Organizing pneumonia complicated by cyst and pneumothorax formation.

We present a case of organizing pneumonia complicated by pneumothorax in association with cyst formation that developed during corticosteroid treatment. Although it has been reported that the check-valve mechanism is a plausible cause of cyst and pneumothorax formation in patients with organizing pneumonia, the details of the corresponding pathological changes that occur in air-trapping have not been elucidated. A pathological examination of lung specimens obtained with video-assisted thoracoscopic surgery suggested that granulation tissues plugging the bronchiole lumens might be a potential cause of the check-valve mechanism in this case. In this report, we also reviewed eight other cases of organizing pneumonia with pneumothorax or cyst formation.