Technical report: Cystic air spaces in the lung: change in size on expiratory high-resolution CT in 23 patients

Abstract

Purpose: To determine the presence of change in size of air-filled cysts in the lung on expiration by comparison between inspiratory and expiratory high-resolution computed tomography (CT) scans.

Materials and methods: Inspiratory and expiratory high-resolution (1-mm collimation) CT scans were obtained in 23 patients with lung cysts due to a variety of lung diseases. The 23 patients had a total of 27 types of cystic lesions including bullae (n=7), honeycomb cysts due to fibrosing alveolitis (n=11), lymphangioleiomyomatosis (LAM, n=2), cystic adenomatoid malformation (n=1), and bronchiectasis (n=6). An adequate expiratory effort, with at least 5% decrease in the anteroposterior or transverse thoracic diameter, was required for inclusion in the study. Inspiratory and expiratory scans at corresponding anatomic levels were compared to determine any change in size of the cysts on expiration.

Results: Cystic lesions due to bronchiectasis, LAM and fibrosing alveolitis decreased in size on expiratory CT. In six of seven cases bullae decreased in size, and in one patient with a single bulla it remained unchanged. In one case a single cyst due to cystic adenomatoid malformation increased in size on expiration.

Conclusion: The majority of lung cysts decrease in size on expiration suggesting that they communicate with the airways.