Medial herniation of the parietal pleura: a useful sign of pneumothorax in supine neonates.

In a series of 235 consecutive infants with respiratory distress syndrome, pneumothorax was demonstrated radiographically in 20. On anteroposterior supine chest radiographs of such infants, the intrapleural gas tends to seek an anteromedial position within the involved hemithorax. When the pneumothorax is large, the gas may cause the ipsilateral mediastinal pleura to bulge and herniate across the anterior mediastinum into the contralateral hemithorax. This was seen in 12 or the 14 right pneumothoraces, but only in two of the 10 left ones. The gas-containing sac appeared radiologically as a crescent-shaped lucency medial to the upper thoracic spine which was sharply delineated laterally by the mediastinal pleural layers and the somewhat atelectatic contralateral lung. In some patients treated with a chest tube, the gas disappeared more slowly from the herniated portion of the pleural sac than from elsewhere in the pleural space. Therefore, in addition to being a useful confirmatory sign of pneumothorax, this finding is also important in assessing the completeness of pleural drainage.