David A. Lynch, MB

Abstract: High-resolution CT (HRCT) can play an important role in the assessment of bronchiolitis. Direct signs of bronchiolitis include centrilobular nodules, bronchial wall thickening, and bronchiolectasis. Indirect signs include mosaic perfusion, hyperlucency, mosaic or diffuse airtrapping, vascular attenuation, and increased lung volumes. Expiratory HRCT scans are considered an essential part of the workup, because airtrapping may be evident only on these scans. In infectious cellular bronchiolitis, the centrilobular nodules typically have a branching, or "tree-in-bud," appearance, whereas in hypersensitivity pneumonitis, these nodules have a round or nonbranching pattern. The HRCT signs of constrictive bronchiolitis include mosaic perfusion, mosaic airtrapping, vascular attenuation, bronchiolectasis, and bronchiectasis; centrilobular nodules are usually absent. (J Respir Dis. 2005; 26(5):222-228)