[A radiologic image to be recognized in patients with thoracic injury: the retroligamentary pneumatocele].

A 17-year-old female patient had a road traffic accident. She suffered from a minor head injury, and a right pneumothorax which had to be drained. However, when admitted, an unusual picture was found on the chest film. It was a left para-mediastinal shadow with a fluid level, its greater axis being vertical. She underwent a computerised tomographic chest scan. This picture was seen to be in the left costo-vertebral gutter, and in contact with an area of pulmonary contusion in the left posterior basal segment. Another smaller similar picture was discovered on the right side. These were interpreted as being infrapleural pneumatoceles on the mediastinal surface of the lower pulmonary lobes. The patient recovered spontaneously. In fact, these effusions of air and blood can be seen in other areas in the chest (mediastinum, pleura, lung); these are discussed.