Round atelectasis in a 20-year-old woman.

Round atelectasis is an unusual pulmonary pseudotumor often associated with primary pleural pathologic conditions or pleural effusion. We report the case of a 20-year-old woman who was found to have a large, circular pulmonary lesion demonstrated on both plain chest x-ray film and computed chest tomography. The patient underwent exploratory thoracotomy, at which time this uncommon entity was identified.