Small airways diseases: detection and insights with computed tomography

Diseases affecting the small airways are difficult to detect by traditional diagnostic tests. Widespread involvement is needed before symptoms and abn ormalities on pulmonary function testing or chest radiography become appare nt. Obstruction of the bronchioles may be detected indirectly by computed t omography (CT) because regional under-ventilation results in reduced perfus ion which in turn is shown as a mosaic attenuation pattern of the lung pare nchyma. When there is inflammation of the bronchioles with accompanying exu date, the airways may become directly risible on CT, for example in cases o f diffuse panbronchiolitis, Quantification of the various morphological features of small airways disea se is possible from CT images and this increased precision has aided invest igations of structure/function relationships. An understanding of the pathology and microscopic distribution of disease i n relation to the airways allows some prediction of the likely computed tom ography appearances in this wide spectrum of conditions, and thus helps to refine the differential diagnosis.