Lung

Other nonneoplastic conditions

Acute lung injury

Organizing pneumonia



Last staff update: 4 August 2022

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PubMed Search: Organizing pneumonia[title] lung pathology

Akira Yoshikawa, M.D.
Sakda Sathirareuangchai, M.D.
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Cite this page: Yoshikawa A, Bychkov A, Sathirareuangchai S. Organizing pneumonia. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/lungnontumorBOOP.html. Accessed August 10th, 2022.
Definition / general
  • Since 1901, organizing pneumonia (OP) has been described with the name bronchiolitis obliterans as an interstitial lung disease with granulation tissue plugs within alveolar ducts and small airways secondary to a variety of causes, including infection, fume exposure, drugs, collagen vascular disease, allergic reactions and obstruction (Chest 1983;83:161)
  • Davison et al. (1983) and Epler et al. (1985) reported a series of cases with organizing pneumonia and no evidence of infection or other etiological agents; after that, the term bronchiolitis obliterans organizing pneumonia (BOOP) was commonly used for a while (Q J Med 1983;52:382, N Engl J Med 1985;312:152)
  • In 2002, the American Thoracic Society / European Respiratory Society suggested the term cryptogenic organizing pneumonia to avoid confusion with airway disease, such as constrictive bronchiolitis obliterans and categorized cryptogenic organizing pneumonia into acute / subacute interstitial pneumonia (Am J Respir Crit Care Med 2002;165:277, Am J Respir Crit Care Med 2013;188:733)
Essential features
  • Organizing pneumonia is one of the most commonly seen lung lesions and is associated with a variety of diseases, such as infections and systemic diseases
  • Cryptogenic organizing pneumonia is a relatively rare disease but often needs to be considered, since its clinical and radiological manifestations are often varied and nonspecific
  • Histologically, both cryptogenic organizing pneumonia and secondary organizing pneumonia are characterized by polypoid fibroblastic aggregations, which plug alveolar sacs, ducts and bronchioles
Terminology
  • Organizing pneumonia (OP):
    • Organizing pneumonia can be either a clinicopathological diagnosis (cryptogenic organizing pneumonia and secondary organizing pneumonia), histological pattern (organizing pneumonia pattern) or microscopic finding (e.g. Masson body)
  • Cryptogenic organizing pneumonia (COP):
    • Idiopathic form of organizing pneumonia
    • Also known as bronchiolitis obliterans, bronchiolitis obliterans organizing pneumonia (BOOP), idiopathic BOOP and cryptogenic organizing pneumonitis
  • Cicatricial organizing pneumonia (ciOP) (Histopathology 2021 Jun 8 [Epub ahead of print]):
    • Also known as collagenized organizing pneumonia, cicatricial variant of organizing pneumonia, fibrosing organizing pneumonia, scarred organizing pneumonia
    • Chronic fibrotic changes of conventional organizing pneumonia with formation of dense collagen fibers within the alveolar space, with no architectural destruction
ICD coding
  • ICD-10: J84.116 - cryptogenic organizing pneumonia
  • ICD-11: CB03.2 - cryptogenic organizing pneumonitis
Epidemiology
Sites
  • Bilateral or unilateral lobes of the lung
Pathophysiology
  • Organizing pneumonia is a repair process (wound healing) of the lung in response to preceding alveolar injury (Thorax 2000;55:318, Eur Respir J 2006;28:422)
    • Injury to capillary endothelial cells and alveolar epithelial cells results in the leakage of plasma protein, especially coagulation factors
    • Intra-alveolar coagulation of proteins and coagulation factors generate fibrin clotting on alveolar surfaces
    • Fibroblasts / myofibroblasts migrate into the damaged area, proliferate and generate loose fibrosis in the form of a small polyp
  • IL6, IL8 and TGFβ1 may play an important role in pathogenesis (Adv Exp Med Biol 2016;911:77)
  • Galectin 9 and regulatory T cells are increased in the lung with cryptogenic organizing pneumonia (Lung 2015;193:683)
Etiology
Diagrams / tables

