Small Airways

  • Small Airways
    • diameter less than 2 mm
    • wall thickness of less than 0.5 mm
    • include
      • terminal bronchi (have cartilage)
      • bronchioles
        • no cartilage
        • supported instead
          • smooth muscle and
          • surrounding connective tissue
        • terminal bronchioles <1mm
        • respiratory bronchioles
          •  narrowest airways in the lungs
    • major site of pathology in many lung diseases

Terminal bronchioles have a diameter of <1 mm. They do not contain cartilage in their walls like bronchi. The epithelium is comprised of simple columnar ciliated cells

 

Membranous bronchioles include terminal bronchioles and are lined by columnar epithelial cells with cilia. The more distal respiratory bronchioles are lined by transitioning columnar to cuboidal epithelium and lead into alveolar ducts and alveolar spaces with flattened epithelium

Representative photomicrographs of individual bronchiolar lesions observed in surgical lung biopsy in patients with small airways disease. a) Cellular bronchiolitis: a narrowed and contracted airway is infiltrated by numerous inflammatory cells without a specific pattern. b) Granulomatous bronchiolitis: the small airway is surrounded by an inflammatory infiltrate with a sarcoid granuloma (arrowheads), which increases the volume of the airway wall resulting in lumen narrowing. c) Follicular bronchiolitis: the small airway is surrounded by a large lymphoid follicule (arrowheads), which increases the volume of the airway wall resulting in lumen narrowing. d) Bronchiolitis obliterans is characterised by lumen obstruction with a fibro-inflammatory polyp. e) Obliterative (constrictive) bronchiolitis: the airways lumen is narrowed by subepithelial fibrosis. Although inflammatory cells and mucous exudates are present within the lumen, no fibro-inflammatory polyp is found. f) Mucous plugging: the airway lumen is obstructed by mucus exudates.
Pierre-Régis Burgel, P.R et al , Small airways diseases, excluding asthma and COPD: an overview European Respiratory Review 2013 22: 131-147; figs only
web lungs 367

Medium Sized Airways and Smaller Airways are Filled with Mucus – Note Centrilobular Impaction of Mucus


Representative images of computed tomography (CT) scans in patients with small airways disease. a) An inspiratory CT scan in a patient with hypersensitivity pneumonitis showing mosaic pattern of attenuation. b) Expiratory CT scan in the same patient showing air trapping that is characteristic of small airways disease. c) Ill-defined centrilobular nodules in a patient with farmer’s lung (personal communication; J.C. Dalphin). d) Localised micronodules branching with bronchovascular structures (tree-in-bud pattern) related to tuberculosis in a patient with rheumatoid arthritis receiving treatment with anti-tumour necrosis factor-α. Reproduced from [21] with permission from the publisher.
Burgel, P-R et al  Small airways diseases, excluding asthma and COPD: an overview European Respiratory Review 2013 22: 131-147; web lungs 368

 

Links and References

 

Pierre-Régis Burgel, P.R et al , Small airways diseases, excluding asthma and COPD: an overview European Respiratory Review 2013 22: 131-147;