Constrictive bronchiolitis is an obstructive lung disease characterized by fibrosis and inflammation of the small airways leading to either partial or complete obstruction. It is commonly associated with lung transplantation, connective tissue diseases, certain drug toxicities, and viral infections. Microscopically it affects the terminal bronchioles and shows peribronchiolar fibrosis leading to bronchiolar lumen obliteration. It is differentiated from other obstructive lung diseases by its site of involvement in the small airways and pathology of mural fibrosis rather than airspace changes.

1. FLASHPATH
H A Z E M A L I

2. CONSTRICTIVE
(OBLITERATIVE)
BRONCHIOLITIS
H A Z E M A L I

3. CLINICAL
Constrictive (obliterative) bronchiolitis is considered one of the
“obstructive lung diseases” that include:
• Chronic bronchitis
• Emphysema
• Bronchiectasis
• Asthma

4. CLINICAL
Obstructive airway disease Restrictive airway disease
General features Increase in resistance to
airflow due to obstruction at
any level
Reduced expansion of lung
parenchyma
Total lung capacity (TLC) Increased Reduced
Forced Expiratory Volume in
one second (FEV1)
Reduced Normal

5. CLINICAL
Obliterative bronchiolitis is commonly associated with:
• Transplantation: especially bone marrow and lung
– In chronic pulmonary rejection, it is associated with what is called
“bronchiolitis obliterans syndrome “
– It is different from bronchiolitis obliterans organizing pneumonia (see later)
later)
• Connective tissue diseases: rheumatoid arthritis
• Drug toxicity: penicillamine or gold therapy
• Post viral infection: especially adenovirus
• Idiopathic

6. MICROSCOPY
• Mainly affect terminal “membranous” bronchioles and higher
• Peribronchiolar and bronchiolar fibrosis
– Fibrosis mainly seen between muscle layer and epithelium = submucosa
• Leading to partial or complete obliteration of bronchiolar lumen
– May show muco-stasis, foamy macrophages, and/or infections distal to
obstruction

7. MICROSCOPY
• Airway chronic inflammation may be seen
– In chronic pulmonary rejection ( C ), it is graded based on whether or not
inflammation is present:
• Active ( Ca ): presence of inflammation
• Inactive ( Cb ): absence of inflammation
• Obliterative Bronchiolitis is patchy and therefore
difficult to diagnose via transbronchial biopsy

8. SPECIAL STUDIES
• Elastic stain:
– In early lesions
• Highlights the diminution of the bronchiolar lumen
– In advanced lesions (total replacement by fibrosis)
• Visualize remnants of bronchiole elastica within the fibrous scars
• Masson trichrome stain:
– In early lesions
• Highlighting the mural fibrous proliferation
– In advanced lesions (total replacement by fibrosis)
• Visualize remnants of smooth muscle within the fibrous scars

9. DIFFERENTIAL DIAGNOSIS
Chronic
bronchitis
Bronchiectasis Asthma
Small-airway
disease
“bronchiolitis”
Emphysema
Site L a r g e a i r w a y s ( B r o n c h i ) Bronchioles Alveoli
Major
pathology
• Mucous gland
hyperplasia
• Excess mucus
• Inflammation
• Airway
dilation &
scarring
• Thickened
basement
membrane
• Smooth muscle
hyperplasia
• Excess mucus
• Inflammation
(eosinophils)
• Inflammatory
scarring &
obliteration
• Airspace
enlargement
• Wall
destruction
• No fibrosis
Other obstructive lung diseases:

10. DIFFERENTIAL DIAGNOSIS
Constrictive (Obliterative) Bronchiolitis
Cryptogenic Organizing Pneumonia
(Bronchiolitis Obliterans Organizing Pneumonia)
(BOOP)
Distribution
Terminal “Membranous” bronchial and
above
Respiratory bronchiole and below (alveoli)
Lesion
Mural fibrosis of the bronchilar wall,
compressing lumen
Granulation tissue-like (Masson bodies) in the
airspace lumen, rather than the wall

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