THE MEDIASTINUM. 191 



major. The vena azygos minor is on the left side of the vertebrae and crosses the 

 sixth to join the vena azygos major. The descending thoracic aorta is not infrequently 

 the seat of aneurism. 



Mediastinal Tumors. Cancer is the most frequent malignant new growth, then 

 sarcoma and lymphoma. Great enlargement of the lymph-nodes occurs in Hodgkin 's 

 disease and is probably a factor in causing a fatal issue. Enlargements also result 

 from tuberculosis and other diseases. They give rise to pressure symptoms. Dyspnrea 

 may be due to pressure on the trachea or heart and great vessels. The circulation 

 may be so much impeded that the enlargement of the collateral veins, especially those 

 of the surface, may be very marked. There may also be difficulty of swallowing due 

 to pressure on the cesophagus. 



Pleural Effusions. Serous effusions into the pleurae are also known to accom- 

 pany heart disease and have been attributed in some instances to obstruction of the 

 circulation. They are apt to be unilateral and are most often found affecting the 

 right pleural cavity. Baccelli attributed the effusion to obstruction of the blood 

 current through the vena azygos major ; the enlarged heart pulling the superior vena 

 cava down drew the vena azygos major tightly over the right bronchus, as is well 

 shown in Fig. 210. Steele ( Univ. Med. Mag., 1897 ; Journ. Am. Med. Asso., 1904) 

 and Stengel ( Univ. Penna. Med. Bulletin, 1901) held that the dilated right heart by 

 extension upward exerts pressure on the root of the right lung and indirectly pinches 

 the azygos major vein as it curves over the right bronchus to enter the superior 

 vena cava. Fetterolf and Landis (Am. Journ. Med. Sciences, 1909) believe that 

 the fluid comes 1rom the visceral pleura and not from the parietal pleura, and that the 

 outpouring, so far as the pressure factor is concerned, is caused by dilated portions 

 of the heart pressing on and partly occluding the pulmonary veins. They point out 

 that Miller (Am. Journ. of Anat. , vii) has shown that the veins draining the visceral 

 pleura empty into the pulmonary veins ; therefore, if these latter are obstructed, 

 transudation may ensue ; this may occur on either side. They point out that if the 

 right atrium (auricle) dilates, it expands upward and backward and compresses the 

 left auricle and root of the right lung; and of the parts composing the root the 

 pulmonary veins are the most anterior, and, therefore, the ones most liable to be 

 compressed. Left-sided effusions are accounted for by compression of the left 

 pulmonary vein by the dilated left atrium (which is the most posterior of the four 

 chambers) and its appendix. The greater frequency of right-sided effusions is due 

 to the more common occurrence of dilatation of the right side of the heart. 



