Bronchiolitis, Constrictive

Melissa L. Rosado-de-Christenson, MD, FACR

Key Facts

Terminology

Concentric peribronchiolar fibrosis of membranous and respiratory bronchioles

Imaging Findings

Radiography
- Normal chest radiographs
- Hyperinflation
CT/HRCT
- Mosaic pulmonary attenuation
- Air-trapping on expiratory CT/HRCT
- Low attenuation; air-trapping and reflex vasoconstriction
- High attenuation; redistribution of blood flow to relatively normal lung
- Bronchial dilatation, bronchiectasis, bronchial wall thickening

Top Differential Diagnoses

Panlobular Emphysema
Pulmonary Hypertension
Asthma

Pathology

Etiologies
- Postinfectious
- Post-transplantation
- Collagen vascular disease
- Inhalational injury
Nonuniform bronchiolocentric fibrosis

Clinical Issues

Progressive dyspnea, cough

Diagnostic Checklist

Expiratory HRCT for detection of air-trapping

Axial HRCT shows mosaic attenuation and areas of decreased lung attenuation

containing small vessels that alternate with areas of higher lung attenuation

and contain normal-sized pulmonary vessels.

Axial HRCT shows the typical findings of constrictive bronchiolitis, including mosaic attenuation, bronchiectasis

, and bronchial wall thickening. Note the subtle middle lobe centrilobular nodules

TERMINOLOGY

Abbreviations and Synonyms

Bronchiolitis obliterans syndrome (BOS)

Definitions

Bronchiolitis = broad spectrum of inflammatory and fibrotic changes centered on small conducting airways
Confusing and often inconsistent terminology
- Bronchiolitis obliterans refers to both constrictive bronchiolitis and bronchiolitis obliterans organizing pneumonia
- Obliterative bronchiolitis refers to clinical syndrome of airflow obstruction associated with HRCT findings of air-trapping
- Various classification schemes
  - Classification based on etiology and clinical syndromes
  - Classification based on histologic features
Constrictive bronchiolitis = peribronchiolar fibrosis with resultant bronchiolar narrowing or obstruction
- No fibroblastic proliferation
- Collagen deposition extrinsic to airway lumen
- Diffuse patchy involvement
- Irreversible process
Swyer-James-MacLeod syndrome = unilateral or focal postinfectious constrictive bronchiolitis
BOS = post-transplantation airflow obstruction
- Clinical diagnosis; decrease in FEV₁ from baseline
- Potential BOS (BOS 0-p) = decrease in forced expiratory flow in mid expiratory phase &/or milder decrease in FEV₁
Bronchiolitis obliterans organizing pneumonia or cryptogenic organizing pneumonia
- Cellular bronchiolitis with fibroblastic proliferation
- Process confined to airway lumen
- Often localized
- Resolution with treatment

IMAGING FINDINGS

General Features

Best diagnostic clue: Lobular mosaic attenuation accentuated by expiratory imaging

CT Findings

Minimum intensity projection (MinIP)
- Projects lowest attenuation voxels on every view through volume onto 2D image
- Optimal visualization of diffuse lung disease, airways, and ground-glass opacity
Maximum intensity projection (MIP)
- Projects highest attenuation voxels on every view throughout volume onto 2D image
- Optimal visualization of nodules and vessels
Mosaic attenuation on inspiratory CT/HRCT
- Heterogeneous lung attenuation
- Alternating ↓ and ↑ lung attenuation
  - Reflects nonuniform bronchiolar obliteration
- Hyperlucent underventilated (air-trapping) and underperfused lung (hypoxic vasoconstriction)
Normal or near normal inspiratory CT/HRCT
- Mosaic attenuation may only be visible on expiratory imaging
Diffuse decreased lung attenuation in severe disease
- May be subtle
Air-trapping on expiratory HRCT
- Geographic areas of decreased lung attenuation
  - Decreased vessel caliber from hypoxic vasoconstriction
  - No decrease in volume of affected lung
- Areas of increased (normal) lung attenuation
  - Increased vessel caliber and blood flow
  - Decrease in volume
  - Well- or poorly defined margins
- May be seen in patients without any disease
  - Typically smokers and elderly individuals
  - Frequent in lower lobe superior segments and inferior lingula
  - Involves < 25% of CT cross-sectional area
  - Lobular air-trapping of < 3 adjacent secondary lobules in 50% of asymptomatic patients
Associated findings
- Proximal bronchial dilatation, bronchiectasis, bronchial wall thickening
  - Common in post-transplantation and postinfectious constrictive bronchiolitis
- Scant centrilobular nodules
- Pulmonary nodules & mosaic attenuation
  - Consider diffuse idiopathic neuroendocrine cell hyperplasia
- Predisposed to pneumothoraces, pneumomediastinum
Swyer-James-MacLeod syndrome
- Focal lung hyperlucency and decreased vascularity
- Normal or decreased volume of affected lung
- Air-trapping in affected lung on expiratory CT/HRCT
- Areas of decreased attenuation and air-trapping of other lobes or contralateral lung

Radiographic Findings

Radiography
- Normal chest radiograph
- Nonspecific findings
  - Hyperinflation
  - Peripheral attenuation of vascular markings
- Swyer-James-MacLeod syndrome
  - Unilateral hyperlucent lung
  - Decreased pulmonary vascularity
  - Normal or decreased volume of affected lung
  - Small ipsilateral hilum
  - Air-trapping on expiratory radiography