Images hosted on other servers:
Typical organizing pneumonia

Classification of interstitial lung diseases

Typical organizing pneumonia

Imaging patterns of cryptogenic organizing pneumonia

Clinical features
Diagnosis
  • Based on clinical features, radiology and histopathology (Am J Respir Crit Care Med 2002;165:277):
    • Clinical investigation for a possible cause of the disease is necessary
    • Surgical lung biopsy or transbronchial lung biopsy is required to establish a firm diagnosis since the clinical and radiological findings are often not specific
    • However, a biopsy may not be necessary if the clinical and radiological features are suggestive enough
Laboratory
  • Increased serum surfactant proteins A and D
  • Negative serum antibodies of connective tissue diseases and hypersensitivity pneumonitis
  • Reference: Respiration 2019;98:534
Radiology description
  • Simple chest radiography
    • Bilateral or unilateral ground glass opacity and consolidation
  • High resolution computed tomography (Respirology 2016;21:810, Chest 2017;151:1356)
    • Typical pattern
      • Patchy ground glass opacity and consolidation with / without air bronchogram
      • Often bilateral and asymmetrical
      • Often peripheral and migratory
      • Size varies from a few centimeters to a whole lobe
      • Typical organizing pneumonia sometimes looks similar to eosinophilic pneumonia, pulmonary lymphoma and lepidic adenocarcinoma
    • Less common patterns
      • Focal organizing pneumonia: nodular or mass-like consolidation mimicking lung cancer (Int J Clin Exp Pathol 2015;8:511)
      • Infiltrative organizing pneumonia: diffuse infiltrative opacity
      • Reversed halo sign: central ground glass opacity surrounded by round consolidation
      • Crazy paving pattern: areas of ground glass opacities superimposed to focal thickening of pulmonary parenchyma
      • Progressive fibrosis pattern: subpleural basal reticulations and architectural distortion, mimicking nonspecific interstitial pneumonia and usual interstitial pneumonia
      • Perilobular pattern: curved or arcade-like bands of parenchymal consolidation with blurred borders and thickening of the interlobular septa, resembling a Roman arch
      • Linear and band-like opacities: thick radial bands of consolidation containing an air bronchogram or subpleural curvilinear bands, parallel to the pleura
Radiology images

Images hosted on other servers:
Typical organizing pneumonia Typical organizing pneumonia

Typical organizing pneumonia

Typical organizing pneumonia Typical organizing pneumonia Typical organizing pneumonia

Typical organizing pneumonia


Chest radiograph Chest radiograph

Chest radiograph

Focal organizing pneumonia Focal organizing pneumonia

Focal organizing pneumonia

Infiltrative organizing pneumonia

Infiltrative organizing pneumonia

Prognostic factors
Case reports
Treatment
Gross description
  • Multiple patchy fibrotic lesions
  • Ill defined, soft to firm gray areas
  • Volume of the lung is usually normal
  • Other changes overlap with secondary organizing pneumonia
Gross images

