Subsegmental and Rounded Atelectasis

The chapter titled subsegmental and rounded atelectasis discusses the radiographic and computed tomography (CT) appearances of subsegmental and rounded atelectasis. Subsegmental atelectasis is linear or platelike atelectasis confined to a single subsegment or extending across multiple subsegments of lung. It is seen in a variety of pulmonary and abdominal conditions including prolonged shallow breathing, pulmonary thromboembolic disease, diaphragmatic dysfunction, and pneumonia. Rounded atelectasis is folded or collapsed lung that develops adjacent to an area of pleural thickening, fibrosis, or effusion. There are several imaging features that must be present before confidently diagnosing rounded atelectasis including significant contact with adjacent pleural abnormality, signs of volume loss, acute angles with the pleura, and the comet tail sign. If these criteria are met, CT followup is sufficient in most cases.