A parenchymal band is a linear opacity, usually 1-3 mm thick and up to 5 cm long that usually extends to the visceral pleura (which is often thickened and may be retracted at the site of contact). It reflects pleuroparenchymal fibrosis and is usually associated with distortion of the lung architecture. Parenchymal bands are most frequently encountered in individuals who have been exposed to asbestos.
Comment:
See Figure 48 of Hansell DM, et al., Fleischner Society: glossary of terms for thoracic imaging. Radiology. 2008;246:697-722.