PRACTICAL CONSIDERATIONS : THE MEDIASTINUM. 1833 



bodies of the vertebrae to the sides of the sternum. The median space between the 

 pleurae is called the mcdiastinal space, and is subdivided into four parts called medi- 

 astina. The above statement of the lateral boundaries of the mediastinal space is 

 only a general one, for in the middle the mediastinal space expands beyond them 

 and in front is restricted by the advance of the pleurae beneath the sternum. The 

 superior mediastinum is that part of the space above a plane passing from the disk 

 below the fourth thoracic vertebra to the junction of the first and second pieces of the 

 sternum. This is occupied by the upper part of the thymus, the arch of the aorta 

 and the vessels rising from it, the innominate veins, and the superior vena cava. It 

 is traversed by the trachea and oesophagus, the thoracic duct, the pneumogastric, 

 the phrenic, and the sympathetic nerves. The region below the above-mentioned 

 plane is subdivided by the pericardial sac into an anterior, middle, and posterior 

 compartment. The middle mediastinum is occupied by the heart within the peri- 

 cardium. The roots of the lungs are partly in this and in the superior mediastinum. 

 The shallow anterior mediastinum is between the middle one and the sternum. It 

 contains the lower part of the thymus, a few lymph-nodes, fat, and areolar tissue. 

 The posterior mediastinum, between the spine and the middle mediastinum, contains 

 the oesophagus, the aorta, the thoracic duct, the azygos veins, the pneumogastric and 

 sympathetic nerves. 



PRACTICAL CONSIDERATIONS: THE MEDIASTINUM. 



Wounds penetrating the mediastinum, even when they do not involve the air- 

 passages, may, in consequence of air being drawn into the space by respiratory 

 movements, be followed by general emphysema or by mediastinal emphysema. This 

 condition is not infrequent after tracheotomy, the conditions favoring its production 

 being free division of the deep fascia, continued obstruction of the air-passages, and 

 labored inspiration. 



If there is hemorrhage into the mediastinal space, or if abscess results from infec- 

 tion of a clot, or from extension of tuberculous disease of the bronchial glands, or as 

 a sequel of typhoid fever, the anatomical symptoms will be those of pressure (vide 

 infra). In the presence of a large abscess, pus may perforate the sternum by ero- 

 sion or may find its way out through the little circular openings sometimes found as a 

 result of developmental failure (page 168). It may also be evacuated through an 

 intercostal space or into the trachea or oesophagus. 



Tumors may be malignant or benign (lymphomata, dermoids, hydatids, fibro- 

 mata), the order of mention being that of their relative frequency. The chief symp- 

 toms are those due to intrathoracic pressure, which is, of course, not uniform, and 

 varies with the origin, extent, and density of the tumor, but in its effects upon the 

 separate structures contained within the mediastinum affords a reasonably accurate 

 basis for an anatomical classification of the clinical phenomena of these growths. 



1. Compression of veins, (a) The superior vena cava : cyanosis or lividity of 

 the face ; dilatation of the superficial veins of the neck, face, and head ; oedema of 

 the same region ; epistaxis ; disturbances of vision or amaurosis ; tinnitus aurium or 

 total deafness ; cerebral effusion or hemorrhage ; oedema of one or both arms. (<5) 

 The greater azygos vein : dilatation first of the right and later of the left intercostal 

 veins ; oedema of the upper part of the chest-wall ; right-sided hydrothorax with 

 secondary or later effusion into the left pleura (Stengel); pericardial effusion ; medi- 

 astinal effusion, (r) The pulmonary vein : oedema of the lung ; haemoptysis. 



2. Compression of arteries (much rarer than of venous channels), (a) The 

 aorta : inequality in the radial pulses ; engorgement of the left side of the heart , 

 pulsation of the growth, if it is visible or palpable (as at the suprasternal notch or 

 over the sternal ends of the clavicles); pallor ; giddiness ; anginose pains, (b) The 

 pulmonary artery : distention of the right heart ; dyspnoea ; ultimately as a sec- 

 ondary result of the cardiac condition ascites ; oedema of the lower extremities ; 

 general anasarca. 



3. Compression of nerves, (#) The pneumogastric : irregular heart action 

 with marked rapidity or slowness ; syncope ; vomiting ; hiccough ; pharyngeal or 

 laryngeal spasm or paralysis ; dysphagia ; spasmodic cough. () The inferior laryn- 



