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

Synopsis

 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)
 focal fibrosis of some alveolar septa
 reactive pneumocytic hyperplasia

Etiology

 organizing pulmonary infections

• viral pulmonary infections
  • cytomegalovirus pneumonitis (CMV pneumonitis)

• bacterial pulmonary infections
• fungal pulmonary infections

 organ allograft

• lung allograft recipients (#8698317#)
• bone marrow allograft (pulmonary GVHD)
• renal allograft
• hepatic allograft (#15004777#)

 organizing diffuse alveolar damage
 bronchial obstruction
 aspiration penumonia
 drug reactions
 toxic reactions
 dysimmunity

• connectivitis (collagen vascular 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

 idiopathic BOOP (cryptogenic organizing pneumonia)

Differential diagnosis

 pulmonary organizing diseases
 constrictive bronchiolitis

See also:

 bronchiolitis obliterans syndrome (BOS)
 chronic airway rejection
 obliterative bronchiolitis

References

 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#