOP). This terminology emphasized the terminal airway obstruction component which varies in prominence from case to case and may be rare or absent in some cases.

Foci of obstructive pneumonia are often seen distal to obstructed terminal airways.


- organizing pneumonia (OP) at the Yale Rosen Collection


There is transformation of intraalveolar exudate into intraalveolar fibro-myxoid nodular masses containing firoblast and chronic inflammatory cells. Corresponds to grey hepatization of lobar pneumonia.

- intraluminal organizing fibrosis in distal airspaces

  • bronchiles
  • alveolar ducts
  • alveoli

- patchy distribution (pulmonary nodules)
- preservation of lung architecture
- uniform temporal appearance
- mild interstitial chronic inflammation
- negative elements

  • lack of interstitial fibrosis (except incidental scars or apical fibrosis)
  • lack of granulomas
  • lack of neutrophilic infiltration or abcesses
  • lack of necrosis
  • lack of hyaline membranes or prominent airspace fibrin
  • lack of prominent eosinophilic infiltration


- diffuse organizing pneumonia
- localized organizing pneumonia


- organizing pulmonary infections

- organizing diffuse alveolar damage
- drug reaction (drug-associated organizing pneumonia)
- toxic-associated organizing pneumonia

  • cocaine abuse

- dysimmune diseases/auto-immune diseases (collagen vascular diseases, connectivitis)
- HIV infection (HIV-associated organizing pneumonia)
-  viral infections (virus-associated organizing pneumonia)

- hypersensitivity pneumonitis (extrinsic allergic alveolitis)
- chronic eosinophilic pneumonia
- myelodysplastic syndrome
- ionizing radiations
- pulmonary hemorrhages
- pulmonary vasculitis

  • Wegener granulomatosis

- airway diseases complicated by infections

  • broncitis and emphysema
  • bronchiectasis
  • pulmonary cystic fibrosis
  • aspiration pneumonia
  • chronic bronchiolitis

- pulmonary airways obstruction
- peripheral reaction around

  • pulmonary abcess
  • pulmonary infarcts
  • pulmonary tumors
  • Wegener granulomatosis

- bronchiolitis obliterans organizing pneumonia
- acute fibrinous organizing pneumonia
- cryptogenic organizing pneumonia (COP) (or cryptogenic BOOP)

Differential diagnosis

- UIP pattern

- acute interstitial fibrosis (AIP)
- DAD pattern

  • organizing phase of DAD (diffuse alveolar damage)

- NSIP pattern (cellualr pattern of NSIP)
- acute fibrinous and organizing pneumonia (AFOP)
- eosinophilic pneumonia (if eosinophilic infiltration)

See also

- pulmonary lesionnal syndromes (pulmonary lesionnal patterns)