Synopsis
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
Variants
diffuse organizing pneumonia
localized organizing pneumonia
Etiology
organizing pulmonary infections
- Pneumocystis carinii pneumonia
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
airway diseases complicated by infections
- broncitis and emphysema
- bronchiectasis
- pulmonary cystic fibrosis
- aspiration pneumonia
- chronic bronchiolitis
pulmonary airways obstruction
peripheral reaction around
bronchiolitis obliterans organizing pneumonia
acute fibrinous organizing pneumonia
cryptogenic organizing pneumonia (COP) (or cryptogenic BOOP)
Differential diagnosis
UIP pattern
- interstitial pulmonary fibrosis (UIP)
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)