Due to the variability in respect to aetiology, histopathology, lung function, imaging and clinical presentation, as well as overlapping parenchymal processes, bronchiolar disorders are generally difficult to diagnose. Thus, diseases of the small airways should generally be considered in the differential diagnostic approach to respiratory conditions. The diagnostic approach can be devided into several steps: in steps 1 (history and physical examination) and 2 (plain chest radiographs and pulmonary function tests) may point towards a bronchiolar pulmonary process. High-resolution CT (HR-CT) scanning of the chest provides three distinct HR-CT patterns (tree-in-bud sign, ill-defined centrilobular ground-glass nodules and/or pattern of mosaic attenuation, especially visible on expiratory images) which confirm a bronchiolic involvement and help to narrow down a likely diagnosis or more specific bronchiolitic diseases. In inconclusive cases, a histological diagnosis may be required. The paper presents a clinically useful algorithmic approach to diagnosis and differential diagnosis of bronchiolar disorders.
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