Inflammation of the small airways is a common pathological disorder; however, the extent of inflammatory lesions is rarely extensive enough to cause clinical symptoms. The most common example is respiratory bronchiolitis characterised by macrophage accumulation in respiratory bronchioles occurring in smokers. Follicular bronchiolitis, another example, is characterised by lymphoid hyperplasia and occurs in connective tissue diseases and immunodeficiency syndrome. The characteristic HRCT pattern is made of ill-defined centrilobular nodular opacities having a diffuse and homogeneous distribution, often associated with CT signs of bronchitis (bronchial wall thickening) and cylindrical bronchiectasis.

Inflammation of the bronchioles may be reversible under specific or anti-inflammatory treatment or lead to subsequent scarring and obliteration (obliterative bronchiolitis).

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