Centrilobular density

Findings on CT scan and HRCT are nonspecific and have a low positive predictive value. Herber et al. (2001) reported ten patients with proven AR, ground glass opacities, bronchial wall thickening, septal thickening, dilatation of the bronchus, pleural effusions and centrilobular densities with a specificity of 30%-50%. 

Associated airway abnormalities can also be depicted by CT. Characteristic CT findings include (1) small ill-defined centrilobular densities representing bronchioles impacted with inflammatory material and peribronchiolar inflammation... 

Small airways disease on CT can be categorized into visible and indirect patterns of the disease. The tree-in-bud sign reflects the presence of dilated centrilobular bronchioles with lumina that are impacted with mucus, fluid, or pus it is often associated with peribronchiolar inflammation (Webb 2006). Cicatricial scarring of many bronchioles results in the indirect sign of patchy density differences of the lung parenchyma, reflecting areas of hypoventilation and air trapping, as well as subsequent hypoperfusion (mosaic perfusion). 

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