Round atelectasis. Pathologic and pathogenetic features.

Round atelectasis is an uncommon pulmonary condition usually presenting in an asymptomatic individual as a peripheral parenchymal opacity on a chest roentgenogram. Pathologic examination of eight cases revealed localized fibrosis of the visceral pleura overlying the roentgenographic abnormality in all instances. Beneath the region of fibrosis, the pleura showed extensive wrinkling and folding, occasionally with deep invaginations into the pulmonary parenchyma. No discrete mass corresponding to the roentgenographic opacity was identified; however, lung parenchyma adjacent to the fibrotic and folded pleura appeared compressed, and in some cases, showed interstitial fibrosis. These findings support the hypothesis that round atelectasis is due to contraction of a focus of visceral pleural fibrosis that results in buckling of the pleura and collapse of underlying lung parenchyma.