Relations

In front of the arch the right lung and pleura cover it slightly, but the left more so; the remains of the thymus gland is between them. The left superior intercostal vein crosses its upper portion to empty into the left innominate vein. The left phrenic and vagus nerves also cross it, the phrenic being the farther forward and the vagus crossing almost in front of the point of origin of the left subclavian artery. Behind lie the trachea, oesophagus, and thoracic duct, also the left recurrent laryngeal nerve. The bifurcation of the trachea is directly behind and below the lower portion of the arch and the left bronchus passes beneath it. The oesophagus lies compressed between the trachea and vertebrae with the thoracic duct immediately to the left. The left recurrent laryngeal leaves the pneumogastric on the front of the arch, then winds around it and ascends between the trachea and oesophagus to reach the larynx above. Above, from the upper surface of the aorta, are given off the innominate, left carotid, and left subclavian arteries. The left innominate vein crosses above its upper edge to unite with the right innominate to form the superior cava. Below is the left bronchus coming off from the bifurcation of the trachea, and winding around the arch is the left recurrent laryngeal nerve. Beneath the arch and in front of the bronchi are the right and left pulmonary arteries. From the latter the ductus arteriosus goes to the arch. The cardiac branches of the pneumogastric and sympathetic nerves lie on the anterior, inferior, and posterior sides of the arch.

Fig. 222.   Heart and great blood vessels.

Fig. 222. - Heart and great blood-vessels.

The ductus arteriosus at birth is about 1 cm. long and runs from the pulmonary artery to the arch of the aorta below the left subclavian artery. It serves in the foetus to carry the blood from the trunk of the pulmonary artery direct to the aorta instead of passing into the lungs. When, after birth, the lungs are used the ductus arteriosus becomes obliterated and is found later in life as a cord running to the under side of the arch of the aorta. Congenital defects in the heart are a frequent cause of death at birth and in infancy and childhood. They cause an undue mixture of the venous and arterial blood and give the surface a dusky, bluish hue, hence the term " blue baby " as applied to this condition. It is due to an absence of a part 14 or the whole of the septa between the atria and ventricles; to a patulous condition of the foramen ovale of the right atrium; and also to a persistent patulous condition of the ductus arteriosus. Children so affected, if they outlive infancy, usually die before reaching adult age.

Aneurism

This portion of the aorta is also a favorite seat of aneurism. The symptoms produced will depend of course on the direction which the tumor takes. If it tends anteriorly it would involve the lungs and pleurae and the phrenic and vagus nerves, also the sympathetic. The displacement of the left lung would be the more marked. Involvement of the recurrent laryngeal nerve might make a change in the voice, or there might be disturbances of the pupil of the eye due to implication of the sympathetic.

Should the tumor enlarge posteriorly the pressure on the trachea would interfere with the breathing. If the tumor is large this pressure would involve the oesophagus and there might be difficulty in swallowing. Compression of the thoracic duct is said to have led to rapid wasting.

If the aneurism bulges downward it impinges on the left bronchus, which may lead to its dilation and cause bronchorrhcea. A large tumor could also interfere with the flow of blood through the pulmonary arteries and so give rise to congestion and dyspnoea.

An enlargement upward would involve the innominate and left carotid and subclavian arteries and also the left innominate vein. Interference with the arteries and veins of the neck and upper extremity frequently gives rise to changes in the pulse on the affected side and also to venous congestion or even oedema. Changes in the voice or even its loss also occur. The sac as it passes upward may show itself in the suprasternal notch.

In all aneurisms of the arch cough is apt to be a prominent symptom. It is often paroxysmal. It is to be accounted for by pressure on the trachea or laryngeal nerves. Difficulty in breathing and swallowing may arise in deep-seated small tumors growing backward and downward. This may be somewhat relieved by sitting up or leaning forward, while reclining or lying on the back may be unendurable.

The great amount of distress which these aneurisms of the arch of the aorta may give rise to is readily appreciated when one recalls that there is only a distance of 5 or 6 cm. (2 1/4 in.) between the upper edge of the sternum and the anterior surface of the vertebral column, a space already filled with important structures.