Accessory diaphragm. Report of 6 cases and a review of the literature.

Six cases of accessory diaphragm, associated with respiratory symptoms are reported and of them two have so far been proved, by operation and autopsy, respectively. The described 15 cases in the medical literature are reviewed. The accessory diaphragm consists of a fibromuscular membrane separating the affected hemithorax into two cavities and in three cases a nerve supply has been reported. The diagnosis can be made by simple frontal and lateral roentgenograms of the chest. Typically they show a small lung with shift of the mediastinum to the affected side, an area of increased hazy density, lack of sharpness of the mediastinal structures and the cardiac border on the affected side and a characteristic strip of increased density paralleling the sternum in the lateral view. Roentgenologic differential diagnosis includes lobar atelectasis and pulmonary hypoplasia. There is a high incidence of associated pulmonary maldevelopment of the ipsilateral side and of vascular and cardiac malformations. Improper timing in the interaction of lung buds and septum transversum with the development of a double diaphragm possibly is responsible for this rare congenital anomaly. Usually it is encountered on the right side. Since pulmonary maldevelopment maintains repeated or chronic respiratory infections, recognition and operative therapy are essential.