Incidental Paratracheal Air Cysts on Thoracic CT and Their Association with Chronic Inflammatory Lung Disease.

. To determine the association between the progression of upper lung fibrosis and paratracheal air cysts (PACs) size. . The thoracic CT images of 4573 patients were reviewed for the prevalence, size, and location of PACs and their communication with trachea. In addition, the presence of upper lung fibrosis, emphysema, and bronchiectasis was evaluated in patients with PACs and compared with a control group without PACs. Upper lung fibrosis was analyzed using a fibrosis score system. . The prevalence of PACs was 6.8%. Communication with tracheal lumen was demonstrated by 31.5% of patients with PACs. The prevalence of fibrosis, emphysema, and bronchiectasis in patients with PACs were 67.5%, 21.9%, and 28.3%, respectively. The prevalence of fibrosis was significantly different in the two groups by univariable and multivariable analysis (odds ratio = 2.077, < 0.001). 140 patients with fibrosis among PAC group underwent a previous or follow-up CT; the prevalence with increase in PAC sizes was higher in patients with increase in fibrosis score than those without it (66.2% versus 17.3%, < 0.001). . PACs appear to be highly related to upper lung fibrosis and moderately related to bronchiectasis. In patients with fibrosis, PAC sizes tended to increase with the progression of upper lung fibrosis.