CT features of rounded atelectasis.

Rounded atelectasis (folded lung syndrome) is a form of pulmonary collapse associated with pleural thickening that can mimic a neoplasm on plain chest radiographs. The abnormality was diagnosed radiologically in nine patients in whom follow-up varied from 1 to 6 years. Four patients had bilateral lesions, making a total of 13 examples. The CT findings were analyzed and compared with previously published criteria for the diagnosis of this disorder. In all cases, CT showed a rounded mass, 3.5-7.0 cm in diameter, abutting a thickened pleural surface in the lung periphery. The margin closest to the hilum was blurred by the entering vessels in 92% of the cases. Our experience suggests that the CT findings of rounded atelectasis are characteristic of the abnormality.