Fig. 6
From: Beyond bronchitis: a review of the congenital and acquired abnormalities of the bronchus
Bronchial wall thickening due to bronchitis. Coronal (a) and axial (b) CT imaging demonstrates bronchial wall thickening and areas of mucous plugging (arrowhead). Tram tracking refers to wall thickening in longitudinally oriented bronchi (solid arrow) mimicking the parallel rail tracks of a tram whereas peribronchial cuffing (dashed arrow) refers to wall thickening of the bronchi seen in cross section, sometimes referred to as the “donut sign”