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

Abstract

Purpose. To determine the association between the progression of upper lung fibrosis and paratracheal air cysts (PACs) size. Materials and Methods. 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. Results. 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, P < 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%, P < 0.001). Conclusions. 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.

Figure 1

(a) Axial CT scan shows fibrosis and irregular pleural thickening in a left upper lobe. No paratracheal air cyst is visualized. (b) CT scan obtained 57 months later shows a paratracheal air cyst at the right posterior side of the trachea (black line arrow). CT image shows subpleural irregularity in the right upper lobe (black arrow) and progression of fibrosis and bronchiectasis in the left upper lobe (white arrow). The total fibrosis score of both upper lungs increases from 5 to 7 points over the 57 months.

Figure 2

(a) Axial CT scan shows a paratracheal air cyst (∗) and fibrosis with volume decrease in a right upper lung and subpleural fibrosis in a left upper lung. (b) CT scan obtained 32 months later shows an increase in PAC size. In addition, fibrosis had thickened (arrow) and the volume of the right upper lobe has reduced. Subpleural fibrosis is more prominent in the left upper lung (black line arrow). The total fibrosis score of both upper lungs increased from 9 to 12 points over the 32 months.