Giant bulla formation in the lung because of a check-valve mechanism.

The pathogenesis of bulla formation has not yet been demonstrated in pathologic examinations or through direct visualization during thoracotomy or thoracoscopic surgery. We present two cases of giant bulla formation after pneumothorax because of cryptogenic organizing pneumonia and lung abscess. The case findings suggested that the pathogenesis was attributable to a check-valve mechanism, secondary to bronchiolitis obliterans, or the presence of an obstructing air leakage due to a lung fistula. The lung fistula had been covered by inflammatory membranes consisting of blood and/or fibrous precipitates with detached visceral pleura.