Contributed by Yale Rosen, M.D.
Pale area of nodular consolidation

Pale area of nodular consolidation

Mass-like lesions

Mass-like lesions



Images hosted on other servers:
Typical organizing pneumonia

Cryptogenic organizing pneumonia

Microscopic (histologic) description
  • Organizing pneumonia (Semin Respir Crit Care Med 2012;33:462):
    • Fibroblastic plugs in alveolar sacs and ducts (organizing pneumonia) and bronchiolar lumen (bronchiolitis obliterans)
    • Formed by spindled fibroblasts in pale staining matrix of immature loose collagen with polypoid shape (Masson body) or serpiginous or elongated form
    • Organizing pneumonia sometimes extends from one alveolus to the next through interalveolar fenestrae (butterfly pattern)
  • Mild to moderate cellular infiltrate in background (Eur Respir J 2006;28:422, Clin Med Insights Circ Respir Pulm Med 2016;9:123):
    • Thickened alveolar septa with lymphocytes, plasma cells and histiocytes
    • Alveolar architecture is usually preserved in cryptogenic organizing pneumonia
      • Because interstitial dense fibrosis, architectural destruction and honeycomb change are not components of cryptogenic organizing pneumonia, the organizing pneumonia lesion is likely to be secondary to other lung disease if these findings are mixed or overlap (J Clin Pathol 2009;62:387)
  • Airspace changes (Thorax 2000;55:318):
    • Foamy macrophage accumulation in surrounding airspace may be present
    • Occasional fibrin deposition
      • If prominent, the lesion is more likely to be infection, eosinophilic pneumonia (especially after corticosteroids), vasculitis (e.g. granulomatosis with polyangiitis) or acute fibrinous organizing pneumonia (AFOP)
  • Cicatricial form of cryptogenic organizing pneumonia (Hum Pathol 2017;64:76):
    • Organizing granulation tissue is collagenized or hyalinized and harbors eosinophilic, lamellar and dense fibers
    • Airspaces can be filled with collagenized organizing pneumonia but alveolar architecture is mostly preserved
Microscopic (histologic) images

Contributed by Akira Yoshikawa, M.D. and Yale Rosen, M.D.
Patchy involvement

Patchy involvement

Fibroblast plug Fibroblast plug

Fibroblast plug

Fibroblast plug

Fibroblast plug

Fibroblast plug Fibroblast plug

Fibroblast plug


Fibroblast plug Fibroblast plug

Fibroblast plug

Fibroblast plug Fibroblast plug

Fibroblast plug

Mononuclear cells infiltrate

Mononuclear cell infiltrate

Foamy macrophages

Foamy macrophages


Cicatricial variant Cicatricial variant

Cicatricial variant

Cicatricial variant

Cicatricial variant

Bronchiolitis obliterans Bronchiolitis obliterans

Bronchiolitis obliterans

Bronchiolitis obliterans

Bronchiolitis obliterans

Virtual slides

Images hosted on other servers:
Cryptogenic organizing pneumonia Cryptogenic organizing pneumonia

Cryptogenic organizing pneumonia

Cryptogenic organizing pneumonia

Cicatricial organizing pneumonia

Cryptogenic organizing pneumonia

Organizing pneumonia in transplant biopsy

Positive stains
  • Elastica van Gieson staining is helpful to evaluate if architecture of alveoli is preserved or not
Negative stains
  • Organizing polyps are negative for elastica van Gieson staining except in cicatricial variant
Electron microscopy description
Videos

Cryptogenic organizing pneumonia

Focal organizing pneumonia

Fibrosing organizing pneumonia

Sample pathology report
  • Lung, right middle lobe, transbronchial biopsy:
    • Organizing pneumonia (see comment)
    • Negative for granuloma, vasculitis and malignancy
    • Comment: Based on the provided patient information, the diagnosis of cryptogenic organizing pneumonia is favored. However, secondary organizing pneumonia from various causes (infection, drug toxicity, autoimmune disease, malignancy, etc.) needs to be excluded clinically.
Differential diagnosis
Board review style question #1
Which of the following findings is against the histologic diagnosis of organizing pneumonia?

  1. Interstitial mononuclear infiltrate
  2. Fibrin deposition
  3. Fibroblastic focus
  4. Foamy macrophage accumulation
  5. Masson body
Board review style answer #1
C. Fibroblastic focus. This finding is rather suggestive for usual interstitial pneumonia (UIP) pattern.

Comment Here

Reference: Organizing pneumonia
Board review style question #2

A 70 year old woman presented with cough, chest tightness and dyspnea. She was a former smoker with 20 pack years. High resolution CT scan of the chest showed bilateral patchy ground glass opacities in the lungs. A transbronchial biopsy was performed. What is the pathologic diagnosis based on the image provided?

  1. Bronchial asthma
  2. Desquamative interstitial pneumonia
  3. Diffuse alveolar damage
  4. Organizing pneumonia
  5. Respiratory bronchiolitis
Board review style answer #2
D. Organizing pneumonia. Fibroblast plug is the diagnostic feature for organizing pneumonia.

Comment Here

Reference: Organizing pneumonia
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