Pleural effusion is a cause of round atelectasis of the lung.

Objective: The purpose of this study was to determine whether or not pleural effusion could be a cause of round atelectasis of the lung.

Methods: The study group consists of 20 patients with round atelectasis who had no evidence of asbestos exposure, who had normal baseline chest radiographs that showed no evidence of preexisting pleural or pulmonary disease, and who developed pleural effusion from a variety of causes. Chest radiographs were examined for signs of round atelectasis at the time of initial presentation of the pleural effusion. Follow-up radiographs, spanning a period of 1 month to 4 years after resolution of the pleural effusion, were also examined in all 20 cases.

Results: Round atelectasis was seen initially as a rounded mass-like opacity that produced a focal, upward bulge in the curvilinear meniscus of pleural effusion in 17 cases. In three cases round atelectasis was seen initially as a spherical mass with a comet-tail sign located slightly above the pleural effusion. As the pleural effusion resolved, typical findings of round atelectasis developed in all 20 cases.

Conclusions: Pleural effusion, in the absence of exposure to asbestos, can cause round atelectasis.