MEDIASTINAL INFLAMMATION. 331 



MEDIASTINAL INFLAMMATION AND SUPPURATION. 



Mediastinal inflammation is frequently associated with pleural 

 and pericardial inflammations or adhesions. The direct con- 

 tinuity of the niediastinal tissue with the connective tissue of 

 the lung and pericardium explains this association. After 

 reaching and ensheathing the root of the lung the connective 

 tissue spreads into the parenchyma of the organ on the one hand 

 and extends over its surface as an extremely thin subpleural 

 layer on the other. In like manner the mediastinal tissue 

 ensheaths the fibrous pericardium and extends forwards in the 

 narrow interpleural space behind the lower part of the sternum. 

 It is also directly continuous, both in front and behind, with the 

 layer of loose connective tissue between the parietal pleura and 

 the chest wall. 



There are many lymphatic glands in the mediastinum, and it 

 is possible that both acute and chronic inflammations may at 

 times spread from these. The bronchial group of these glands 

 is very apt to be tuberculous. 



When the mediastinal tissue becomes indurated the structures 

 most likely to be compressed are the systemic and the pulmonary 

 veins. This is accounted for by the thinness of their walls. 

 The pulmonary artery, the aorta, and the trachea and bronchi, 

 having thicker walls, suffer less. Although there is only a 

 fraction of the circumference of the inferior vena cava in the 

 thorax, yet it has been obstructed by mediastinal induration. 

 The phrenic nerves, the vagi, and their recurrent laryngeal 

 branches, all lie in the mediastinal connective tissue planes, and 

 may suffer compression. The same holds for the sympathetic 

 chain which lies over the heads of the ribs in the subpleural 

 layer. It is exceptional for dysphagia to occur in chronic 

 mediastinitis, although the oesophagus lies in the mediastinum. 



Mediastinal suppuration may originate from structures which 

 lie in the spaces or reach the mediastinum by extension from 

 other parts. The mediastinal glands, the thymus, and the 

 oesophagus may all originate the mischief. Extension may 



