[Clinical and pathologic features of rounded atelectasis in patients with empyema].

Rounded atelectasis (RoA) is an uncommon pulmonary condition presenting as a peripheral round opacity on a chest roentgenogram. Six cases of empyema who underwent regional lung and pleural resection, had local atelectatic induration beneath the pleura. Their clinical and pathologic features were examined. Five cases had past histories of pulmonary tuberculosis with therapeutic pneumothorax, and one other case had tuberculous pleuritis. Five of seven atelectatic indurations displayed RoA on preoperative plain radiography ++ and/or CT and on soft X-ray films of resected lung preparations. With pathological examinations, the pleura showed one or several indentations, often with deep invaginations into the pulmonary parenchyma. In these regions, the appearance was occasionally more complex due to several small folds emanating from the larger fold. Outside the pleural folds, there was dense fibrous thickening. Fibrosis of the pleural interstitial layer itself was mild. Lung parenchyma adjacent to the folded pleura appeared collapsed with mild interstitial fibrosis. These findings lead to the hypothesis that RoA may result from pleural invaginations occuring after pleural effusion or therapeutic pneumothorax and from fibrous adhesions of the outer regions.